Bletchley

Allies: Floating to Victory on a Tide of Oil At a meeting of the Inter-Allied Petroleum Conference after the end of the war, in December 1918, British Cabinet member Lord Curzon claimed that the Allies had "floated to victory on a tide of oil." Although Germany and the Central Powers had struggled to find adequate supplies of fuel oil and gasoline throughout the war for an increasingly mechanised army and expanding air force, the British and French forces opposing them on the Western Front had never been in any serious danger of running short of either, quantitatively or qualitatively, despite German U-boat sinkings in the Atlantic and elsewhere. It is true that tanker ship sinkings, together with a huge rise in military mechanisation and demand for gasoline led to a temporary hiatus in Entente distribution capacity at the end of 1916, which in turn led to some domestic restrictions and much political concern (particularly amongst the French, who were the least prepared to meet this sudden increase in demand) that strategic sources of oil might become insufficient. But the US entry into the war, domestic restrictions, and a re-organisation of the Allied supply and distribution system meant that, by the signing of the Armistice, Curzon could claim that the stocks of oil in Allied countries had been "brought up to a point of absolute safety", an achievement that "reflected the greatest credit on the Petroleum Council and on the great oil companies that had subordinated their own interests to the Allied cause." French problems in mid to late 1917 stemmed largely from a lack of mechanisation before the war, a corresponding lack of an oil producing or refining infrastructure, and a consequent failure to grasp the importance of gasoline supply and distribution to an increasingly mechanised army and a hugely expanding air force until it was almost too late. Whilst American, German, English and Dutch oil companies established a series of port installations, refineries, and depots before the war for the import of fuel from company owned oil fields, France, sheltering behind its tarif barriers, had only a loose association of small distributing companies that imported refined or semi-refined oil, mostly from the US, in foreign owned tankers for onward distribution by barge through the French river network. At the outbreak of the war, total French oil consumption was some 400,000 tons annually, the bulk of this being heavy fuel oil for industrial and naval use. By comparison the French air force alone, by 1918, was consuming 110,000 tons of aviation gasoline a year. By early 1917 the French army and air force was entirely dependent on the British Shell company for 100% of its aviation fuel and much of its motor gasoline, and whilst the British flying corps laid claim to the best grade of fuel from Sumatra, the French had to make up for any shortfall with a suposedly second-grade 'Light Borneo' gasoline from the Kalimantan oil fields. In May 1917 Henri Berenger, Rapporteur to the French Senate Army Committee, warned of a looming transportation crisis due to difficiencies in the French distribution system, and the French Government responded in July of 1917 by forming a Comite Generale du Petrole, with Berenger as Chairman, to negotiate a better deal with Britain through the new Inter-Allied Petroleum Conference. French aviation fuel needs were by now being estimated at 10,000 tons a month, and the French Chambre Syndicale de l'Industrie du Petrole claimed, rather dramatically, that they would run out within the next three months unless something was done. When this failed to impress their British allies, the French Premier Clemenceau sent an appeal to the US in December 1917, warning of an impending paralysis of the French armed forces and requesting immediate shipment of 100,000 tons of gasoline in US tankers directly to French ports (thus bypassing the 'pool' system, controlled by Shell and the other British oil companies). This request was met, and with the entry of the US into the war supplies of US aviation gasoline now made inroads into the Shell company's monopoly of the supply and distribution of Allied aviation fuel - although the US "X" (or Export) grade aviation fuel, although it was light enough to meet all aviation fuel specifications, was paraffinic and low in aromatics, and therefore had a tendancy to detonate and produce slightly less power in the higher compression Allied aero engines then coming into use. Whilst the British continued to use their more aromatic Shell aviation fuels from the Dutch East Indies, a fuel that would support these higher compression ratios, the French air force was forced by distribution difficulties and politics into an ever greater dependence on US supplies of this 'inferior' "X" Grade 'Export' and 'Fighter' grade fuel that the US forces were themselves now using in France. The British supply of aviation fuel was dominated and controlled largely by one company throughout the war - the Anglo-Dutch Shell group of companies, which was 60% Dutch and 40% British. Within this group of companies, the British owned Shell Transportation company controlled the distribution of fuel (and owned abput 50% of the world's tanker fleet), whilst the Royal Dutch Shell company exploited the Shell oil fields in the Dutch East Indies and had a controlling interest in the Romanian oil fields via a majority share-holding in the Romanian 'Astra' Oil Company. The Shell group also had substantial holdings in Russian oil production. In 1914 the Group faced some minor competition from two other British companies: the Burmah oil company, a Scottish oil company established originally to exploit the Scottish shale oil resources but then expanded into Burma; and the Anglo-Persian oil company established to exploit the newly discovered oil resources of Persia (Iran), Turkey (Iraq) and the Near East. Both these latter companies had, by 1914, contracts with the Admiralty to supply heavy fuel oil to new British oil-fired naval cruisers, but were not a serious competitor at that time in the British or European motor gasoline and aviation fuel markets. The best aviation fuels at this time were regarded as the light gasoline fractions from straight-run distillations of crude oil, with quality measured by the specific gravity and volatility of the fuel, and some of the best oil fields for this 'light' gasoline were to be found in Sumatra (in the Dutch East Indies), and in the oil fields of Romania. These were all owned or controlled by the Shell group, although in quantitative terms the Group accounted for little more than 5% or 6% of world oil production. The US was by far the largest world oil producer, accounting for about 65% of world production, but it exported mostly heavy fuel oil and kerosene for industrial and domestic use, and gasoline for motor vehicles. Russia, the second largest world producer (16% of world production in 1914) exported predominantly heavy fuel oil, whilst the Austro-Hungarian oil fields in Galicia (around 2% of world production) were mostly producing fuel oil, kerosene and heavier gasoline for themselves and for export to Germany. The US gasoline exports to Europe were controlled largely by the giant US Standard Oil (New Jersey) company, and were the main competitors to Shell in the pre-war European motor gasoline market. There was also some minor competition to Shell from a small association of companies promoting benzol, an alternative motor fuel produced from coal as a by-product of the coking process used in steel manufacturing. Before the war, British oil policy had been dominated by the requirement to obtain a strategic and secure supply of fuel oil for their new oil fired naval warships. The Burmah oil company was contracted first to supply heavy fuel oil to the Admiralty, but as the naval demand increased the British government went so far as to acquire a controlling interest in the Anglo-Persian oil company (later re-named British Petroleum) to secure further supplies. The British Shell Transportation Company could also supply some heavy fuel oil from the Borneo oil fields controlled by Royal Dutch Shell, but as the wartime naval demand grew until it started to outpace supply from these sources in 1916, the Shell company realised that it could use crude oil resources from its new oil fields in South and Central Americal (Mexico and Venezuela) to give it leverage into the British motor gasoline market and, more importantly perhaps, secure influence over British policy on the supply and distribution of gasoline to Entente military forces in Europe. They arrived at an agreement to supply the Admiralty with as much fuel oil as the Navy needed from Shell oil fields in the Americas, offering the tankers to transport it directly to naval bases, thereby regaining much of the influence on British oil policy that had been lost by an earlier decision of the Royal Dutch Shell to use its Dutch neutrality to continue supplying Germany with light gasoline via the Astra company in Romania. Astra, a local company controlled by Royal Dutch Shell, continued to supply both the Allies and the Germans with light gasoline until Romania then entered the war in 1916. In a subsequent move to ensure the loyalty of the Shell group, the British attempted to gain a controlling share in the British company by the purchase of British shares in Shell, but failed, and, largely due to Admiralty opposition, had to pull back from further moves to interfere in or 'nationalise' the company. Threats by the Shell executive that it would be "quite useless to disguise that the position of this Group might become so intolerable that they would withdraw the administration of their business from the United Kingdom" also threatened the supply of toluene (an essential ingredient of TNT, or Trinitrotoluene, used in many British and French munitions) which was being extracted by Shell from their aromatic-rich Borneo crude at a refinery in Portishead. This accounted for about 50% of the wartime toluene consumption of the British armed forces. Shell agreed instead to increase production of toluene in return for a much less interventionist government policy on oil, and they offered the Group's technical expertise to help improve the quality and distribution of motor gasoline and aviation fuel to the British forces in Europe. By early 1917 the British Shell company had a complete monopoly on the supply of aviation fuel to both the British and French armed forces, and also controlled the distribution of gasoline in France via the 'pool' system in which petrol companies 'pooled' their gasoline in Britain for transport by Shell tankers to ports across the channel in France, where the Shell company then established canning centres for the onward supply of gasoline in jerry cans to British and French military forces. They maintained this monopoly until the end of 1917, when the arrival of the US forces brought their own gasoline supply network and (a novelty!) gasoline pumps to replace cans. But Shell aviation fuel was so ubiquitous by this time that contemporary British references to aviation fuel of this period are often made just to "Shell A" (the 'A', presumably, for 'Aviation' or 'Aircraft'). The French, though, continued to make a distinction between "Sumatra" and "Light Borneo" (both of them, however, supplied exclusively by Shell). Not only was the Shell company involved in the direct supply and distribution of fuel to forces in France, but by 1917 it also effectively controlled government policy on issues regarding the quality and use of the different grades of fuel. Shell chemists and research scientists provided the armed forces with technical advice (there is very little evidence for independent military research into fuel by organisations such as the RAE at Farnborough until after the war) whilst Sir Robert Waley Cohen, the Managing Director of Shell Transport, was Chairman of the influential Petroleum Committee responsible for making day to day decisions on the distribution of fuel to the different branches of the armed forces. Harry Ricardo records having to present himself before this committee in the spring of 1917, in an attempt to get a better grade of fuel for the new Mk.V Tank then under development. By this period the lightest gasoline (60 octane plus, according to Ricardo) was reserved for the flying corps, the middle grade (50 to 60 octane) for 'fast staff cars', whilst the lowest grade (around 45 octane) was allocated to heavy vehicles, tractors and tanks. Ricardo knew that if he could obtain the Committee's permission to use the readily available commercial benzol, or add benzol to the low-octane fuel allocated to Tank engines, he would be able to raise the compression ratio of these engines. He also knew that the same could be done for the aero engines then under development, including his own, but his request was turned down flat by the Committee, chaired by Robert Waley Cohen. This is, perhaps, not surprising. Although it was well known before the war that benzole would suppress detonation in engines and could be used to support a higher compression ratio (a statement by the British Petrol Substitutes Joint Committee in October 1913 advised that "the use of benzol will stop knocking in practically all cases where engines are inclined to knock on petrol...