Was a competitive pre-Hercules Bristol-powered single-seat monoplane fighter feasible?
- Thread starter Admiral Beez
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So basically the answer is "no" if "competitive" is vs Spitfire or even Hurricane in 1939/40.
A Taurus engined J22 might do it if the engine was reliable, which it isn't at that time.
The problem is the Taurus isn't available and reliable meaningfully earlier than the Hercules, the Perseus has little advantage over the Mercury, and the Pegasus is a bomber engine - same diameter as Wright Cyclone but less power.
IMO the real missed opportunity with the Mercury was the crash of the Bristol Type 133 and adoption of the Gladiator (all the F.7/34 designs came too late). Presumably you could have fit a Perseus or Taurus into it later but that won't be anything special by wartime.
A Taurus engined J22 might do it if the engine was reliable, which it isn't at that time.
The problem is the Taurus isn't available and reliable meaningfully earlier than the Hercules, the Perseus has little advantage over the Mercury, and the Pegasus is a bomber engine - same diameter as Wright Cyclone but less power.
IMO the real missed opportunity with the Mercury was the crash of the Bristol Type 133 and adoption of the Gladiator (all the F.7/34 designs came too late). Presumably you could have fit a Perseus or Taurus into it later but that won't be anything special by wartime.
Incidentally there is an incredible range of power ratings out there for the Mercury.
Bristol Mercury XV (used in Blenheim) hp is given as:
Bristol Mercury XV (used in Blenheim) hp is given as:
- 825 Bristol Mercury - Wikipedia
- 920 Bristol Blenheim - Wikipedia
- 840 Bristol Engine Co: Mercury - Graces Guide (87 octane)
- 995 Bristol Engine Co: Mercury - Graces Guide (100 octane)
- 905 Bristol Mercury XV
IMO there is no such thing as a 'bomber engine'. Engine either provides the power vs. size & weight at a desired altitude, or it does not.
A Bf 109 or He 112 airframe with Mercury will be pretty competitive vs. Hurricane I of 1939-40.
There were basically two types of Mercuries in late 1930s/early 40s - the 'medium superchaged' (like the Mk.XII; engines mostly used on trainers) and 'fully supercharged' (like 7, 8, 9, 15 - hate the roman numerals; mostly used on fighters and Blenheim). On 87 oct, former gave better power down - 840 HP take off, 890 HP at 6000 ft - at expense of altitude power, while later gave 840 HP at 14000 ft and sacrificed low-alt performance (~735 HP for take off).
Advent of 100 oct fuel improved the low-alt power of FS versions a lot, the power graph indeed shows 995 HP at for them at 9250 ft; take off power was supposed to be 910 HP per graph. The data sheet for Blenheim IV shows 955 HP at 8500 ft, though.
I also hate when they say '840 HP Mercury' or '1030 HP Merlin III' - such 'data' is as misleading as it gets.
The Pegasus AFAIK was never used in a fighter, and its characteristics (good power/weight but large frontal area) make it more suitable for bombers and other larger aircraft. So I think calling it a "bomber engine" is reasonable in a military context.
With 100 octane and >900hp a Mercury fighter might get close (against a Hurricane using 87 octane!), but the P-36 is just about competitive by this standard and it needed 1050+hp.
With 100 octane and >900hp a Mercury fighter might get close (against a Hurricane using 87 octane!), but the P-36 is just about competitive by this standard and it needed 1050+hp.
We can take a look at R-1820 - good power/weight ratio + large frontal area (= very similar to Pegasus), but it was still used on fighters.
P-36 was a much bigger aircraft than the Bf 109 or He 112, a Mercury-powered P-36 will not cut it.
Seems like P-36 needed 950 HP at 17000 ft (with ram) to perform about as good as Hurricane I - link.
