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Naval Ten was one of the elite units of the British Flying Services.

I think it might be instructive to spell out the statistics:

Draw your own conclusions.

122 pilots served from it's formation until it's reorganisation as 210 Sqn RAF on April 1, 1918.

KiA 21. WiA 13. DoW 1. PoWDoW 1. PoW 9. Kifa 4. Iifa 7.

78 made 0 claims

22 made 1

6 made 2

3 made 3

1 made 4

2 made 5

1 made 6

4 made 7

1 made 8

1 made 13

1 made 16

1 made 19

1 made 26




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Pips: Historical Snippet 1 – British Air Power

The Air War, from the British side, has always been portrayed as very much a secondary aspect by official Historians and by key players the likes of Churchill and Haig. For example Haig, in his final dispatch of the War (892 pages) gave air power just two sentences: "Though aircraft and tanks proved of enormous value, their true value is as ancillaries of infantry, artillery and cavalry. The killing power of the aeroplane is still very limited as compared to the three principal arms."


Churchill, more imaginative than Haig and more radical in his thinking, gave only two of the 1,400 pages of his text in "The World Crisis" to the work of the Air Service.

Even the great British historian Basil Liddell Hart, writing with the advantage of the greater availability of material s decade later, gave only six pages of his 450 pages on the Great War to the air. And this in the form of a postscript inserted apparently at random in the middle of his text.


Most statistics would tend to support this view. Numerically the RFC/RAF had always been insignificant. In September 1914 the Expeditionary Force manpower was made up of 64% infantry, 19% artillery, 9% cavalry, 6% engineers and 0.6% air. Using the same order of arms for the following years it'll read as:


1915: 70%, 17%, 4%, 8% and 0.4%

1916: 65%, 19%, 3%, 10% and 1%.

1917: 62%, 19%, 2%, 12% and 2%

1918: 58%, 24%, 1%, 10% and 3%


Yet numbers fail to tell the true story, for air power gave the land war on the Western front its two basic features.

First, the aeroplane caused the roles of day and night to be reversed, night becoming the time of movement in the rear areas, supplies brought up, men moved for an offensive etc. By day roads were deserted and movement kept to a minimum.


The second basic feature was the sustained stalemate, which seemed to follow upon the impossibility of achieving surprise in attack. Right at the start of the war RFC information had prevented the encirclement of the BEF at Mons, later it spotted the widening gap between the advancing German Armies and initiated the battle of the Marne. When AA drove aeroplanes higher the camera was used. From 16,000ft an area measuring two miles by three would be covered with remarkable clarity by a single exposure. Little could be concealed from the camera, especially so as the staff became more conversant with this new form of reconnaissance e.g. V-nicks of a new machine gun position, trampled grass associated with newly erected barb wire, shadows of gun barrels or muzzle blasted bleached grass in front of a gun pit, and so on.


The tactical conclusion on the use of airpower had already been drawn two years before the war, when aerial observation cut short the annual 1912 British manoeuvres and allowed General Grierson's invading 'Germans' to embarrass a certain General Haig's defending 'British'. Grierson used aerial reconnaissance to discover a gap in Haig's lines, and exploited it to surround Haig. Haig didn't make use of his aeroplanes. Grierson concluded from the war games "Warfare will be impossible unless we have mastery of the air".


Fortunately for Britain the RFC came under the control of Hugh Trenchard, a man of unique vision, who had a sound understanding of the principal role aeroplanes should play in the conflict. In August 1916 he formalised the RFC's policy in this way:

"It is sometimes argued that our aeroplanes should be able to prevent hostile aeroplanes from crossing the Line and this idea leads to the demand for defensive measures and a defensive policy.... supposing we had an unlimited number of machines for defensive purposes, it would still be impossible to prevent hostile machines from crossing the Lines if they were determined to do so because the sky is too large to defend... the sound policy which should guide all warfare in the air would seem to be this - to exploit the moral effect of the aeroplane on the enemy. This can only be done by attacking and continuing to attack."


To achieve this end meant that the single-seater fighter became to crucial aeroplane of the Great War, because it was thought to hold the key to what some called "the war of the lenses". The importance of this role can be expressed best in statistical form. In June 1918, for example, fighters constituted 58% of the RAF's aeroplanes against 27% of two-seater reconnaissance machines and 15% of bombers. The growth of fighter squadrons as registered in April of each year suggests in addition the progressive realization of such importance:


1914 - 0 squadrons

1915 - 0 squadrons

1916 - 4 squadrons

1917 - 19 squadrons

1918 - 36 squadrons


Looking beyond the fighters to the overall importance of the air war, the fact that one quarter of Britain's military budget in 1918 was spent on the air force and that half of the £160 million in contracts outstanding at the end of the war were air force contracts should put the matter of the importance played by the aeroplane in the Great War in a fresh perspective.



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Pips: Historical Snippet 2 – The Canadians

It would seem that Canadian pilots horrified the 'stuffy' RFC establishment with their rough behaviour and laisse faire attitude as much as the Australian soldier did with the British Army. And yet, as they did with the Australians, the British came to deeply appreciate the skill and courage of the Canadian pilot. RNAS ace Leonard Rochford recalled: "they were a really wonderful bunch of fellows, although coming as I did from a rather sheltered home, they often shocked me". McFarlane Reid (an instructor at Stamford flight school described them as "a strange, rough, uncouth crowd; one wouldn't want to mix with them in society", nevertheless he approved of their "wild, keen spirit".


In late 1916, when RFC wastage was running at 25% monthly, the War Office approved an offer made by Canadian industrialists to build at their own expense an aviation factory and flight training school at Toronto. By 1918 this school was sending 200 pilots over to England monthly, and by the end of the war this Dominion with just under 10% of the Empire's population was producing a third of the pilots for the RAF.


Not only did the Canadians make up large numbers of the RFC/RAF they also provided the lions share of top killers. Bishop 72, Collishaw 60, Maclaren 54, Barker 50, Atkey 38, Claxton 37, Fall 36, McCall 35, Qiugley 33, Carter 31, McKeever 30 - without such men the RAF would have been hard pressed to have maintained it's cutting edge.



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Pips: Historical Snippet 3 - RAF Blues


Ever wondered why the newly fledged RAF chose blue as it's uniform colour on formation in April 1918?


Ironically this material had only recently become available in large quantities because the Russian Revolution had put that country out of the war; with the result that Russian officers uniforms, hitherto manufactured in Britain, had lost their market.



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Pips: Historical Snippet 4 – RFC Humble Beginnings


In 1909 The Committee Of Imperial Defence (CID) reported, "It had yet to be shown whether aeroplanes are sufficiently reliable to be used under unfavourable weather conditions. The Committee has been unable to obtain any trustworthy evidence to show whether any great improvement was to be expected in the immediate future."


In inimitable English fashion the Committee stated that it did not hold with the inflated claims emanating from across the Channel as to either the aeroplanes worth or it's achievements. The Committee went on to note the high cost of the aeroplane - £1,000 - and recommended instead that £45,000 should be invested in airship research.


As a result of this recommendation it was soon announced by the War Office that experiments with aeroplanes had ceased, "as the cost has proved too great, namely £2,500." Meanwhile by 1909 the French has spent £47,000 on aeroplanes for it's army, the Germans £35,000 on aeroplane research alone.


Despite such short-sightedness, with the aid of public pressure generated through the efforts of many enthusiastic young men the likes of Fulton, Dickson, Gibbs and Brancker, the Army undertook to establish on 28 February 1911 an Air Battalion of the Royal Engineers, effective from 1 April. Officer recruits could be selected from any Branch, dependant upon they having gained a Royal Aero Certificate independently at one of the many private flying schools around the country. The Army reimbursed the standard cost of £75 if and when the candidate passed. By the end of 1911 the Army had 17 aeroplanes in service, compared to 200 in the French Army.


In the same year Cabinet requested a technical sub-committee of the Committee of Imperial Defence (CID) be formed to consider future policy and make recommendations. The key members were David Henderson (then Director Of Military Training), Frederick Sykes (a staff officer) and Bertram Dickson (an early army pioneer). The committee moved quickly, recommending the formation of a new flying corps, divided into two wings, one naval, and one army. In addition a Central Flying School to be established (Upavon on the Salisbury Plain being chosen); and the army aircraft factory at Farnborough to become the Royal Aircraft Factory. Finally, that an Air Committee of the CID, with representatives from both Services, to act as an advisory body. Cabinet accepted the recommendations and the Royal Flying Corps, embracing all naval and military flying, was established under a Royal Warrant on 13 April 1912.


The Royal Navy resented that naval aviation be subservient to Army control, so independently and without authority the Admiralty, having already developed it's own training centre at Eastchurch, established an autonomous existence for it's flying branch by proclaiming the birth of the Royal Navy Air Service in May 1912. Such was the power of the Admiralty that this outrageous act went unchallenged. However it was not until 1 July 1914 that the RNAS was 'officially' recognised.


With Britain's declaration of war at midnight on the 4th August 1914 the RFC was in a sorry state. It possessed just 197 active service pilots. A fortnight after war had been declared, Sefton Brancker, as Director General of Military Aeronautics, drew up a list of all men left in the UK able to fly and discovered that only 862 men held the Royal Aero Clubs certificate (compared to 1,751 in France) and that of these just 55 were sufficiently advanced to leave immediately for active service, including middle-aged men such as Hugh Dowding, who was recorded as 'having had no practice of late'.

For some time such slender resources were not considered a great handicap, given that no aerial combats were taking place, and the wastage (from landing accidents and occasional ground fire) could be made up. Even as late as the summer of 1915 there were only 200 pilots in training on the eleven flying stations in Britain, and it was still assumed that gentlemen weekend flyers would keep the supply topped up. Indeed the War Office decreed that "members of the public who own their own aeroplane by encouraged to bring them to the Central Flying School where they can undergo their training there".


This lassie-faire attitude changed quite dramatically when casualties started to rise alarmingly due to improved ground fire with the advent of the static frontline. It was further exacerbated with the introduction of the Fokker E series fighter. A determined effort was made to recruit young men into the RFC through both newspaper advertisements and offering the opportunity for transfer from regular army units. Given that the pay was much higher in the RFC for pilot (even an observer), and that many men had quickly become disillusioned with trench warfare, the RFC recruiting stations quickly became inundated with enthusiastic young men. By the autumn of 1916 a team of sixteen doctors were examining approximately 200 applicants a day.


From that point on the RFC grew at a rapid pace. By the Armistice the original 197 pilots had become 26,000.



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Pips: Historical Snippet 5 – Squadron Rigging Maintenance


I should warn all readers that this is a lengthy explanation on what rigging maintenance involved, which was done on site at the Squadron base. Spare a thought for the riggers often working day and night was a quite common feature of their lot - and seldom appreciated by the pilots other than in a very general way. But woe betide any pilot who had a duff rigger assigned to his aircraft - his it would be that would fall apart in the air!


Usually after a week's flying (or with some Squadrons after a set number of hours aloft), or after a combat, the machine would be pulled from its hanger by the tops of the undercarriage struts and set in its fly position on top of padded trestles for what could be a two day check. The truth of the wings would first be checked with a steel tape and the truth of the fuselage by a string from the centre of the engine to the rudderpost. If there were any doubt, the whole team would get out templates, protractors, plumb lines and straight edges or invoke the skilled glance of the master rigger. If there was still doubt, the fabric would be unstitched and the machine reduced to its skeleton for re-rigging.


In such a naked condition the aeroplane might seem a flimsy structure of wood and wire. In the absence of more modern easily worked metal, engineers of the day-constructed machines of deceptive strength using materials and skills most readily available - those of coachbuilder and farm machinery manufacturers. Rigid and resilient, wooden airframes could absorb more punishment and be more easily repaired than metal ones. They required fewer tools in the making, and strength for weight was a match for duralumin, being weaker only in torsion. Great War aeroplanes, like Nelsons ships, represented the greatest achievement of an age-old technology whose passing was close to hand - hand shaping of wood in large structures with emphasis on feel, eye and experience.


The basic materials were of wood and wire. A process of elimination by 1916 had determined that ash and silver spruce was the perfect blend. Easily bent without splitting, yet able to resist sudden shock, ash was as useful to the aeroplane maker as to the ancient bow maker. In the fighter it became the four longerons which ran the length of the fuselage. Yet even the best ash was weak in compression and here silver spruce was found the perfect support, as it was able to withstand a compression force up to 5,000 pounds. With a propeller of Spanish mahogany or black walnut, no other types of wood were necessary.


The sinews, which held the timber in place, were of high tensile Swedish wire. Basic or acid process home -produced steel could not pass the Ministry of Munitions test which required it to be bent through 180 degrees in a vice five to thirty times according to gauge, let alone the pressure test of 120 tons per square inch. Two types were produced bearing the Ministry stamp - control wires of seven-strand cord, each strand of nineteen separate wires; and solid fuselage wire, stronger than cord by diameter but less so by weight.


About a hundred such wires held the aeroplane in shape. If the machine were to be rebuilt, each wire had to be tuned by turning its individual turnbuckle; the riggers adhering to a strict system and sequence. The principle was simple. An aeroplane, both fuselage and wires, was made of a succession of boxes, each box held in shape by cross-braced wires. One by one, each box had to be tuned to geometrical truth, starting with the engine-bearing wires and concluding with tailplane wires.

