Why Castor Oil?

[Bullethead 12]

Me ol' gov's a retired petroleum engineer. He won't fly OFF but thinks it's cool and really likes reading about WW1 planes. Anyway, he was reading my book about Austrian planes and noted how it says many times that the reason the Austrians had so few planes with rotaries was because they could get neither castor oil nor the German Voltol substitute. That set his oil-based mind wondering why rotaries needed castor oil, so he started researching and bothering me with his results. That got me curious, too, so I've been looking into it also. Problem is, neither of us can find a definitive answer as to why rotaries needed castor oil.

 

Everybody seems to agree that castor oil was a better lubricant in many ways than the mineral-based oils then available. Being polar, it bonded to the mdetal better, so was more likely to remain between moving parts. Also, its viscosity was more stable over a wider range of temperatures. However, castor oil has some bad properties, such as polymerizing when heated, thus forming gunk and varnish in the motor. This means that unless you have a total loss oil system like a rotary engine, what you gain in wear protection you lose in downtime. Thus, some experts argue that this was the reason for using castor oil in rotaries. You got the benefits of using the best oil then available while dodging its bad properties. The implication here is that all engines would have used castor oil if they could have affiorded the downtime.

 

Other experts, however, say that castor oil was actually required for rotaries precisely due to their total loss oil systems. In rotaries, the oil has to enter the engine along with the fuel. Petroleum-based oils are diluted by gasoline so lose a lot of their lubricating ability in this way. Castor oil, however, doesn't mix with gasoline so remains intact.

 

Those of favor the 1st theory discount this 2nd theory by saying that there are many instances of petroleum-based oils working in rotaries. They mostly cite US work in 1917. However, champions of the other theory say this was only possible with oil from Pennsylvania, which was only available in the US, and note that the German Voltol substitute (made from coal) wasn't really that effective (as in lots of engines failed due to insufficient lubrication).

 

So, I'm at a loss here. Both theories have their merits, but if I had to choose, I'd say it was really because of the immissibility of castor oil and gasoline. Anybody here know the real answer?

 

 

[zoomzoom 2]

And here all this time I thought it was cuz it tastes sooooo good.

 

 

ZZ.

[+Nightshade/PR 7,952]

http://www.century-of-flight.net/new%20site/frames/WW1%20engines_frame.htm

 

http://www.century-of-flight.net/index.htm

[Dej 17]

Interesting question, one to which I 'd like to have he answer from a true expert. I can only offer an observation. In BH's original post he mentions in Para. 2 that unless an total loss oil system is present the build up of gunk negates the benefits of castor oil's superior lubricating qualities. In Para. 3 BH cites experts opining that the use of castor oil was dictated by the rotary's total loss system.

 

Now, it seems logical to me, unless I'm missing something, that if one needs to use a superior lubricant but one recognises that leaving it in the system is detrimental, one would design one's engine such that it got rid of the oil totally thereby mitigating against the build-up of undesirable elements.

 

There must be some documented history of rotary engine development that indicates some bright spark postulating something along the lines of "we need a bloody good lubricant for these things but the best one stuffs the engine unless we replace it on every flight... Iknow, why not design the engine to get rid of it as it uses it?"

 

I'd more readily believe in the idea of total loss being a deliberate measure to cope with the detrimental effects of castor oil build up rather than the total loss sytem being a given and castor oil the only type that lubricated sufficiently before it was lost.

 

As I say, an observation

[shredward 12]

Perhaps Bletch will spot this - he's forgotten more about this stuff than the rest of us will ever know.

shred

[Olham 164]

Well, Nightshade above sent two links. In the first, it says:

 

During World War I, rotaries attained tremendous popularity. They were less complex and easier to make than the water-cooled type.

They powered such outstanding fighter planes as German's Fokker DR-1 and Britain's Sopwith Camel. They used castor oil for lubrication

because it did not dissolve in gasoline. However, they tended to spray this oil all over, making a smelly mess.

[Bullethead 12]

Now, it seems logical to me, unless I'm missing something, that if one needs to use a superior lubricant but one recognises that leaving it in the system is detrimental, one would design one's engine such that it got rid of the oil totally thereby mitigating against the build-up of undesirable elements.

