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Shortround6 · Apr 17, 2022

If somehow Allison could have built an equivalent to the Merlin XX (or 24 or whatever) it might have actually done quite a bit.
They tried to jump from, in Merlin terms, from the Merlin III to the Merlin 61 without going through any of the in-between stages.
And then they tried to get around the lack of inter-cooler with water injection and get to the Merlin Merlin 76/86 level.

Redo the basic supercharger (get it up to Merlin XX/45 level), put a two speed drive on it and stuff it in the P-40 in the spring or summer of 1943.

Trouble was that was admitting they were 2nd class and they wanted to be contenders.

tomo pauk · Apr 17, 2022

Shortround6 said:
Redo the basic supercharger (get it up to Merlin XX/45 level), put a two speed drive on it and stuff it in the P-40 in the spring or summer of 1943.

Even the 9.60:1 step-up drive for the S/C is a major boon if done in a timely manner and in a reliable fashion. With such an early engine (but with the unreliable S/C drive, in late 1941), only 2 HMGs and some nip & tuck, the P-39C was supposed to go 400+ mph. Cimb rate above 1000 ft would've been also improved.
P-40 will also benefit from that an engine, that historically became a reality by late 1942.

The supercharger will certainly need a physically bigger impeller, perhaps use the unit from the V-3420 (10 in diameter, vs. 9.50 in on the V-1710s)? Although the 12 in unit from the 2-stage V-1710s is also attractive, together with it's hydraulic drive, installed instead of the legacy S/C.

GregP · Apr 17, 2022

Within its altitude limitations, the Allison wasn't a second-class engine. It was more reliable than a Merlin and had a longer TBO. Allison delivered what the government ordered, and asked several times to develop a real 2-stage engine. Each time the answer was no. The auxiliary-stage supercharger was an Allison in-house development. They didn't have a Sir Stanley Hooker, true, but had the 2-stage research been funded, it very well may have worked out better than the aux-stage that was developed. That is a nice "what if" to contemplate, but I'm not much into "what ifs."

In my eyes, the U.S. government got what they asked for and Allison did a good job building what they were asked to build. Today, warbirds fly almost exclusively VFR, and the Allison is right in its design element ... 5,000 - 15,000 feet. It lasts longer than a Merlin in use and is cheaper to overhaul as well. Nothing second-class about it except maybe poor choices made during WWII about its development as a higher-altitude engine. The turbo system employed by the P-38 worked well enough after it was sorted, but would be tough to put into a single-engine fighter.

The Merlin was. far and away, a better engine for higher altitude work, no question. But, the Allison was no slouch in it's designed altitude band and very definitely wasn't and isn't a bad engine.

Shortround6 · Apr 17, 2022

GregP said:
Within its altitude limitations, the Allison wasn't a second-class engine. It was more reliable than a Merlin and had a longer TBO. Allison delivered what the government ordered, and asked several times to develop a real 2-stage engine. Each time the answer was no. The auxiliary-stage supercharger was an Allison in-house development. They didn't have a Sir Stanley Hooker, true, but had the 2-stage research been funded, it very well may have worked out better than the aux-stage that was developed. That is a nice "what if" to contemplate, but I'm not much into "what ifs."

In my eyes, the U.S. government got what they asked for and Allison did a good job building what they were asked to build. Today, warbirds fly almost exclusively VFR, and the Allison is right in its design element ... 5,000 - 15,000 feet. It lasts longer than a Merlin in use and is cheaper to overhaul as well. Nothing second-class about it except maybe poor choices made during WWII about its development as a higher-altitude engine. The turbo system employed by the P-38 worked well enough after it was sorted, but would be tough to put into a single-engine fighter.

The Merlin was. far and away, a better engine for higher altitude work, no question. But, the Allison was no slouch in it's designed altitude band and very definitely wasn't and isn't a bad engine.

The engine itself was very good.
The problem is that having a good or even very good/excellent power section wasn't enough.
It took P & W a number of years to really get up to snuff on their two stage superchargers. And P & W had flying hardware in 1938/39. Two planes used P & W two stage engines in the Jan 1939 fighter trials (and nether one was a Grumman F4F).
P & W had also developed some much improved single stage superchargers right at the end of the war. The Sidewinder set up on the R-2800-32 showed where high altitude engines needed to go. A supercharger section (with intercoolers) that was nearly as big as the power section (Cylinder block and cylinders).
Wright never really got it's act together either and it depended on the GE turbo superchargers for altitude performance.

Bristol never equaled RR with superchargers.

Allison had problem in that their design staff was too small and the government was asking them to to do a lot of things.

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