Author Topic: WWII Inline engines: Daimler Benz vs Rolls Royce vs Allison vs Klimov vs Jumo (Read 26616 times)

Angus · « **Reply #30 on:** May 24, 2007, 08:12:05 AM »

As for the Griffon, AFAIK the final version ended with some 2400 hp, pushing the Supermarine Spiteful over the 490 mph limit, with full military load.
Weights some 900 kg's though (2000 lbs roughly)
As for reliability, the Avro Shackleton ran on Griffons, but overhauls were frequent. Well, not compared to WW2 lifetime, - top overhaul for some 400 hours, but that happens fast on long tours, and the aircraft did indeed go on very long tours.

Captain Virgil Hilts · « **Reply #31 on:** May 24, 2007, 08:26:06 AM »

The USAAF downrated the Allison in the P-38L by nearly 200 HP per engine. The P-38K engines made over 1825HP, and they'd do it at nearly 30,000 feet. Try that with a Merlin.

Why wasn't the non turbocharged Allison making 2000HP, and making decent HP at high altitude? Because the USAAF and the War Production Board never allowed General Motors to develop and install a two speed two stage supercharger on the Allison. The ONLY advantage a Merlin has over an Allison is the two speed two stage supercharger. It is NOT the engine itself.

The Merlin wasn't making 2000HP, but it was close, and it sure as Hell wasn't doing it at high altitudes. By 29,000 feet, the Merlin in a P-51D isn't making ONE thousand horsepower, never mind making double that.

NO piston engine with a crank driven supercharger, even WITH a two speed two stage supercharger, makes sea level power at high altitude.

In the as produced form, the Allison has a stronger crankshaft, stronger connecting rods, a better oiling system, a larger capacity margin in the cooling system, and stronger cylinder heads.

The last piston engine powered unlimited hydroplane to win a race was Allison powered. The last competitive aircraft piston engine powered pulling tractors are Allison powered. And for AT LEAST the first 30 YEARS after the war, no Merlin could last long enough at Reno to win a competitive Gold race, and they only became a contender after one of the engine builders put Allison connecting rods in one. Even today, the most common failure in Reno is a Merlin eating the bearings.

gripen · « **Reply #32 on:** May 24, 2007, 09:20:48 AM »

Quote

Originally posted by Captain Virgil Hilts
The USAAF downrated the Allison in the P-38L by nearly 200 HP per engine. The P-38K engines made over 1825HP, and they'd do it at nearly 30,000 feet. Try that with a Merlin.

This has been discused here several times, the Merlin utilizes exhaust thrust which in practice balances the situation. And the P-38K never saw service.

Besides, 2000hp Merlins saw quite wide service during war and were type tested for over 2600hp. The Allisons maxed around 1800hp during war (very limited use in the P-63).

Quote

Originally posted by Captain Virgil Hilts

The last piston engine powered unlimited hydroplane to win a race was Allison powered. The last competitive aircraft piston engine powered pulling tractors are Allison powered. And for AT LEAST the first 30 YEARS after the war, no Merlin could last long enough at Reno to win a competitive Gold race, and they only became a contender after one of the engine builders put Allison connecting rods in one. Even today, the most common failure in Reno is a Merlin eating the bearings.

The race use has pretty much nothing to do with practical service use and in the service the Merlin proved to be more powerfull and more reliable than the Allison.

Wes14 · « **Reply #33 on:** May 24, 2007, 09:39:25 AM »

Whats the engine in the tempest?

Masherbrum · « **Reply #34 on:** May 24, 2007, 09:40:13 AM »

Quote

Originally posted by gripen
The race use has pretty much nothing to do with practical service use and in the service the Merlin proved to be more powerfull and more reliable than the Allison.

I'd have to disagree.

gripen · « **Reply #35 on:** May 24, 2007, 09:51:06 AM »

Ok, let's disagree, no problem.

Captain Virgil Hilts · « **Reply #36 on:** May 24, 2007, 01:48:10 PM »

There's no way that the exhaust thrust from a Merlin makes up for the fact that it is 700HP short of a turbocharged Allison at 29,000 feet. They're exhaust headers, they're not rocket boosters. Hell, the radiator installation with the boundary layer scoop on the Mustang comes closer to adding enough thrust to make up some of the difference. At 26,000 feet, a Merlin in a P-51D is down to 1100 HP or so, and at 29,000 feet, it's down to just barely 900HP. The "-30" Allison in the P-38L is still making 1725HP at 26,500 feet. And more than that at the Lockheed/Allison ratings of 80" and 3200RPM.

