BMW 803

[SpicyJuan11]

Hello, I must admit I'm not very knowledgeable on engines, thus I have a few questions on the BMW 803 cotra-rotating prop engine. Here is some criticisms wiki has to offer:

For all this weight it delivered 3,900 PS (3,800 hp; 2,900 kW). Although this made it the most powerful German engine design, its power-to-weight ratio was only about 0.98 kW/kg (0.60 hp/lb), comparing rather poorly with other large designs like the Junkers Jumo 222 at 1.7 kW/kg, the primary powerplant design for the advanced Bomber B design competition, which was designed to use only two engines of over 1,500 kW (2,000 hp) output. Specific power of the complex BMW 803 was likewise poor, at about 34.4 kW/l, compared to the 222's 40 kW/l, as was specific fuel consumption, at 380 g/kWh (0.63 lb/hp·h), comparable to late generation turboprops.

Is this low power-to-weight ratio really that horrendous? How could it be improved? Would it have been better to throw out the entire design (which "coupled" two BMW 801's) and try to create a "single" engine being a completely different design? Would it have been workable to place it in the Fw 238, considering the aircraft had a weight-to-power ratio of 16.18 lbs/hp(in other words is this ok)?

Any help would be greatly appreciated

 

[camman]

The 803 was actually a clean-sheet design which weighed a lot less than what wikipedia states. According to the AEHS, the 803 had a total dry weight of 5143 lb and made 4000 hp for takeoff at 2800 rpm. This works out to a power to weight ratio of .777 hp/lb which is better than the 801 and almost on par with contemporary allied engines which is a truly remarkable feat of engineering considering the limitations that the german designers had to work under.

 

[SpicyJuan11]

The 803 was actually a clean-sheet design which weighed a lot less than what wikipedia states. According to the AEHS, the 803 had a total dry weight of 5143 lb and made 4000 hp for takeoff at 2800 rpm. This works out to a power to weight ratio of .777 hp/lb which is better than the 801 and almost on par with contemporary allied engines which is a truly remarkable feat of engineering considering the limitations that the german designers had to work under.

Interesting! Would you mind giving the source of the info? Also, why was the project then abandoned? Many thanks!

 

[tomo pauk]

Von Ghersdorf et al give 2600 kg of dry weight, 4000 PS at 2950 rpm (!) for take off, rated height (with 2-stage S/C) of 12000 m, where the 'Steig und Kampfleistung' was supposed to be 2650 PS at 2500 rpm. 83.6 L, C3 fuel, 2650 mm long, max width 1340 mm.

 

[SpicyJuan11]

Von Ghersdorf et al give 2600 kg of dry weight, 4000 PS at 2950 rpm (!) for take off, rated height (with 2-stage S/C) of 12000 m, where the 'Steig und Kampfleistung' was supposed to be 2650 PS at 2500 rpm. 83.6 L, C3 fuel, 2650 mm long, max width 1340 mm.

Thank you tomo, who is Von Ghersdorf, and how much max HP did the BMW 803 have? According to my sources, its max was 4500 HP.

 

[tomo pauk]

He is an co-author of this book (though I didn't pay that outrageous price of 430 $). Max power is stated at 4000 PS also by the book about BMW aero engines.

edit: at abebooks people are more reasonable, link

According to my sources, its max was 4500 HP.

Interesting. What are your sources.

 

[SpicyJuan11]

He is an co-author of this book (though I didn't pay that outrageous price of 430 $). Max power is stated at 4000 PS also by the book about BMW aero engines.

edit: at abebooks people are more reasonable, link

Interesting. What are your sources.

Ah ok, thanks for the links! The source that states this is Luftwaffe Secret Projects Strategic Projects 1935-1945 by Dieter Herwig and Heinz Rode. I'm not sure how correct this number is though, as in the Powerplants section it lists it as 4,500 HP (page 131) but on the section of the Fw 238 (one of the primary projects to be powered by the BMW 803, it lists it at 4,000 HP (page 53).

I think the latter is more correct as in another book Luftwaffe Advanced Aircraft Projects to 1945 Volume 1 By Ingolf Meyer lists the engine to have 4,000 HP (page 10 107).

Perhaps Dieter Herwig (on page 131) gave the target or perhaps the planned production version, or the performance with boost?

 

[WJPearce]

I think there is confusion among sources between the 803 and the 803A engines. The 803 had steel cylinders and crankcase and weighed more than the 803A, which had aluminum cylinders and crankcase. Reportedly, the 803's crankcase alone weighed almost 1,000 kg (2,200 lb). Unfortunately, exactly what the 803 and 803A weighed seems to be a matter for debate.

The info camman posted came from an article accessible to members only on the Aircraft Engine Historical Society's (AEHS) website. That article was written based on evaluation reports from Wright-Patterson AFB on a captured BMW 803A. These reports are now in the US National Archives. I feel these numbers are good because the US had the engine to test and measure and had no reason to record any inaccurate figures. At the same time, there could have been an accessory or two unknowingly missing.

