Oh boy, were to begin.
Allison had been leaning heavily towards exhaust-driven turbochargers instead of the more common mechanically-driven superchargers, feeling that their added performance more than made up for the added complexity.
Allison had very little to do with the exhaust-driven turbochargers, they were government specified equipment and government supplied equipment as were the turbo controls. The exhaust-driven turbochargers were supplied by General Electric. Both th exhaust turbines and the intake air compressor. GE had been supplying ALL US aircraft manufacturers with supercharger designs and parts until about 1937. Allison had done sub-contract work for GE making impellers and such but had no supercharger design staff of their own. The ARMY felt that the turbo was the way to go, Allison and other companies just did what the Army told them to do or paid them to do. See the Continental I-1430 and Lycoming O-1230 for a few other examples of the Army projects.
edit>The turbo set up was a two stage supercharger, the turbo supplied sea level air pressure to the carburetor deck up to the rated altitude of the supercharger. the second impeller (compressor) in the system was between the carburetor and the intake manifold and was gear driven.
P&W flies a two stage mechanical system in 1939 and is is adopted for use in the F4F-3 in late 1939 but production difficulties force some F4F-3s to be fitted with single stage engines as F4F-3As.
Bristol has used a two stage system (mechanical driven) to set some worlds records in the late 1930s but aside from a few experimental Wellingtons no WW II production Bristol engine uses a two stage system.
Rolls-Royce doesn't get the 60 series Merlin into production until 1942.
For aircraft use two stage superchargers of any type (turbo or mechanical) were mighty scarce in the late 30s or even the first couple of years of the war.
Hookers work on superchargers doesn't affect anything until the introduction of the Merlin XX and 45 engines.<edit
Thus little effort was invested in equipping the V-1710 with a reasonable supercharger, and when placed in aircraft designs like the P-39 or P-40 which lacked the room for a turbo the engine suffered tremendously at higher altitudes.
With the entire US supercharger knowledge held by one company until 1937 it is rather amazing that the US did as good as it did in 1939-41 with superchargers. Allison, P&W and Wright all decided at different times in 1937-38 to design their own superchargers as it was becoming obvious that the GE designs weren't that good. The Supercharger on the Allison was actual just about equal to the supercharger used on the Merlin III or Merlin X. There were a few detail differences that kept the Allison from performing quite as well at altitude as the early Merlins but they had little to do with the actual supercharger itself.
It was for this reason in particular that the V-1710 was later removed from the P-51 Mustang and replaced with the Rolls-Royce Merlin.
This was done because R-R was the second company to get a 2 stage mechanical supercharger into production. Yes Allison was behind the curve in making a two stage mechanical supercharger.
The Merlin was a better developed aero engine and more appropriate for the needs of WW2 fighters. Mind you, the lack of power was not Allison's fault but,the US Army's thing about turbo chargers.
That is a rather simplistic way of looking at it. The Allison was perfectly capable of making power, it had trouble making power at altitude. At low altitudes using similar levels of boost there wasn't that much to chose between the two engines.
Turbosuperchargers were indeed highly successful in U.S. bombers, which were exclusively powered by radial engines. The P-47 fighter had the same combination of radial engine (R-2800) and turbosupercharger and was also successful, apart from its large bulk, which was caused by the need for the ductwork for the aft-mounted turbosupercharger.
However, mating the turbocharger with the Allison V-1710 proved to be problematic. As a result, designers of the fighter planes that utilized the V-1710 were invariably forced to choose between the poor high-altitude performance of the V-1710 versus the increased problems brought on by addition of the turbosupercharger. The fates of all of the V-1710 powered fighters of World War II would thus hinge on that choice.
The P-38 gets a bit of a bum rap because it helped pioneer the turbo-superchager in combat. Turbo-ed P-43 with their radial engines had their share of turbo woes as did early B-17s. It took a while to straighten out the turbo in ALL US aircraft.
The P-38 was the only fighter to make it into combat during World War II with turbosupercharged V-1710s. The operating conditions of the Western European air war – flying for long hours in intensely cold weather at 30,000 feet revealed several problems with the turbosupercharged V-1710. These had a poor manifold fuel-air distribution and poor temperature regulation of the turbosupercharger air, which resulted in frequent engine failures (detonation occurred in certain cylinders as the result of persistent uneven fuel-air mixture across the cylinders caused by the poor manifold design). The turbosupercharger had additional problems with getting stuck in the freezing air in either high or low boost mode; the high boost mode could cause detonation in the engine, while the low boost mode would be manifested as power loss in one engine, resulting in sudden fishtailing in flight. These problems were aggravated by suboptimal engine management techniques taught to many pilots during the first part of WWII, including a cruise setting that involves running the engine at a high RPM and low manifold pressure with a rich mixture. These settings can contribute to overcooling of the engine, fuel condensation problems, accelerated mechanical wear, and the likelihood of components binding or "freezing up."
Details of the failure patterns were described in a report by General Doolittle to General Spatz in January 1944. In March 1944, the first Allison engines appearing over Berlin belonged to a group of P-38H pilots of 55FG, engine troubles contributing to a reduction of the force to half strength over the target. It was too late to correct these problems in the production lines of Allison or GE, and so the P-38s were steadily withdrawn from Europe until they were no longer used for bomber escort duty with the Eighth Air Force by October 1944. A few P-38s would remain in the European theater as the F-5 for photo reconnaissance.
Part of the problem was change in the allowable "ingredients" for 100/130 fuel which changed it's volatility. This was known as a potential problem in the spring/summer of 1943 and Allison worked on a new intake manifold to help solve the problem, as it would affect ALL Allisons, not just the turbo-ed ones. It went into production in the fall of 1943 and was being fitted to new engines in Nov of 1943. Many manifolds were shipped overseas for refitting in service engines.
The Army's initial design of turbo control was not well thought out, it sought to control the turbo by measuring the pressure in the exhaust ducts or close to the turbine. By maintaining a constant exhaust back pressure they thought this would regulate the intake boost. It was slow responding and subject to freezing, as anybody you has seen the plume of water vapor coming out of a tail pipe on a cold day might have guessed. The turbo control was changed to a system that measured the intake pressure and adjusted the turbo waste gates accordingly. Please note that this was an "Army" or government furnished piece of equipment and not supplied by either Allison (or any other engine maker) or even by GE.
The problems had been sorted out/solved by the spring of 1944 and all new P-38s from Dec of 1943 on (which may take weeks or months to get to a combat theater) have most of the basic engine problems solved. Mis rigged turbo controls and bad piloting technique (against the directions of both Allison and Lockheed) do cause problems. Decision in favor of the P-51 is made before operational experience with corrected P-38s can be accumulated. It was still the right decision but given a few more weeks it might have been a bit tougher to make. The P-38H that made that flight over Berlin was being built side by side with P-38Js because of a shortage of the intercoolers used in the J. First Js are delivered in Sept of 1943.
In post war civil use Merlins were fitted with an intake charge heater to solve a similar fuel mixture distribution problem in cruising flight.
