R-2800 Double Wasp vs. BMW 801

[wiking85]

https://en.wikipedia.org/wiki/BMW_801
https://en.wikipedia.org/wiki/Pratt_&_Whitney_R-2800
How do these engines compare? I know they aren't exactly in the same league, though they were designed around the same time, as the Double Wasp was 18 cylinder vs. the 14 of the BMW and the PW had a higher displacement, but these seem to be the closest radial engines I could find that match up between the Germans and Americans.

 

[Shortround6]

compare how?

The R-2800 used slightly smaller cylinders but had more displacement so it made more power from the start. It was also helped in that it had two different 2 stage supercharger set ups being worked on so that the single stage engines could be better optimized for low/medium altitude work. It had better fuel for most of it's life ( or better fuel sooner).

The BMW 801 was a good engine but it is like trying to compare a 6 liter car engine to a 6.6 liter car engine.

The BMW 801 is actually a better match to the Wright R-2600.

 

[wiking85]

The BMW 801 is actually a better match to the Wright R-2600.

I didn't even know that that existed.
https://en.wikipedia.org/wiki/Wright_R-2600
In that case how did the BMW stack up against the R-2600?

 

[davebender]

Both engines received priority for development and high octane fuel. Aircraft designers were encouraged to use these engines.

IMO P&W delivered the goods with plenty of power and good reliability. BMW801 was ok but not in the same league.

Ironically airframe situation was reversed. Fw-190 airframe was outstanding while P-47 airframe was expensive and had mediocre performance. Consequently @ typical combat altitude of 2,000 meters I think BMW801 powered Fw-190A8 has a better then even chance to defeat the R2800 powered P-47D. Naval F4U is a different story but that aircraft was unlikely to encounter a BMW801 powered aircraft.

 

[Jabberwocky]

Both engines received priority for development and high octane fuel. Aircraft designers were encouraged to use these engines.

IMO P&W delivered the goods with plenty of power and good reliability. BMW801 was ok but not in the same league.

Ironically airframe situation was reversed. Fw-190 airframe was outstanding while P-47 airframe was expensive and had mediocre performance. Consequently @ typical combat altitude of 2,000 meters I think BMW801 powered Fw-190A8 has a better then even chance to defeat the R2800 powered P-47D. Naval F4U is a different story but that aircraft was unlikely to encounter a BMW801 powered aircraft.

The R-2800 was hardly limited to the P-47 and F4U. It was also in the F6F, P-61, B-26, PV-2, F8F, F7F and a host of less high volume aircraft.

When was the typical combat altitude in the ETO 2000 m? ETO combat stretched from ground level to above 30,000 ft. Typical combat altitudes varied wildly, depending on mission, location and phase of the war.

You could have just as well written "Consequently @ typical combat altitude of 6,000 meters I think BMW801 powered Fw-190A5 has a less than even chance to defeat the R2800 powered P-47D."

 

[davebender]

B-26 and P-61 are only aircraft in that group likely to appear in Europe before May 1945. I suppose we could compare them to BMW801 powered Ju-88 bomber and night fighter variants.

 

[tomo pauk]

The comparison between P-47 and Fw-190A involves much more factors than their engines. P-47 was from the get-go tailored around a powerful turbo system, that supplied air to an engine eventually making 2800 HP at 30000 ft and above, without much or any troubles. The target for P-47 were to be enemy high flying bombers, so the heavy weaponry was also there from day one, along with plenty of ammo. 2000 HP demands plenty of fuel, so it got it, too. For a fighter to be of any use in high altitude, the wing also needed to be of decent size. One of problems was that big power demands a good prop to produce big thrust, the P-47 got that in late 1943/early 1944, along with power increase and better drop tank capability.
Contrary to that, the Fw-190 was designed as an all-around fighter, combining a small airframe (wing area was somewhere between the Bf-109 and Spitfire; the 1st prototypes have had an even smaller wing) with a hefty and powerful engine. That is in contrast with K. Tank's statement that Fw-190 was 'dienstpferde' - it was a true racing horse, and arguably the best fighter when introduced, clocking 400 mph in 1941, and 410 mph in early 1942 at latest, with great roll rate and RoC, good visibility, useful punch and protection. The engine problems lasted about than a year, though.
Where the Fw-190A came short was combat radius, and there the USA and Japan were able to offer more. The BMW-801, despite it's good power under 20000 ft, was not that good above 25000 ft, plus the heavy weight combined with small wing was not well suited for hi alt, too. We can read comparison test reports at Williams' site, where the Fw-190 have had no problems with P-47 under 20-25000 ft, depending what versions are compared. Once in 1944, when Germans introduced the even heavier Fw-190A-8, the P-47D have had decent chances at lower altitudes, too.