 

But here's the thing..... Even the rather primitive petroleum-based oils of the WW1 era (and indeed up to about 1930, according to the papers of lubricant engineers that I've recently read in pursuit of this answer) worked fine in stationary engines. Now, "worked fine" is a relative term, so I'm talking about pre-1930 standards here. These oils were total crap by today's standards. You could run the engine hard (but still mostly within its operational parameters) every day, but you'd have to overhaul it at the end of the year. New piston rings, new liners perhaps, maybe new crank- or camshaft bearings. IOW, the sort of things you only have to replace these days after 200,000 miles or so, assuming you can still get parts. Back then, however, motor companies built the same engine for decades so this wasn't a problem.

 

With castor oil, OTOH, if your motor diidn't have a total loss oil system, you had to tear it down and remove the gunk and varnish after every few hours if you wanted to maintain peak performance. This is why castor oil was associated with racing back in the day, because they tore down their engines after every race anyway. If you only run the motor on weekends, you can afford the downtime on weekdays. So essentially, the racers used a total loss oil system, only the total loss was manual and happened as a result of disassembly after a run. As a result, they could use the enhanced lubricating properties of castor oil in their very hard running during races without suffering (much) from the gunking effects.

 

This is why I favor the "immissibility theory" over "better lubrican theory". If castor oil was the only thing that worked well enough for high-performance combat engines, then every airplane would have used castor oil. OTOH, if rotaries could have used anything else and not blown up too frequently, then rotaries would have used petroleum-based oils and the Austrians would have used them. I noted in one of the erudite articles I read on this subject that the US planted massive fields of castor beans in WW1, despite the supposedly successful test of various petroleum-based oils in rotaries.

 

Perhaps Bletch will spot this - he's forgotten more about this stuff than the rest of us will ever know.

shred

 

 

Damn, I haven't talked to Bletch in years. I hope he does show up here.

[Bletchley 8]

"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

[Bletchley 8]

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.

[Bullethead 12]

Andrew Nahum's "The rotary aero engine" (HMSO, 1987 ISBN 0112904521)

 

Whole thing is now on googlebooks :)

 

Yup, I found that one myself while researching this. He's the guy who says the US ran rotaries successfully on petroleum-based oils.

 

Here's a contrasting view from folks with I think more specialized knowledge of lubricants: Chemestry and Technology of Lubricants, by R. M. Mortier, S. T. Orszulik. It's on page 266 if the link below doesn't take you right to it. These guys state that the reason for using castor oil was that it was insoluable in gasoline.

 

http://books.google.com/books?id=gbBQ2pRRhRUC&pg=PA266&lpg=PA266&dq=castor+oil+rotary+engine&source=bl&ots=VQXgCR3uxd&sig=0UDoaz3QHv2YBogfQdHdywPQbrI&hl=en&ei=3Rr0Sub4Ooaj8AaRqLHzCQ&sa=X&oi=book_result&ct=result&resnum=10&ved=0CCYQ6AEwCQ#v=onepage&q=castor%20oil%20rotary%20engine&f=false

 

Another article in favor of the immissibility theory:

 

http://www.penriteoil.com/uk/techbulletins/V3_RiseandFallofCastor.pdf

 

This article is mostly concerned with vintage race car engines and mentions rotaries only in passing (sometimes misnaming them radials). However, while going into all the properties of various types of oils, the author says that immissibility was the reason for using castor oil in rotaries. Note, however, that it says that castor oil DOES dissolve in alcohol. Very interesting.

 

So as you see, the experts disagree (assuming all these guys are real experts ).

 

From my lay POV, I think logic favors the argument that castor oil and gasoline don't mix. My thinking goes as follows:

 

Back then, you had 2 types of lubricants available. Mineral oil (either from crude or coal) was available in Europe in reasonably sufficient quantities although its quality varied based on where it came from. Still, that available in Europe was good enough by the standards of the day for almost all applications whether on the ground or in the air. There was also castor oil, which was better in some ways and worse in others, but had rather limited availablity due to the plant itself favoring tropical habitats. Thus, Europe had to import it or make an ersatz like Voltol from coal or petroleum. From an economic standpoint, therefore, especially under wartime blockade conditions, you'd think that mineral oil would have been used in everything.