Truing-up was done for the upwards and sideways planes separately as riggers turned the thumbscrew fitment with which each wire terminated until the diagonals of each section were equal. This equality would be measured by a trammel - a wooden rod with two separately adjustable pegs on it. Then a plumb line would be used to establish verticality. When the whole system seemed about right, a string would be stretched from the centre point of the engine bearings to a marked point on the rudderpost. If all were in order, the string would be perfectly horizontal - a straight edge and spirit level were used to double check the eye's judgement. The rule was that, if any slight adjustments were needed, diametrically opposite wires should be loosened in proportion as analogues were tightened, the final test being an ear twang before the turn-buckles were locked to establish rigor mortis. The fuselage was complete.


Like the fuselage, the wings too consisted of struts and wires. Leading and trailing edges took no load, so that steel tubes in simple sockets kept the edges parallel and firm. Between these rods and eighteen inches apart was a sequence of H-section plywood ribs whose job it was to support the wing fabric tacked to rib centre. Since these ribs were compressed in flight, they were built with a bulge in the centre and, like the fuselage, made of spruce toughened with spliced-in ash. Cross-braced internal wires between the wings cancelled rival forces on the two planes, all such wires being duplicated for safety and sandpapered and painted against rust. If correctly tensioned, wing wires never sang whatever the pressure of flight (so if a pilot mentioned that to his riggers on landing they knew immediately that what had to be done).


Once they were attached to the fuselage, the angle of the wings was known to be critical, so wing adjustments took longer than the construction of the whole fuselage. Firstly they had to be true relative to the fuselage. Plumb lines were dropped from four points on the leading edge of the upper wing and various wires adjusted until the plumb lines were as one, viewed from the side. Then came the dihedral, that slight upward tilt of the wings away from the fuselage, which made for greater stability and checked a tendency to slither in a crosswind. The angle was commonly three degrees and on the top wing only. To achieve this, a straight edge would be placed against the leading and trailing edges, and the angle read off an inclinometer. Once correct, the front landing wires would be locked. By placing the upper wing in advance of the lower (stagger), lift could be increased. A stagger of about half the wing's width increased lift by roughly 10%. Such a distance would be set by measuring with a rule the distances either side of a plumb line dropped from the upper wing. Finally came the setting of the incidence. The leading edge always had a slight downward tilt, reinforced by the slightly hollow underside. By tinkering with incidence, the side profile was inclined to the line of flight, a low angle of incidence giving a higher speed and a higher angle giving a better lift and a slower landing speed.


Adjustment was by checking straight edges placed under the ribs with a inclinometer or Abney level, care being taken that incidence was not greater at the tip than at the root (wash-in) or conversely (wash-out).

Similar checks had to be finally made on the tailplane unit. The Abney level measured incidence to flight direction (never vertical so as to counter the spiralling air stream from the revolving propeller) and the spirit level checked that the front spar and hinged tube were horizontal before the fin was bolted on and the rudder hinged to fin and stern post. The elevators, similarly checked, were then hinged to the rear of the tailplane and rigidly connected, so that if the controls on one side were damaged, the elevators could still e operated from the other side alone.


The whole machine was ready for the inspection of the master rigger, whose skills were more related to a cooper or freestone cutter than to any mechanic of the present day. He would perform both eyesight tests and measure and level tests. Once he was satisfied with the result but one stage remained. Clothing the skeleton.

For this about 250 yards of fabric was required for a small fighter. The best material was unbleached flax linen of F1 British Standard, with eighty ends in the wrap and ninety picks per inch in the weft. Such fabric weighed 4 ounces per square yard and could withstand pressure of up to 90 pounds per square inch, stouter threads being woven in at intervals to check any tendency from tearing forces. Towards the end of the war, when linen ran in short supply, long staple American cotton took over. It was much cheaper, slightly lighter, but only half as strong as the original fabric. There was never an acceptable substitute for aeroplane linen.


Hide glue fastened the fabric to the wooden ribs, with sewed kite cord as doubling security, each stitch at three-inch intervals and knotted with a Flemish slipknot with exposed portions taped. When this had been done, the whole skin would be washed with dope. This was of two kinds. Nitrate cellulose with wood chemical solvent, though faster to burn in the air, was easier to obtain than acetate, for which shell makers competed. Five coats of this dope would be applied, time for drying being allowed between each application and painting done with care, since sandpaper could not be used to eliminate error. It was reckoned that the first two coats tightened the fabric and the third filled t, proofing it against petrol or oil splashes as well as giving it a good base for camouflage. The final coat of varnish smoothed and reduced water absorption by 1,000%. Such varnish was of lacquer and, since resin dissolved in oil took three days to dry, turpentine was the usual solvent, with the addition of camouflage paint. The effect of these liquid additions was to increase the strength of the fabric by 25% and the weight by 100%.


The completed aeroplane would then be handed over to the 19 strong armoury section... but that's another story!



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Pips: Historical Snippet 6 – The Armoury Section


The Armoury Section of a standard RFC single-seat fighter Squadron was nineteen strong. A reconnaissance Squadron had twenty-six, and both a day-bombing Squadron and a two-seater fighter Squadron each had thirty-three men attached to the Armoury section. Although nominally under the command of the squadrons Engineering Officer, the unit was directed in day-to-day activities by a senior Sergeant.


Much of the armoury's time was spent with bullets, carefully examining each of the 50,000 (three days supply in battle conditions), which were in stock. A hangfire by a single bullet of just 1/250th of a second could shoot off a propeller blade and shake the aircraft to pieces in the sky, so that by 1918 the checks on each bullet were such that an accident due to faulty ammunition was reckoned just once per 35,000 shots.


Then came the equally time-consuming routine of belt filling. Just fitting bullets of a single type into a magazine of a Lewis took ten minutes for a ninety-seven round magazine. The Vickers needed 500 per belt, each fitted into the metal linkage and each belt load varied by the requirements of the individual pilot. The choice was between the standard nickel-coated lead bullet, the armour-piercer with a steel core, the tracer, the Buckingham or the Pomeroy. The Tracer, with one part of magnesium to eight part of Barium peroxide in the base, made accurate shooting at close range easier, but it also burnt itself out of shape making it's trajectory unreliable. The blunt nose of the Buckingham was ideal for balloon busting and did greater damage if it hit any target. On the other hand, the lack of streamlining made it's trajectory as variable as the tracer's, quite apart from the reactions of the Germans if they captured a prisoner with such blunt-nosed ammunition in his belts. The heavy punch of the Pomeroy also had its drawbacks. The nipping of the explosive mixture between bullet core and envelope made it liable to premature explosion in the gun barrel. Each pilot therefore had to work out his own preference between reliability, heavy impact and projectile visibility - and then inform the Armoury section so that they had sufficient time to load his guns and fit them to his aeroplane. The American Hartney liked to have his guns fitted in the sequence of tracer, standard, Pomeroy and armour piercing. Sholto Douglas on the other hand specified four standard to one tracer, and Porter one to five. Elliot Springs sequence was tracer, Buckingham, standard. Mick Mannock preferred two standard, one tracer, one Buckingham.

(When the war ended, Buckingham's Coventry factory was employing 500 men who had produced 26 million bullets for the air force during the was at a cost to the Service of 2 shillings per bullet!)


Once an aeroplane was finished with for the day it was first serviced by the engine and riggers sections, then placed in the hands of the Armoury. If fitted with a Lewis gun it would be removed, dismantled and serviced, then reassembled and refitted to the aeroplane. The Vickers gun would usually be left on the machine and just cleaned on the outside with an oily rag after dry oil had been removed with spirit of turpentine and the innards purged with boiling water poured down the barrel, followed by cleaning rods and flannelette. A stipulation that all aircraft manufacturers had to abide by (who fitted Vickers to their machines) was that the gun had to have the provision to be tilted "in situ" to the vertical position for this crucial cleaning process.


The aeroplane would then be pushed to the armourers ground target area and set-up in it's flying position so that sample ammunition belts could be fired at the target and the gun zeroed in. Each belt (or mag if a Lewis) would be fitted with however the pilot preferred his ammunition loaded, and the sights adjusted and harmonised so that bullet flow came together at the point required by the pilot.


In addition to servicing the aeroplanes machine guns the armoury section was also responsible for maintaining the Squadrons store of 20lb, 50lb and/or 112lb bombs, bomb racks, bomb release equipment, servicing each pilots' Webley service revolver (handed over by the pilot after completing his last patrol of the day), Verey pistols, flares and the cartridge case bags that caught expended ammo casings. A typical day commenced around 3.00am and finished roughly at 9.00pm.



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Pips: Historical Snippet 7 – Practical Rules Of Air Fighting


It's fairly safe to say that almost everyone is aware that Oswald Boelcke was the first man to formalise the art of air fighting in his famous 1916 Dicta Boelcke. These rules were widely published and distributed amongst the Jasta's, and became in time the bible of German air tactics.


Across the Lines British and French aces were also spreading the knowledge on how to fight in the air. Unlike the structured German approach however this knowledge was very much a word of mouth approach and as such was limited to within Squadrons. There were no formalised set of rules (as such).


In early 1918, on appointment to a new Squadron as a Flight Leader, one man put down on paper for his new Squadron the benefit of his hard earned knowledge on how to fight successfully in the air. He titled this "Practical Rules Of Air Fighting". That man was Mick Mannock. How right the Rules were is borne out by the success of 74 Squadron: in eight months of combat it claimed a creditable 140 aircraft destroyed and 85 'out of control', for a modest 15 pilots killed or taken prisoner. By war's end most fighter Squadrons had received a copy of Mannocks Rules, which were:


1. Pilots must dive to attack with zest, and must hold their fire until they get within one hundred yards of their target.


2. Achieve surprise by approaching from the East. (From the German side of the front.)


3. Utilise the sun's glare and clouds to achieve surprise.


4. Pilots must keep physically fit by exercise and the moderate use of stimulants.


5. Pilots must sight their guns and practise as much as possible as targets are normally fleeting.

6. Pilots must practise spotting machines in the air and recognising them at long range, and every aeroplane is to be treated as an enemy until it is certain it is not.


7. Pilots must learn where the enemy's blind spots are.


8. Scouts must be attacked from above and two-seaters from beneath their tails.


9. Pilots must practise quick turns, as this manoeuvre is more used than any other in a fight.


10. Pilot must practise judging distances in the air, as these are very deceptive.


11. Decoys must be guarded against — a single enemy is often a decoy — therefore the air above should be searched before attacking.


12. If the day is sunny, machines should be turned with as little bank as possible, otherwise the sun glistening on the wings will give away their presence at a long range.


13. Pilots must keep turning in a dogfight and never fly straight except when firing.


14. Pilots must never, under any circumstances, dive away from an enemy, as he gives his opponent a non-deflection shot — bullets are faster than aeroplanes.


15. Pilots must keep their eye on their watches during patrols, and on the direction and strength of the wind.

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Pips: Historical Snippet 8 – The Appalling Strain Of Air Combat


During WWI it was an almost universally held belief by all non-flyers that the pilots of any air force, be it the RFC, Aviation Militaire or the Luftstreitkräfte fought a cushy war. Even some pilots held that view, for example Cecil Lewis wrote:

"Under the most arduous conditions we were never under fire for more than six hours a day. When we returned to our aerodromes the war was over. We had a bed, a bath and a Mess with good food and peace until the next patrol. Though we always lived in the stretch or sag of our nerves, we were never under bodily fatigue, never filthy, never soaking wet for days on end, never verminous or exposed to the long, disgusting drudgery of trench warfare".


A casual visitor to a Squadron might easily have gained exactly that impression. For he would have seen pilots possibly swimming, playing tennis or slumped in armchairs. And being waited on by uniformed batmen. By all apearances a real Gentleman's war.


But he could not have been more wrong. A serious observer would not have paid attention to the light and carefree banter, but rather would have focused on the drawn faces, the clench hands, twitching eyelids, loss of appetite, men constantly glancing at the clock, tempers flaring and the quick birdlike movements that give lie to the outwardly relaxed atmosphere. Sholto Douglas was often surprised at just how quickly the faces of new pilots aged almost overnight following their first couple of missions over the Front, and how tea-totallers quickly became heavy drinkers. Elliott Springs too thought that the faces of twenty-four year olds were like those of men aged forty or more. Friends of Lanoe Hawker, on his first leave in April 1915, were surprised by how serious he had become, they’re being almost no leftover carefree boyishness in his manner.


The reasons for such changes in men were the depth of anxiety, uncertainty and fear of the unknown that gripped each man on each patrol. Not so much the fear of actual death, but the waiting of death and the undignified, self-destructive thoughts which went with the waiting and tension that built up to the point that a pilot was exhausted emotionally and physically.


Sleep was the worst time for most men. During the day a pilot could almost always keep busy on the ground awaiting his next mission and, perversely, actually flying was the best time, as a man did not have the time to reflect on the fears that plagued him. But nighttime, when all was quiet and a man's defences were down in slumber, and then the devil came to play. Almost every diary or memoir mentions nightmares. Ira Jones once wrote:

"Had a terrible nightmare last night. Jumped out of my bed eleven times even though I tried to stop myself by tying my pyjamas strings to the bed. Poor old Giles got fed up to the teeth as I kept waking him up. It was the usual old business of being shot down in flames and jumping out of my aeroplane. One of the nightmares took a new line though. I was forced down and crashed on top of a wood. As I wasn't hurt, I slid down a tree and tried to hide in a bush but the Hun kept chasing me and shooting me up wounding me every time. At last he landed in a clearing and chased me with a revolver until he caught me and killed me".