[and]... benzol permits of higher compression without causing preignition or knocking"), the British had a plentiful supply of light high quality gasoline from Shell's Sumatra oilfields, an aviation fuel that would support a compression ratio up to around 5.25:1, and this fuel was actively promoted by Shell, both before and after the war, as both the best and the 'purest' aviation fuel then available. To the Shell executives such as Waley Cohen it would have been commercially unthinkable that this 'pure' fuel should be 'diluted' by the addition of any fuel additive that was controlled by a direct competitor in the form of the National Benzole Association. A similar resistance much later, to the use of the TEL anti-knock additive,patented by the US General Motors and Standard Oil companies, meant that the Group spent a great deal of time and money on an unsuccessful search for TEL alternatives in the 1920s and 1930s, and was the last major fuel producer to adopt it as an anti-knock additive in the inter-war period. Nevertheless, Waley Cohen must have recognised that benzol was a potential threat to the company's post-war share of the European motor gasoline market, and must also have known that the aromatic rich East India crude (already being exploited for its toluene content) could be the key to maintaining the company's position against the small but growing competion from benzol-petrol blends, such as that being promoted by the National Benzole Association (later to compete directly at petrol stations with their National Benzole brand). In order, one suspects, to keep Ricardo quiet, but also to gain a technical lead on their commercial rivals, Waley Cohen then approached Ricardo with a proposition - to test a sample of the Shell gasolines for their 'highest usable compression ratio', using equipment that Ricardo already had, but closely watched and assisted by Shell's own research chemist, Kewley. This produced a surprising result for both Shell and Ricardo. As expected, perhaps, most of the Shell samples were very similar to one another in the compression ratio supported - but one sample of 'heavy' Borneo gasoline indicated a very high 'usable compression ratio', or suitability for use in high compression engines. At this time, the straight run Borneo gasoline fraction from the Kalimantam oil fields was being further refined into at least two distinct narrow cuts by distillation - a benzol-rich 'Light Borneo', with approximately twice the aromatic content of Sumatra straight run gasoline but less favoured as an aviation fuel, and a 'heavy' Borneo from which toluene was extracted to leave a heavy gasoline very rich in naphthenes. This 'heavy' Borneo gasoline was too heavy, and distilled at too high a temperature to meet any existing specification for gasoline, and was being burned off at the refinery as commercialy unusable. When Ricardo discovered the value of this fuel, however, Waley Cohen immediately sent a message to the refinery telling them to stop burning this fraction and to blend it back into the other Shell gasolines. It is unlikely, however, that the resulting blends would have been used as an aviation fuel in 1917/18, as the resulting blends would have been too heavy to meet the current specifications for aviation fuel, and there would have been no commercial advantage to Shell, at that time, in promoting a higher octane blend against their own Sumatra fuel that was available in much greater quantities. Between 1917 and 1918 Ricardo and Kewley did, however, refine the Borneo fraction further to produce a small quantity of some very highly aromatic 'super' Borneo, and sent this away for testing by Rolls Royce. The Rolls Royce company discovered that with this new fuel they could then raise the compression ratio of their Eagle aero engines to 6:1 without detonation, and went on to recommend in their Eagle engine manuals that, although the engines would run satisfactorily on existing aviation gasolines, they would run better on a fuel later known as "F12 Spirit", a 20/80 blend of benzole and aviation gasoline. Although only a very small quantity of 'super' Borneo was ever refined by Shell, it was this fuel that was used in the RR Eagle engines that powered the first post-war transatlantic flight by Alcock and Brown. Due largely to the commercial interests of the Shell company, the Entente therefore lost the opportunity in early 1917 to produce an aromatic rich or benzol-petrol blend of aviation fuel that would have supported the development of much higher compression aero engines, effectively condemning Allied aero-engine designers to a maximum compression ratio of no more than 5.3:1. It is known, for example, that the compression ratio of the SE5a's Wolseley 'Viper', originally raised to 5.68:1, had to be reduced back to 5.3:1 (Bruce). The Shell company ensured Ricardo's silence by offering him a very generous contract, funding an extensive period of research into the chemical nature and anti-knock potential of a wide range of gasolines and hydro-carbon fuels supplied by them, with the proviso that he would not publicise or publish the results of this research until 18 months after the completed report and conclusions had been handed to them. The results of this ground-breaking research project were eventually released for publication in 1921, in the Automobile Engineer, and had a huge impact on the post-war development of aviation fuels and aero engine design. As most of the reference fuels examined by Ricardo were from the war-time period, and appear to have been supplied by Shell, or were of US origin, these results also include a valuable snap-shot of the aviation fuels in use at the end of the war. Although Ricardo did not identify his 'reference fuels' by name, only by identification letter, in the published report of his investigations into the properties of the various fuels supplied to him, most of them are readily identifiable by their chemical composition and distillation curves, and from close comparison with the features of named fuels in other contemporary sources. The four lightest of these reference fuels can be identified as the standard WWI aviation fuels - Shell "Sumatra" ©, Shell "Light Borneo" (B), German "Flugbenzin" (E) and US "X" or Export Grade (F). There are also reference fuels that appear to match the published descriptions for Shell 'Super' Borneo (A), Shell 'Heavy' Borneo (H), and a straight run Borneo (D), with a probable but unidentifiable motor gasoline (G) included for purposes of comparison. Sumatra © is listed with a specific gravity of 0.727: 61% paraffins, 8.5% aromatics, 30.5% naphthenes and a 'highest useful compression ratio' of 5.25:1. Distillation curve: 11.5% by 80 deg. C; 47% by 100 deg. C; 79% by 120 deg. C; 92% by 140 deg. C; 98.5% by 160 deg. C. A straight run distillation, the relatively high aromatic content ensured that it would have supported the highest compression ratio used by the Allies (5.3:1) without fear of detonation, but no higher. This was the dominant aviation fuel used by both the British and the French, at least up to early 1918 when the French, in particular, started to supplement this with US "X" grade 'Export' and 'Fighter' grade fuels. Light Borneo (B) is listed with a specific gravity of 0.723: 62% paraffins, 14.9% aromatics, 23% naphthenes and a 'highest useful compression ratio' of 5.7:1. The distillation curve identifies it as a close-cut fraction: 4% by 60 deg. C; 37.5% by 80 deg. C; 79% by 100 deg. C; 99% by 120 deg. C. Available, apparently, in only relatively small quantities (as compared to the more abundant Sumatra), the very high aromatic content meant that it provided slightly less power (about 1% or 2% less), probably due to a slightly lower calorific value, than Sumatra (above) in all engines with a compression ratio of 5.3:1 or less. It appears to have therefore been regarded as a 'second-grade' aviation fuel, although with a much higher aromatic content it could have been used to support a significantly higher compression aero engine without risk of detonation. US "X" Grade (F) is listed with a specific gravity of 0.704: 80% Paraffins, 4.3% aromatics, 15.2% naphthenes and a 'highest useful compression ratio' of 5.05:1. Distillation range: 1% by 60 deg. C; 27% by 80 deg. C; 65% by 100 deg. C; 86.5% by 120 deg. C; 94.5 by 140 deg. C (final at 153 deg. C). This paraffinic, very light gasoline is characteristic of the standard US "X" grade 'Export' and 'Fighting' gasolines that were derived mostly from Pennsylvania crude, complying with Specification no.3512 (Export) or no.3513 (Fighting) of the Bureau of Aircraft Production for export aviation gasoline used by the French and the AEF in 1918. The exact chemical composition of this straight run US "X" grade aviation gasoline varied somewhat, depending on the source of the crude oil and distillation, with the 'Fighting' grade being very slightly lighter and having a slightly narrower range of distillation but otherwise being very similar to that of the 'Export' in terms of performance. Tests run by the US Bureau of Standards indicated that, in an engine with a compression ratio of 5.3:1, the US "X" grade aviation gasolines were slightly inferior in their power output to the Shell 'Sumatra', but slightly better than Shell 'Light Borneo' (but only by a difference of 1% or 2%, either way). This can probably be accounted for by the tendency of the US fuels (with a HUCR of just over 5:1) to mild detonation in the highest compression (5.3:1) aero engines then in use by the French and British. Of the remaining 'reference' fuels detailed by Ricardo, 'H' is a very close match for the 'Heavy' Borneo described by L.J. Simon in the French comparative analysis of Allied and German fuels quoted in NACA Report no.47 Part II. This appears to be a close cut distillation of Borneo crude from Kalimantan, specific gravity 0.767: 10-28% paraffins, 2%-4% aromatics, 70%-85% naphthenes and a 'highest useful compression ratio' of 5.9:1. Distillation range: 7% by 100 deg. C; 55% by 120 deg. C; 83% by 140 deg. C; 94% by 160 deg. C (final at 176 deg. C). This may have been the sample that was tested by Ricardo in 1917, and is probably the heavy, very naphthenic gasoline fraction of the .Borneo crude remaining after the toluene content had been extracted by the Shell refinery in Portishead. From late 1917 onwards this was blended back into other Shell gasolines, although because of the high specific gravity it is very unlikely that it would have been blended back into either the 'Sumatra' or the 'Light Borneo' fractions supplied as aviation fuel. The 'reference' fuel 'A' is very close to the description of the 'Super' Borneo refined by Kewley and Ricardo in 1918, from a straight-run Kalimantan Borneo, a heavy gasoline fraction with a very high aromatic content (39%) and a 'Highest Useful Compression Ratio' of 6:1, whilst 'reference' fuel 'D' , similar but with a much lower aromatic content (14.6%) and HUCR of 5.35:1 is likely to be the straight-run Kalimantan Borneo gasoline fraction that probably forms the base for the close-cut gasolines 'A', 'B', and 'H'. The 'reference' fuel 'E' is a close match for the standard German 'Flugbenzin', and will be examined later, whilst 'reference' fuel 'G' with specific gravity of 0.750 and a 'Highest Useful Compression Ratio' of 4.55:1 is probably a commercial motor gasoline. Research by Tizard and Pye into the chemical characteristics of these fuels showed that they were all, when used in a carburettor adjusted to give maximum power for each