- Thread starter
- #27
Admiral Beez
Major
Taurus has a smaller diameter than Mercury and more power. Perhaps that's the engine for the P-36.
swampyankee
Chief Master Sergeant
- 4,022
- Jun 25, 2013
For the speed range of piston-prop aircraft, the best fineness ratio is about 8:1, and nose shape is not important as long as there is no separation. Similarly, cooling drag for well designed installations is similar for radials and liquid-cooled engines. It's harder to get a good cooling system with air cooling, as you can move radiators to a convenient spot, far enough away from interference from the propeller, but you still need to get rid of the same amount of waste heat.
The US, Japan, and Italy were able to build competitive fighters with 1,000 hp radials; that the UK didn't just means they didn't.
The UK also spent much more time and money on liquid-cooled engine development than on air-cooled.
The US, Japan, and Italy were able to build competitive fighters with 1,000 hp radials; that the UK didn't just means they didn't.
The UK also spent much more time and money on liquid-cooled engine development than on air-cooled.
We do know that one of the most streamlined radial engine installation - that of the BMW 801 - was still making almost twice the cooling drag the Jumo 213A and 213F with annular radiator. ('Kuehlung' (cooling) item at the 'Widerstandsenteile' (drag breakdown) group), and about 15% greater fuselage-related drag ('Rumpf' in the same table).
UK probably spent more time and money on air-cooled engines. Bristol, Alvis and Armstrong-Siddeley were producing several air-cooled engine types each, while RR was mostly making liquid-cooled engines. Napier was doing air-cooled engines in better part of 1930s.
As I said: Pegasus was "same diameter but less power" than R-1820 (actually 1 inch bigger diameter, 55.3 vs 54.25in, topped out at 1010 vs 1200 hp if you trust Wiki). And if one engine was used on fighters and another wasn't, it is not unreasonable to call one and not the other a "fighter engine"!
Fair point on size, however given the premise of the thread is "pre-Hercules" I think 100 octane is cheating a bit.
(A lot of sources say Zero type 21 made 331 mph with 940hp and 241ft2! Admittedly the Sakae was only 45in diameter, smaller even than Taurus.)
Not "pre-Hercules" it's not. And why would you ever pick it over a R-1830?
swampyankee
Chief Master Sergeant
- 4,022
- Jun 25, 2013
I think you should consider the possibility that the US was better at radial installations than Germany. Miley's data show well-designed radial installations had similar cooling drag to liquid-cooled inlines.
Which data are you referring to?
swampyankee
Chief Master Sergeant
- 4,022
- Jun 25, 2013
S. J. Miley is probably the expert on cooling piston engines in aircraft. It was reported in one of his papers.
Try this for a start.
Review of liquid-cooled aircraft engine installation aerodynamics
S. J. Miley
Published Online: 22 May 2012 AIAA Aerospace Research Central (behind a paywall)
He surveyed about 500 reports published on reciprocating engine cooling.
Thanks, there appears to be a free version here: http://acversailles.free.fr/documen...of_liquid_cooled_aircraft_engine~SJ.Miley.pdf
But as the title states, it is focused on liquid cooled engines, and is more a general survey of the theory than a comparison of specific planes.
I find your assertion about the Americans vs. the Germans quite surprising as the Fw 190 is generally considered to set the bar for radial streamlining during the war. The Americans did pioneer NACA cowlings but that was in 1927!
The P-40 (no letter) was making 315 mph on 745 HP at 15000 ft*. The best performance figure we have firm data for P-36 is 317 mph at 950 HP at 17000 ft (all figures are with ram effect accounted for). Granted, P-40 was making better use of exhaust thrust than P-36, however nobody was calling the V12 installation on P-40 as ground breaking either.
* hmm, one wonders how fast would be a Bf-109 or MC.200 airframe with later 'FS' RR Kestrel types - 745 HP at 14500 ft ...
* hmm, one wonders how fast would be a Bf-109 or MC.200 airframe with later 'FS' RR Kestrel types - 745 HP at 14500 ft ...
Shortround6
Major General
In a word, NOPE.