 

However, it seems beyond doubt that European petroleum-based oils didn't work in rotaries. If they had, they would have been used. But instead the Germans had to make Voltol and apparently this wasn't particularly successful. Thus, the use of rotaries in Germany declined significantly and the Ausrians never had very many. Conversely, the Entente empires owned most of the world's castor-producing regions and ready access to the rest, so continued to use castor oil in rotaries on a large scale throughout the war. However, they don't seem to have used castor oil in other engines.

 

So, if you take Nahum's position that castor oil was used in rotaries simply because it was a superior lubricant, why didn't the Entente use it in all its engines, ground and air? They had enough available to use it more than they did had they wanted to. And the Entente had to import most of its petroleum anyway, so importing castor oil was no greater burden on them.

 

Thus, I am led to the conclusion that castor oil, despite its superior lubricating properties, was not the ideal lubricant for most engines. The obvious reason for this is the gunk and varnish it produces if retained in the motor, which requires frequent engine teardowns to remove, to the extent of making castor oil impractical for daily use. There must also have been some mechanical reason for rotaries requiring castor oil. The obvious answer there is that the oil had to come in with the fuel, and that castor oil doesn't dissolve in gasoline. And because the castor oil blew out of the engine at every stroke, the rate of sludge build-up was greatly reduced, meaning that rotary engines had to be torn down no more than usual.

 

Or so it seems to me.

[themightysrc 5]

Hi BH,

 

I think the two lines below from your last post give us the reasons.

 

 

"So, if you take Nahum's position that castor oil was used in rotaries simply because it was a superior lubricant, why didn't the Entente use it in all its engines, ground and air?"

 

and

 

"because the castor oil blew out of the engine at every stroke, the rate of sludge build-up was greatly reduced, meaning that rotary engines had to be torn down no more than usual."

 

So, you end up with a situation where castor oil was used because it was well suited to rotary engines due to its tenacity as a lubricant, and because it could be carried in the petrol - I assume that rotaries, unlike convention piston engines, don't require a sump. A car or truck motor would not be as stressed or as powerful and therefore you can get away with crappy mineral oil which is less good as a lubricant, but which doesn't require the maintenance overheads of an aircraft engine.

 

I suspect my argument's a little circular, but effectively it's horses for courses.

[Bullethead 12]

I assume that rotaries, unlike convention piston engines, don't require a sump.

 

Actually, they COULDN'T have a sump. With the whole motor spinning, all the oil is slung to the outer fringes. If it wasn't allowed to escape out the exhaust valve, it would soon not only oil up the plugs but fill the entire combustion chamber. Hence rotaries HAD to have a total loss oil system. As a result, they had to have a continuous flow of oil into the motor to replace what it was losing. But the only place the oil could come into the motor was through a hole in the center of the back, the same place the fuel had to come in. Thus, the unavoidable intermingling of fuel and oil and what I think is the unavoidable need to use a lubricant that wouldn't be dissolved by the fuel.

 

A car or truck motor would not be as stressed or as powerful and therefore you can get away with crappy mineral oil which is less good as a lubricant, but which doesn't require the maintenance overheads of an aircraft engine.

 

But consider inline aero engines. Some of these were up to twice as powerful as any rotary in service and had the same concerns with daily availablity and reliability.

[Bletchley 8]

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

Edited November 6, 2009 by Bletchley

[Bletchley 8]

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.

[Bullethead 12]

If this is correct, then that leaves immissibility (and the yummy taste) as the only real advantage for its use in rotary engines.

 

Don't forget the lovely slime spewed on the airplane's outer surfaces .

 

Nahum's comments, however, reminded me of my childhood, which I spent from age 8 to 18 flying model airplanes, U/C and then R/C. The 1-banger 2-cycle model engines were like rotaries in that they were lubed by castor oil, had total loss oil systems, and the oil came in mixed with the fuel. However, they burned nitromethane, which dissolves castor oil. In fact, when you bought fuel, you got a mix of castor oil and nitro in the same bottle, and there were several grades available with different ratios.