 

[GregP]

If we look at the 3 engines, the BME 801, R-2600, and R*2800, we can make some observations,

Displacement: The R-2800 is 2,805 cubic inches displacement and weighed 2,360 pounds dry (at least in the single-stage units). The R-2600 is 2,603 cubic inches displacement and weighed 2,045 pounds dry. The BMW 801 is 2,550 cubic inches displacement and weighed 2.325 pounds dry. So they weren't far apart in displacement from one another or weight. The R-2600 seems to have the weight advantage.

Early power for the BMW 801 was 1,580 HP for takeoff. Later power was 2,400 for takeoff. They didn't make too many late model BMW 801F engines.

Early power for the R2600 was 1,600 HP for takeoff. Later power was 1,900 HP for takeoff.

Early power for the R-2800 was 1,800 HP for takeoff. Later power was 2,400 HP for takeoff and better. Some late models even made 3,800 HP! They didn't make WWII, but the potential was there. I'll used 2,400 HP.

HP/cubic inches for the BMW 801 was 0.620 to 0.940 with the vast majority at 0.705 or so. HP/pound was 0.680 to 0.870 with the vast majority being at around 0.833.

HP/cubic inches for the R-2600 was 0.615 to 0.730 with the vast majority at 0.615 or so. HP/pound was 0.782 to 0.929 with the vast majority being at around 0.782.

HP/cubic inches for the R-2800 was 0.641 to 0.856 with the vast majority at 0.749 or so. HP/pound was 0.847 to 1.020 with the vast majority being at around 0.890.

So the R-2800 started out with the highest power per displacement and highest HP per weight. Their weights were close enough that any could have been made to work in any airframe. For sheer horsepower, the R-2800 was best, but the very late-war BMW 801F was no slouch and the R-2600 had a clear advantage as far as weight goes.

The R-2800 established an enviable reputation for reliability, but I have little feel for the reputation of the BMW 801. I have not heard of any massive engine problems, but am also unaware of times between overhaul or how much time an overhaul took. We know the R-2800 required a good amount of man hours for overhaul, but also gave good reliable service when in field use. In airline service after the war, the R-2800 had a 2,000 hour TBO for twin engine aircraft and a 3,000 TBO for 4-engine aircraft. Now that's great service life for a high-strung engine.

Based on accumulated knowledge of the engine, I'd take an R-2800 any day. But the BMW 801 does not have a bad reputation and I'd also fly behind one any day. I think the Germans built a very good engine in the 801. They made about 28,000 of them versus 50,000 R-2600's and 125,000 R-2800's.

To me the engines stack up quite well against one another, with the 801 having the smallest diameter at 51 inches, the R-2800 diameter is 52.8 inches and the R-2600 diameter is 55 inches. Their numbers are close enough to be comparable to one another, making a choice tough based on numbers alone.

One place where the R-2800 could reign supreme was at high altitudes in the P-47. With the turbocharger in the P-47 it was quite happy at very high altitudes whereas the BMW 801 tended to start puffing around 20,000 feet. Without the turbo, the R-2800 also was puffing around 20,000 feet, too, so the difference was the turbocharger.

There was very little to worry about if you were behind an R-2800 in a head-on pass. It made the power and could take hits while protecting you and still get you home. I bet the Fw 190 pilots felt quite comfortable behind their BMW 801's, too. One area where the Fw 190 might have been suffering a bit is susceptibility to fire. The Fw 190 hung the oil coolers around the cowl in front of the engine. If they got holed in a gunfight, the engine could get washed with oil, making for a very fire-prone few moments. But I am not aware that proved to be a major issue in actual use and the placement of the oil coolers in the Fw 190 was an airframe decision and had nothing to do with the BMW 801 itself.