fuel, and in the absence of detonation or distribution problems, producing the same amount of power to within 1% or 2% either way (an experimental result largely confirmed by the tests run by the US Bureau of Standards) stating that "there is no consistent difference in the maximum power obtainable with any hydrocarbon fuel, provided the conditions... are the same in each case" and "all reports to the effect of greatly increased power caused by a change in fuel are due either to one fuel being on the point of 'detonation' ... or, in the case of multi-cylinder engines, to bad distribution in one case... provided the initial temperature of the change is the same (i.e the volumetric efficiency is constant)." It seems very likely, therefore, that the problems encountered with US aviation fuels were due not to any 'inferiority' in the fuel, as such, but by a lower resistance to knock that led to mild detonation and slight loss of power in the higher compression French and British aero engines designed to run on more aromatic fuels from the Dutch East Indies. The Compression ratio that could, potentially, be supported by the 'Light Borneo' fraction and refined straight-run Borneo also indicate that there was the potential for the Allies to exploit the anti-knock capacity of these aromatic fuels, or of British (and then US) benzol resources (Britain was the largest world producer of benzol after Germany, at this time, and had enough benzol to make up for any short-fall in the naturally aromatic gasolines of the East Indies) to produce the higher compression engines that could have competed more successfully with the very high compression German aero engines of 1918. This potential was however knocked on the head, as early as the spring of 1917, by the influence and the commercial priorites of the Shell group, who not only supplied the German refineries with large quantities of high quality light petroleum, via their 'Astra' subsidiary until the entry of Romania into the war, but also very effectively blocked any attempt to upset their control of the Entente military aviation fuel market by 'diluting' their fuel with benzol obtained from commercial rivals. Far from "subordinating their own interests to the Allied cause" they appear to have used the war to firstly consolidate and then to extend their share of the European gasoline market, and gain leverage over government policy. References:- 'Floated to victory on a wave of oil: Earl Curzon tells how Allied ingenuity overcame petroleum crisis of 1916', New York Times, 23 November 1918. 'A substitute for gasoline described', New York Times, 5 October 1913. Bruce, J.M. Fighters, vol.2 (War Planes of the First World War). Macdonald, 1968. Dickinson, H.C. (and others). 'Power characteristics of fuels for aircraft engines', NACA Report no.47. Ferrier, R.W. 'French oil policy, 1917-30: the interaction between state and private interests', in: Coleman, D.C. and Mathias, Peter (eds.). Enterprise and history. Cambridge University Press, 1984. Ferrier, R.W. The history of the British Petroleum Company, vol.1: the developing years 1901-1932. Cambridge University Press, 1982. Friedensburg, Ferdinand. Das Erdol im Weltkrieg. Enke, 1939. Hoffert, W.H and Claxton, C. Motor Benzole: its production and use. The National Benzole Association, 1938. Howarth, Stephen. A century in oil: the "Shell" Transport and Trading Company, 1897-1997. Weidenfeld & Nicolson, 1997. Jonker, Joost and Luiten van Zanden, Jan. A history of Royal Dutch Shell, vol.1: from challenge to joint industry leader, 1890-1939. Oxford University Press, 2007. McBeth, B.S. British oil policy, 1919-1939. Frank Cass, 1985. Ricardo, H.R. 'The influence of various fuels on the performance of internal combustion engines: an experimental investigation into their behaviour', in The Automobile Engineer. (Part 1, February 1921, pp.51-54; Part 2, March 1921, pp.92-97; Part 3, April 1921, pp.130-133; Part 4, May 1921; Part 5, June 1921, pp.201-205; Part 6, July 1921, pp.242-247). Ricardo, Harry R. Memories and machines: the pattern of my life. Constable, 1968. Tizard, H.T. and Pye, D.R. 'The character of various fuels for internal combustion engines: the influences of specific heat and dissociation of the working fluid', Part 1, in The Automobile Engineer, February 1921, pp.55-59. Central Powers, 'Making a little go a long way ?' At the otbreak of war in 1914 Austria-Hungary was producing 890, 000 tons of crude oil a year, or 1.6% or world production - 875,000 tons of which was from a large number of small producers in Galicia. Of this 400,000 tons was exported, over 50% of it to Germany. Germany produced only 110,000 tons from within its own borders, 0.2% of world production - ten times as much as France (10,000 tons), but less than half as much as Britain (290,000 tons, mostly from Scottish shale). With stocks of only 340,000 tons (around 85,000 tons of this in the form of gasoline and lubricants, 50,000 tons of which was allocated as aviation fuel), and consumption running at 1,400,000 tons per year in 1914, Germany (even with Galician oil from Austria-Hungary) was not prepared for a long war of industrial attrition. Germany required a further one million tons of oil a year, from other countries through or around the Allied blockade, just to maintain pre-war levels of consumption. Of this, between 127,00 and 155,000 tons a year were being imported from Romania up to the middle of 1916. This still left a huge shortfall in the early to mid part of the war, particularly when the Galician oilfields were briefly occupied by the Russian army (Galician consumption fell to 677,000 tons in 1915, recovering to 928,000 in 1916 but declining thereafter to 900,000 tons in 1917, and then 840,000 tons in 1918), whilst the crude oil from Romanian oil fields was also blocked briefly when Serbia closed the Danube to oil barges in 1914. Most of this oil was for domestic lighting and heating and for industrial use, but the Army was consuming around 25% of all gasoline imported into the country. Gasoline for both the army and an expanding air force was an immediate priority, and in the early spring of 1915 very severe restrictions were imposed. on private motorists, including on order from the Bundesrat on March 15th 1915 to take 25,000 automobiles off the roads. Despite this shortfall in the supply of crude oil, there is nevertheless little evidence that the German army or air force went short of fuel in this first period of the war, up to the spring of 1917. Domestic restrictions, and the use of alternative fuels in the form of benzol petrol or of benzol petrol alcohol mixtures in motor vehicles, ensured that the lighter gasoline fractions in particular, from the German refineries, could be diverted to meet the expanding needs of the air force. At the outbreak of war Germany, unlike France, had some extremely good oil refineries, probably amongst the best at that time in Europe, if not the world, and was quite capable of taking any crude oil from any source to refine and blend into fuels that could match the Entente's straight run gasoline fractions from the East Indies. In the early years of the war, however, with access to good quality light crude from Romania, and with existing pre-war stocks to draw from, the German refineries appear to have been producing just two basic grades of gasoline for aviation use - a 'Leichtbenzin' or 'light gasoline', a close cut distillation with a specific gravity of 0.68 - 0.70 and distillation range: 20% by 60 deg. C, 60% by 80 deg. C, approx. 98% by 100 deg. C (final, 115 deg. C); and a 'Schwerbenzin' or 'heavy gasoline', another close cut distillation but with a specific gravity of 0.70 - 0.75 and a distillation range: 10% by 100 deg. C, 40% by 120 deg. C, 60% by 130 deg. C, 80% by 140 deg. C, 90% by 150 deg. C (final 170 deg. C) (Reinhardt). The Leichtbenzin appears to have been reserved for front-line units and aircraft industry, whilst the heavier 'Schwerbenzin' appears to have been allocated to training and home defence (AchimEngels). Although apparently low in aromatic content, this Leichtbenzin would have supported most of the low compression aero engines then in use without much danger of detonation. By the spring of 1915, therefore, reports filtering through to the Allies indicate that, despite the blockade, there was little sign of fuel shortages amongst German military units on the Western Front, either on the ground or in the air. United States neutrality at this time meant that the US reporters and diplomats in Germany were in a good position to feedback information on the situation in Germany, and in an interview between Lord Kitchener and Irvin S Cobb, published in a London newspaper and reported in the New York Times on 10th January 1915, Kitchener asked Cobb: "Is there any shortage of the supply of available petrol in the field ?" Cobb replied that "there is no actual shortage of fuel, as distinct from petrol" as "the Germans have been using large quantities of a benzine product... commonly known as benzol" The report goes on to add that "More light is daily being shed on the subject through the examination of captured or destroyed transports. To eke out their petrol supplies German military cars and wagons are making considerable use of a benzol-alcohol mixture" in such quantities that, according to other reports, "except for her aerial fleet, Germany could almost dispense with petrol, and still continue her warlike activities", as German industry was able to "manufacture all the benzol and alcohol neccessary for the military motors." This, the report states, at least in part: "solves the problem which has been baffling many on this side: Where is Germany getting her fuel from ?" ("Germany using substitute fuel"). Between the spring of 1915 and the summer of 1916 there were similar press reports, confirming in detail that Germany was using a variety of heavy gasoline-benzol and benzol-gasoline-alcohol or benzol-alcohol mixtures both domestically and on the ground at the Front to substitue for gasoline ("25,000 Berlin autos stop", "Use gasoline mixture", "Tells Germany;s motor mixture"). There is no indication, however, from any of these reports that benzol or alcohol mixtures, with or without gasoline, were being used before the end of 1916 in aviation fuel. Benzole is not the same as benzene, although benzene is the main constituent of benzol. A typical refined benzol (or benzole) of this period, suitable for use as a fuel, typically had a 90% aromatic content (and so was sometimes referred to as "90s benzole", the remaining 10% being heavy gasoline or kerosene, and the aromatic content was about 75% benzene, 20% toluene and 5% xylenes (Hoffert). The ratio of constituents could vary, though, and the aromatic content of the German refined benzole used in fuel mixtures has been listed as 84% benzene, 13% toluene and 3% xylenes (Reinhardt). By 1910 Germany was using half of German benzol production, a byproduct from coke ovens and gas works, for motor fuel and the German producers had joined together in the 'Westdeutsche-Benzol-Verkaufsvereinigung' (later it was renamed the Benzol-Verband, still exists today as Aral AG & Co.), and formed a distribution network for motor benzol in Germany, even importing large quantities from Britain and the US. By 1913 it was receiving government support, with a new state-funded benzol plant producing 6 million gallons a year on goverment property, and even royal sponsorship in the form of Prince Henry of Prussia (Miller). But as benzol production was closely linked to the coking industry, it was relatively inelastic and could not be increased dramatically between 1914 and 1918, so total production in Germany rose from a pre-war level of 230,000 tons in 1913 to only 248,000 tons in 1918 (Friedensburg) - this was, however, much greater than the output in any other European country or the USA, and made a huge contribution to filling the gap left by the reduction in gasoline supplies from foreign oil imports. But even though it was known before the outbreak of war in 1914 that benzole could be used on its own, or in a mixture with either gasoline or alcohol (or in a combination of all three) to suppress the 'knocking' in petrol engines, and would support a higher compression ratio than any gasoline used on its own, it was also 'heavy' with a very high specific gravity of 0.87 to 0.885 and a slightly lower calorific value than gasoline. When