 

So, at 1st glance you'd think this a blow against the immissibility argument. However, IIRC the fuel mix was always more than 1/2 castor oil even in the hottest racing fuels, and for the general "farting around" fuel I normally used I think it was like 7/8 castor oil. Thus, I'd assume the dilution of the castor oil by the nitro wasn't severe enough to inhibit the lubing properties enough to matter. Plus the engines were made of modern materials under modern quality control. In any case, I never had any problems with internal wear (or gunk build-up, for that matter) even when getting INSANE revs out of them, like about 20,000 RPM for a racing 0.051 in^3 .

 

If you had the engine tuned correctly, very little of the castor oil burned or polymerized. Engines that were tuned too lean got all varnished inside and out, but otherwise you were OK there. However, all this castor oil spewed out the exhaust pipe so that the planes left thin contrails of it, and were absolutely dripping with it when they landed. And if you didn't clean it off ASAP, it would turn to shellac, not brown like varnish but clear although with hunks of dirt and pieces of grass stuck in it. And yes, it had a yummy smell

[RAF_Louvert 101]

.

 

Bullethead and all, the period writings I have come across from the war that mention castor oil indicate it was simply the best choice available in terms of its ability to offer "superior" lubrication even at high temperatures and under high internal pressures, and did not break down when mixed with the petrol, as has already been noted here in this thread. I have found no writings anywhere to indicate the design of the rotary engine itself was dictated by the availability of castor oil, but rather once they had it sorted out they chose castor oil for the previously stated reasons. Remember that the whole exercise of the rotary engine was to develope a very light motor with the greatest possible power output, and they approached that problem by minimizing the amount of parts needed to do the job. Given the metals they had to work with at the time and the relative newness of the internal combustion engine, the end result was, and still is, quite amazing. A fixed crankshaft with the pistons and connecting rods fitted to a single journal, and the cylinders, case, hub, and prop spinning around that, eliminating the need for a flywheel or counterbalance. In the case of the Gnome, one valve per cylinder to control all intake and exhaust functions, with the petrol/oil mixture drawn into the crankcase by vacuum and distributed by centrifugal force. And, because the cylinders themselves spun there was no need for any other cooling system, a further weight savings which resulted in roughly a 3 lbs/1 hp ratio. Keep in mind that although the castor oil did make a mess, the entire engine could be torn down, serviced, and reassembled in less than eight hours by the mechanics in the field. That is pretty darned good for 1914-18.

 

Cheers!

 

Lou

 

.

[Bullethead 12]

Keep in mind that although the castor oil did make a mess, the entire engine could be torn down, serviced, and reassembled in less than eight hours by the mechanics in the field. That is pretty darned good for 1914-18.

 

But how many mechanics did a squadron have? I'd assume doing 1 engine in that time took 4 or 5 guys, first to remove it from the plane, and then to service various bits of it simultaneously, and finally to put it back.

 

How many mechanics did a squadron have? Did a squadron have enough of them to put 4-5 on ever one of its aircraft simultaneously? I've never actually bothered to look up the ground TO&E of a WW1 RFC squadron--heretofore I've only been interested in how many airplanes and pilots it had on strength.

[RAF_Louvert 101]

.

 

BH, on average each RFC/RNAS pilot had a four-man ground crew assigned to his aircraft: a crew chief, (who had worked his way up and could do pretty much anything that needed to be done on a plane), two mechanics, and a rigger. When a big push was on the crews worked round the clock keeping planes ready. From what I've read, two mechanics could rebuild a rotary overnight and have it ready to go for dawn patrol. Also, the Gnome rotary engines were rebuilt after every 20 to 40 hours of running time.

 

.

[JimAttrill 24]

In my youth, Castor oil was used in two-stroke scramblers (before they were called MotoCrossers), glow and diesel model aircraft engines, and especially J.A.P and Jawa speedway bike engines. Notably these all had total-loss lubrication systems. The two-stroke scramblers used it because it was considered the best oil for a racing two-stroke, and I was told the other engines could not use mineral oils because they used alcohol and nitromethane fuels. I was told that alcohol turned mineral oils to glue. I certainly used to love the smell and stopped going to moto-cross when they stopped using Castor oil.

 

In 1968 I bought a Honda CB77 production racer that used Castrol 'R' for road use, and had to convert it to mineral oil because otherwise the oil had to be changed at least once a week, and that was expensive stuff.