In his diary for June 1917 Mannock wrote how much he was looking forward to leave, since he couldn't sleep. Unable to eat or sleep, Balfour's noted in his diary in 1916 how 'the old troubles are coming back' and how he and his roommate would light candles 'to hide the dark'. During August 1918 Springs found himself fighting Germans all night, as did Lee who wrote:

"Trench strafing was beginning to get on my nerves. Apparently I was yelling in a dream and Thompson had to come into my cubicle and waken me. I was shaking and sweating with it. In the nightmare I was diving, diving into a black and bottomless pit with hundreds of machine guns blasting endlessly up at me".


Although aerial medicine was in it's infancy stress, fatigue and their effects had been recognised by those in authority, consequently in the RFC a 'tour' was set at six months, with a two-week break half way. Some observant Squadron commanders however would be on the look out for a pilot acting out of character and send him on a short leave (even if he wasn't due for it) to help break the pressure build-up. But many did not. The air service medical laboratory issued a report to Trenchard which surmised that 80% of groundings were nervous related and that 50% of all operational pilots developed serious neurosis during their tour of duty.


What wasn't realised then, indeed wasn't for many years to come, was that flying was physically demanding in itself, even without the added horror of being a target of machine gun bullets or anti-aircraft shells. It all added to the physical wear and tear that robbed a pilot of his ability to withstand stress.


And it began even before he took-off. An engine warming up at full revs generated about 120 decibels and propeller tips revolving added a second source of noise at 125 decibels. That compares with an unsilenced pneumatic drill at 110 and meant that about a quarter of all war pilots suffered marked permanent hearing loss. In addition to the noise, the engine vibrated in its wooden mounting. Bearing in mind that vibrations of one tenth of a Hertz are detectable to the human body, a fighter aeroplane at full throttle vibrated between 100 and 200 Hertz, which was sufficient to arouse sensations of fear and make a pilot physically unable to relax.


On a conscious level windblast was perhaps the first change to become noticeable to a pilot. At ground level a wind blast of 40mph has no noticeable effect on the body. In an open cockpit at 10,000ft it chaps the lips and skin, alters breathing rhythms and increases general body metabolism by approx 30%. High altitude means penetrating, paralysing cold, perhaps the biggest enemy. A comfortable ground temperature of 65 degrees Fahrenheit (18 degree C) would have dropped progressively to 1 degree Fahrenheit (-16 degree C) at 16,000ft - a fairly common patrol altitude. Factor in wind chill and the pilot would be operating in a -45 degree Fahrenheit (-42 degree C) environment!


The effect on the body is pronounced. At 50 degrees (F) the body works effectively. By minus 30 degrees (F), a common enough temperature at fighting altitudes even in mid-summer, 75% of efficiency would be lost, with circulation slowed, breathing diminished and body temperature falling. The combined effect could almost turn a pilot into a sleepwalker.


In WWI the pilot wasn't aware of the above. But he would have been aware of the physical effect nevertheless. First he would lose sensation in his feet and hands, then the back and chest, finally abdomen and legs. Parsons described one occasion when he felt the bitter cold throughout his body and the sensation of a contracting scalp, while in December 1916 McCudden felt so cold on one occasion that he didn't bother to look around and didn't care if he was surprised and shot down! Flying at 17,000ft Crundell described a similar experience, writing of a feeling of breathing ice and of crouching down in his cockpit and steering blind, just relying on his compass.


Lack of oxygen at high altitude was less uncomfortable than the cold, but much more serious in it's effects. An American mission was the first to remark on how pilots became unfit for flying following prolonged work at altitude. RFC doctors Birley, Corbett and Flack then did a study using pilots flying with and without bottled oxygen and found that the critical height was 10,000ft, at which level oxygen pressure in the lungs became insufficient to saturate the haemoglobin of the blood. The great danger was that lack of oxygen impaired the ability of the brain to function, but being a gradual effect it was often hard for pilots to realise what was happening and take corrective action i.e. drop down in altitude. Admittedly tolerance could be built up over time, but even McCudden and Fonck often complained of intense headaches and a persistent pain behind the eyes after high altitude flights.


Intense cold, oxygen deprivation. If that wasn't enough for the pilot to handle regarding the physical effects of flying at high altitude there was one more - increased blood pressure. At ground level a healthy pilot would have a blood pressure of around 120. At 6,000ft it would have become 200, causing dental fillings to throb and congesting the surface blood vessels of the brain, so that by 10,000ft the gap between the brain and the skull would have disappeared, giving the pilot the sensation of the flying helmet holding the skull in a vice-like grip.


The final physical hardship for the pilot was gravity, or 'G' forces. Zooms from a dive of 160mph could result in at least 5G on the pilot, perhaps even as high as 7G. Wild manoeuvring during dogfights often resulted in a pilot pulling between 3 and 6G for a considerable time, which was physically and mentally exhausting.


As the pilot completed his patrol and lost altitude for his return to earth, so the temperature increased, the oxygen became richer and the flying slightly more relaxed. The physical strain however has not finished with him. Increased oxygenation and improving circulation were both intensely painful initially, so much so that Fullard wrote of often climbing for short periods several times during his decent to slow down the agonising process of thawing out. Vincent considered the high point of pain at around 3,000ft when it became very difficult to clutch the joystick. Ears would also play up, forcing pilots to constantly blow their nose or chew gum to equalise the pressure. Approximately 15% suffered ear trouble at some point, Udet being one, Rickenbacker another.


The final act of landing was perhaps one of the most dangerous moments for a pilot. His was tired, neck and back muscles still tensed and tight, concentration low and his nervous system would be showing signs of acute fatigue. Yet at that point he would have to exhibit clear identification of distance, height and speed, manipulating several controls of a complex machine in precise order to bring the aeroplane down smoothly and safely. No wonder there was so many more aeroplanes lost to landing accidents than to actual combat losses.


Rickenbacker's solution to the above was to circle the aerodrome twice so as to give himself time to calm down and adjust focus. As a veteran Rickenbacker well knew the hazards of crash landings, where 70% wrote off the aeroplane and 50% injured the pilot.



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Pips: Historical Snippet 9 - Most Claims By German Fighter Type


Detailed below are the figures of claims by fighter type compiled over many years by Dr. Frank Olynyk, who has drawn them from a wide range of sources and historians. He is arguably the most knowledgable man on the subject. They are as complete as Dr. Olynyk (and others) have been able to determine. Hopefully one day he will actually get around to publishing his wealth of information in book form.


They don't constitute all claims, as there are many instances of where the aircraft type is unknown for a claim being made. A not unusual situation given that many Jasta's operated a mix of aircraft at differeing periods. The figures below only relate to when the type of fighter flown is definitely identified in relation to the claim made.


Albatross Series D.I to D.V



Fokker E. Series



Fokker Dr.1



Fokker V.III Series



Hablerstadt D.II to D.V Series



Pfalz D.III Series




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Olham54: Field or Trench Maps from the Great War


Here, you will find original trench maps, with hand drawn trench lines, having names like "Curry alley", "Chutney alley" etc.

The best for us pilots: the airfields are drawn in. Mostly German ones though, because they were so close to the "mud".

You can zoom into the maps by several percentage steps - until you can read everything, or make a screenshot of your field.




Unfortunately, the McMaster people have some trouble with the viewing software right now (Feb. 09), but assured me in a Mail, they are working on it. And it should be possible to view them in standard Internet Explorer.



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Dej: Interactive Map of Airfields


Here you will find an interactive map showing a large part of the Western Front and plotting most airfields and the movement of Squadrons or Jastas:




With this you can get an idea of whom you might be facing in your time and place and campaign, which helps (for me anyway) with the immersion factor by substituting for intra-unit gossip about who's where.


It's pretty accurate, but not 100%. If you find an error, the developer's email is available on the Help link, and he'll welcome corrections.



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Bletchley: Shooting Down 2-Seaters


From: 'Fighting in the air' by Maj. L W B Rees, 1916


"When one sees a machine one is apt to think that hits anywhere will be effective. One is trained to imagine that a small thing, such as a frayed cable, is certain to cause a wreck. Yet machines go up every day and return absolutely under control, but having dozens or even hundreds of holes in different places... The only useful target to really attack is the pilot himself. This target is very small, being of a size about 2 ft by 1 ft 6 inch, and even then shots which hit this target are not certain of putting the Pilot immediately out of action. Therefore, one must concentrate one's attention and one's shooting on this small target, the Pilot, til one has attained one's objective.


If we attack a machine from directly in front or in rear the engine may cover the Pilot's body, or vice versa. This is the minimum target which the machine can present, and any shots hitting the target do damage, but there is a lot of room round the target in which shots which do not actually strike do no damage.


Now, if we imagine a machine being attacked from the side, or straight from above or below. The target which we must aim for still remains the same small one, but now the rounds, which before were non-effective, will hit the engine and Observer, and will become effective... This leads one to suggest that the way to attack is straight at an enemy from above, below or from the side"


He compares the use of tracer rounds for deflection shooting with the practice of using "the garden hose on the nurse or gardener" smile.gif



From: 'Fighting the S.E.' by Capt. J T B McCudden, 1918


"The position from which a pilot can do most damage to a 2-seater at the least risk to himself and machine, is 100 yards behind it and 50 feet below... I find that it is very difficult to shoot the pilot from directly behind because you probably hit the gunner first, who collapsed in a heap in his cock-pit, and you go on shooting and are simply filling the gunner with lead, and also a huge petrol tank which is usually situated between pilot and gunner, and the pilot gets off without a scratch...


Most 2-seaters will stand a lot of shooting about before giving any evidence of damage ...[but]... one should be very alert when firing at an E.A. at close range, so that, when E.A. falls to pieces, as they very often do, after being fired at a lot, that one does not fly through the wreckage. I narrowly missed flying through a pair of E.A.'s wings recently"



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Bletchley: Sopwith Camel Engine and Performance Figures


Hello All,


We have only the one Camel in OFF currently, but in anticipation of further variants I'm posting some info. here that might be helpful/interesting to devs. and others:





Firstly, Clerget:



As well as the British Gwynnes/Bentley built 'long stroke' Clerget 9BF, rated at 150 hp at 1250 rpm(Gwynnes) and with a compression ratio of 5.1:1 (Kacey) or either 5.14:1 or 5.29:1 (Bruce) and delivering around 148 hp at msl (Air Board), there were several French built versions of the Clerget 9B (including the 9Ba, 9Bb, 9Bc) with outputs ranging from around 125-145 hp, although only the 9B and British licence built versions of the 9B (Gwynnes for the Admiralty, and Ruston & Proctor for the RFC) appear to have been used on the Camel. The French built Clerget 9B was nominally rated at 130 hp at 1250 rpm, with a compression ratio of 4.36:1 (Kacey) or 4.56:1 (Bruce), and it delivered around 125-126 hp (Air Board), whilst British licence built 9B Clergets, although rated at the same 130 hp, are known to have been less reliable and suffered from a loss of compression and a lower output (Bentley / Gwynnes / Kocent-Zielinski ). The RFC obtained their Clerget 9B engines either from French suppliers or from British licensed contractors such as Ruston and Proctor, at least until April/May of 1918 when the more powerful and reliable British built Clerget 9BF became available from RNAS stocks after the formation of the RAF (TomVrille). The Admiralty also had a contract with a British supplier, Gwynnes, to supply them with a licence built Clerget 9B, but this appears to have been used mainly on RNAS Strutters and Triplanes, although some of them may have been used on early RNAS Camels in the early summer of 1917 when the new Bentley AR1 engine was still not available in sufficient quantity to meet demand, and before the Gwynnes/Bentley Clerget 9BF was available to make up the shortfall.



Secondly, Le Rhone:



There appear to have been at least three variants of the French built 110 hp Le Rhone in use by the British, and a somewhat less reliable British built version used on the DH5 and possibly elsewhere. All were used primarily, if not exclusively, by the RFC, as all the Sopwith built Le Rhone Camels that are known to have been sent to the RNAS appear to have had the Le Rhone engines changed out for either the Bentley or Clerget engines (Bruce). The Le Rhone 9J (or 9Ja) and 9Jb appear to have been the two main Le Rhone engine variants used to power the RFC Camel, although the 9Jby may also have been used from late 1917 or early 1918 onwards.



The Air Board Data Sheets list these three versions, all nominally rated at 110 hp, as (1) Le Rhone with C. I. (Cast Iron) pistons (War Office), normal full rpm 1250 with an output estimated at 82.5 hp at 10,000 ft (approx. 120 hp at msl); (2) Le Rhone with aluminium pistons (War Office), normal full rpm 1250 with an output estimated at 92.8 hp at 10,000 ft (approx. 135 hp at msl); and (3) Le Rhone, normal full rpm 1300 with an output estimated at 99.25 hp at 10,000 ft (approx. 145 hp at msl). From the Air Board Data Sheets we can also see that one of these variants was flight tested in July 1917 on the Strutter and the DH5, delivering 125/126 hp at 1250 rpm, whilst in the same month another of the variants was flight tested on the Camel, delivering 137 hp at 1250 rpm. By bringing these two data sets together, I would guess that the engine tested on both the DH5 and Strutter was probably the Clerget 9J (or 9Ja), whilst that tested on the Camel was probably the 9Jb. I would also guess that the third variant, running at 1300 rpm, was probably the Clerget 9Jby (normal full rpm 1350, according to Hartmann).