used as an aviation fuel, benzole also had the severe disadvantage of a very high freezing point - when used on its own, it will start to freeze at +3 deg. C, and even in a mixture with gasoline it can raise the fuel's freezing point from the -50 to -55 deg. C of a gasoline to a figure as high as -20 deg. C or more, although the freezing point will depend on the proportion of benzol to gasoline and on the toluene content of the benzol, so that a fuel with a 20% or less of benzole content, or with an increased proportion of toluene, could nevertheless meet even a specification for fuels such as the British postwar DTD 224 Specification with the requirement that it would not freeze above -50 deg. C (Hoffert). But something happened in August 1916 that changed everything - Romania entered the war on the Allied side, attacking Austro-Hungarian forces in Transylvania, and suddenly Germany (and Austria-Hungary) no longer had access to the light crude oil from the Romanian oilfields. German forces counter-attacked, and by mid November 1916 had captured the Romanian oilfields. Before they arrived, however, the Romanian engineers - with the urging and assistance of the British military mission to Romania, had comprehensively destroyed all of the above-ground stocks of petroleum and most of the equipment, pipelines, tanks, refineries and installations. It took the German engineers about six months to get the oil flowing again, leading to a hiatus in supply that lasted through until mid to late 1917. Total Romanian oil production dropped from 1,673,000 tons in 1915 to 1,244,000 tons in 1916, and then to just 517,000 tons in 1917. By the spring and summer of 1918, however, it was back up to 1916 levels at 1,214,000 tons, the bulk of which, 890,000 tons, was being sent to Germany with 231,000 tons to Austria-Hungary, 13,800 tons to Turkey and 5,900 tons to Bulgaria (Friedensburg). Between the autumn of 1916 and the end of 1917, however, the German refineries had to rely largely on their remaining stocks of the Romanian oil and the dwindling supply of somewhat heavier Galician oil. This was a severe blow to the German and Austro-Hungarian air forces as, up to this time, they appear to have been getting sufficient supplies of light gasoline to meet most of their front-line requirements, but now faced imminent shortages from the spring of 1917 when air activity would increase. A decision appears to have been made at this time to produce a new blended aviation fuel (possibly just for two-seater units, to start with), a 'Mittelbenzin' or 'Flugbenzin' that was not a straight-run distillate, but a blend of approximately 60% 'Leichtbenzin' and 40% 'Schwerbenzin' from a variety of sources (Reinhardt). The chemical composition of this blend, according to the analysis of two captured samples of this fuel by the French in the summer of 1917 (Dickinson), was very similar to that of the Shell East India gasolines and had, very strikingly, a relatively high aromatic similar to that of Sumatra and Borneo. It is known that the Germans had access to the Shell East India gasolines before the war, they had analysed the content of these fuels and were aware of their relatively high aromatic content (Reinhardt). It seems likely, therefore, that they were using these as 'reference fuels' in the creation of the blended 'Flugbenzin', and as neither Galician nor Romanian oil was noted for its high aromatic content (Hoffert), it seems probable that, from the winter of 1916, at least, they were adding some benzol to the blend to achieve a very similar aromatic content. This would help to explain the remarkable similarity in the chemical composition and distillation properties of the Flugbenzin and East India gasolines, noted by the French and the Americans. In Ricardo's immediate post-war analysis of the chemical and anti-knock properties of the gasolines then in use, one 'reference fuel' (E) stands out as a close match to the Reinhardt's distillation curve and the German Flugbenzin samples analysed by the French in 1917. This is listed with a specific gravity of 0.719: 68% paraffins, 11.3% aromatics, 20% naphthenes, and a 'highest useful compression ratio of 4.7:1, and is a close match to the chemical composition of the two different samples of Flugbenzin captured and analysed by the French: 68-78% methanes, 24-26% naphthenes, and 7-8% aromatics. As Flugbenzin was a blend of several very different gasolines, it is not surprising to find some variation, even between the French samples, and the resulting blends probably varied somewhat in their capacity to resist detonation - but appear to have been generally lower in this respect than the Allied Sumatra gasoline, at 4.7:1 according to Ricardo's analysis of Highest Useful Compression Ratio, or between 4 and 5 to 1 according to AchimEngels' source. It is notable that very few of the German aero engines of this early to mid period had a compression ratio higher than 4.7:1 (KACEY). Despite the introduction of Flugbenzin, which appears to have largely replaced Leichtbenzin as the main aviation fuel by the end of 1917, this period between the winter of 1916 and the spring of 1918 was a difficult one for the Germans, as it coincided with a big increase in the front-line aircraft strength from 2,270 aircraft in the spring of 1917 to 3,600 aircraft in the spring of 1918 - but a corresponding fall from 11,000 tons of fuel a month from early 1917 to 7,000 tons a month at the time of the Spring Offensive in 1918. The response to this was to make even greater use of the benzol still available in very large quantities, and experiments with a variety of petrol-benzol and petrol-benzol-alcohol at Adlershoff and elsewhere led to the creation of a new petrol-benzol aviation fuel named 'Fliegerbenzin', in both a summer and a winter variety, that made use of this benzol. The summer variety was a mixture of 40% 'Leichtbenzin' and 60% benzol, and with a relatively high freezing point of -20 to -24 deg. C it was clearly not going to be suitable for the increasing altitudes at which air operations were being conducted by the German fighter and high-flying recon aircraft during the winter months. The 'winter benzin' that replaced this for the colder winter months was a 50/50 mixture of 'winter benzol' (77% benzol, 23% solentnaphtha) and 'Schwerebenzin', with a reduced aromatic content (to around 35%) that reduced the freezing point and allowed for high-altitude winter flying (Reinhardt; also Dechamps & Kutzbach). For home defence, a benzin benzol alcohol Spiritus-Benzol-Mischung was developed (Rammjaeger; also Dechamps & Kutzbach). Although the initial urgency to find these gasoline substitues was almost certainly generated by the developing fuel crisis of 1917, the introduction of benzolated fuel in increasing quantities and a gradually increasing aromatic contentalso enabled engine designers to increase compression ratios, cautiously at first in the spring and summer of 1917 (increasing the compression ratio of the Daimler Mercedes D.IIIa, for example), and then more dramatically from the winter/spring of 1917/1918 with some innovative 'Hohenmotoren' such as the BMW IIIa. British tests indicate that these very high compression late-war engines appear to have required the new Fliegerbenzin to support their very high compression ratios, but between them and the early to mid-war lower compression engine types there appear to have been a wide range of hybrid intermediate types, such as the overcompressed Mercedes and Benz, or the Maybach Mb.IVa, that seem to have functioned well on either Flugbenzin or Fliegerbenzin. According to British tests of a captured Maybach Mb.IVa, for example, this engine could be used as a high-powered low altitude engine when running on a rich mixture setting - but it could also function very well as one of the new Hohenmotoren when it was run, as intended, on a weak mixture of Fliegerbenzin in the high altitude recon aircraft or airships. Similarly, tests of the Daimler Mercedes D.IIIau by the British indicated that, when run on a Sumatra gasoline (or on a similar Flugbenzin) the engine would run well at low altitude or ground level when it was throttled back to 160 hp at 1400 rpm, but when unthrottled to 1500-1600 rpm (well within the mechanical limits of this engine) it appeared to loose power, probably from detonation (Piston aero engines of the Great War). German pilots, however, appear to have got 180 PS at ground level from this engine, presumably using the higher rpm range with non-detonating Fliegerbenzin, although it was still officially rated at 160 PS at 1400 rpm. This was happening at a time, in the spring and summer of 1918, when supplies of light oil from Romania were arriving in great quantity, and there should have been no shortage of lighter Leichtbenzin coming out of German refineries from the spring of 1918 onwards. Despite this, the fuel shortage appears to have got worse. By June 1918 gasoline supplies to front-line units had fallen from 7,000 tons a month in 1917 to 5,000 tons a month in 1918, whilst their aviation fuel consumption had apparently risen from 7,000 tons to 9,000 tons a month in 1918 (a shortfall, presumably, being met by supplies of Fliegerbenzin), and restrictions were being placed on the number of sorties that could be flown from German airfields. It is likely that these shortages were not due to any real shortfall in the supply of a suitably light crude oil to German refineries - as Romanian oil was once again flowing into Germany and Austria-Hungary, and in much greater quantities than ever before - but to an increase in demand at the front combined with severe distribution difficulties on the home front, due to lack of spare parts and other industrial resources, disruption caused by civil disturbance and Allied strategic bombing, and the difficulties presented by the movement of fuel forwards from these refineries and rear areas to the front line units, particularly under the almost continuous low-level Allied bombing and strafing of German lines of communication from the spring of 1918 through to the end of the war. Bletchley References '25,000 Berlin autos stop: government cuts down the use of gasoline and rubber', New York Times, 31st March 1915. 'Germany's new problems: substitutes for rubber and gasoline found perpexling', New York Times, 27th December 1914. 'Tells Germany's motor mixture: proportions in alcohol-benzol combustible used as economy substitute for gasoline', New York Times, 6th August 1916. 'Germans using substitute fuel: employment of benzol and alcohol may increase life of war motors', New York Times, 10th January 1915. 'Use gasoline mixture: Germans overcome shortage of fuel for motor vehicles', New York Times, 15th July 1916. Brewer, Robert W. The motor car: a practical manual for the use of students and motor car owners. 1909. AchimEngels. Aerodrome Forum, 29th July 2002. Dechamps, H. and Kutzbach, K. Prufung, Werung und Weiterentwicklung von Flugmotoren. Richard Carl Schmidt, 1921. Dickinson, H.C. (and others). 'Power characteristics of fuels for aircraft engines', NACA Report no.47. Friedensburg, Ferdinand. Das Erdol im Weltkrieg. Enke, 1939. Hoffert, W.H and Claxton, C. Motor Benzole: its production and use. The National Benzole Association, 1938. Howarth, Stephen. A century in oil: the "Shell" Transport and Trading Company, 1897-1997. Weidenfeld & Nicolson, 1997. Jonker, Joost and Luiten van Zanden, Jan. A history of Royal Dutch Shell, vol.1: from challenge to joint industry leader, 1890-1939. Oxford University Press, 2007. KACEY. Aerodrome Forum. Miller, J.C. Popular Mechanics, February 1913. Piston aero-engines of the Great War. Hampshire County Library, 2009 (2 CD). Rammjaeger. Aerodrome Forum, 3rd May 2003. Reinhardt, Bruno. Vergaser, Brennstoffe und Brennstoffzufurung (Flugtechnische Bibliothek, Band 9), Richard Carl Schmidt, 1919. Ricardo, H.R. 'The influence of various fuels on the performance of internal combustion engines: an experimental investigation into their behaviour', in The Automobile Engineer. (Part 1, February 1921, pp.51-54; Part 2, March 1921, pp.92-97; Part 3, April 1921, pp.130-133; Part 4, May 1921; Part 5, June 1921, pp.201-205; Part 6, July 1921, pp.242-247). Riedler, A. 'Disturbing effect of free hydrogen on fuel combustion in internal combustion engines', Technische Berichte vol.III no.2, pp.25-26, 1918 (translated in NACA Technical Notes no.133, March 1923). Bletchley

