The XB-42 "solved" this problem by putting two 12-bangers side-by-side. One engine could fail and the aircraft still fly--- and fast it did!
A 'proper' way to have a 24 cylinder liquid-cooled aero engine for the ww2?
- Thread starter tomo pauk
- Start date
wuzak
Captain
I'm sure having 4 connecting rods on a crankshaft pin is no worse than having 7, 9 or 11 as on radials.
The Sabre was very compact for a 24 cylinder engine, particularly an H-24.
The Daimler-Benz DB606 (and later 610) was two complete engines joined to a common gearbox. It was possible to disconnect one engine from the prop drive and shut it down.
Having two of everything made the 606 very heavy. It was also capable of ~2,600hp early in the war, which wouldn't be matched by any allied engines until late in the war.
wuzak
Captain
It's a wonder that the greatest 24 cylinder engine of them all hasn't been mentioned - the Fairey P.24 with 4 speed, 2 stage supercharging! 
Spindash64
Airman
- 89
- Oct 21, 2021
It also caught on fire. A LOT. And as you said, it was 2 1,300hp engines glued together. That MAYBE saves some space over using a 4 engined bomber with 1,300hp engines, but at the cost of complexity, pricetag, and, you know, turning your crew into the Human Torch every 10 flights. Maybe the Allies didn't have equal hp per engine, but the B-17G had the same total Horsepower and could hold it to higher altitude, the A-20G was only around 66% as powerful but was more reliable… Hell, I'd rather fly a Po-2 on a combat sortie than the Greif.
That's the point I'm getting at: it doesn't matter if you have more engine power, if you sacrifice manpower, fleet size, or even crew mortality, IT'S NOT WORTH IT. If your plane threatens a higher mortality rate for its crew than enemy fire, it's junk. The potential gain in power isn't worth the risk of Fire or the inability to maintain effective supply of these engines to tens of thousands of aircraft. If we were building racing aircraft or experimental record setters, it might be, but not for a War Machine. Mr Murphy won't be as kind when you don't have a dedicated team that knows the ins and outs of this particular engine
wuzak
Captain
Yes, it caught fire, possibly because the engines were inverted and the inner exhausts went straight down. Oil leaks would then get on the hot exhausts and ignite. The fault is not completely with the engine, though, as the installation seemed to be poor. For instance, the He 177 did not have a firewall behind the engine.
Essentially the He 177 was a 4 engine aircraft. But with only two propellers.
Other aircraft fitted with the DB 606/610 didn't seem to have as many issues, though they weren't built in large numbers.
The B-17G could hold its power to higher altitudes because it coupled the engine with a turbocharger.
It's a wonder that the greatest 24 cylinder engine of them all hasn't been mentioned - the Fairey P.24 with 4 speed, 2 stage supercharging!
Fairey P.24 Monarch Aircraft Engine
Designed by Richard Forsyth, the P.24 Monarch was Fairey Aviation’s final attempt to enter the aircraft piston engine business. The 24-cylinder Monarch was essentially two engines in a common crank…
oldmachinepress.com
Shortround6
Lieutenant General
Well, putting 7 or 9 connecting rods on a very short, fat crankshaft (one crank pin) seemed to work OK.
Putting 7 or 9 connecting rods on a bit longer fat crankshaft (two crank pins) was a lot harder. See Armstrong Siddeley two row radials, See also the troubles P&W had with R-2800, and they had 3 different two row 14 cylinder radial engines before they built the first two row 18 cylinder R-2800s. A lot of 18 cylinder radials that were announced in the late 30s never made it anywhere in the 1940s. What could go wrong? just stick two existing 9 cylinder radials on a common crankcase, right?
As engines ran faster and as the cylinders made more power on each revolution/power stroke the vibration problems got much tougher to solve. This was one of the major stumbling blocks of engine development in the 1930s and 40s. A number of designers/design teams thought they could just add cylinder or cylinder banks or rows of cylinders to existing engines and with a little tweaking everything would be all right.
Quite a few engines running at 2200-2400rpm and at low boost ran OK in 1920s and very early 1930s. But getting just a few hundred more RPM often required new crankshaft and new crankcases. And much more often than not vibration dampers.
The Wright R-3350 went through several generations. The first few (XB-19) differed considerably from the engines that gave so much trouble to the B-29s. They actually used bigger crankcases and more space between the crank throw's than the early version. The extra space was used to better counter weighting and vibration dampers. Wright had put the R-3350 on hold while they went down the Tornado rat hole. When they went back to it they did use some what they learned about vibration in the meantime.