Thirdly, AR1/BR1:



There appear to have been three distinct variants of this in use operationally, all on RNAS Camels, from June 1917 onwards:



The Air Board Data Sheets list two of these: the original AR1 protoype flight tested in a Camel in May 1917, rated at 150 hp (but by Morse at 130 hp) at 1250 rpm, with a net output of about 127 hp (Heron) and a compression ratio of either 4.9:1 (Kacey), 5.2:1 or 5.29:1 (Bruce); and a later high compression BR1 rated at 150 hp, delivering 154-158 hp (sources vary, but 158 hp according to Nahum) at 1250 rpm with a compression ratio of 5.7:1 (Bruce), and with larger induction pipes and 2mm holes. After delivery of the first Camels with the early AR1 had already been made to units in France, W.O. Bentley discovered that drilling 2mm holes in the induction pipes could raise output by an extra 11 hp (gross?), and this new intermediate AR1/BR1 variant, with a compression ratio of 5.2:1 was tested on Camel B.3835 in July 1917 (Bruce), and this became the standard low compression version until the high compression BR1 was tested in August 1917 (Air Board) and phased in to operational use during the autumn of 1917 (Bentley).



Fourthly: Gnome Monosoupape 160 hp: although used by the US Air Service, this engine appears otherwise to have been used in only very small numbers, mostly on trainers. This was rated at 150 hp at 1200 rpm, although maximum output was 202 hp (manufacturer's figure) or 168 hp at 1380 rpm (tested Air Board figure). The estimated output at altitude was 127 hp at 6000 ft., 113 hp at 10,000 ft., 96 hp at 15,000 ft. (Air Board)






(The following is based on the official British test data reproduced by J.M. Bruce in his 'Sopwith Camel F.1' Profile no.31. As the British did not usually differentiate by name between the many different types or variants of Clerget, Le Rhone or even Bentley engines, using just the nominal engine rating in most cases, I have added the French notation myself using the 'educated guesses' introduced above. If these guesses turn out to be awry, please adjust nomenclature accordingly)



The first batch of RNAS Camels, delivered to France in June 1917 with the unimproved early AR1 engine appear to have had little better performance than the early RFC Camels, as although this Admiralty version appears to have been somewhat faster than the R&P Clerget 9B and the Le Rhone 9J/Ja Camels (111.5 mph at 10,000 ft , as against 104.5 mph for the Ruston & Proctor built Clerget 9B Camel, and 108.5 mph for the Le Rhone 9J/Ja Camel), it was slower than both the standard Clerget 9B Camel (113 mph at 10,000 ft) and the Sopwith built Le Rhone 9Jb Camel (111.5 mph at 15,000 ft). Although the modified 'intermediate' AR1 / BR1 Camel (with the 2mm holes drilled in the induction pipes) improved on this (110 mph at 15,000 ft), and was better than these early R&P Clerget and Le Rhone Camels, it was still not as fast as the Le Rhone 9Jb Camel or the Clerget 9BF (113.5 mph at 15,000 ft). The final version of the BR1 (high compression) Camel (with a level speed of 114 mph at 15,000 ft) was slightly faster than the Le Rhone 9Jb Camel and roughly equivalent to the Clerget 9BF Camel.



In climb performance both the early RNAS AR1 Camel (5 min 30 sec to 6,500 ft / 9 min 50 sec to 10,000 ft / 20 min to 15,000 ft) and the 'intermediate' AR1/BR1 Camel (5 min 30 sec / 9 min 25 sec / 18 min) were better than either the R&P Clerget 9B Camel (6 min 40 sec / 11 min 45 sec / 23 min 15 sec) or the standard Clerget 9B Camel (6 min / 10 min 35 sec / 20 min 40 sec), but both were slower than either the RFC's Le Rhone 9J/Ja Camel (5 min 15 sec / 9 min / 17 min 20 sec) or Le Rhone 9Jb Camel (5 min 10 sec / 9 min 10 sec / 16 min 50 sec). The Clerget 9BF Camel was faster still (5 min / 8 min 30 sec / 15 min 45 sec), although the final high compression BR1 Camel was just marginally faster (4 min 35 sec / 8 min 20 sec / 15 min 55 sec) than the Clerget 9BF Camel.






The RNAS were the first to deploy the Sopwith Camel in France, in June 1917, and the first batch of Admiralty Camels were powered by either the early Bentley/Humber AR1 or the Gwynnes Clerget 9B, the AR1 being the preferred power unit (Mottram). But the RFC were not far behind, with the delivery of R&P Clerget 9B Camels, Clerget 9B Camels, Le Rhone 9J/Ja Camels (from Portholme Aerodrome, and others) and 9Jb Camel (Sopwith) from July of 1917 onwards (J.M. Bruce). The RNAS AR1 engines were soon 'upgraded' to the intermediate AR1/BR1, in or after July 1917, by drilling 2mm holes in the induction pipes (either at the factory, or at the RNAS squadrons for those AR1 engines already in service). This was followed by the introduction of the high compression BR1 to RNAS squadrons from the autumn of 1917 onwards (Mottram / Bentley / Air Board). During the Winter of 1917 the RFC tried to standardise on the Le Rhone engines (because of their slightly better climb) in preference to the Clerget 9B, although it appears that there were never really enough of the Le Rhone engines to do this fully (Kocent-Zielinski). When the RFC and RNAS came together to form the RAF on 1st April 1918, former RFC stocks were made available to the former RNAS units - with, for example, No.8 RNAS being refitted with Clerget engines from RFC stocks after it 'lost' all its Bentley engines in the German spring offensive (Draper) - and it seems likely that Admiralty stocks of the Clerget 9BF engine were also being sent to replace remaining RFC Clerget 9B engines by May of 1918 (TomVrille). At least some of the remaining 9J and 9Jb Le Rhone engines may also have, at that time, been replaced by the Clerget 9BF engines, although it is also possible that these were instead replaced by Le Rhone 9Jby engines - as there were still 821 Camels on strength at the Armistice with either a Le Rhone or Gnome Monosoupape engine (the latter used only in small numbers, mainly on trainers) as compared to 1342 with the Clerget engines and 385 with the Bentley BR1.






Although the RNAS Camels would appear to have had a general performance edge over the RFC Camels for much of the period under examination (and particularly from the autum of 1917 through to the spring of 1918), this edge does not seem to have been either so clear-cut or so distinctive as most general accounts would lead us to believe. In the summer of 1917, in particular, at least some of the RFC Camels (those with Le Rhone engines) may even have had the edge over the RNAS Bentley Camels (at least in terms of their climb performance), whilst from April 1918 through to the end of the war most of the former RFC Camels appear to have been up-engined to a more or less identical performance level as that of the former RNAS Bentley Camels. In addition to this, at any one time there would have been a mix of engine types in use as new engines were phased in to replace older ones, and as some suppliers continued to supply the obsolete variants from their existing contracts. Although evidence of aircraft wastage and replacement rates (Fill) indicates that this process might have been a rapid one, even in quiet periods, this process of overlap would nevertheless blur such distinctions even further.









Gwynnes Ltd. Clerget patent aero engines (9B & 9BF): instructions and list of parts. c.1917 (facsimile reprint by Camden Miniature Steam Services, 2001. ISBN 0953652319).



Air Board. Data for structure and stability calculation of aircraft. Air Board, August 1917



Kacey: http://www.theaerodrome.com/forum/ai...2-engines.html



Bentley, W.O. W.O.: the autobiography of W.O. Bentley. Hutchinson, 1958



TomVrille http://www.theaerodrome.com/forum/ai...-rh-ne-9j.html



Hartmann, G. Moteurs de legende: le Clerget 130 ch



Kocent-Zielinski, Edward. Sopwith Camel. Kagero, 2003



Bruce, J.M. The Sopwith Camel F.1. Profile Publications, no.31



Morse, William. Rotary engines of World War One. Nelson & Saunders, 1987 (ISBN 0947750061)



Heron, S.D. History of the aircraft piston engine: a brief outline. Ethyl Corp., 1961



Nahum, Andrew. The rotary aero engine. HMSO, 1987 (ISBN 0112904521)



Mottram, Graham. W.O. Bentley's aero-engines. W.O. Bentley Memorial Foundation (Publication no.5), 2003 (ISBN 0954090128)



Draper, Christopher. The mad major: the autobiography. Air Review, 1962.



Fill http://www.theaerodrome.com/forum/ai...e-figures.html

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Bletchley: WWI Altitude Compensating Carburettors


One more for Shredward's file smile.gif


Altitude Compensating Carburettors



The need for altitude compensation was not apparent at the start of the war, as the aircraft rarely flew above 5000 feet and the early rotary and stationary engines of that period therefore had no need for any additional mechanism to compensate for the effects of the reduction in air density experienced at higher altitudes. The early Gnome rotaries, for example, had a bloctube carburettor but no throttle or mixture control levers in the cockpit for the pilot to adjust either engine speed or fuel/air mixture - this was done on the ground, before the aircraft took off - and the early stationary engines appear to have had somewhat primitive float-chamber carburettors that were almost identical to those used on motor vehicles (but cast in aluminium, rather than bronze, to save on weight). It was nevertheless well understood that, as an aircraft ascended, there would be a corresponding reduction in engine power roughly proportional to the reduction in air density (itself dependent on changes in temperature and pressure, and therefore variable according not just to height but also to season, geographic location and weather). But it was at that time less well understood that there would also be an increase in the fuel consumption and eventually a drop in engine power and rpm associated with a growing imbalance in the fuel/air mixture - a gradual over enrichment of the mixture as air density decreased. This was not fully understood at the time as the full effects of this were not immediately apparent at altitudes much below 6,000 feet.



The first response to the problem was to build bigger engines. As it was known that the 50 hp or 80 hp engines then in use would only deliver up to half this engine power at higher altitudes, because of the lower air density, a 100 hp or 160 hp engine would therefore be required to deliver the same power up to these altitudes. But it was only when they got to operational heights above 10,000 feet that they appear to have realised that, even with these bigger engines, they were still not getting the power expected and the engines were consuming more fuel than they should have done. The Allies appear to have been the first to have fully realised why this was so, or at least the first, in mid 1916, to design and then implement a mechanism for correcting this imbalance in the fuel/air mixture. They designed and developed a new type of float chamber carburettor employing a "vacuum" or "leak hole" mixture control for their stationary engines (the rotary engines did not require one as, with the exception of the early Gnome monosoupapes, the use of a bloctube carburettor with separate throttle and mixture controls gave the pilot full manual control over the air/fuel mixture for both load and altitude changes). The first of these new carburettors was probably a Zenith, and probably the 48 D.C. Zenith carburettor fitted to the 150/180 hp Hispano-Suiza engines used to power the Spad VII in mid to late 1916. This was followed by the Zenith 55 / 58 D.C. and the Claudel C7 carburettors used in the 200 hp Hispano-Suizas and the Wolesley Viper aero engines; RAF1A carburettor fitted to the RAF4a engine of the RE8 and BE12 (not to be confused with the RAF1a engine, that had an early non-compensating Claudel carburettor); the Claudel Hobson (Hobson Claudel to the British) HC7 and HC8, and various other 'custom' adaptations of these Zenith and Claudel carburettors added to the Siddeley, Salmson, Rolls Royce and Liberty engines; the Zenith D.C. 65 used on the 300 hp Hispano-Suiza; and then the 48A carburettor used on the ABC "Wasp" radial. They were all different in design detail, but they all worked in much the same way, by metering down the fuel to compensate for the decreasing air density



The difference this 'vacuum' control made is illustrated by a test flight made with this type of carburettor, where "the aeroplane had a ceiling of no more than 12,000 ft so long as the vacuum control was not used", but with the control in action "the aeroplane climbed steadily to 17,000 ft" before reaching the limit of this altitude control's ability to keep the fuel/air ratio constant. (ABC Wasp manual).



This is from the instructions for use of the Zenith 65 D.C. carburettor:



"Below 6000 ft use of the altitude control lever will not perceptibly effect the power or rpm; but if the control is left shut after climbing to 3000 ft the petrol consumption will be unnecessarily high. To obtain the maximum air endurance...the altitude control lever should always be partially opened at heights of 3000 ft and over. The precise amount of opening should be determined by the tachometer reading, the control being opened to the point at which any further opening will cause loss of rpm. The throttle and altitude control levers open and shut in the same direction. The pilot pulls them both towards him when climbing, and pushes them both away from him when diving". (from the 300 hp Hispano-Suiza maintenance manual. Note: French throttles were opened by pulling them towarsds the pilot, whereas British and German throttles were worked by pushing them away from the pilot).



Although German engineers certainly became aware of this new type of carburettor soon after the Allies started to use it in 1916 (probably from examination of a captured Spad VII), and used the same principle in the altitude control used on the Basse & Selve engine used in some variants of the Rumpler high altitude recon. plane from about mid 1917 onwards, they were already going down a very different path involving the design of a new series of altitude engines using a special benzol/petrol mixture to fuel advanced high compression/over dimensioned engines fitted with a new type of carburettor that would not meter down the fuel, but would instead compensate for higher altitude by increasing the amount of air in the mixture. The first of these was probably the Maybach Mb.IVa, used in the Rumpler recon. aircraft from the autum of 1917, although this was quickly followed by the overcompressed versions of the Mercedes D.IIIa and Benz Bz.III/Bz.IV in the winter/spring of 1918, and finally the very high compression BMW IIIa.