"For much of the war the rate of fire for german machine guns appears to have been much slower than that of Allied machine guns" Yes, sorry - re-reading the Aerodrome thread, it was only later in the war (as Bullethead states) that the Allies managed to raise the rate of fire significantly above that of the German machine guns. I guess the rate of fire for both Allied and German MGs firing through the prop might be reduced in OFF for the early/mid part of the war - but I am no expert on this, and am not aware of how far this has already been implemented (and I hadn't realised that we could tinker with this ourselves, as well - thanks Her Prop-Wasche). Bletchley :)

For much of the war the rate of fire for german machine guns appears to have been much slower than that of Allied machine guns, so the twin-gun arrangement was not quite the advantage that it might appear. See this thread at the Aerodrome: http://www.theaerodrome.com/forum/aircraft/41918-synchronized-rate-fire-reality-urban-legends.html http://www.theaerodrome.com/forum/aircraft/45073-mountings-comparison-rates-fire.html The different rates of fire for German and Allied MGs has now been modelled by Greybeard for RB3D (WFP5 beta), and it has a very significant impact on one's ability to shoot aircraft down - gone are the days now when I could rack up a huge score flying a German campaign (and also suffering from stoppages, as well as jams, now). If this could be implemented for OFF as well, then I think people would notice quite a difference. Bletchley

