Right ! Reverse flow cooling performed very well in this splendid aircrat !
Realistic limits of the small 12 cyl engines, 1935-45
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Right ! Reverse flow cooling performed very well in this splendid aircrat !
The "little" engines, i.e. with small cylinders, need much less finning on each cylinder owing to their very low individual capacity.
Same for the piston/rings (and crank and pushrods bearings) friction , owing to the very low stroke.
In the '60, Honda drawn some racing engines whose revving was unbelievable (more than 20,000 rpm !) with 25 cc or 41 cc individual capacity. These engine were air-cooled and ran at relatively low speed, about half of that of a plane.
Shortround6
Lieutenant General
Well, in motor cycle terms, one cylinder from a Dagger is 700 ccs and is making just under 42hp at 4200rpm. Granted it has the aid of a supercharger to do it. Of course we have to figure out the power needed to run the supercharger.
Now run a 1939 motorcycle through the same type test as an aircraft engine.
Or
Continental O-170 engine. 2.8 liters, topped out a 80 hp but needed 80 octane to do it. Same displacement cylinders (a little more bore and a little stroke than the Dagger) and was running at 2700rpm. Note the relatively crude head fins on even a 20hp cylinder. Of course most planes it was in had trouble hitting 100mph so airflow is a little limited.
History is not on the side of fast running, supercharged small displacement engines. They look good on paper. Not so good when maintenance costs/problems are looked at.
During the 50s and early 60s both Lycoming and Continental built a series of engines (including 4 cylinders) where they increase the rpm limits and mounted superchargers on the engines, by the early 60s they were starting use turbos. In the mid 60S (?) they started building larger displacement, slower running engines and they got rid of the superchargers and got rid of the reduction gears and went back direct drive. The larger displacement engines weren't much different in weight because they were not carting around the reduction gears and the supercharger. They ran at lower rpm and would run on lower octane fuel. On some of the last 6 cylinder opposed engines the superchargers and reduction gears could almost double the cost of the overhaul and they needed overhauling more often.
All of the big American radials needed redesigning for every jump in power. The R-2800C needed 10% less airflow through cowling than the R-2800B at the same power levels. But the R-2800C was just about an entirely new engine with a lot more and deeper fins on the cylinders and heads. Not sure how much they tweaked the oil system.
The Dagger had the same number of valves as a Merlin (or other V-12s) because they only used two valves per cylinder, but they needed twice the spark plugs.
The engine had nowhere to go. You want 1000hp at 15-16,000ft you may need double the power to the supercharger (another 100hp in the cylinders) on an engine that has trouble cooling. Yes you can tweak the cooling system but you need more air. It was an interesting experiment but trying to improve/fix it took manpower the British did not have.
Now run a 1939 motorcycle through the same type test as an aircraft engine.
Or
Continental O-170 engine. 2.8 liters, topped out a 80 hp but needed 80 octane to do it. Same displacement cylinders (a little more bore and a little stroke than the Dagger) and was running at 2700rpm. Note the relatively crude head fins on even a 20hp cylinder. Of course most planes it was in had trouble hitting 100mph so airflow is a little limited.
History is not on the side of fast running, supercharged small displacement engines. They look good on paper. Not so good when maintenance costs/problems are looked at.
During the 50s and early 60s both Lycoming and Continental built a series of engines (including 4 cylinders) where they increase the rpm limits and mounted superchargers on the engines, by the early 60s they were starting use turbos. In the mid 60S (?) they started building larger displacement, slower running engines and they got rid of the superchargers and got rid of the reduction gears and went back direct drive. The larger displacement engines weren't much different in weight because they were not carting around the reduction gears and the supercharger. They ran at lower rpm and would run on lower octane fuel. On some of the last 6 cylinder opposed engines the superchargers and reduction gears could almost double the cost of the overhaul and they needed overhauling more often.