But before these engines arrived at the front in late 1917 and early 1918, German aircraft (other than the rotary engined Dr.1, that had a bloctube carburettor similar to those used in the Allied rotary engines) would have been at a serious disadvantage, only partially compensated for by increases in power and compression ratio of the transitional Mercedes D.IIIa type, when facing Allied aircraft at altitudes of 15,000 ft or more, as none of them appear to have had a separate mixture control or any other form of altitude control, and their engines would have become gradually over-rich, would have started to loose power and become increasingly sluggish above 10-12,000 feet. It is clear from several articles and references in the Technische Berichte for this period that German engineers were not unaware of this problem (Bader, H.S. The decrease in engine power with altitude, in Air Ministry English abstracs of the Technisches Berichte, 1917/18). But they were committed to the development of high compression engines that, although they did not start to appear in any numbers until the spring of 1918, ultimately proved to be more effective at higher altitudes than the Allied engines fitted with the 'vacuum' type carburettors.



Although rotary engines had the advantage of a separate fuel regulator, so that manual adjustments could be made for altitude, they do appear to have been more effected by altitude change than the stationary engines with float chamber carburettors. This is commented on in the Technisches Berichte for 1917 where Everling notes that engine speed drops with altitude "according to the type of engine (mostly in the case of rotary engines)" and that in climbing performance the "deviation on the rotary motor is here also greatest" (Everling, E. A simple procedure for the climbing performance of an aeroplane, in Air Ministry. English abstracts of the Technische Berichte, vol.1 1917, Air Publication 1120, 1925). In a later article, Kutzbach explains this by noting that "The fuel supply of most rotary engines depends principally on the static head between the fuel tank and the carburetor jet, which is regulated by means of a cock or a needle valve, since the suction pressure produced by the flow of air at the jet is generally slight. The fuel supply to rotary engines is, therefore, only slightly influenced by the air density. The result is an excess of fuel in the air available for combustion, and an increasing waste of fuel with increasing altitude, to which the pilot puts a stop only by turning the fuel cock when he observes a perceptible decrease in the revolutions. It is still worse when a pump injects a measured amount of fuel...". By contrast "there is less variation in the proportions of the mixture with changing air density with the most common types of carburetor...in which the fuel is exposed only to the dynamic reduction of pressure in the air current in a choke tube...[where]...the flow of fuel...is directly proportional to the fall of pressure in the carburetor, and therefore also to the density of the air" (Kutzbach, K. Adaptation of aeronautical engines to high altitude flying. Translated from Technische Berichte, vol.III 1918 and issued by NACA as Technical Note no.142, May 1923).

Early French and British carburettors were designed to give a full-rich mixture at both slow running and at fully open throttle, and a more closely balanced mixture in between. The early Renault 70 hp air-cooled stationary engine, and the later 90 hp RAF1a that was based on it, were both designed to run with a slightly over-rich mixture at full open throttle, as vaporization of the excess unburnt fuel was required to cool the engine. This slightly over-rich mixture at fully open throttle would also have given a very slight boost in power, of no more than 5 per cent (and at the expense of much increased fuel consumption, 'sooting up' of the engine, and poorer altitude performance) for take-off and full power running at altitudes of up to 3000 ft. Later Allied stationary engines appear to have been more-or-less stoichiometric, providing a balanced mixture at all throttle settings, which would have delayed the onset of altitude effects between 3000 ft. and 6000 ft. as the gradual enrichment of the mixture cancelled out the effects of an increase in altitude. It seems very likely that German engineers took advantage of their more powerful motors to adjust existing carburettors to give a very slightly 'lean mixture at fully open throttle, which may have slightly decreased engine power at ground level but extended the delayed onset of these altitude effects to altitudes above 6000 ft. The British capture report on the Benz Bz IV, for example, notes that the carburettor for this engine supplied slightly less fuel to the mixture at fully open throttle than at intermediate throttle settings, and it is clear that the later German high compression engines were fitted with carburettors that provided a lean mixture at fully open throttle (and then an increasingly leaner mixture as the over-gas was engaged, to compensate for the lower air density at higher altitude). The British capture report on the Daimler Mercedes D.IIIau engine, for example, indicates that the main jet capacity of the new Mercedes altitude compensating carburettor was significantly less than that of the standard Mercedes D.IIIa carburettor, and the report on the BMW IIIa notes that the carburettor was designed to provide the engine with a very lean air/fuel mixture of 20:1 on the ground at fully open throttle, with the altitude throttle closed. Starting with a lean mixture on the ground would have clear benefits for altitude performance (and fuel consumption), as the effects of decreasing air density would be delayed, compared to engines that started with a full-rich or stoichiometric mixture at ground level (and so the engagement of the altitude throttle could also be delayed). It was also possible to use a leaner mixture with the German over-compressed engines at low altitude, because the benzol additive to their fuel delayed the early onset of detonation.



References: the principle of these different types of altitude compensation, and the wide variety of aero engine carburettors in use during the war, is fully described in a useful textbook from the 1920s, "The aeroplane engine" by Lionel S. Marks, McGraw-Hill, 1922, although Bacon, John B.F. "Elements of aviation engines", Paul Elder & Co., 1918, and Chadwick, John C. "Aviation engines", Edwin N. Appleton, 1919 are also useful but avoid mentioning altitude compensation in detail. Most of my detailed information on the Allied engine carburettors comes from original engine manuals and reports of the period: the first quotation is from Ministry of Munitions, Technical Dept., Aircraft Production. "ABC Aero Engine, Type 'Wasp' (Marks I and II) Preliminary Instruction Book", June 1918; and the second is from Ministry of Munitions, Technical Dept., Aircraft Production. "The 300 hp Hispano-Suiza aero engine", December 1918. Detailed information on German carburettors can be obtained from the British capture reports of German engines, and for general information on German high altitude engine development from English translations of articles from vol. 3 of the Technische Berichte in the NACA reports series, and from the British Air Ministry's "Translated abstracts of Technische Berichte" vols. 1 and 2 (corresponding to vols. I and II of the Technische Berichte 1917-18), Air Publication 1120 and 1121 respectively, 1925. Many thanks to FlyXwire for pointing me in the direction of the old aero engine texts (available online as ebooks), to YavorD for pointing me towards the NACA reports (also available online), and to Greybeard for correcting some of my earlier errors. Most of my more obsxure print sources come from the excellent Aviation Collection at Farnborough Public Library.




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Bletchley: Control of Rotary Engines


The earliest rotary engines did not have either a throttle or a fuel regulator that the pilot could use in flight. The fuel/air mixture was adjusted on the ground by the pilot or engine fitters to provide the maximum rated power for take-off. This would provide the pilot with an engine that gave maximum power (for continued use) up to about 3000 ft, and above this altitude the decreasing air density would 'enrich' the engine leading to a decrease in power until it eventually cut out (although the aircraft would have ceased to climb long before that). The pilot was provided with a 'blip' (or 'coupe') switch to temporarily cut ignition to the engine, mostly for use whilst taxiing on the ground or for landing, although the pilot also had a on/off petrol stop-cock that could also be used to cut the engine for landing (as most of these light rotary aircraft could glide in, or 'volplane' well with the engine off). The engine valve-timings could also be adjusted on the ground, and there were early experiments to provide pilots with a cockpit lever that could be used to adjust power by making such changes to the Gnome Monosoupape. These appear to have been abandoned, although the Gnome Monosoupape did introduce a fuel regulator lever that could be used by the pilot to finely adjust the amount of fuel entering the engine. This was in addition to the on/off fuel cock, and was mainly introduced to give better engine performance at altitudes above 3000 ft, as the pilot could now 'lean' the engine as altitude increased - but it also provided the pilot with some ability to reduce engine power at lower altitudes. Lt. R T Leighton gives this description of taking off in an Avro with a 100 hp Monosoupape: "The engine should give 1,150-1,200 rpm, as height is gained, and then petrol should be cut down until engine is giving 1,050-1,100 rpm" ('Pilots' notes for the handling of World War I warplanes' 1917, published by the Shuttleworth Collection 1968). For landing "Shut petrol off... Glide down... Taxi in by 'buzzing' engine with petrol about 1" on adjustment" (Ibid.). The later 160 hp Monosoupape (used bt the Americans in their version of the Sopwith Camel) had an additional five-way switch labelled 0-1-2-3-4 (0 fully off, 4 fully on) connected to the right hand magneto (blip switch connected to the left) to give the pilot some control over the firing impulses to the cylinders in order to reduce power, mainly for landing and taxiing ("Shooting down the myths of the rotary engine", Great War Times, vol.6 issue 4).


The Le Rhone engine introduced the further innovation of a throttle to regulate air, an addition to the fuel regulator and the on/off fuel cock found on the Monosoupape. Lt. Leighton describes these levers on the 80 hp Le Rhone Sopwith Pup: "1. Petrol main tap, 2. Petrol fine adjustment lever, 3. Throttle lever, which in addition to opening and closing the throttle in the ordinary way, opens and closes a needle valve, which regulates the petrol supply" and goes on to say that "Theoretically, the position of the fine adjustment can be found once and for all for every position of the throttle, so that having set fine adjustment once, it need not be moved again. The throttle lever then being worked as on a stationary engine. Practically, the engine will run if worked this way, but better results are obtained by varying the position of the fine adjustment with varying positions of the throttle lever". He adds that after taking off with rpm at 1,200 rpm the engine should be "throttled down to 950 rpm when the scout will fly at 60, 70 or 80 mph", and for landing "the throttle and petrol should be closed as far back as possible but with the engine running smoothly... [then] ...Glide down at 65 mph".


Clerget rotaries (and later derivatives such as the Bentley) appear to have dispensed with this unreliable linkage between the throttle and fuel regulator, leaving the pilot to manually adjust the fuel regulator for every change in throttle setting. Lt. Leighton describes the controls in the 110 hp Clerget Sopwith 1 1/2 Strutter as "1. Petrol main cock, 2. Petrol fine adjustment lever, 3. Throttle lever". He describes take-off as "Fine adjustment about 1/4 of quadrant, throttle about 1/2 of quadrant. These positions cannot be given definately as they vary on different machines but the right position can easily be found...Try and taxi out on throttle using the [blip] switch as little as possible. Always remember to cut down your fine adjustment when you throttle down. If your engine starts popping it is most likely because you have not cut down your fine adjustment sufficiently... To open up your engine, advance throttle, then fine adjustment... this engine should give 1,150 rpm in the air... [but] ... 1030-1,100 is sufficient".


Most sources are in agreement that the Le Rhone, Clerget and their derivatives could be throttled back to about 50% of full engine power in the air, and somewhat further on the ground (windmilling of the prop in a shallow descent added a further 100-150 rpm in the air), but there is little agreement on exactly how far. About 600-800 rpm in the air, according to engine type, the condition of the engine, etc. (the major exception being the German SH Contra-rotating engine which could be throttled down to 350 rpm, according to the author of Profile Publication no.86, 1966). Pilots appear to have 'cruised' at about 75%-80% of full rated power when at their operating altitude. Not only did this conserve fuel, but it allowed the engines to cool down after a long climb at full power and allowed those with less powerful engines to catch up and maintain formation (as, even in aircraft with the same engines, their engines would vary somewhat depending on the quality of construction, maintenance, age, etc.).


Contemporary sources also mention that these engines could be over-revved slightly in flight to give a brief period of extra engine power over and above the rated maximum. This appears to vary, although for rotaries it seems to be something like 5% or less in excess of the rated maximum power. On these early aero engines there do not appear to have been any real physical barriers on the throttle quadrant to limit pilots from exceeding the maximum rated engine settings (the maximum rated power was obtained at about 7 on a throttle quadrant that went from 1 to 10), but it is clear from contemporary sources that the pilots could, and did, exceed the rated rpm (often inadvertently in a dive, but also sometimes in level flight or climb). This, like the use of the blip switch at full power, was frowned on officially and by commanding officers. Christopher Draper, CO of Naval Eight, quotes these instructions on control of Clerget rotaries to all new pilots ("The mad major", Air Review, 1962) "Don't exceed 1,250 rpm at any time. It causes the ball-races to 'creep' and other unpleasant things", and "Don't 'blip' except when throttled right down. It is extremely bad flying and puts unnecessary strain on the whole machine". L F E Coombs notes (Control of the sky: the evolution and history of the aircraft cockpit, Pen & Sword, 2005) that the Pup's throttle could be opened even further forward, beyond the maximum effective power setting, but that pushed beyond this point the engine rpm then starts to fall again.



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Bletchley: World War I Supercharchers and Turbo Superchargers


The title of this is a bit tongue-in-cheek, because although all the developments outlined here took place during the First World War, none of them (to the best of my knowledge) ever saw combat or entered operational service before the end of the war. They never got beyond the prototype stage, but nevertheless present an intriguing look into what might-have-been had the war continued into the winter of 1918 or the spring of 1919.



The basic principles behind the supercharging of aviation engines were recognized as early as 1910, when the New Engine Company in the USA built a a small 2-stroke V4 engine with a Roots-type blower (Setright). This was followed by experiments with forward facing 'scooped' air intakes to the carburettor, to increase the air density by creating pressure in the air intake that was the sum of the atmospheric pressure and the pressure created by the velocity of the aircraft or the propeller slip stream. It was calculated, however, that the best that could be achieved by an aircraft with such a 'scoop', making 120 mph near ground level, was 0.24 lb per square inch, which was not enough to make a really significant difference (Marks).