In the DB 601 / 605 series of engines the Germans had a powerplant that was close in performance to the British Merlin in many ways. The two traded superiority back and forth in the Spitfire and Bf 109 airframes over the course of the war. In the BMW 801 the Germans had a powerplant that was close in performance to the R-2600 and R2800. You can throw in the Centaurus, too. So it looks to me like both sides had good engine and airframe designers who came up with designs that had NOTHING whatsoever to do with one another yet were surprisingly comparable in performance to one another.

Verdict from me is they were quite well matched with one another.

 

[Shortround6]

R-2800 also powered the C-46 transport.

I would add my name to those arguing that the P-47 could do things the Fw 190 could not do. I also doubt very highly that the typical combat altitude was 2,000 meters in Western Europe.

The P-47 did what it was was designed to do. It may have come up a bit short in range for what was desired/needed in 1943/44 but since that radius of action was not in the original specification ( and it's range/radius was better than the Fw 190) I am not sure it can be called a failure because of that. The late model "D"s with the big fuselage tank had a range of about 50-60% more than a 190 on internal fuel.

I am not sure that the R-2800 was "national favorite" to the extent it enjoyed any "special" priority in either development or fuel allocations. P W certainly did spend a lot of time and money in developing the R-2800 series but then Wright also developed the R-1820, the R-2600 and the R-3350 engines through several different series each during the same time frame and the Army was still trying to do something, anything with it's rat-hole IV-1430 engine as late as 1944 when it should have been obvious that it was a waste of time and money.

The Wright R-2600 is a much closer match for the BMW 801 in displacement, cylinder size, power output and supercharger capability of production engines.
Arguments may be made about reliability, durability (Wright didn't have the alloy shortages the Germans had) fuel economy and so on.

 

[Shortround6]

Trying to compare the engines get a bit tricky as they changed over time. The R-2800 started at 1850 hp for production engines ("A" series) and they were 2270-2300lblbs. The "B" series engines were about the same but could vary depending on supercharger (Single speed versions for early P-47s could weight 2265lbs not counting the turbo, two stage engines for F4U and F6F could go 2480lbs without intercoolers) and were good for 2000hp with out WER settings. The "C" series engines were good for 2100hp and gained around 60-100lbs depending on supercharger. They also went from cast cylinder heads to forged cylinder heads with a LOT more finning and ran cooler with less airflow than the early engines. Later engines (the "E" series and CAs CBs etc) were pretty much post war and had changes of their own.

The R-2600 went through 3 different series which included changing from an aluminium crankcase to steel one and changing type of cylinder finning and heads went from cast to forged. Early R-2600s were around 1940lbs.

The Problem for the Wright engine was it was the same diameter as the R-3350 that powered the B-29. It may have been lighter than the R-2800 but at any given time it was 200-300hp behind the R-2800 ( without counting WER) and had higher frontal area which counted against it for fighter use.

While P&W was trying to sort out the R-4360 starting in 1940 P W wasn't doing a whole lot of R&D on R-1830 or R-2000 engines, things they learned on the R-2800 may trickle down but no big effort was put into developing them. Wright was struggling to get the R-3350 going at the same time it was improving the the R-2600 and the R-1820. In some cases new "technology" could be applied to all three engines ( forged heads, the "W" fin, sheet metal fins "rolled" into place on the cylinder barrels instead of machined fins) but Wrights engineering staff may have been stretched thin.

 

[Denniss]

BMW 801 A/C/L take-off power at sea level was 1560 PS, the often reported 1600PS were at ~700-1000m
801 D-2/G-2/Q-2 had 1700 PS, the often reported 1730 PS were at ~700m (actual engine power was ~1800 PS but power for the fan had to be taken-off)
801D-2 with C-3 injection/boost had about 1900PS for take-off
801S startet with 1930PS (2000 minus fan power), in 45 raised to ~2200

 

[tomo pauk]

Against the US competition, the BMW 801 have had several advantages and disadvantages. The advantages include:
- smaller front section, further improved by tiht cowling. Necessitated the fan, but it seems to be a good trade off?
- armored oil cooler ( only for the Fw-190 installation?)
- an exemplary exhaust stacks layout, the R-2600 never received something like that, seems that installations for the F6F and later A/C seem to come close to the BMW's in that category. The well-executed exhausts can give anywhere between 10 and 15% of additional thrust, depending on altitude
- the Kommandogeraet (unified control of engine and prop), easing the pilot's workload

