In retrospect, were the BMW radial engine developments a mistake?

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To flip the things around - what might be the best way for the BMW to much improve the fortunes of the 801?
(hopefully the OP will forgive me here )

There was 80 of 801E engines made, but that version didn't make in production (engine have had, among other things, a much improved S/C, thus the engine power at 5.7 km was same as with 801D at km, ie. in low gear). Seems like both BMW and RLM were of opinion that it will take some time to modify the tooling for the 801E to be made in existing factories, so the 801E never went into series production.
(question is then - how much time they were expecting for the 802, let alone for the 803 to materialize....)
So press on with the 801E by winter of 1942/43, so the equivalent of performance of the 190D-9 can be had almost two years earlier with lighter and more streamlined A-3 to A-6 basic airframes.
A 2-stage supercharged 801 would've also been a sight to see, ie. something like the BMW P.8028.
A 3-speed drive for the 801E, with 3dr gear clutched in above 7 km?

(eventually the 801E's supercharger and plumbing for it were shoehorned on the 801D to make the 801S, but that was too late)

Copy the Sydlovsky-Planiol control mechanism for the S/C for a really smooth power curve?
Introduction of MW50 system?
Greater proliferation of GM1 for the Fw 190s?
Better fresh air intake is a must, but much better streamlined than it was the case historically.
 
tomo pauk said:
To flip the things around - what might be the best way for the BMW to much improve the fortunes of the 801?
(hopefully the OP will forgive me here )
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My name is Inigo Montoya. You desecrated my thread. Prepare to die!

... snip...
Click to expand...

Yes. A good 2S2S supercharger could have kept the FW190A competitive at high altitude with the Spit IX and other allied mid-late war fighters. A really good and focused effort on improving the 801 particularly around supercharging could have obviated the need for the FW190D?

Some other random things that might have improved the fortunes of the 801:
  • Figuring out the issue with the sparmetall valves and fixing it with the chrome plating sooner. The FW190/801 apparently got a very poor opinion early due to the reliability problems thanks to the valves burning, and while BMW was the first one to figure it out and fix it, it still took quite a while. Oh, and while not improving the competitive position of BMW vs. the other engine manufactures, the failure to quickly get this information out (which arguably lies at the RLM as much if not more than with BMW) was a big overall hit to German engine performance mid-war.
  • Manufacturability improvements. The 801 was apparently(?) a pretty expensive engine to make. I'm not really sure what particularly was the reason for this, and what could have been done to improve it.
  • In connection with the above, if they could have manufactured a lot more 801's, I think it could have made a very good bomber engine (vs. historically where the 801 was used in some bombers, but AFAIU in relatively small numbers). A slightly detuned 801, but still with a 2S2S supercharger for decent altitude performance, capable of running on B4 could have made an excellent bomber engine, where the increased drag vs. an inline would matter less, and the improved battle damage resistance due to lack of a liquid cooling system would be very nice.
  • Drop the 802 and 803 (or even better, never start these projects in the first place!), and concentrate on improving the 801 instead.
  • Better availability of C3 fuel. Again, I'm not sure what could have been done to produce higher volumes of C3 at less cost.
  • Some kind of automatic MW50 system could have kept the engine competitive even with lower octane gas (didn't the Homare have something like that?).
 
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Shortround6 said:
The Sabre VA went 2500lbs while the Griffon VI was 1790lbs. The engines were remarkably close to each other in BMEP, Identical in power to weight and nearly identical in piston speed (uncorrected).
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Yes. Though I think the Sabre was hobbled by the choice to use sleeve valves, both due to fundamental issues in the sleeve valve design (e.g. boost limit due to deforming the sleeves, poor heat conduction through the sleeves), and having to spend so much time getting the thing working in the first place that they just ran out of time leveraging the headroom in the design. IIRC some prototypes after the war reached some quite spectacular numbers, though of course by then it was too late as the jet age was coming fast.

You will notice I keep sticking corrected and uncorrected piston speed in. Corrected piston speed is figured by dividing the mean piston speed by the square root of the stroke/bore ratio.
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Yes I see the point, though that formula is awfully ad-hoc..


Low power civilian engines are obviously more optimized for cost of ownership rather than maximum power/weight. But yes, maybe the success of a high rpm design like the Rotax in this market wouldn't have been possible earlier.

Anyway, so far in this thread you have tried to shoot down every suggested approach for a hypothetical BMW inline that would be more powerful than the ~35L V-12's of DB and Junkers, be it a larger V-12, a V-16, or a high rpm design. As you clearly know quite a lot about aero engine design, what is your suggestion then?