All of the big American radials needed redesigning for every jump in power. The R-2800C needed 10% less airflow through cowling than the R-2800B at the same power levels. But the R-2800C was just about an entirely new engine with a lot more and deeper fins on the cylinders and heads. Not sure how much they tweaked the oil system.
The Dagger had the same number of valves as a Merlin (or other V-12s) because they only used two valves per cylinder, but they needed twice the spark plugs.
The engine had nowhere to go. You want 1000hp at 15-16,000ft you may need double the power to the supercharger (another 100hp in the cylinders) on an engine that has trouble cooling. Yes you can tweak the cooling system but you need more air. It was an interesting experiment but trying to improve/fix it took manpower the British did not have.
Admiral Beez
Major
What can we get out of the 18.4 L air cooled de Havilland Gipsy Twelve? Original spec was low compression, 6:1, with a limited 5-min output of 425 hp at an unboosted and low 2,450 rpm.
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wuzak
Captain
I did some calculations based on BMEP and piston speeds for the Peregrine years ago.
For the standard Peregrine I with 100 octane fuel:
885hp @ 3,000rpm, BMEP 1,244kPa/180psi, piston speed 13.97m/s.
For same BMEP and piston speed of Merlin (15.24m/s) I get 966hp.
For Merlin XX BMEP of 1,634kPa/237psi (1,480hp @ 3,000rpm) the Peregrine makes 1,163hp @ 3,273rpm.
The ultimate Merlin was the RM.17SM.
Maximum tested power was 2,620hp @ 3,150rpm, BMEP 2,755hp/400psi. Piston speed 16.0m/s.
Applying those parameters to the Peregrine gives 2,246hp @ 3,436rpm.
For Merlin 70 series power (1,710hp @ 3,000rpm) the BMEP is 1,563kPa/273psi.
With the same BMEP at 3,000rpm the Peregrine would give 1,112hp, and if the rpm is increased to match the Merlin's pistone speed it would be 1,213hp @ 3,273rpm.
As a counter-point, the Rotax 900 series engines have been very successful. 4 cylinders, 1.2-1.35L displacement depending on model, so about 0.3L per cylinder. 5800 rpm max. 2000 hours TBO, including the turbocharged versions, which I believe about matches other widely used piston aviation engines today.
Granted, the stroke is very short at 61mm, so even at a blistering 5800 rpm the mean piston speed is a pedestrian 11.8 m/s.
Originally introduced in 1984, so let's say ~late 70'ies 'technology level', might not have been feasible in the 1940'ies.
yulzari
Tech Sergeant
With its supercharger at 2,600rpm at only 3.5 psi boost it produced 525bhp and did so for 5 hours. Presumably on civil aviation petrol of the time so there is still room for more boost if the cooling system is up to it. It's reverse flow system was very effective in normal use at 425bhp which it could maintain but normally only used long enough for take off and ran lower for cruise and climbing for fuel economy. I would not put a hard figure on what it might be made to do but I would hazard a guess possibly 750bhp for a limited time combat use.
Shortround6
Lieutenant General
Might be a good guess. Or it may depend on materials/manufacturing.
The Gypsy 12 was two banks of Gypsy 6 cylinders on a common crankshaft.
By some time in the 1950s they had gotten the Gypsy Queen up to 380hp using a supercharger with 7.5lbs of boost and 10/130 fuel but I have no idea of what was done to the cylinders
to improve cooling or what was done to the engine to use that power rating.
don4331
Senior Airman
One thing we will note about the Rotax engines - while the sleeves are finned and air cooled, the heads are liquid cooled.
I would be interesting to see what could have been done with the deHavilland Gypsy King/Ranger V-770/Argus As 410 with similar mix of air and liquid cooling.
That's honestly one of the features I don't really understand the justification for on the Rotax. If you already have a water cooling system with pump and radiator etc, why not just have the water channel extend down around the cylinder barrels as well?
