1941: the best radial engine

[tomo pauk]

I'd like to hear peoples opinions & data about what radial engine, in service in 1941 (at least in Dec 1941), could be considered the best. The performance, both down low and high up (leading to suitability both for fighters and bombers), lower weight & cross section, reliability, etc. should determine the winner.



We can devote a 'space' for the engines that were flying, albeit not used in the mass produced planes in 1941, but that takes the second seat to the engines in combat use.

[Shortround6]

Is this a trick question?

The P&W R-2800 had over 1700 engines produced in 1941 but NONE were in combat.

The 2 stage R-1830s saw very little combat in 1941 ( Wake Island?)

R-2600s were in use over Europe but only in A-20s (Boston/Hovacs)

We are getting down to the single stage R-1930 and the Wright R-1820 Cyclone and a raft of other 9 and 14 Cylinder radials with single speed superchargers and from 870-1100horsepower.

[Gixxerman]

I have no idea which was actual best but any engine that can have cylinder heads (or cylinders) shot off in combat & still bring its pilot safely home has my utmost awe & appreciation.
That's one hell of a feat.

[tomo pauk]

Not a trick question

We need to include Japanese, Soviet & British engines here, too, along with German stuff; some will better suit than another. The R-2800 (and other produced-but-not-yet-used ones) are covered:

but that takes the second seat to the engines in combat use.

ie. we can talk about them, but the main discussion should cover those that were in combat use.

[Vincenzo]

Sakae?

[Shortround6]

My apologies Tomo. I was in a hurry, I had spend two hours driving my wife to work.

Russian engines are the M-62 & 63 which are developments of the license built Wright Cyclone.
And the M-88 which is a development of the license built Gnome-Rhone 14K.
By 1941 both types are behind developments of the original engines in the home countries.
The Ash-82 is too late for 1941.

British engines are the Hercules and the ...............wait...........still thinking..................
The Tiger was a turkey and Mercury and Taraus both too small. The Pegasus was a step behind the R-1820. A bit lighter, just as big in diameter and a bit low powered.

German engines Are the BMW 801 depending on how you feel about it's problems and when they were soloved in1941 and the BMW 132, a developed license built P&W Hornet A, an R-1690 and The Bramo 323 which dates from an engine equally as old and is a bit smaller.

The Japanese really don't have much at this time as the Sakae's main claim to fame is it's ability to run really lean for long periods of time giving it great range but it's power output isn't so great. The Larger Japanese 14 cylinder radials are not making competitive power with the American engines and the Hercules at this time.

Italians really don't have much in service over 1000hp even though they have a variety of types and sizes.

[buffnut453]

Shortround,

I don't quite understand some of your points. There was nothing in the original question about absolute HP (indeed, gearing and torque have as much significance if, given the question, we're looking at both fighter and bomber implementations). Seems you're creating size parameters (eg "too small") without defining the use case or justifying the selection. Any chance you could provide some deeper insights?

Thanks,
B-N

[Shortround6]

Without getting into splitting hairs or winning bar bets the 9 cylinder engines were actually strikingly similar. Diameters varied from about 51.5 inches to about 55.5 inches and weight went from just under 1000lbs to about 1350lbs. The smaller size and weight go with the under 1000hp Bristol Mercury and the larger size and weight go with a 1200hp Wright Cyclone. Older versions of the Cyclone were lighter but less powerful. All the others fell somewhere between.
Power to weight ratios and power per sq ft of frontal area are all going to be rather close and can depend on exact model of engine as much as which different engine.

14 cylinder engines get tricker. They were usually heavier for their power although at this point more development was going into them. But compare the Cyclone to the Twin Wasp. Both 1200hp for take off engines. The Cyclone is lighter but bigger in diameter, which is better? For many US Planes they were interchangeable. Curtiss Hawks, Wildcats, Lockheed Hudsons, DC-3s.
They offer more power for the same frontal area/cross section. But again, power follows weight and frontal area. You have roughly three categories of 14 Cylinder engines.

Light weight but slow turning engines like the Tiger, the Gnome-Rhone and it's clones and some Italian engines. Many of these ran on two main bearings instead of three and while light in weight power improvement was nearly impossible. Max power is 1000-1100hp regardless of size and weight. The Tiger was closer to 900hp.

Faster turning smaller displacement engines like the R-1830 and some of the Japanese engines. These offered smaller frontal areas for better streaming but still topped out at around 1200hp give or take in 1941/42.

The hi powered 14 Cylinder engines. Now you have the big R-2600 vs the smaller Hercules and BMW 801. Some of the Japanese 14 Cylinder "bomber" engines fall in here like the Mitsubishi Kasei.