Exhaust thrust can offer SOME measurable gains in speed, in fact, Kelly Johnson wanted to do it with the P-38, but the increased back pressure at the turbocharger cost more HP and speed was decreased. But the exhaust thrust from an engine making 900HP or so won't make up for being short 700HP or more.

The speed of the Mustang had more to do with light weight, reduced parasitic drag, and a drastically more efficient propeller than JUST the Merlin. The Merlin only improved performance at altitude, and in fact, down low, the Allison was more than a match.

It should also be noted that the Allison developed for the P-82 Twin Mustang, with higher compression and a 12 counterweight crankshaft for higher RPM performance and durability is nearly as powerful as a turbocharged Allison from a P-38, without the turbocharger, and extremely durable. And it still didn't have a really good centrifugal supercharger (again, the USAAF and the War Production Board are the reason behind the problem) even then.

Captain Virgil Hilts · « **Reply #37 on:** May 24, 2007, 01:53:01 PM »

Quote

Originally posted by gripen
Besides, 2000hp Merlins saw quite wide service during war and were type tested for over 2600hp. The Allisons maxed around 1800hp during war (very limited use in the P-63).

The race use has pretty much nothing to do with practical service use and in the service the Merlin proved to be more powerfull and more reliable than the Allison.

Actually, the use in racing has EVERYTHING to do with the quality and superiority of the engine design. The Allison had far more room to grow in power without sacrificing reliability. The Allison was rated by the manufacturer at well over 1800HP, the USAAF down rated it. Further, the same basic engine was used later with compound turbosupercharging to reliably produce around 3000HP. The only problem with that engine was the exhaust temperature was too great for the typical aircraft exhaust system. But the engine itself tested beautifully.

Furball · « **Reply #38 on:** May 24, 2007, 02:01:30 PM »

Those Rolls-Royce licensed built Allisons were great!!!

zorstorer · « **Reply #39 on:** May 24, 2007, 02:30:27 PM »

Quote

Originally posted by Wes14
Whats the engine in the tempest?

Napier Sabre, just google it...amazing engine

Angus · « **Reply #40 on:** May 24, 2007, 02:45:17 PM »

Virgil Hilts: Please please explain to me P51 had to be powered by a merlin to get alive above 15k.

Angus · « **Reply #41 on:** May 24, 2007, 02:52:10 PM »

"Actually, the use in racing has EVERYTHING to do with the quality and superiority of the engine design. The Allison had far more room to grow in power without sacrificing reliability. The Allison was rated by the manufacturer at well over 1800HP, the USAAF down rated it. Further, the same basic engine was used later with compound turbosupercharging to reliably produce around 3000HP. The only problem with that engine was the exhaust temperature was too great for the typical aircraft exhaust system. But the engine itself tested beautifully."

A factory made juiced-up Spitfire was making 3000 hp in 1939 and making nice and fast tours between places, like England-France. The engine ran beautifully, but the whole thing was perhaps not practical for military ops.
Anyway, if a starting power of an engine in development is 1800hp as easy-go (Merlin at 1030?), as well as the alt performance being spectacular, why on earth would that not be THE main mount of all western allied inline engined aircraft?????????????????????????????

Angus · « **Reply #42 on:** May 24, 2007, 02:53:27 PM »

Quote

Originally posted by Furball
Those Rolls-Royce licensed built Allisons were great!!!

hehe, so were those RR license-built Packards

gripen · « **Reply #43 on:** May 24, 2007, 03:14:08 PM »

Quote

Originally posted by Captain Virgil Hilts
Actually, the use in racing has EVERYTHING to do with the quality and superiority of the engine design. The Allison had far more room to grow in power without sacrificing reliability.

Well, you see the problem in that logic; historically the Allison had problems to do 1600hp reliably while the Merlin did quite well 2000hp. That was the situation at spring 1944.

Besides, the Allison design went towards the concepts used in the Merlin like lower compression ratio and mechanical supercharger etc. In practice the developement of the Allison was couple years behind the Merlin during war.

gripen · « **Reply #44 on:** May 24, 2007, 03:36:31 PM »

Quote

Originally posted by Captain Virgil Hilts
There's no way that the exhaust thrust from a Merlin makes up for the fact that it is 700HP short of a turbocharged Allison at 29,000 feet.

I made a calculation based on 1943 USAF test here. Assuming 80% prop efficiency and 250lbs exhaust thrust at FTH 29800ft, the equivalent hp increase is about 370hp ie without exhaust thrust the plane would have required about 1640hp instead the 1275hp to reach same performance. Note that this is far above the critical altitude of the P-38J/L.