Once the war had started, however, all the main combatants were soon experimenting with more sophisticated superchargers, or turbo superchargers. In Britain, the first experimental work on supercharging was initiated by F.M. Green at the Royal Aircraft Factory, Farnborough. The experiments started with piston compressors and moved on to Roots blowers and turbochargers, but these early attempts were eventually dropped in favour of the development of a new gear driven centrifugal compressor. Most of the design work on this was done by James Ellor (who later went on to make a significant contribution to the post-war development of Rolls-Royce superchargers before World War II). The very first prototype supercharger developed at the RAF was fitted to an RAF1A engine, and flight tested in a BE2c. The supercharger increased the climb of the BE2c from 8500 ft in 35 minutes (without supercharger) to 11,500 ft in 35 mins (with supercharger), but S.D. Heron (who was also involved) notes that the gears were near the fuel tank and "were quite inadequate... [and] ...failed in flight, producing showers of sparks and a feeling of distinct concern" to Elliott, who was the flight project engineer (Heron). Undaunted, in 1916 they moved on from this supercharger to design a built-in gear driven centrifugal supercharger for the new air-cooled RAF8 radial engine, but the Factory decided to drop further development of the RAF8 after continued trouble with the gears and impeller (the RAF establishment was not overly fond of rotary or radial engines), and the design was given to Siddeley-Deasy. Although the problems with the gears may then have been solved by the use of centrifugal clutches, Siddeley-Deasy shelved development of the engine until 1922, when it was ultimately reborn as the supercharged Jaguar radial to finally enter operational use in 1926 (Heron).



In Germany very similar experiments and supercharger developments were taking place by firms such as Schwade and Brown, Boveri & Co., AEG, and Siemens Schuckert. The first prototype was probably a centrifugal blower produced by Brown, Boverie & Co. to a design by W.G. Noack and developed sometime between January and November 1917. This supercharger was powered by a single Daimler D.II engine, and provided compression to the four D.IVa 260 hp engines of a giant Staaken type aircraft. Initial tests were then conducted on a single D.IVa at the high altitude test bench (vacuum chamber) at the Zeppelin Works sometime between November 1917 and February 1918. These tests were followed by flying tests on a Staaken, and the aircraft achieved an altitude of almost 6000 m, compared to less than 4000 m without a supercharger (Noack). The most developed supercharger, however, was probably that by Schwade & Co. of Erfurth. Like the British supercharger, it was a geared centrifugal blower and appears to have been developed in single-, three- and even four-stage versions to be coupled to either a stationary or a rotary engine (Noack). Prototypes were designed for the Daimler Mercedes D.IVa and flight tested on an AEG G type aircraft, and also fitted to the rotary Oberursel Ur.II and Ur.III (designated Ur.IIa and Ur.IIIa respectively). It seems likely that one was also fitted to a captured Le Rhone 9c rotary and test-flown on a Fokker Dr.1, and there appear to have been plans to fit it to the Fokker D.VIII (Taz). The Schwade supercharger is reported to have maintained aircraft full engine power up to an altitude of between 3500 m and 4000 m (Schwager).



During the same period French engineers at Rateau were busy developing their own prototype turbo superchargers. Flight tests with a turbocharged Renault 300hp Breguet 14 A2 indicated an improved climb to 16,400 ft from 47.5 minutes without turbocharger to 27 minutes with the turbocharger, and an increase in speed at that altitude from 91 to 120 mph. British tests with the Rateau turbocharged engine showed that an air-cooled engine could develop within 12% of ground power to altitudes of around 17,000 to 20,000 ft. Similar tests done with a prototype Moss turbo supercharger in the USA (General Electric Co.) on a Liberty engine indicated an increase in power for this engine from 251hp to 367hp at 1800 rpm (Marks, Devillers).



Although all these superchargers and turbochargers could clearly confer a very significant advantage to an aircraft's altitude performance, they were all mechanically complicated and chronically unreliable. The post-war slump in military aviation and applied research led to something of a hiatus in supercharger design, and it was therefore not until the mid to late 1920s or early 1930s that more reliable and effective superchargers and turbo superchargers could be designed and developed, just in time for the next war..






Setright, L.J.K. The power to fly: the development of the piston engine in aviation. Allen & Unwin, 1971.



Marks, Lionel B. The airplane engine. McGraw-Hill, 1922.



Heron, S.D. History of the aircraft piston engine: a brief outline. Ethyl Corporation, 1961.



Noack, W.G. Tests of the Daimler D.IVa engine at a high altitude test bench. Technische Berichte, vol.III 1918 (translated into English and published as NACA Technical Note no.15, October 1920).



Noack, W.G. Airplane Superchargers. NACA Technical Note no.48, May 1921.



Taz. http://www.theaerodrome.com/forum/ai...gaskammer.html



Schwager. Recent efforts and experiments in the construction of aviation engines. Technische Berichte, vol.III 1918 (translated into English and published as NACA Technical Note no.12, September 1920).



Devillers, Rene. The problem of the turbo-compressor. NACA Technical Note no.11, August 1920.



The full-text of these NACA reports are available in pdf format online, either directly from the NASA website, or from the British mirror site maintained by Cranfield University (AERADE).

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Bletchley: Did They Have WEP (War Emergency Power)?


A quick answer to this would be "No", as WEP depended upon a supercharged engine and/or water/methanol injection into the engine, and neither was available until WWII (the term itself dating from this time). But if the question was rephrased, "Could they exceed their engine's maximum rated power in flight?" then, in many cases, the answer would be "Yes".



Most WWI aircraft engines had three entirely different figures for 'maximum power': nominal rated power (the one that is often quoted in books); then normal full power for 'continuous running'; and then a higher output at an increased engine rpm for just 'a few minutes only'. The Hispano-Suiza Viper for example, was nominally rated at 200 hp/2000 rpm/msl, but had an actual normal full power output of about 212 bhp/2000 rpm/msl, and could be run at 2100 rpm for 'a few minutes only' with an output of about 224 bhp at msl - a 'WEP' of approximately 12 bhp at msl, which is an increase of just over 5% of normal full power (1).



The distinction between normal full power for 'continuos running' and maximum power for 'a few minutes only' is explained in a WWI instruction manual, "Hispano Suiza Engines: Notes for Squadrons in the Field", where it defines normal full speed rpm as 'the speeds that may be maintained continuously for periods of three hours or more at a time', and maximum speed rpm as 'the speeds at which it is permissible to run the engine for short periods only (say, five minutes)' (2).



This distinction between rated power, normal full speed, and maximum speed of WWI engines can be seen again for British and French engines in the Air Board's Data Sheets, where the first three columns for each engine are labeled as 'Rated H.P.', and then under 'R.P.M. of engines in flight' the two sub-divisions 'Normal Full Speed Maxm for Long Periods' and then 'Maximum Permissable Speed for Few Minutes Only' (3). In the case of rotary engines there was also a distinction between 'gross' and 'net' power, 'net' power being the 'real' power rating after adjustment for 'windage' (the amount of power required by the spinning engine to overcome air resistance) which could vary according to how effectively the rotary engine was cowled. Manufacturers generally preferred to quote the 'gross' power, so Gwynnes rated their Clerget 9BF at 150 hp (4) but the Air Board continued to rate it at the nominal 130 hp whilst noting that it had an actual (net) output of 148 hp at 1250 rpm (5). Heron, who had the job of determining the windage losses on the early Bentley BR1/AR1 rotary notes that, although nominally rated at 150 hp/1250 rpm, "gross horsepower... was about 142. The windage horspower was 24 with the engine in the open air and 16.5 when cowled" (6). This gave it a 'real' (net) hp of about 126 when cowled, more-or-less identical to that of the (nominally rated) 130 hp Clerget 9B, which also had a net output of around 126 hp (7).



There was, in nearly all cases, no 'gate' or 'wire' (as was common in WWII) to prevent the pilot from inadvertently over-revving the engine into the 'maximum' rpm 'for a few minutes only' range (the only exception to this that I have found being for the overcompressed Benz Bz.IVa engine, where the pilot had to press a button in before pushing the throttle forwards into the highest rpm range). It is clear, however, that use of 'maximum power' was frowned upon in all situations other than dire emergency - as it certainly stressed the aero engine, shortened engine life, and could lead in extreme cases to sudden engine failure. Christopher Draper, the CO of No.8 Squadron RNAS, included in his list of "Don'ts" for new pilots the instruction 'Don't exceed 1,250 rpm [normal full power of the Clerget rotary engine] at any time. It causes the ball-races to "creep" and other unpleasant things' (8). The Clerget 130 hp rotary engine's max rpm for a 'few minutes only' is noted as being 1300 rpm in the Air Board's Data Sheets, an increase of 50 rpm above the normal full power rpm of 1250.



In the absence of a physical 'gate', British and French pilots were expected to maintain a close eye on the RPM gauge at all times and listen to the sound of the engine, as normal full rpm could also be exceeded by the 'windmilling' of the prop in a shallow dive. R.T. Leighton notes that for the 110 hp Clerget 'Fine adjustment about 1/4 of quadrant. Throttle about 1/2 of quadrant' would give full power on the ground (9), and another pilot, Neil Williams, noted that for the 80 hp Le Rhone "Even at full power one cannot push the levers beyond half-way as the rpm will fall" (quoted in 10). The quadrant was marked from 1 to 10, with the idle position being about 3 and maximum power about 7, although the exact position could vary from one engine to another or with changing atmospheric pressure and temperature. With direct drive and fixed-pitch props the maximum power was generally obtained at maximum permissable engine speed - so opening the throttle beyond this point usually resulted in a loss of power and damage to the engine - and so, in the example of the 80 hp Le Rhone C 'somewhere around 1500 rpm the cylinders can begin to stretch, followed closely by departing' (11).



But it is possible that for most German pilots with the early or mid-war 'low altitude 'stationary engines, this might not have been a problem - as it appears that their engines may have been 'limited' to a maximum of 1400 rpm by either throttle stops/governors or by calibration of the throttle lever. It is notable that nearly all of the German stationary engines of this period had their power output specified at a standard 1400 rpm. If we look at the throttle curves for captured examples of these engines it is remarkable that in almost every case the throttle curve also stops at 1400 rpm, although the power curve continues to go up in most cases for at least another 100-200 rpm (indicating that these engines may have had more power than the pilot could access via the throttle controls). In the British tests on a captured Daimler Mercedes D.IIIa, for example, the normal full power is quoted as 179.5 bhp at 1400 rpm (the point at which the throttle curve stops), but the maximum power is quoted as being 188 bhp at 1500 rpm, with a peak of 197.5 bhp at 1700 rpm for a very short time (12). Similarly, the report for the Mercedes D.IVa indicates that the normal full power was 252 bhp at 1400 rpm, the point at which the throttle curve stops, but increasing to 260 bhp at 1500 rpm and finally around 268 bhp at 1600 rpm on the power curve (13); and on the Austro-Daimler a normal full power of 200 bhp at 1400 rpm, again at the point where the throttle curve stops, but an increase on the power curve to 212 bhp at 1500 rpm and 222 bhp at 1600 rpm (14).



If this is so, it certainly changes with the introduction of the new high or overcompressed 'altitude' engines in 1918. These engines had to remain throttled back at low altitudes, to prevent damage to the engine, but they were designed to take advantage of the higher engine speeds of up to 1600 rpm at altitudes of 2000-3000 m and upward. In nearly all examples this altitude control was integrated with the throttle control: in the case of the overcompressed Daimler Mercedes D.IIIau, for example, there was merely an admonition to the pilot above the throttle quadrant, warning the pilot not to push the throttle lever forward into the 'high altitude' section of the throttle range at low altitudes; but in the Maybach Mb IVa there was a clearly marked divide to separate the 'low' from the 'high' section of the quadrant (15). In the overcompressed Benz engines there was a physical 'gate' in the form of a button that had to be pressed in by the pilot before the throttle lever could be advanced into the high altitude section of the quadrant (16), and in the case of the BMW IIIa there was a secondary, and entirely separate throttle lever that had to be engaged to increase engine speed above 1400 rpm (17).



The pilots were instructed not to engage this 'over-gas' at low altitude, as this extract from a letter by Lothar von Richthofen illustrates: 'In order to not unnecessarily stress the motor, and maintain advantage, the "over" gas throttle position should be used only over 2000 meters with direct climbing or in aerial combat. It is absolutely necessary that each pilot is informed in the mode of operation of the BMW motor, (in order to avoid unnecessary motor failure)'. There is evidence, however, in particular that of a letter from Goering, that pilots could, and did, sometimes use the 'over-gas' at very low altitudes: he states that 'As a rule, the "over" gas throttle position is not used under 3000 meters", but he goes on to immediately qualify this by saying that "Not only have we been operating in the "over" gas throttle position almost constantly throughout aerial engagement, but also at low altitude, and without any damage to the engine' ending with an anecdote to show that this was so, and moreover a lifesaver (18). I am a little suspicious of this letter (from the text of the letter, Goering was clearly trying to get the authorities to give his unit first priority in the supply of the new engine, and his anecdote is remarkably free of any facts that could be checked), and in particular because there is no further evidence of this from either Lothar von Richthofen (see above) or Ernst Udet (19). But there is, apparently, an entry for the BMW IIIa engine in "Typenhandbuch der deutschen Luftfahrttechnik" by Bruno Lange, to say: "Notleistung in Bodennähe bis 200 kw (230 PS)..." or "Emergency performance near ground level 230 PS" (20, but there is some confusion over the actual figure as 200 kw does not eqaute to 230 PS). In contrast to this, the British report from tests on a captured BMW IIIa indicates that at 1400 rpm, the BMW IIIa was already producing 234 bhp at normal full power, before the 'over-gas' was engaged, and a msl equivalent of 254 bhp with the over-gas fully open at 1600 rpm (a 20/80 benzol/petrol mixture in use). The British tests with the 'over-gas' control fully open were, however, only made possible with use of a "blower" to simulate the conditions at altitude (21): and it remains unclear just how much 'over-gas' could be employed, and therefore just how much 'boost' a pilot could get, by engaging the secondary throttle at such low altitudes.