Leaving aside reliability you can pretty well sort the engines by what you want to do, especially if the BMW 801 is out.

Best engine for a twin engine bomber, the R-2600, challenged by the Hercules and the Japanese engines. For the power everybody else needs to go to 3 engines.
Best engine for large single engine torpedo plane or dive bomber, same choices.

For 4 engine aircraft "in service" in 1941/42 things get a little tricker. Some of the airframes were too small to get full use of the R-2600.
The R-2600 while powerful down low wasn't so good at altitude and it's size and weight are against it as a fighter engine. Japanese followed the same thinking but gave in and used their big 14 Cylinder engines on the Ki-44 and the Raiden.
Hercules might have been useful as a fighter but it to lacked supercharger development.

[tomo pauk]

Tanks for the analysis.
What engine should be the best for applications between 15000-30000 ft, without resorting to the turbo applications? What were power figures for Hercules in 1941, especially above 10000 ft? Just how good/bad was the 801 in 1941; IIRC it the issues could be partly blamed to the installation, too?

(anybody can chime in with some info & opinions )

[Shortround6]

Without a turbo you are pretty much left with the two stage R-1830 if the BMW 801 is out. None of the "9"s ever had a two stage and in almost all cases the ones that had a two speed supercharger had a critical altitude in high gear around 12-14,000ft.
Most if not all of the Italian engines had single speed superchargers.
The Russian M-88 Gnome-Rhone clone wasn't going to do anything at high altitude.
You have done the charts for the R-2600 and in 1941 it was pretty much the 1600hp version. was it down to 1350 at 19,000ft or so? The R-1830 has 1000hp at 19,000 ft and is 6-7 inches smaller in diameter and 400lbs lighter. Put together with it's smaller fuel requirement and all round lighter installation does the performance equal out?

I don't think the Sakae got a two speed supercharger until 1942? Sakae 21 vs Sakae 11?

[tomo pauk]

The R-2600-8, with 1700 HP for take off, was good for just under 1100 Hp at 20000 ft if we extend the military rating line (it was 1450 @ 12000 ft). But, judging from the chart (not my 'product', BTW ), the line for military rating was not extended above 15500 ft - wonder why? If we go by the highest line drawn, it's 1050 HP at 20000 ft.

[Shortround6]

Well, there is your answer. 1050-1100hp at 20,000ft or 1000hp at 19,000ft for the smaller lighter engine and lighter propeller.

443 of the 1700hp version made in 1941 and 206 of them in December. Combat use???

[tomo pauk]

Combat use is nil, since US B-25s were not to drop any bombs in 1941. However, they were in combat-worthy planes, in combat-ready units, ie. in service.

[Siegfried]

The BMW 801 is definetly in. It was reliable and in service by October 1941.

the FW 190A1 saw service through much of 1941 with BMW 801C1, it was somewhat troublesome with about 25-30 hours meant time between overhaul but over 100 were produced and saw service in that year.

Towards the end of that year, in October 1941, the FW 190A2 with BMW 801C2 came into service. The C2 still used B4 fuel but the exhaust ducting had been rerouted and improved coloing gills added which greastly improved reliabillity. All work by the Luftwaffe's own mechanics. These FW 190A2 were full and potent fighters armed with 20mm canon.

These is little distinction between FW 190A2 and the A3, the latter merely had the BMW 801D engine which used higher octane C3 fuel and could therefore use a higher compression ratio.

The BMW 801 first ran in 1939 so its entry into service was meteoric compared to the Sabre, R-2800, R-3350.

Now also factor in other achievments, such as a unified fully automatic controls for propellor pitch, mixture and altitude compensation it definetly deserves at least a runner up. The unified control wasn't just a constant speed propellor: it knew to feather the prop in a dive. You didn't have to adjust that yourself. It also came with an two speed supercharger straight of the bat.

While the PW 2800 developed fantastic machining methids BMW developed vcuum casting technology that could make ever finner fins.

Final version that saw service the BMW 801TS was providing 2200hp with a substandard fuel and MW50 and the BMW 801F was likely to offer 2600hp this version had tooling/production issues.

The BMW801TJ was offering 1500hp at 40,000ft in 1944/1945 (used on recon Ju 38 and the BMW 801TQ 1715hp at the same altitude. They would have outperformed the R-3350 at altitude though not quite at takeoff.

[tomo pauk]

What power levels we are looking at with BMW-801C of 1941? A good info about Hercules would be fine, too.