 

Apparently US drag racers used to use Castor oil because it could cope with the massive blow-by of alcohol and other stuff without diluting. Again, the oil would be changed after every run.

 

But recent experience of reading the specs of some Redline oils specifically made for drag racing is that the oils can be drained and then the nitro/alcohol boiled off in a saucepan and the oil reused. This seems to show that the oils do not mix with the fuel.

[MajorMagee 0]

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.

 

This points out one of the cardinal rules of being a historian of technology. Don't assume they knew why they were doing what they were doing. It worked well enough, and that was that.

 

The fact that this research was done in the early 20s shows that they didn't really know the relative properties prior to that. It's fair to conclude that their decision to use castor oil in WWI rotary engines was based on various assumptions about what to choose, (not unlike how we've all been postulating about their reasons) and not based on definitive data.

 

Another example of this was the use of Pennsylvania gasoline for aviation fuel after 1917 because it had a higher specific gravity which they assumed meant it was higher quality than the light California gas. It turned out that the knock resistance of the California gas was a much better indicator of quality, but tests to prove that would have to wait for the inter-war years to be developed. In the meantime the Allies blamed the US for sending them our crap aviation fuel, and we felt slighted thinking we had sent them our best.

Edited November 11, 2009 by MajorMagee

[Bullethead 12]

This points out one of the cardinal rules of being a historian of technology. Don't assume they knew why they were doing what they were doing. It worked well enough, and that was that.

 

No kidding. History is replete with examples of people doing things the same way as their forebears, without ever considering there might be a better way.

 

I saw an interesting TV show about this a while back which was about the differences between the through processes of humans and chimps. One of the experiments compared kids to chimps using an experiment involving a box containing a treat. In the intial test, the box was opaque and the tester showed the kids and chimps how to get the treat out of it. Getting the treat required use of a "magic wand" and the only thing it really did was reach into the hole containing the treat and drag it out with the sticky area on its tip. The box had no moving parts, but the scientist doing the experiment gave the impression that there were some by tappingon the top of the box with the wand a few times, then poking it into several meaningless holes in the box, before finally sticking it in the hole with the treat. Both chimps and human kids assumed all these precursor moves were actually necessary to "unlock" the treat hole, so copied the sequence and got the treat. Then the scientist repeated the experiment with the same subjects, only this time the box was clear plastic. The chimps immediately saw that all the "magic" was bogus and went straight for the treat, but the humans repeated the "magic ritual" anyway.....

 

And IMHO, that's why we're "civilized" and chimps "aren't".

[Bletchley 8]

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

[Bletchley 8]

Another example of this was the use of Pennsylvania gasoline for aviation fuel after 1917 because it had a higher specific gravity which they assumed meant it was higher quality than the light California gas. It turned out that the knock resistance of the California gas was a much better indicator of quality, but tests to prove that would have to wait for the inter-war years to be developed. In the meantime the Allies blamed the US for sending them our crap aviation fuel, and we felt slighted thinking we had sent them our best.

 

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

[Bullethead 12]

"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"

 

I'm no expert on the subject, but it seems to me this argument has problems. The reason why castor oil absorbs heat and has a high ignition temperature is because your basic castor oil polymerizes below its ignition temperature, and the resulting polymer has a higher ignition temperature than the basic oil. However, this polymer takes the form of sticky gunk and varnish, which is much more likely to stay within the engine than un-polymerized oil. IOW, the more heat the castor oil absorbs, the more likely it is NOT to be blow out even in a total loss system. Therefore, it would seem to me that most of the heat absorbed by the castor oil would be staying in the engine.

 

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.

 

One of the articles I linked above was about the "cult of the castor bean". Perhaps this recommendation was an example of that? As in, castor oil's perceived benefits outweighed its actual deficiencies? After all, engines for fighter aircraft were just racecar engines, only they had to go several times every day instead of once per weekend.

 

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

 

That seems to be the concensus from my POV, too. But as mentioned above, one of the problems of taking technology back to its roots is assuming the old-timers really knew what they were doing .

 

 

Sorry, gone a bit off-topic.

 

But it was worth it. I never knew any of that stuff.