The Sabre managed to keep the piston speed down by using small cylinders. The use of 12 cylinder crankshafts also helped keep problems at bay. The Sabre was very compact but it was also one of the smallest 24 cylinder engines and tradeoffs are interesting compared to the Griffon. Both engines are identical in displacement. The Griffon, with it's larger cylinders has a much lower revving engine, but the Griffon was much lighter. As fuel went up (or more as known about the fuel and how to "tweak" the engines) the Griffon made up quite a bit of the Sabre's advantage in power from it's higher rpm. The Sabre was not able to use the higher fuel grades to best advantage but that has little to do with engine layout and a lot to do the sleeve valves.
The Vulture was about 16% large in displacement but very similar in weight to the Sabre. Because of the problems with the Vultures crankshaft (and there were more than just the connecting rod problems) the Vulture was unable to capitalize on any hi-rpm benefit before cancelation.
In fact the Vulture has a strong parallel to the DB 606.
If a Peregrine offered 885hp for just over 1100lbs of engine weight and a Vulture offered 1770hp for 2450lbs of engine weight, just what was the advantage the Vulture offered?
Just like two DB 606 were estimated to save about 3% in aerodynamic losses vs four DB601 engines the Vulture doesn't seem to offer much (low single digits?) over using two Peregrines. Granted the Vulture doesn't offer quite the same complications of installation that the DB 606 did (Engines that would uncouple from the propeller, totally separate cooling systems, oil systems, Vulture only has one supercharger, etc).
Howard Gibson
Staff Sergeant
In the real war, the RAF developed the Griffon and the Sabre. As noted previously, the Griffons fit into Spitfires. They probably would have fit into Mustangs if jets had not come along. Once they got the Sabres working, they had a super powerful engine with tomo pauk's twenty four cylinders.
Where does the Rolls Royce Vulture fit into this, and what problem does it solve that the above two engines did not do better?
SaparotRob
Unter Gemeine Geschwader Murmeltier XIII
Griffon powered Mustang. Cool.
Probably a great performer in everything except long range escort.
Howard Gibson
Staff Sergeant
Look up Precious Metal , Red Baron, and Miss Ashley II. The world's Mustang speed record still is held by Voodoo, which appears to still have a Merlin engine.
fastmongrel
1st Sergeant
Apart from the name/numberplate it doesn't have much to do with a WWII Merlin. Or a P51 for that matter.
GrauGeist
Generalfeldmarschall zur Luftschiff Abteilung
Those racers were all using post-war Griffon 57 series engines surplused from Shackletons.
SaparotRob
Unter Gemeine Geschwader Murmeltier XIII
Who cares?
don4331
Senior Airman
S
Shortround6 : DB 601 was very efficient packaging, and DB 606 packaging is more/less 2 DB606s so I can understand the frontal area being similar - within your quoted 3%, but 2 cowlings with 2 sets of wing/cowling interference should have way more drag than one large. And 2 - 3.0m 3 blade propellers should be less efficient than 1 - 4.5m 4 blade. Coupled with engine turbulence around 6m (2 * 3.0m) vs 4.5m of wing on each side should result in far more than 3% overall efficiency improvement. IMHO.
That said the Peregrine is rather poor in packaging (taller than Merlin while nearly as wide), while Vulture is extremely efficient (even better than Sabre). The result is a Vulture enjoys almost 25% advantage in frontal area over 2 Peregrines. Add in the Vulture's 13' 3 blade propeller versus 2 - 10' 3 blade (based on Whirlwind) propellers advantage and the interference drag of more cowling and you can see why designers wanted the single large engine over 2 smaller ones.
Howard Gibson : The RAF didn't develop any engines: Rolls-Royce (RR) developed Merlin and Griffon during war, Napier the Sabre, and Bristol the Hercules and Centaurus.
The OP's requirement was for a 24 cylinder engine of 1,500+ hp in '39 (which just about guarantees 87 octane fuel), that will be up-gradable to remain relevant until VJ-Day. The only engine that historically meets the '39 date in the Vulture. And RR needs to keep the 'A-team' focused on the Vulture to make it a 3k hp engine in Aug/'45.
If nothing else keeping Vulture in production provides 2nd source for all designs wanting Sabre.
SaparotRob : RR Merlin and the last Allisons were keeping up on power with the Griffon through VE-day. I haven't read of any serious plans to replace the Merlin with Griffon at production line level (our Mustang experts might correct me) - the extra 300lbs of Griffon + bigger (heavier) propeller having negative effects on balance. As was pointed out, the speed record for a Mustang based air frame is still held by one powered by Merlin.
K Kilkenny : I was leaving out the "separated" V-12: X-42, Bolkhovitinov S "Sparka", Kawasaki_Ki-64, Arsenal VB 10 & Latécoère 299A as they really didn't meet OPs requirement. I'm still not sure the Fiat AS.6 does although it is single piece crankcase, single supercharger (I'd want RR flame traps or fuel injection on my V-24 to prevent backfires that plagued the AS.6.