Summary: it is clear that most WWI aero engines had both a 'normal full power' and then a 'maximum' power for short-duration or emergency use only, although the difference between them appears to have been not much more than 5% of full engine power in most cases (or even less, probably, for rotary engines). It is possible, however, that this 'maximum' power 'for a few minutes only' might not have been available to the pilots of the many 'low altitude' German and Austrian aircraft, at least until the introduction of the new overcompressed high altitude engines in 1918. It is apparent that these altitude engines could be 'over-revved' at low altitude, but the resulting 'boost' in performance from this, although it might have been potentially significant, still remains uncertain - but did have the potential to wreck the engine and was therefore discouraged for anything other than emergency use.






1. "Viper" Hispano-Suiza power curve. 1917/18. PRO AVIA 6/25950



2. British Ministry of Munitions. Notes for squadrons in the field: Hispano-Suiza engines. 1918. PRO AIR 10/352.



3. British Air Board. Data for structure and stability calculations of aircraft. 1917. PRO DSIR 36/4828.



4. Gwynnes Ltd. Clerget patent aero engines: instructions and list of parts. c.1917 .Facsimile published by Camden Miniature Steam Services, 2001.



5. British Air Board (as above).



6. Heron, S.D. History of the aircraft piston engine: a brief outline. Ethyl Corp., 1961.



7. British Air Board (as above).



8. Draper, Christopher. The mad major: autobiography. Air Review, 1962.



9. Leighton, R.T. Pilots' notes for the handling of World War I warplanes and their rotary engines. The Shuttleworth Collection.



10. Coombs, L.F.E. Control in the sky: the evolution and history of the aircraft cockpit. Pen & Sword Aviation, 2005.



11. Shooting down the myths of the rotary engine, in: 'The Great Times', vol.6 no.4.



12. British Ministry of Munitions. Report on the 180 hp Mercedes aero engine, 1918. PRO AIR 10/268.



13. British Air Board. Report on the 260 hp Mercedes aero engine, 1917. PRO AIR 10/250.



14. British Ministry of Munitions. Report on the 200 hp Austro-Daimler aero engine, 1918. PRO AIR 10/355.



15. British Ministry of Munitions. Report on the 300 hp Maybach aero engine, 1918. PRO AIR 10/338.



16. LVG. Pilotweb. http://www.pilotweb.aero/content/articles.



17. British Air Ministry. Report on the 230 hp Bayern aero engine, 1919. PRO AIR 10/397.



18. Extracts from translated letters by Goering and Lothar von Richthofen, posted by Dave Watts on The Aerodrome forum.



19. Udet, Ernst. My experiences with the BMW motor type IIIa, Cross & Cockade journal vol.2 no.2 Summer 1961 (originally published in German in 'Motor' May-June 1919, and translated by Alex Imrie).



20. Rammjaeger, posted on The Aerodrome forum.



21. (see above, 17)

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The attached aerial photograph from the family archives shows the German airfield (50°54'55.88"N 3°14'36.91"E) to the west of Ingelmunster (Flanders-Belgium) during WW1. Ingelmunster is located in western Flanders, within easy airplane striking distance (less than 20 km) from the front. There was another German airfield about 3 km away to the NE of Ingelmunster along the road to Meulebeke.


North on the photograph is approx. at 10.00 o'clock. The diagonal main road (from Ingelmunster station to Izegem) and the parallel canal across the picture run east-west. My grandparents owned the property outlined in yellow and when the Germans created the field, they basically found themselves with their 9 children in the middle of a German airfield.


Three aircraft hangars are visible against the eastern edge of my grandparent's property and another building (Starthaus?) at the southeast corner. Take-off would have been mostly to the SW from the field portion to the south of the property. That is why I think the building on the SE corner was the "Starthaus".


Some 300 meters to the west of the property and also bordering on the main road there is a whole system of trenches and shell holes. Ingelmunster was never part of the front line, so these were not "fighting" trenches. Maybe this was dug to take shelter against Allied attacks on the field (not probable because too far from the field and too extensive) or it was created as a practice ground for strafing trenches.


I do not know when the picture was taken, (nor do I know if the source is German or Allied) but there are no airplanes visible and the trees have leaves, the sun is low in the west, the field shows clear traces of usage in front of the hangars. So maybe it was taken after the Germans started pulling back in early autumn 1918, or maybe even the following year in the summer (this is not likely because the trench system looks rather freshly dug)


When the Germans decided to create the airfield, the rather large size of my grandparent's house must have been one of the deciding factors. The family with its nine children was ordered to live in the servant quarters in the basement and the German pilots took over the 3 upper floors, so that they were immediately next to the aircraft hangars. The German orderlies shared the kitchen in the basement to prepare food for the pilots. This was not without its positive aspects, because the Germans military had a lot more and better food than the civilians and they would occasionally share. With such a large family this must have been a welcome supplement to the food rations. My two eldest uncles were then around 10-12 years old and were the favorites of the German's cook, who was actually a Frenchman and who would very often give them some extra snacks. One day they had pilfered the Chief Mechanic's "Spritzkanne" (Oilier), when he found out he gave them both a good spanking. The relationship with the occupiers in general seems to have been quite correct


On a more macabre note, when an English pilot crashed in flames at the back of the field while strafing, the two boys explored the wreck and noticed grease from the pilot that had "cooked off" and dripped into the fuselage. They collected it and made an "English pilot candle" out of it.


My mother told us that Goering as a pilot was billeted there for while and that during WWII he came back to visit and say hello.



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Thank you Galand!


That is the sort of fascinating detail that only a family source can provide.


Photo-recon photographs would often be taken in the early morning or late evening, as the shadows cast by objects would reveal details for analysis that would otherwise be missed. Possibly a practice shot of their own field by a recon pilot based there?


Thank you for sharing this, and the history of the field.



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The Claims Process




During the early period of the war in the air, from 1914 through to the Spring of 1916, air to air combat was a rare occurence and there appears to have been no official or systematic procedure for recording combat or filing claims. Although the British National Archives (the PRO or Public Record Office as it used to be called) have many, and perhaps most of the combat reports filed during the war (a still unknown number are missing due to theft) those from before April/May of 1916 are rare and far between. During this very early period any air encounter that resulted in an enemy aircraft being forced to apparently break off its mission and dive for home, either 'driven down' or 'forced to land' behind its own lines, was regarded as a 'victory' for the pilot or the aircrew concerned - but not 'awarded' or 'credited' officially to those individuals, as it was seen as bad for the unit's morale if such individuals were singled out for special recognition. Completing the asigned mission was grounds for recognition; fighting the enemy was grounds for unofficial notoriarty; and medals or a mention in despatches would be dependent on the favourable reaction of both the Squadron CO and senior staff at Wing or Brigade HQ. Although combat reports, 'Combats in the Air' as they were officially designated, were prepared by most British squadrons in France and Flanders on a more systematic basis from about April 1916 onwards, using Army Form W 3348, the attitude that individual success was subordinate to the team effort persisted throughout the war, or at least until early 1918 when the authorities reluctantly conceded to pressure from the press to release the names of British and Dominion 'Aces' alongside those of the French and German air services. There was never, however, any systematic or centralised recording or awarding of 'victory' credits to individual pilots, aircrew or units. The different Squadrons, Brigades and Wings had their own ways of dealing with or responding to individual successes of this kind. There was, importantly, no direct link between awards and medals and an individual's 'score' (as this invariably discriminated against two-seater crews, and those condemned to fly the outdated machines), and even the keeping of individual or unit scores at a Squadron level was sometimes discouraged as 'bad for morale'. Pilots who were later singled out for press attention were also often unhappy, as it did indeed seem, in some cases at least, to lead to division or discomfort within the mess. Until June of 1917 the Army form W 3348 did not even have a section for the 'Results' where a claim could be made. From June 1917 onwards the form was belatedly changed to add a 'Results' section, where a number could be placed for Destroyed, Driven down out of control, or Driven down. Pilots would fill in the form after returning from a mission, and then if approved by the Squadron CO this would be forwarded to Wing or Brigade HQ. Some but not all reports had short notes added at this stage, such as 'Decisive' or 'Indecisive', 'Approved' or 'Not Appoved', and typically a short description of the combat from these reports would appear in the next RFC Communique if the enemy aircraft had been destroyed, or was merely listed there if the enemy aircraft had been driven down 'Out of control'. Claims did not necessarily require 'confirmation' from witnesses or the evidence of a crash site - this would have been difficult, anyway, as many of these combats were over the enemy side of the lines - as it was regarded as enough in many cases that the pilot was, generally, both an officer and a gentleman (and 'shooting a line' was regarded as 'bad form' within the mess anyway). During the course of the war the early 'Driven down' and 'Forced to land' claims disappeared from these combat reports, but were replaced by an ever increasing number of claims for driven down 'Out of control' and not seen to crash, about 40% of all claims by the end of the war, and multiple claims were also allowed for cases where an enemy aircraft was shot down by several pilots. Bill Lambert, in his memoirs of serving with 24 Squadron (Combat Report), comments that by mid 1918 "Although the official policy did not countenance the keeping of either unit or individuals 'scores' squadrons and pilots, in some instances, did maintain their own totals...The circumstances surrounding airfighting were such that the exact number of E.A. destroyed or damaged by a unit or pilot could not be precisely determined except in very rare instances and a difference in totals was inevitable. The fact is that while the H.Q. figure was undoubtedly appropriate to the official requirements, that at squadron level probably did fuller justice to the unit or individual".




Although the French Service Aeronautique officially credited their pilots only for enemy aircraft destroyed or captured (no 'Out of control' or 'Driven down' claims), in the early period of the war at least some of the early 'aces' were credited with victories that were never confirmed as crashed. In addition, the French press were the first to coin the term 'ace' and, particularly after Verdun in 1916, there was also a clear desire to publicly promote these 'Knights of the air' to boost morale on the home front. So the top-scoring French pilots, unlike the British and Dominion pilots, received substantial early press exposure - and it is possible that, under these circumstances, the claims of some pilots might not always have been given the same thorough scrutiny that the system required. And although the French system allowed for multiple claims on a single enemy aircraft, as the British did, a large proportion of the victories were credited to these aces with very few of their claims being listed as collaborative. The French pilots were required to make an immediate claim on landing, or risk loosing the credit. The claim was then passed up to the HQ of the operational Zone where it was evaluated. Each operational Zone HQ then published the successful claims in a daily Compte Rendu or Resumee, and the credits published here were regarded as the official confirmation of a victory.


United States


Those American units under British control (17 and 148 Aero Squadrons) followed British procedures and practice, whilst those under French control followed French procedure and practice. Victories by US pilots under British control were published in the Communiques, and those under French control in the Resumees. After being brought under US control and organised into Groups, victories were then published in the General Orders of the relevant Army, although the claims process continued to reflect predominant French procedures and practice. Multiple claiming appears to have been common in this period.




On paper at least, and probably in practice for most of the war, the German system of claim and credit for air to air victories appears to have been the most organised and thorough of all the combatants. Combat reports were required by each pilot for every victory claim, and were claimed as 'ds' or 'diesseit' (our side); 'js' or 'jenseit' (their side); or as 'zLg' or 'zur Landung gezwungen' (seen to land). the 'zLg' claims, although they could be a part of the pilot's personal score, were not officially acknowledged as a 'victory' unless the enemy aircraft landed behind German lines, and as the war progressed these appear to have been largely phased out. All 'js' or 'ds' claims required witnesses, although as most 'ds' claims fell behind the German lines the wreckage of the aircraft or captured aircrew were usually there to support the claim. The 'js' claims were more problematic, as there was no evidence on the ground to support the claim - in practice, very similar to the British 'Out of control' type of claim. After claiming a victory the Jasta pilot would prepare a combat report, which would go to the CO for approval. This would then be passed to the HQ of the relevant Army for approval, and from there to the Kommandierende General der Luftstreikrafte (Kogenluft) for final approval and confirmation. If it was then approved at this level a document, with a victory number asigned, would go back down the chain of command to unit level. The victory was then published in Kogenluft's Nachrichtenblatt der Luftstreikrafte (the Intelligence Report of the Air Service) and in the weekly 'Wochenbericht' reports of the relevant Army. It was a strict system of one credit to one 'victory', without allowance for multiple claims (except for the multi-seat aircraft, where each crew member received one credit). Disputed claims often went to 'the biggest Kannone', but if such a dispute could not be resolved the credit was awarded to the unit rather than an individual. This system was not in place immediately the war broke out, and it is likely that the early victories of 1914 and early 1915 would have been evaluated less thoroughly. By early 1917 there is also some evidence that the system may have started to 'loosen up' as the war dragged on into its third year and more 'aces' were required by the press to bolster morale on the home front. From January 1917 onwards the precise location for each victory was no longer required for publication, and further details were dropped from May 1917. Although some aces (Manfred von Richtoften amongst them) maintained scrupilous details for all claims submitted, others did not (Goering, for example, apparently stopped supplying serial numbers for aircraft claimed after the end of 1916). The system might then have gone into something of a 'melt-down' in the final months of the war, the last official victory credits, up to August 1918, being published at the end of October 1918, and an apparent increase in the more nebulous 'js' claims (up to about 40% of the total, perhaps the same proportion as the 'Out of Control' claims being made by British and Dominion pilots). There is also a suspicion that at least some of the later German aces, who went on to add a significant number of victories in a very short period of time in the final months, were by then overclaiming at a similar rate to that of some pilots on the Allied side.