In BMW Aero Engines (Jakobs, Kroschel, and Pierer), the BMW 803A's weight is given as 2,686 kg (5,922 lb) or 2,800 (6,172 lb) with accessories. Power is listed as 4,000 hp at 2,950 rpm. One would think these BMW supplied numbers would be accurate. The weights are heavier than the AEHS numbers but lighter that the Wikipedia numbers.

The AEHS article and the book mentioned above state the development of the 803A was halted by the RLM who wanted BMW to focus on increasing output of the 801 engine and the development of jet engines.

Most sources say the BMW 803 was good for 4,000 hp. The BMW Aero Engines book states cylinders using a disc valve would have increased the engine's output to 5,460 hp, but a complete engine was never assembled with these cylinders. Only disc valve cylinder pairs were tested. In reality, the engine's output with disc valves would have probably been less than the 5,460 hp figure based on cylinder pair tests.

In my opinion, the BMW 803A did not have all that bad of a power-to-weight ratio, and the engine probably would have produced more power as it was developed.

 

[Denniss]

BMW Historical Archive has it with 4500PS at 3000 rpm. It does not state whether it's 803 or 803A.

 

[SpicyJuan11]

I think there is confusion among sources between the 803 and the 803A engines. The 803 had steel cylinders and crankcase and weighed more than the 803A, which had aluminum cylinders and crankcase. Reportedly, the 803's crankcase alone weighed almost 1,000 kg (2,200 lb). Unfortunately, exactly what the 803 and 803A weighed seems to be a matter for debate.

The info camman posted came from an article accessible to members only on the Aircraft Engine Historical Society's (AEHS) website. That article was written based on evaluation reports from Wright-Patterson AFB on a captured BMW 803A. These reports are now in the US National Archives. I feel these numbers are good because the US had the engine to test and measure and had no reason to record any inaccurate figures. At the same time, there could have been an accessory or two unknowingly missing.

In BMW Aero Engines (Jakobs, Kroschel, and Pierer), the BMW 803A's weight is given as 2,686 kg (5,922 lb) or 2,800 (6,172 lb) with accessories. Power is listed as 4,000 hp at 2,950 rpm. One would think these BMW supplied numbers would be accurate. The weights are heavier than the AEHS numbers but lighter that the Wikipedia numbers.

The AEHS article and the book mentioned above state the development of the 803A was halted by the RLM who wanted BMW to focus on increasing output of the 801 engine and the development of jet engines.

Most sources say the BMW 803 was good for 4,000 hp. The BMW Aero Engines book states cylinders using a disc valve would have increased the engine's output to 5,460 hp, but a complete engine was never assembled with these cylinders. Only disc valve cylinder pairs were tested. In reality, the engine's output with disc valves would have probably been less than the 5,460 hp figure based on cylinder pair tests.

In my opinion, the BMW 803A did not have all that bad of a power-to-weight ratio, and the engine probably would have produced more power as it was developed.

Thank You! I had not heard about the 803A before, very interesting!

 

[SpicyJuan11]

BMW Historical Archive has it with 4500PS at 3000 rpm. It does not state whether it's 803 or 803A.

Thanks Denniss, would you mind posting the link? I can't seem to find it.

 

[WJPearce]

Below is some information from BMW Aero Engines (Jakobs, Kroschel, and Pierer) to try and highlight the 803 vs the 803A.

The BMW 803 engine design was started by Bramo in 1937 before the company was taken over by BMW. The 803 was made up of two engine sections mounted back-to-back. Each engine section had a single-stage, three-speed supercharger. Each engine section could be run independently of the other. Each engine section was geared to a three-blade propeller hub (making a six-blade contra-rotating unit). The engine had a steel crankcase and individual steel cylinders. Single cylinder tests were done in 1940, and a complete engine section was run in 1941. Because of the high power output of the complete 803, the engine sections were tested independently and they accumulated 385 hours up to February 1942. The first full 803 engine was completed in October 1942. (No info of its testing or disposition is given.)

The BMW 803A design started in 1940, after Bramo was taken over by BMW (the takeover occurred in 1939). Two engine sections made up the 803A. Each engine section had a two-stage, four-speed supercharger mounted on the rear accessory section of the complete engine. Each engine section could be run independently of the other. Each engine section was geared to a four-blade propeller hub (making an eight-blade contra-rotating unit). The 803A had an aluminum crankcase with integral cylinder pairs. This was a very complex aluminum casting. The cylinder barrels for each pair of cylinders were attached to a common aluminum cylinder head. This unit was bolted to the cylinders cast integral with the crankcase. The first 803A engine section was completed in October 1943, and the first complete engine was assembled by February 1944. The engine had run 28 hours before it was damaged in a bombing raid. A second engine was tested too, but it had some cracks in the crankcase. The complex crankcase mold was destroyed in a bombing raid, so a replacement crankcase was not available.

The 803 project was suspended by the RLM in 1944. The surviving engine in the Deutsches Museum is an 803A.

 

[SpicyJuan11]

Below is some information from BMW Aero Engines (Jakobs, Kroschel, and Pierer) to try and highlight the 803 vs the 803A.