The disadvantages:
- reliability was a major hurdle, with engines barely making 25 hours at 1st. Remedied in October 1942.
- US engines were usually more powerful, especially the 2-stage R-2800. BMW never received 2-stage compressor.
- the BMW never well 'cooperated' with MW-50 sytem.
- internal air intake hampered the gains through ram effect, the external intakes were rarely employed in service aircraft, despite better high altitude properties

The turboed BMW-801 appeared too late and were produced in token numbers, and were used on Ju-388 aircraft. Due to use of aircooled blades, it was possible to locate the tubrbo close to the engine, giving a very compact installation, with substantial power at high altitudes.

 

[Shortround6]

Some R-2600s used ejector exhausts.

a bit more drag than a V-12s ejector exhaust

I am not sure the R-2600 really co-operated well with water injection or WER settings.

And this article does not present a pretty picture; R-2600 Case History

 

[davebender]

Was this unique to German turbochargers and turbojets?

 

[tomo pauk]

Americans (Wright, maybe Birrman?) were experimenting with air cooled turbine blades for their turbos, but those were never used in ww2 IIRC.

 

[davebender]

Ta-152 H. | Forums - Page 13

Might have made sense to pour resources into mass production of turbocharged BMW801J engine. Then you don't need resources for mass production of Jumo 213 engine and Fw-190D9 airframe. Just upgrade existing Fw-190A8 airframe with more powerful BMW801 engine.

 

[wiking85]

What was the raw material requirements for these? IIRC Germany was hamstrung by its lack of heat resistant metals and couldn't produce the turbosuperchargers it had developed. Of course given the amounts poured into the V-2 program, perhaps this was more an issue of proper allocation rather than prohibitive requirements.

 

[davebender]

Nickel and chromium are the two most important alloy metals for high temperature steel.

Finland quit the war during September 1944. Until then Albert Speer suggests Finland was producing more nickel then Germany was willing to haul away. Nickel ore was piling up at the mines.

Chromium remains an issue but how much of an issue? I'll hazard a guess BMW801J engine (including turbo) requires less chromium then Jumo 213 engine which powered Fw-190D9.

 

[tomo pauk]

...

Might have made sense to pour resources into mass production of turbocharged BMW801J engine. Then you don't need resources for mass production of Jumo 213 engine and Fw-190D9 airframe. Just upgrade existing Fw-190A8 airframe with more powerful BMW801 engine.

Some hot discussion on that forum, with everybody waving his flag as much as possible
The 'just upgrade existing Fw-190A-8 aiframe with turbo BMW engine' was unlikely to happen. The turboed BMWs were produced in penny packets, most likely the Jumo 213E/F and 2-stage DB-603 being more readily available by late 1944.

What was the raw material requirements for these? IIRC Germany was hamstrung by its lack of heat resistant metals and couldn't produce the turbosuperchargers it had developed. Of course given the amounts poured into the V-2 program, perhaps this was more an issue of proper allocation rather than prohibitive requirements.

The whole point in employing hollow blades is that need for rare materials is much decreased - the air stream cools the turbine blades as they spin, so the hot exhaust presents a less problem for the blades.

 

[GregP]

About upgrading the Fw 190A-8 airframe with a turbo 801, I would point out that there was almost zero extra space in an Fw 190. All of it was used very creatively, and that doesn't leave much extra volume for use later.

It you upgraded it, you'd have to come up with the space somehow. If you move the engine forward, then you'd have to move the wings for CG purposes or, alternately, extend the rear fuselage for CG purposes. If you did that, what other effects would be generated?

It's not that simple to shoehorn something like a turbocharger. If it was, the P-39 would have had that done, too, as would have the P-40. That would have made them different animals in flight, just like it would have changed the Fw 190A-8.

The trick is actually DOING it. People in here spent almost an entire thread explaining why the P-51 with the Allison could never have been fitted with a turbocharger and, when compared with the Fw 190A-8, it has a ton of extra internal volume room to spare. Ever looked inside an Fw 190? It is well stocked with internal equipment.

Not saying it was impossible; I'm saying it would have been a major rework (not a simple upgrade) and, more importantly, was never accomplished by the very people who would have benefitted the most from it. There is probablya very good reason for that.