Yes, before the US entry into the war both British and the French aviation fuel was supplied entirely by the Anglo-Dutch Shell company, a very light gasoline (low specific gravity) from Sumatra. This was lighter, less paraffinic and therefore had a better knock resistance, than US X-grade (X for Export) gasoline which therefore caused 'knock' problems in the higher-compression engines, such as the Hispano-Suiza. As Shell was, at least in part, a British company, the British obtained the lion's share of the better "Shell A", and the French got the Pennsylvania gasoline. Ironically, perhaps, the Shell company was burning off heavier (high specific gravity) gasoline fractions from their Borneo oil wells because they thought it would be useless as a motor or aviation fuel and uneconomic to transport to Europe - it wasn't until too late in the war that they 'discovered' that the high specific gravity was due to the presence of aromatic benzol, and with further refining made a very good knock-resistant aviation fuel (it fueled the first post war transatlantic flight by Alcock and Brown). A British aero-engine designer, Ricardo, wanted to add benzol to gasoline, to increase its anti-knock rating and enable higher compression engines, as early as 1917 but this request was promptly 'vetoed' by an Allied Petroleum Committee chaired by the Managing Director of the Shell company who, I think, wanted to protect their own share of the post-war gasoline market in Europe (threatened by the small benzol producers, who came together to form the National Benzole Company in 1919 to market a higher octane motor benzole benzol-gasoline blend fuel). Instead of blending this high-aromatic Borneo gasoline with their Sumatra gasoline to produce a better aviation fuel, Shell initially chose to blend this with their 'heavier' fractions to produce a better quality second-grade motor fuel (a good economic move, I guess, as it increased the quantity of gasoline for onward sale). This meant that Allied aircraft were limited to engines with a Compression Ratio of 5.3:1 (the highest that the straight-run Sumatra gasoline would support), whereas the Germans, who had plenty of benzol to spare as a byproduct of the their coking industry and were not averse to blending it with their very limited supply of gasoline, could develop some very high compression engines such as the BMW IIIa (Compression Ratio 6.4:1), used in the Fokker D.VIIF. Sorry, gone a bit off-topic. Bletchley