Historically, I guess the most likely path would be for BMW to keep developing the 117, but that's a bit "boring", if you will, in the sense that that engine would be squarely in the same size and power class as the DB 605/Jumo211/213 so wouldn't really give aircraft designers anything new except for a third source for the engine.
 
z42 said:
Manufacturability improvements. The 801 was apparently(?) a pretty expensive engine to make. I'm not really sure what particularly was the reason for this, and what could have been done to improve it.
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Looking at Calum's book, Germans reckoned that, against R-2600 and Hercules, it was the fuel delivery system that was a culprit for the much longer manufacturing time of the BMW 801. Granted, I'm not sure how that can be quantified into cost of manufacture, but it surely adds to it. Perhaps the BMW 801 for bombers would've been viable if the pressure carb is used? Accept the - give or take - 5% power loss so there is 10-20% more engines to be had?
z42 said:
Drop the 802 and 803 (or even better, never start these projects in the first place!), and concentrate on improving the 801 instead.
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100% agree. A bird in the hand (801E in early 1943) is worth far, far more than two in the bushes (802 and 803).

z42 said:
Better availability of C3 fuel. Again, I'm not sure what could have been done to produce higher volumes of C3 at less cost.
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This might be beyond BMW's abilities
OTOH - Germans knew that ethanol and water (80% 20% mixture, with a bit of TEL added) added to the low-octane fuel produces the very high-octane fuel; they also knew that French were messing with ethanol + water both before and during the war to much improve octane rating of the fuel available (the pre-war experiments were killed by the benzene lobby in France).
Adopting the BMW 801 for MW50 is also a way to improve knock resistance, and should go well both with B4 and C3 fuel.
So there are less costly alternatives.
 
Ethanol (knowing about it from when E10 and E85 were used in the IMSA American Le Mans Series) is pretty good for making power, but, especially in the World War II context, does have a couple of drawbacks. One, ethanol is hard on conventional fuel lines and other items, such as self-sealing fuel tank liners (race cars use self-sealing fuel tank liners similar to World War II aircraft). The Italians flew a captured P-38 for a while, but had to ground it due to problems that higher ethanol content fuel caused with the fuel system.

The other big trade off is energy density. E100 (like what Indy Car has used for years) has about 2/3rds the energy density of 100 octane unleaded gasoline (of course, most if not all WWII era Avgas used lead for anti-knock). Granted I don't know how much ethanol/water mixture would be required to boost octane significantly of fuel depending on native octane rating, but if you have to use a lot of it, fuel economy can take a hit(?).
 
A critical thing for the BMW 801 (and for all radial/air cooled engines ) is the cooling, which in many (all ?) cases comes down the fin area.
The Americans and Germans used it as a "booster". It was only used at max throttle or close to it an was held in a sperate tank and injected through a separate nozzle.

I believe, but could be very wrong, that the Japanese held the water/alcohol mix in a separate tank a likewise a separate metering system. The Japanese seem to have used it for high speed cruise (welcome correction) which requires a bit different rigging/metering.

We also have a couple of different things going on, The Americans were not using it as a octane booster. They were using it as a internal cooling system. They didn't care (mostly) about the energy density of the alcohol. The alcohol was just there to keep the water from freezing and plugging up the pipes. They actually set up the carb (or single point fuel injection) to use less fuel when the water injection kicked in. They had been using excess fuel as a coolant at high boost levels. Water absorbs much more heat energy per lb/kg than gasoline does.
Alcohol's also have a much higher latent heat of evaporation than gasoline does.

For car racing alcohol works because alcohol needs less air per pound/kg of fuel. You can burn a bit more alcohol in regards to BTUs for the same amount of air as gasoline. The knock rating of alcohol is all over the place but when running rich and under high compression it is somewhere between 109-114? but you are burning a lot more alcohol than gasoline.

I am not saying the Japanese weren't using it as claimed in the Homare engine but it sounds like they were using it differently than the US and Germans used it. I don't know if this gave more trouble or not.

For the US it was either on or off. Post war a number of US airliners (and British ones) used water injection for take-off but they had quite a bit of time to get any water/alcohol back out of the engine (blow by into the oil?) before the plane landed.
 
Interesting - care to provide some back-up to the notion that Italians used ethanol (either sometimes or often?) in their avgas?
From the German perspective, outfitting the engines with fuel lines that are made from ethanol-resistant material would've been easier than to make whole production lines in order to 'elevate' the 87 oct to 100 oct?