I can sort-of understand it if you start off with an air-cooled engine, and then at some point in the future you want to make a version generating more power while changing as little as possible; at that point adding liquid cooled heads might be a prudent decision. Particularly for something like an air cooled inline engine, where you'd otherwise might have issues with having to increase the bore spacing (at which point you're designing a mostly new engine anyway) in order to fit the necessary finning.
The Argus As-411 was an As-410 with enhanced features such as, among other things, an increased fin area and a special venturi-type system that used the exhaust flow to accelerate the cooling air.
Its final development was carried out by Renault/Snecma in the late 1940s (Snecma 12T). In this version, the engine produced 575 hp for takeoff at 3,300 rpm with 1,320 mm Hg boost, and 495 hp continuous at 2,400 m and 3,250 rpm (1,065 mm Hg). These performances were little different from those of the Argus As-411, but with a significantly greater reliability.
Howard Gibson
Senior Airman
Look closely at the Ranger V-770 powered Bell XP-77. The engine was not supercharged. The aircraft went 330mph at 5000ft. This actually is impressive, and comparable with all the other contemporary aircraft at low altitude. Its performance fell off above 5000ft, rendering it tactically useless for any missions carried out by the USAAF.
Add a supercharger, and you may have a daylight air superiority fighter. The small engine limits the weapons you can carry. The XP-77 was supposed to have a 20mm cannon and a pair of .50 calibre machine guns. Did it have these when it went 330mph? Its bomb load would be pathetic. Could a supercharged XP-77 shoot down heavy bombers?
By WWII standards, the Rolls Royce Merlins were small engines, at a piddling 27_litres.
wuzak
Captain
Did it get to 330mph?
Bell XP-77 - Wikipedia
My understanding is that the XP-77 was supposed to use a supercharged Ranger, and with that the expected performance was 330mph.
Still, that's not very good for an aircraft that was being developed in 1944.
Hardrada55
Airman
I've always wondered about the Czech engines. Here's what I have on the ESVR:
CKD Praga ESVK aircraft engine
Brand: CKD-Praga, the Prague-Liben
Year: 1932
Performance:
Start (k): 770
(RPM): 2100 (BMEP = 151)
Nominal (k): 650
Shortround6
Lieutenant General
The Ranger V-770 used in the XP-77 was supercharged. It was supposed to make somewhere between 450hp and 520hp at 12,000ft. According to some accounts it was supposed to get a version with a Szydlowsky-Planiol supercharger was supposed to give over 400hp (or more) at around 25,000ft. Strangely this miracle engine never showed up (sarcasm).
The Original sales pitch was that the plane would do 400mph.
Performance figures are somewhat iffy. The initial rate of climb often listed does not match well with the time to 9,000ft sometimes given.
The Original sales pitch was that the plane would do 400mph.
Performance figures are somewhat iffy. The initial rate of climb often listed does not match well with the time to 9,000ft sometimes given.
Andre Planiol went to US after french collapse in June 1940 and worked for some years for Ranger.
Did you know that a Planiol-Szydlowski supercharger was tested on the Ranger V-770 ?
Shortround6
Lieutenant General
I did know that tested a Planiol-Szydlowski supercharger on the Ranger engine and I believe they intended if for production on the "D" model. Or one of the "D"s.
I am not sure how far it got as post war aviation boom (everybody was going to fly to work instead of driving) never happened and the market for new 500-600hp engines
pretty much cratered.
There are photos of a possible candidate in several editions of Wilkinson's, at least a very sizable supercharger/housing on the back of the engine compared to some of the other V-770 engines. They may have combined it with a 2 speed supercharger drive?
I am not sure how far it got as post war aviation boom (everybody was going to fly to work instead of driving) never happened and the market for new 500-600hp engines
pretty much cratered.
There are photos of a possible candidate in several editions of Wilkinson's, at least a very sizable supercharger/housing on the back of the engine compared to some of the other V-770 engines. They may have combined it with a 2 speed supercharger drive?