PROCAT (British National Archives catalogue)


Lambert, Bill. Combat Mission. Corgi, 1975.


Olynyk, Frank. Claims documentation (The Aerodrome Forum)


Barrett, Tilman. Victory claims (The Aerodrome Forum)


The information for an apparent 'melt-down' in the German system in the final months of 1918 is taken from a recent discussion of German claims on The Aerodrome Forum, from information supplied by Russ Gannon and others, although responsibility for this interpretation is mine.



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Weather Forecasting


At the outbreak of the war there was no military meteorological service, and weather forecasting as a science was still in its infancy. But as the military situation in France and Flanders settled into its pattern of opposing trench systems, there was a growing need on both sides to predict short-term weather patterns There is little information available in English on either French or German weather forcasting during the war, or on their meteorological service's contribution to the war effort on the Western Front. It is known that the French Meteorological Service already had a well-established network of weather observation stations, and prepared simple daily plotted charts and weather summaries based on daily observations from these stations and on 3-hourly observations at Paris. These French weather charts and summaries are still available today, for the whole of the war period, from the Britsh Met. Office archives in Exeter (England), and presumbly from the French Met. Service archives also. It is very likely that the German Army and Air Service also had access to its own meteriological information, although if there are any surviving records relating to this I am not aware of them.


The British Met. Office had access to the French meteorological data, to the data from British weather stations and ships, and from its links to weather organisations in Spain and Scandinavia. This was enough to prepare forcasts based on larger scale weather patterns, such as frontal systems (the term 'weather front' was itself coined at around this time), but was not fine enough to predict local changes in weather along the Western Front. It also provided little information on changes to wind strength and direction above ground level (needed, increasingly, not only by the artillery but also by the Flying Corps and the anti-aircraft units along the Front). Initially, however, the requirement was for accurate and timely predictions of wind strength and direction at ground level, both along the Front as a whole and in specific sectors, to help the Army prepare against the new threat of gas attack from the German lines, and also to support the Engineers by predicting favourable local conditions for British gas attacks against the Germans. In June 1915, therefore, after the first German gas attack at Ypres, two Met. officers went to France to form the Meteorological Field Service, GHQ - 'Meteor' as it was soon to become known. Observers were recruited, mostly from the Artists Rifles. The new service was successful in accurately predicting local wind conditions for Allied gas attacks during the Battle of Loos, and was thereafter established as a section of the Royal Engineers to support RE gas companies. Although observations of surface winds formed the bulk of this early work, both the artillery and the RFC also needed infomation that the Met. observers could provide. The artillery needed information on temperature, wind strength and direction up to 2,000 ft (later to 6,000 ft), to be able to predict the 'drift' caused by wind on artillery shells. The RFC needed information on both wind and cloud formations at altitudes above this - as, at an early meeting with Met. officers at RFC HQ in France, General Henderson remarked that air reconnaisance had to be conducted above 3000 ft because "if they fly lower they are shot down like rabbits".


Met. officers were recruited and asigned to Army HQs, establishing a network of weather observation stations along the Front. As the war progressed, the emphasis changed away from gas attacks and towards closer support and integration - first with the artillery, and then increasingly with the RFC and the Independent Air Foce operating from Nancy. Small Met. sections were also sent with RFC detachments to the Dardenelles, Salonika and Italy. The night bombers also required up to date information on the 'sleep winds', the prevailing upper winds that were formed during the hours of darkness. Small weather pilot balloons were used at first, along with sound-ranging and observations of anti-aircraft bursts at different altitudes, and a kite balloon was also obtained for collecting weather observations. But from early 1918 a dedicated meteorological aircraft section was formed to take regular observations of the wind, humidity and temperature in the upper air up to 14,000 ft. These observations are said to have been especially useful before the opening of the final offensive on 8th August. From May 1917 weather observations were also being taken at Calais, initially four times a day, but rising to every two hours by the end of the war. By the end of the war the new Met. Service was producing daily weather reports (these, along with the reports from Calais, are also retained at the Met. Office archives in Exeter) and had expanded from the initial two officers in June 1915 to a final establishment of 28 officers and 187 other ranks. It had become an integral part of the organization of the RAF - subsequently rising to 750 officers and men by 1939, and nearly 6,800 by 1945.




Gold, E. Meteorology in the First World War. Weather, vol.5 no.9, 1950.


Gold, E. The Meteorological Office and the First World War. Meteorological Magazine, vol.84 pt.996, 1955.


Stagg, J.M. The Meteorologic Office and the Second World War. Meteorological Magazine, vol.84 pt.996, 1955.


Personal correspondence with Ian MacGregor, Archive Information Manager, Met. Office Archive



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Gwynnes, Clerget & Bentley


It has long been assumed (see, for example, Mottram, but also my own posts here) that the long stroke Gwynnes Clerget 9BF engine was developed by Bentley during his time at Gwynnes - and that it was indeed a direct ancestor to the AR1 (later BR1) later developed by Bentley at Humber. But after re-examining some of the available French and English sources I now think that this is probably wrong, that the Clerget 9BF was a collaboration between Clerget et Blin and Gwynnes with very little, if any, direct involvement by Bentley (although the engineers at Gwynnes certainly seem to have incorporated much of what he had passed on to them whilst working there to improve production and reliability of the Gwynnes licence built Clerget engines - in particular, his use of aluminium alloy pistons). Bentley himself was adamant that the AR1/BR1/BR2 design had very little in common with the Clerget, with the exception of the cam. mechanism (Bentley).


We know that Gwynnes was the contractor to the Admiralty for the Clerget engines used to power RNAS Nieuport and Sopwith Strutter two-seaters, having obtained a licence from Clerget et Blin & Cie just before war broke out in 1914 (Mottram; Bentley; Gwynnes; Hartmann). Before the war Gwynnes already had a long history of making marine pumps, but there was serious production and quality-control issues with the Clerget rotary engines that they were then supplying to the RNAS by early 1915. Mottram comments that "It is likely that Gwynnes were trying to apply fairly coarse marine pump quality standards to high precision aero-engines, and in cutting corners were running into serious problems" (Mottram). This led directly to poor performance and reliability from these British-built Clerget engines, when compared to those engines being obtained directly from the French manufacturers.


W. O. Bentley had been recruited into the Admiralty 'E' Section responsible for supply, production and inspection of aero engines bought under contract for the RNAS. Early in 1915 he was despatched by Commander Briggs to Gwynnes at Chiswick, with the instruction "They're to do what you tell 'em to do". Bentley records in his memoirs that his main task was to "put in hand experimental work that would lead to the substitution of aluminium for iron pistons in the Clerget", but it is clear that before he could do this he first had to bring the quality of production and manufacture of Clerget engines at Gwynnes up to an acceptable standard - a task that appears to have been achieved with some difficulty, due to resistance from the Chairman, Neville Gwynne. He was to remain at Gwynnes for over a year, when not engaged in visits to front-line RNAS squadrons to assess the problems with Gwynnes built Clerget engines, and comments that "The routine at Chiswick was ceaseless and gruelling", whilst "In spite of the position of authority I occupied, I was soon neck-deep in the politics, manoeuvrings and jealousies that arise when an outsider is let into the design department" (Bentley). Although Bentley managed to diagnose and correct the immediate problems with the engines coming out of Gwynnes, he also diagnosed a more fundamental problem with the Clerget design - the 'obturator ring' common to all of the Clerget rotary engines. The rotary engine had a problem with unequal cooling of the alloy steel cylinders, which have poor thermal conductivity. The air cooling of the cylinders led to an unequal operating temperature at the leading and trailing edges of the cylinders, and eventual distortion of the cylinder into an oval shape. The obturator ring was an L-shaped ring of copper-silver alloy that was designed to conform to this distortion of the cylinder to maintain compression within it. Any wear to the obturator ring would lead to a gradual loss of compression (and therefore loss of engine power), and cracking or failure of the ring would lead directly to engine failure. Bentley comments that "It was very thin, very fragile and very unreliable; and when it broke the piston seized at once. They were given a life of around fifteen hours in France, and this was an expensive way to try to gain air supremacy over the Western Front" (Bentley).


Bentley recalls that he "managed to persuade Gwynnes to raise the compression, and, because they were ordered to, they accepted the aluminium pistons", but he met "a series of carefully contrived obstructions" when he tried to "improve the obturator ring and incorporate a cylinder with good conductivity formed of aluminium with a cast-iron liner shrunk into it which would equalize the temperature". He was convinced that this would solve the problem, but he recollects that Gwynnes "thought they were being led into an entirely new design to my specifications, which would mean dropping the French Clerget rotary" and that "they were also occupied with a new rotary of their own, for which they had brought over a designer from France" (Bentley). I think this 'new rotary of their own' was probably another Clerget (I have found no evidence that Gwynnes produced any other engines at this time other than, later, the rotary BR2 and a small number of Wasp radials), and that Gwynnes had seen an opportunity to work together with Clerget et Blin to incorporate some, but not all, of Bentley's ideas into an upgraded version of the existing Clerget 9B: the long-stroke, high compression, aluminium-alloy pistoned Clerget 9BF. It is also clear that Gwynnes wanted to get rid of Bentley, as Bentley recalls that they would "rather drop me than their Clerget, and they made this so amply clear that I was forced to put my case to Briggs". Bentley left Gwynnes at this point, some time in the early summer of 1915, but was persuaded by Briggs to "return to Chiswick, work on one piston and cylinder to my specification and fit it to a Clerget to prove my case". But it is clear that Gwynnes were not thrilled to have him back, as "the results were as satisfactory to me as they were disturbing to Gwynnes", and after some "tiresome consequences" Bentley was "soon back at the Admiralty" and requesting his own removal from Chiswick "to be allowed to develop my own aero engine design elsewhere". He was then re-asigned to Humber, sometime in the summer or early autumn of 1916, who were apparently very glad to see him, having been engaged in "churning out Army bicycles - thousands and thousands of them - and terrible things like travelling kitchens" (Bentley).


Back at Chiswick, it appears that Gwynnes continued to make Clerget 9B engines under contract to the Admiralty, but were now also working on the development of their new Clerget 9BF. At some point Ruston & Proctor also obtained a licence from Clerget et Blin to build the Clerget 9B rotary engine, although I can find no evidence that they were involved in development or manufacture of the 9BF. Between the two of them, these two companies produced 1300 Clerget 9B engines under licence, and Gwynnes built a further 1750 Clerget 9BF (Hartmann) - although Ruston and Proctor appear to have been contracted to make Clerget 9B engines for the Clerget Camels that they were building for the RFC from 1917 onwards, whilst Gwynnes were still contracted to supply their Clerget 9B engines to the RNAS. From March 1917 the separate supply organisations for the War Office and Admiralty were combined into a single organisation under the Ministry of Munitions, although the legacy of separate organisation continued to shape supply of aero engines to RFC and RNAS squadrons until they were themselves combined into the new RAF in April 1918 (Bentley, Meekcoms).


Note on Aluminium Alloy


The references often made to 'aluminium' pistons and cylinders are not quite accurate, as the metal that was actually used by Bentley is reported to have been an aluminium alloy 'L.8' that contained 12 per cent copper (Morse). Later, however, it may have been another aluminium alloy altogether, one named 'Y' alloy that was then under development by the National Physical Laboratory. The development of this alloy was itself stimulated by the pre-war development in Germany of Duralumin, and before the war had been coordinated in Britain by the Alloys Research Committee of the Institution of Mechanical Engineers. It seems likely that Bentley would have known of of this. It contained 4 per cent copper, 2 per cent Nickel and 1.5 percent magnesium, retaining its strength to moderately high temperatures and, by 1921 at least, was being used extensively "for pistons and cylinder heads" in cast form (McNeil). It was also an alloy known to Peter Hooker Ltd. of Walthamstow, which built Le Rhone engines under licence during the war (Nahum), whilst Air Board data sheets for August 1917 list a Le Rhone 9J engine with the entry 'aluminium pistons'. It is likely therefore that the otherwise rather strange 'y' designation in the Le Rhone 9Jby is an early reference to the use of this 'y' alloy.




Mottram, Graham. W.O. Bentley's aero-engines. W.O. Bentley Memorial Foundation (Publication no.3), 2003.


Bentley, W.O. W.O.: the autobiography of W.O. Bentley. Hutchinson, 1958


Gwynnes Ltd. Clerget patent aero engines (9B & 9BF): instructions and list of parts. Gwynnes Ltd, c.1917 (facsimile reprint by Camden Miniature Steam Services, 2001).


Hartmann, G. Moteurs de legende: le Clerget 130 ch.


Meekcoms, K. The birth of aeronautical inspection. 198.


Morse, William. Rotary engines of World War One. Nelson and Saunders Aviation Collection, 1987.


McNeil, Ian. An encyclopaedia of engine technology. Taylor & Francis, 1990.


Nahum, Andrew. The rotary aero engine. HMSO, 1987.


Air Board. Data for structure and stability calculation of aircraft. August 1917. DSIR 36/4828



Edited by Bletchley

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