BTW, see here for just 68 oct fuel geting to almost 100 oct with addition of 30% of 80/20 mixture of alcohol/water + 0.08% (!!) of TEL.


You can note that I'm not advocating for total replacement of the avgas with ethanol, but that aircraft use perhaps up to 25% of ethanol as fuel content. Higher octane rating allows for greater compression ratio that can be used, so that is going to cancel out most, if not all of the mileage lost. Greater CR will also increase the engine power a bit.

Shortround6 said:
The Americans and Germans used it as a "booster". It was only used at max throttle or close to it an was held in a sperate tank and injected through a separate nozzle.
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Alcohol used as a 'booster' was predominantly methanol, not ethanol.
 
tomo pauk said:
From the German perspective, outfitting the engines with fuel lines that are made from ethanol-resistant material would've been easier than to make whole production lines in order to 'elevate' the 87 oct to 100 oct?
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Making materials resistant against two different solvent families (Alcohols and Petroleum) caused trouble up to the 1980s.
 
marathag said:
Making materials resistant against two different solvent families (Alcohols and Petroleum) caused trouble up to the 1980s.
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Seems like the Ford Model T managed it before 1930s:

The Ford Model T, produced from 1908 through 1927, was fitted with a carburetor with adjustable jetting, allowing use of ethanol, gasoline or kerosene (each by itself), or a combination of the first two mentioned fuels
 
Just so we are all on the same page here

Material...................................Lantent heat of Vaporization.......................BTU/lb..........................air/fuel ratio
Methanol............................................473..............................................................8600...................................6.42 to 1
Ethanol................................................370............................................................11,500..................................9.7 to 1
Isopropanol.......................................290............................................................13,100.................................11.4 to 1
water.....................................................970............................................................................................................................
Straight run gasoline......................140............................................................19,000................................14.7 to 1
Cracked gasoline..............................140............................................................19,000.................................14.7 to 1
Aviation fuels...............................................................................................18,700-18,000....................................

Alcohols absorb water.
They also make different combustion by products than gasoline, which may be harmful to the engine.
 
tomo pauk said:
Seems like the Ford Model T
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Engine lasted around 20-30,000 miles before bearing and ring replacement. Valve work might have been more often.
Most original engines use cast iron pistons. Many owners today use aluminum pistons.
You can control the spark advance from a lever on the steering column.


Yes, they had 10-20 years to sort some of that stuff out.
 
I think I misread about the captured P-38 that Italy used before they swapped sides in mid-1943. It was the low octane/low grade Italian fuel that corroded fuel tanks and messed with the engines. But it def. seems that there's good reasons why ethanol (especially the grades available in World War II) wasn't used in World War II for aviation fuel in quantity.

Actually, thinking about this (and probably better for another topic), is there a good way to make synthetic/semi-synthetic aviation fuel? I know that Germany tried at least coal extract for synfuel.
 
Gravity fuel feed, so no fuel pump. rubber lines, either other suction of pressure, even at the low psi the pump ran at, would cause problems as the rubber swelled and softened.

If you had one of the carbs with a brass float, you out be ok, but ones with the shellac coated cork float, not so much

The other advantage of the Model T, you had manual controls for both fuel mixture and spark advance, plus a separate choke, all adjustable from the drivers seat as the car was running.

This was for allowance of the terrible original quality of what passed for Gasoline, it could be from 40 to 80 octane.
One the engine was fully warm,up you could even run on kerosene with minor changes to the mixture and spark controls
 
BarnOwlLover said:
Actually, thinking about this (and probably better for another topic), is there a good way to make synthetic/semi-synthetic aviation fuel? I know that Germany tried at least coal extract for synfuel.
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Something like >90% of the aviation fuel Germany used during WWII was synthetic. The standard B4 type fuel (around 87 MON) was basically coal -> Bergius process (Bergius process - Wikipedia ) -> TEL. C3 was much more complicated to make (which is why they struggled so much to make it in sufficient volumes). Take the fuel produced from the Bergius process, run it through a dehydrogenation step (increase aromatics, if you remember your organic chem aromatics have lower H:C ratios than alkanes or alkenes, hence "dehydrogenation" a.k.a. removing hydrogen which produces aromatic compounds). And then add iso-octane which was produced via a complicated process (not the alkylation processes refineries use today AFAIU). And then finally add TEL.
 
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C4 is not what you want in a fuel. C3 is probably what you mean.

Eng
 
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