This has been niggling me, so I had a search on 'castor oil' on the Aerodrome forum to see if I could find out anything more. No real consensus there, either, although I did come across this idea to do with cooling, posted by Hank Jarret (Cooling issues Rotary vs. Radial 31/7/2009): "Oil that doesn't burn, but does get hot and then gets thrown away would have a significant cooling effect. That is a good reason for Castor Oil. It gets VERY hot before it burns and all of that heat is passed out of the exhaust" Also, YavorD pointed out in another thread (2 Questions for the Experts, 21/4/2009), that castor oil was officially recommended for the 300 hp Hispano Suiza (I guess they would have changed the oil regularly, on a daily basis or after each flight, as it was not a rotary with a total loss system), so it was not restricted to rotary engines. Most commentators there seemed to think that it was used because it did not dissolve in the petrol, and the lubricating effect was not thereby diluted as a petrol-based lubricant would be in a rotary engine - and it was regarded as a superior lubricant at the time even if, as Ricardo's subsequent post war tests showed, it wasn't, and it was therefore used in other engines as well (so long as it was changed regularly, to prevent a build up of gunk). I guess petroleum based oils could have been used in rotary engines, but would have had their effectiveness diluted somewhat by mixing with the petrol and might not have been so effective in carrying heat away from the engine - which is, perhaps, why the German ersatz castor oil was less effective, and contributed to overheating of the engine? Bletchley

Edit: just to contradict the above, I remembered that Harry Ricardo did some research into lubrication oils for the Shell company and the RAF in the early 1920s, looking at both vegetable oils and mineral oils, and I have looked up the reference to this in his memoirs (Ricardo, Harry R. Memories and machines. Constable, 1968). He concluded that vegetable oils were no better than mineral oils: "...the coefficient of oiliness to which so mauch importance had been attached was, in fact, of little or no significance...This had been the keystone of the arguments of the advocates of vegetable rather than mineral oil, in fact almost the only argument. Our engine tests extending over three years proved the superiority of straight mineral oils in such respects as the formation of heavy carbon deposits and piston ring sticking, while as to wear we could find no difference as between a straight mineral, a compound oil, vegetable oils such as castor oil, or animal oils such as sperm oil. This conclusion was later endorsed both by Farnborough [Royal Aircraft Establishment] and by the leading manufacturers of high-speed internal combustion engines. This was the end of any serious use of vegetable oils as engine lubricants" If this is correct, then that leaves immissibility (and the yummy taste) as the only real advantage for its use in rotary engines. B.

Thanks for the links Bullethead - I read them with interest. It seems to me that it comes back to the poor quality of the mineral oils then available, that were just not as good at providing reliable lubrication under the high operating temperatures of these air cooled engines. I guess castor oil would have been used in stationary engines also, but for the problem of the residues. This made castor oil only suitable, for practical operational use, in those engines working on a total-loss system. Rotary engines were generally overhauled more frequently, after about 30 hours or so (as against 80-100 for most stationary engines) so any remaining build-up of hard residue could be dealt with then. I guess the immissibility may not have been strictly necessary, but would nevertheless have been another very clear advantage of castor oil over the alternatives. Thanks for raising this question, it is a good one :) Bletchley

Andrew Nahum's "The rotary aero engine" (HMSO, 1987 ISBN 0112904521) Whole thing is now on googlebooks :) http://books.google.co.uk/books?id=gRzsTSKAlDAC&pg=PA46&lpg=PA46&dq=castor+oil+aero&source=bl&ots=doY7N1j4Bo&sig=SPyOd0syuPZU1QPNXB8UlbryNRI&hl=en&ei=shL0St7SIonE4QatsencAw&sa=X&oi=book_result&ct=result&resnum=1&ved=0CAoQ6AEwAA#v=onepage&q=castor%20oil%20aero&f=false B.

"Perhaps Bletch will spot this - he's forgotten more about this stuff than the rest of us will ever know" I'm still here, and reading this post with great interest - just been a bit busy helping to test the latest RB3D mod (Moving Front Patch 5) :) I have been doing a lot of research recently into WWI aviation fuels, but I do not know much about the lubrication systems or oils used - if you drop a line over at The Aerodrome I am sure that KACEY will pick it up - he has a background in chemical engineering and has added some interesting posts in the past about WWI fuels and lubricants. In the meantime, this is from Andrew Nahum's "The rotary aero engine" (HMSO, 1987 ISBN 0112904521): "One of the hoariest rotary engine myths concerns the use of castor oil...The question of solubility is...a red herring. Castor oil was the natural choice for rotaries because it was (and still is) a superb lubricant and was unquestionably superior to the mineral oils then available...the oil film provided by castor is exceptionally tenacious...and it excels where high loads and temperatures tend to break down hydrodynamic (fluid film) lubrication and only residual boundary lubrication can prevent scuffing and seizure...These are conditions which would be met almost routinely at the piston cylinder surface in rotaries, and which specifically made them extremely sensitive to oil quality...Castor, therefore was the natural choice, especially under the arduous operating conditions of war service. However, mineral oils could be used..." I am looking forward to buying the new Add-on Aircraft Pack :) Bletchley

One of the problems not already mentioned so far, is that these rotary engines had a very high "idle" speed of around 800 rpm in the air (somewhat lower, at 500-600 rpm on the ground), and the effective range of power control was not therefore 10% to 100%, but was more like 60% to 100% (or from 80% to 100% for the early monosoupape) when in flight - so your throttle controls should be calibrated to give this narrower range, if possible. This is the reason that they had the blip switch - as this (or switching off the fuel flow via the 'fine adjustment' or fuel cock) was the only way to slow the engine rpm and reduce power for landing or whilst taxiing on the ground. The pilots would then remember, or mark their throttle quadrant, with the positions of the throttle and fine adjustment levers for a small number of preset engine conditions (usually 'idle plus' at about 60%, 'cruise' at about 80% and 'full power' at 100%), and then move the fine adjustment lever for any necessary small increases or decreases in power (using this mixture control to control the power output) or for altitude adjustment. These engines were also run 'full rich' for full power, and so were more sensitive to altitude changes than most of the stationary engines of this period (with the exception of the 'fuel cooled' Renault and RAF engines, which also ran on the rich side). Bletchley

Excellent summary, Stiffy :) The Oberursel (Fokker Eindecker) selector switch could be used to cut out just one cylinder at a time - it was not a form of engine control, I think, like that for the 160 hp Gnome mono. (N28) but was used instead to isolate a faulty cylinder that might be running rough or misfiring. Even the earliest Oberursel rotaries had both the throttle and fine adjustment controls (as well as a blip switch) extended into the cockpit for pilot use - as compared to the early French Gnome types that they were based on, which appear to have been run full-out in the air (not usual to have throttle or fine adjustment controls in the cockpit, just a blip switch, although these could be added) but could have throttle and fuel controls adjusted on the ground. The Le Rhone rotaries also had a mechanical linkage between throttle and fuel controls so that, in theory, opening the throttle also increased the fuel supply to the engine to automatically supply the correct fuel/air mixture for each position of the throttle - but in practice this was sensitive to wear, temperature and pressure changes and did not work well unless constantly re-adjusted. I don't think any flight sim does a good job of simulating rotary engine control (I think even ROF ignores this), although if you want to have a taste of what it might have been like to control these engines in flight (and you still have RB3D on your system) try Gabi's ReLoad mod for RB3D and set the engine type to 'Type 1' for the early Gnome, 'Type 2' for the Gnome Monosoupape, or 'Type 3' for the later rotaries (Clerget, Le Rhone, Bentley, and Oberursel) :) Bletchley

See this link: http://www.theaerodrome.com/forum/aircraft/43574-aircraft-repair-depot-footage.html Bletchley :)

My wife's grandfather was an engineer, joined the RFC as an Observer, and ended up flying the SE5A in the final weeks of the war - the family (my wife's cousins) still have his log book. He re-joined the RAF as a Squadron Leader in WWII (non-flying, station commander). Bletchley