And you do need to include the Mercury. It was a 24.9 L engine and since it used the same bore and stroke as the Perseus the Perseus was the same displacement.
The Power ratings are deceptive as they do not include altitude.
The too small Mercury made 840hp at 14,000ft.
The Perseus XII made 905hp at 6,500ft, lots of luck flying a fighter with that engine.
There was a Perseus XVI rated at 905hp for take-off and 955hp at 5,000ft.
The Pegasus used the same bore as the first two but a longer stroke. A few had a two speed supercharger. Because of the longer stroke it could not turn as many rpm as the Mercury.
However on 87 octane fuel a Pegasus XVIII was rated at 965hp for take-off ((+5.5lbs boost) and 1,000hp at 3,000ft in low gear and 885hp at 15,500ft in high gear.
When using 100 octane fuel the Pegasus XVIII was rated at 1050hp for take-off (+6.75lbs boost) and 1065hp at 1,000ft in low gear and 965hp at 13,000ft in high gear.
The Pegasus was larger in diameter and heavier.
The Taurus was pretty much a failure.
The Bolded part is debatable. The Gloster F.9/37 flew briefly with a high altitude (OK, a 14-15,000ft engine) but there were cooling problems and that engine disappeared, rarely to be heard from again. All but one subsequent versions were low altitude engines. The Taurus II having 1,060hp for take-off and 1,110hp at 4,000ft. The Taurus III was rated at 935hp for take-off and 1,060hp at 14,500ft. It was used in some Australian Beauforts? The Taurus VI and later versions on 100/130 fuel were pretty much around 1085-1090hp for take-off and 1130hp at 3,100ft. The Taurus was plagued with overheating problems for most of it's life. Since the air at 14,000ft has about 73% of the mass (weight) per cubic ft as air at 4,000ft we can see that unless there was a major rework of the Taurus it had little future as anything but a low altitude engine.
The British radials made zero use of exhaust thrust in the early part of the war and the cowling design left a lot to be desired.
Shortround6
Major General
Not a lot faster than a 109 Airframe using a Jumo 210 engine, just under 700hp at 12,500-13,000?
Shortround6
Major General
Most writers doing a brief history tend to over simplify things. Yes the the Americans did start introducing the NACA cowling in the late 20's however that by no means translates into the Americans (or others) sitting on their hands a nodding their heads saying "yup, yup, we solved the radial air cooled engine problem, yup, yup" the original NACA cowling used NO internal baffles either between the cylinders of the engine or on the cylinder heads to force the air into the fins on the head. There was also no way to regulate the amount of airflow through the cowling. Way too much air was flowing through the cowling at high speed as the inlet and outlet (slot between the cowing and fuselage) were not adjustable in any way. some baffles came first and by 1935 or so adjustable cowling flaps began to be fitted to NACA cowlings. More baffling was added and a lot of work was done on the size of the opening and curve of the cowling, some cowlings were double walled, outside contour did not match the inside contour. A late 1930s cowling was major improvement over a late 1920s NACA cowling.
The German use of exhaust gases to help move cooling air through the cowl in addition to providing exhaust thrust was a definite improvement. The Americans were working on exhaust thrust for radials but not using it to aid cooling. I believe wind tunnel experiments were done with a P-35 (or model?) using multiple exhaust stubs? Some A-20s and B-25s got multiple exhaust stubs for exhaust thrust.
British were screwed because the Bristol engines were set up to have the exhaust ports on the front of the cylinder heads (Bristol poppet valves) or the front of the cylinders (sleeve valves) and you have to turn the exhaust 180 degrees and route it through the cylinder gaps to try to get exhaust thrust. P&W and Wright engines had the exhaust port facing to the rear. a bunch of short a short pipes with an "S" bend and you had your exhaust thrust (at least on a twin, trying to keep the exhaust out of the cockpit on a single was bit harder)
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Admiral Beez
Major
Is flipping the motor around such an impossibility?
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