As for the X-42, the failure one V-1710 resulting in fire/failure of the other engine due to their close proximity doesn't bode well for the configuration as "silver bullet". I has merit, just not total solution.
swampyankee : V-3420 had vibration and mixture issues from the single supercharger initially, and still had mixture issues after the change in phasing between the 2 engines. 20% (1 of 5 flying P-75 crashing from engine failure/fire isn't great numbers.
That said the Peregrine is rather poor in packaging (taller than Merlin while nearly as wide), while Vulture is extremely efficient (even better than Sabre). The result is a Vulture enjoys almost 25% advantage in frontal area over 2 Peregrines. Add in the Vulture's 13' 3 blade propeller versus 2 - 10' 3 blade (based on Whirlwind) propellers advantage and the interference drag of more cowling and you can see why designers wanted the single large engine over 2 smaller ones.
Howard Gibson : The RAF didn't develop any engines: Rolls-Royce (RR) developed Merlin and Griffon during war, Napier the Sabre, and Bristol the Hercules and Centaurus.The OP's requirement was for a 24 cylinder engine of 1,500+ hp in '39 (which just about guarantees 87 octane fuel), that will be up-gradable to remain relevant until VJ-Day. The only engine that historically meets the '39 date in the Vulture. And RR needs to keep the 'A-team' focused on the Vulture to make it a 3k hp engine in Aug/'45.
If nothing else keeping Vulture in production provides 2nd source for all designs wanting Sabre.
SaparotRob : RR Merlin and the last Allisons were keeping up on power with the Griffon through VE-day. I haven't read of any serious plans to replace the Merlin with Griffon at production line level (our Mustang experts might correct me) - the extra 300lbs of Griffon + bigger (heavier) propeller having negative effects on balance. As was pointed out, the speed record for a Mustang based air frame is still held by one powered by Merlin.K Kilkenny : I was leaving out the "separated" V-12: X-42, Bolkhovitinov S "Sparka", Kawasaki_Ki-64, Arsenal VB 10 & Latécoère 299A as they really didn't meet OPs requirement. I'm still not sure the Fiat AS.6 does although it is single piece crankcase, single supercharger (I'd want RR flame traps or fuel injection on my V-24 to prevent backfires that plagued the AS.6.
As for the X-42, the failure one V-1710 resulting in fire/failure of the other engine due to their close proximity doesn't bode well for the configuration as "silver bullet". I has merit, just not total solution.
swampyankee : V-3420 had vibration and mixture issues from the single supercharger initially, and still had mixture issues after the change in phasing between the 2 engines. 20% (1 of 5 flying P-75 crashing from engine failure/fire isn't great numbers.Not me, but thats how the P-51 became famous, a WW2 Griffon Mustang would have no influence on history but would have huge discussions about "what ifs" There werent enough enough engines to be of use at all.
SaparotRob
Unter Gemeine Geschwader Murmeltier XIII
Exactly!
SaparotRob
Unter Gemeine Geschwader Murmeltier XIII
....and we'l paint them blue.
Howard Gibson
Staff Sergeant
The engines were developed for the RAF. Those fancy twenty four cylinder engines were military only. For civilian use, you want something simple, reliable and cheap. Postwar British airliners were powered by some Merlins, and a lot of Hercules and Centauruses. I am not aware even of a Griffon powered airliner.
The OP's requirement was for a 24 cylinder engine of 1,500+ hp in '39 (which just about guarantees 87 octane fuel), that will be up-gradable to remain relevant until VJ-Day. The only engine that historically meets the '39 date in the Vulture. And RR needs to keep the 'A-team' focused on the Vulture to make it a 3k hp engine in Aug/'45.
If nothing else keeping Vulture in production provides 2nd source for all designs wanting Sabre.
The Vulture and Sabre were developed at the same time. They went with the Sabre.
The Merlins were doing something like 2600HP by running 150 octane fuel and water injection. All the numbers I have seen for Griffons were with 100/130 octane, and no injection. The Griffons were capable of 3000+HP.
If you can replace a Spitfire's Merlin with a Griffon, you can do it with the heavier Mustang. I think Rolls Royce investigated a Griffon Mustang. For the USA, that means setting up production of Griffons somewhere. By 1944, it was pretty obvious that the next important fighter aircraft were going to be the Gloster Meteor, the de Havilland Vampire, and the Lockheed P-80. There was no point in upgrading the Griffon. They even stopped manufacturing the now excellent Napier Sabres.
They were developed for the British government, under government contracts. Not all "Merlins" went into aircraft, some were de tuned and went into tanks as Meteors. The intellectual property was the UK governments which is why they could contract Packard to produce Merlins under license, RR obviously profited from the deal but that is normal in a war, RR were in no position to refuse.