The BMW 803 engine design was started by Bramo in 1937 before the company was taken over by BMW. The 803 was made up of two engine sections mounted back-to-back. Each engine section had a single-stage, three-speed supercharger. Each engine section could be run independently of the other. Each engine section was geared to a three-blade propeller hub (making a six-blade contra-rotating unit). The engine had a steel crankcase and individual steel cylinders. Single cylinder tests were done in 1940, and a complete engine section was run in 1941. Because of the high power output of the complete 803, the engine sections were tested independently and they accumulated 385 hours up to February 1942. The first full 803 engine was completed in October 1942. (No info of its testing or disposition is given.)

The BMW 803A design started in 1940, after Bramo was taken over by BMW (the takeover occurred in 1939). Two engine sections made up the 803A. Each engine section had a two-stage, four-speed supercharger mounted on the rear accessory section of the complete engine. Each engine section could be run independently of the other. Each engine section was geared to a four-blade propeller hub (making an eight-blade contra-rotating unit). The 803A had an aluminum crankcase with integral cylinder pairs. This was a very complex aluminum casting. The cylinder barrels for each pair of cylinders were attached to a common aluminum cylinder head. This unit was bolted to the cylinders cast integral with the crankcase. The first 803A engine section was completed in October 1943, and the first complete engine was assembled by February 1944. The engine had run 28 hours before it was damaged in a bombing raid. A second engine was tested too, but it had some cracks in the crankcase. The complex crankcase mold was destroyed in a bombing raid, so a replacement crankcase was not available.

The 803 project was suspended by the RLM in 1944. The surviving engine in the Deutsches Museum is an 803A.

Woe, ok interesting, thanks for the info! I suggest that you should edit the BMW 803's wiki

 

[Denniss]

BMW Classic
->enter 803 in the search mask and hit "Suchen"

The 803 engine in the Munich museum is labeled as 803A V5 (prototype 5)

 

[camman]

If anything, the 803A probably could have produced over 5000 horsepower if the Germans had access to 130 and 150 octane gasoline like the allies did but that's just theory at this point. The relatively low octane ratings of German fuels generally forced the Germans to get very crafty with their engine designs and make engines that are far more radical and advanced than their British and American counterparts.

 

[tomo pauk]

If anything, the 803A probably could have produced over 5000 horsepower if the Germans had access to 130 and 150 octane gasoline like the allies did but that's just theory at this point.

The 803A run on C3 fuel, like the 801D - that was close to the Allied 100/130 grade fuel in 1944?

The relatively low octane ratings of German fuels generally forced the Germans to get very crafty with their engine designs and make engines that are far more radical and advanced than their British and American counterparts.

I'm not sure that British and American engines were not advanced, some times more advanced than what Germans produced.
Germans missed the 'lower the compression ratio' trick - more boost for same fuel octane rating, like what RR and Mikulin did.

 

[camman]

C3 fuel is often listed as being in the 96-100 octane range.

 

[SpicyJuan11]

C3 fuel is often listed as being in the 96-100 octane range.

So what was the 130/150 octane fuel called?

 

[Shortround6]

it wasn't.

The difference is the lean and rich response. 100/130 acted like 100 octane fuel (or 100PN) when the mixture was leaned out. When running rich it would have a PN of 130.

The German C3 fuel seemed to change over time without getting a new name. The early blends seem to be around 96 lean and 120 or so when rich (from memory, may be wrong), late war batches went over 130 when running rich but didn't change much when running lean. Few batches of C# made it to 100 when running lean although some could exceed 96 fairly well.

The thing is that the ONLY way to measure fuel was to compare it to an existing fuel. SO a British lab testing German fuel can tell you if it responds worse, the same or better than the British fuel they have on hand the day the tests are run. If all the lab has is 100/130 as an upper level reference fuel then they can say that sample XXX of C3 equals or exceeds the 130 rating (if it does do better) but they cannot say say by how much. To give it a 140 rating they would need a 140 PN fuel sample to compare it to.

The Germans didn't set their engines up, for the most part, to use maximum boost.

 

[SpicyJuan11]

it wasn't.

The difference is the lean and rich response. 100/130 acted like 100 octane fuel (or 100PN) when the mixture was leaned out. When running rich it would have a PN of 130.

The German C3 fuel seemed to change over time without getting a new name. The early blends seem to be around 96 lean and 120 or so when rich (from memory, may be wrong), late war batches went over 130 when running rich but didn't change much when running lean. Few batches of C# made it to 100 when running lean although some could exceed 96 fairly well.


The thing is that the ONLY way to measure fuel was to compare it to an existing fuel. SO a British lab testing German fuel can tell you if it responds worse, the same or better than the British fuel they have on hand the day the tests are run. If all the lab has is 100/130 as an upper level reference fuel then they can say that sample XXX of C3 equals or exceeds the 130 rating (if it does do better) but they cannot say say by how much. To give it a 140 rating they would need a 140 PN fuel sample to compare it to.

The Germans didn't set their engines up, for the most part, to use maximum boost.

Ok, thanks Shortround. So how did German C3 usually compare to the fuel of the Allies?