DukeIronHand, I have an even lower spec PC than you, I think: 3.4 CPU, 1 Mb RAM, 128 Mb ATI 9800 Pro AGP graphics card, WinXP SP3. I used to get bad stutters and FPS drops within sight of airfields (i.e. almost everywhere), down to single figures, but the devs. took note (I wasn't the only one) and they tweaked something in one of the early patches (thank you!) and I now get smooth play in low 20s FPS most of the time. The important things for me are Ground Object Density = Low (Workshop settings), and both the Terrain Detail and Scenery Detail at 1 in Config. I also 'capped' my FPS at around 25, and this helped to reduce stutter by smoothing out any wild swings. I 'tweaked' the other things in Config. as well, as advised in OFF FAQ, but I think it is the above three things that helped me most. Yes, it doesn't look too good down low - but I can live with that until I get a new PC, and at least all else looks fine :) My settings are: Aircraft Detail = 4 Terrain Detail = 1 Scenery Detail = 1 Effects Quality = 4 Cloud Quality = 5 Bletchley

As well as rigging adjustments, engine maintenance was a more or less continuous on-going process - rotary engines, typically, required a complete overhaul every 30 hours or so of flying time, and stationary engines every 80-100 hours (early period engines generally had a shorter time between overhaul than later engines). In some cases (such as Rolls Royce, and possibly Daimler Mercedes) they had to be returned to the manufacturer or to a rear area depot for this major overhaul, although in most cases there were also several lesser overhauls at prescribed intervals between the complete overhauls. Rotary engines were easier to access, and were therefore easier to maintain in the field. All engines had to have their petrol filtered regularly, to remove dirt and dust that might otherwise clog fuel lines etc., and the water and oil had to be changed regularly in the stationary and water-cooled types. Burnt valves were also common, as were distorted or fractured obturator rings, and required regular replacement. Cylinders would also distort or crack and require replacement, particularly on rotary types. Running the engine rich would 'soot-up' the cyclinders, whilst running lean or over-revving would cause heat damage or mechanically stress various parts of the engine and lead to damage to bearings and such like. Metal fatigue was unknown at the time, and metalurgical knowledge was generally poor - so sudden failure of a vital part, leading to incomplete loss of power or complete engine failure, was a common occurence. In the RFC each aircraft had a dedicated fitter (and rigger) for the day-to-day ongoing adjustment and maintenance of the engine, whilst major overhauls or repairs would be done by a whole team of fitters or another of carpenters and riggers at squadron level or at the rear maintenance depots. There was also an armourer for the guns and ordnance, and others who had the tasks of looking after the electrics and the wireless equipment, the cameras and optical sights, maps and photographs, the motor transport and horses, the pilots (a batman, mess stewards), airfield security, the squadron paperwork... Bletchley

Carrick58, "Panzer Elite" is a good WWII tank sim. (old, but none better so far, and with lots of mods to extend it). I have just recently got into the re-issued and expanded Close Combat series being produced by Matrix Games. Silent Hunter III is also one I take out for a dive now and then :) Bletchley

I have been taking a rest from OFF, so although I am fully patched I havn't flown yet - so I havn't voted in this poll. I would like to say, however, that as wide a range of options as is possible is best, from my experience with older versions. Three was good for me with the last version - I could fly 'easy' in 1915/16, and normal in 1917/18, reserving 'hard' for balloon busting missions and during offensives in 1918, and this worked well for me. If this has changed so that 'normal' has become the equivalent of the old 'hard', then a new setting between 'easy' and 'normal' (to bring back the old 'normal' setting) might be a good idea - but if this is not the case, then I am happy with the existing three settings. Something that is missing from this debate, however, is the linked issue of the mission-type - I routinely skip all missions that I feel are unrealistic for my particular pilot at a particular location in a particular period of the war. So, if I am flying with a German Jasta I would skip all missions (offensive patrols) that flew across the Front, and all ground attack missions. As an Allied pilot I would skip all 'scramble' missions, all ground attacks that were not in support of an ongoing offensive, etc. (and no ballon busting, except in support of an ongoing offensive or through choice). Restricting yourself in this way also restricts your exposure to AA artillery, and therefore makes it less likely that you will suffer too much from it whilst still maintaining its historical effectiveness... As a historical rule of thumb, an average of one pilot career out of ten should end due to AA artillery, but less in the early years (say, 1 in 20) and more in the last year (say, 1 in 5), so if you are experiencing a higher average (and you would only know that after a dozen or so pilot careers) it would be 'realitistic' to move back one notch to an easier setting. And I don't fuss about the 'realism' percentage - my last early-war campaign was flown at 20, but I feel my settings were as realistic as i could get them for that period. Bletchley

If you come across the GTS250, this is essentially the same as the 9800GTX+ I think (and it comes in either 512 or 1 GB version), and it might be cheaper (or at least more available) here in the EU than the older 9800 0r 8800 GTX cards. It is considerably cheaper than the GTX260, with only slightly inferior performance I believe, takes up less space and easy on the PSU :) http://www.hexus.net/content/item.php?item=17411 Bletchley

Double post, sorry Bletchley

The only changes I would make to my earlier recommendations above is to ignore the "(lean) = 'lean' to reduce rpm by approx. 20-40 immediately after take-off, and use this as the new default setting, just as for 'NO'", as subsequent changes to the flight models for the German scouts make this unnecessary now (you should find that they are already 'leaned' at ground level as the default). So NO (lean) is now just NO. I am not sure if Flyby's advice will still work in this case - it might :) Bletchley

I guess the scale is linear at the moment (?), but a logarithmic scale might work better - so that the lower promotions come quicker than the higher promotions. Bletchley

If you are in a quiet sector then you are probably completing a lot of succssful missions - and it seems to be this, not shooting things down, that leads to promotion. Bletchley

The French also had a collimating sight (not telescopic) similar to the Aldis, called the 'Collimateur Chretien', and there were several optical sights made by Zeiss, Goertz, and Busch but the one most often seen on German WWI aircraft would either be a captured Aldis (or Chretien) sight or the Oigee tubular sight. I believe this may have had 3x magnification, but suffered from 'fogging' (unlike the Aldis sight, that was filled with an inert gas or mixture of gasses to prevent this). See this link for further details, including a technical drawing of the German Oigee sight and a photo of the view through an Aldis sight: http://www.theaerodrome.com/forum/other-ww...l-gunsight.html The Aldis sight appears to have been popular with pilots, as they did not have to get their eye directly behind the sight to use it (as in a ring-and-bead sight) and could keep the other eye open, thus maintaining peripheral vision and situational awareness. It continued in use for some time after the war, I think, so it can't have been that bad. Early 'open' sights used by both the Allied and Germans appear to have been square rather than round (more box-and-bead than ring-and-bead). Bletchley

There is an interesting discussion going on at The Aerodrome forum on the effects (to rate of fire) of MG synchronization and interrupter gear: http://www.theaerodrome.com/forum/aircraft...an-legends.html I don't know if these effects have been built in to OFF, but if not then the OFF Team might want to have a look, with a view to adding them to the P4 development. Bletchley

I experience much the same as Creaghorn, flying RFC late in 1915 - on most missions I encounter Fokker E.III patrols, when I am flying as other than the flight leader. Never any 2-seaters. Given the replies above, then I think this must be down to the combined bionic eyes of the friendly and the enemy AI - they just always see each other, if they are in the same general area. The 2-seaters must run, whilst the scouts stay to fight. If there is any way in P4 to reduce the current visual range of the AI (by making it scaleable, perhaps, so that those who want to keep the frequent encounters can leave it as it is), or making it variable (random, or scaled on AI pilot quality or experience), then this might solve the 'problem' (for many, I guess, it isn't a problem). Bletchley