Allison V-1710

The V-1710 has often been criticized for not having a "high-altitude" supercharger.

The comparison is usually to the later, two-stage, versions of the [Vous devez être inscrit et connecté pour voir ce lien] built by Packard as the [Vous devez être inscrit et connecté pour voir ce lien]
and used in the P-51B Mustang and subsequent variants.

The US Army had specified that the V-1710 was to be a single-stage supercharged engine and, if a higher altitude capability was desired, the aircraft could use their newly developed turbosupercharger as was featured in the P-37,
P-38, and XP-39.

The benefits of a two-stage supercharger eventually became so clear that Allison did make some efforts in this direction. Allison attached an auxiliary supercharger in various configurations to the existing engine-mounted supercharger and carburetor.

Early versions of these two-stage supercharger engines were used on the P-63.

No intercooler, aftercooler, or backfire screen were incorporated into these two-stage V-1710 engines (except for the V-1710-119 used on the experimental P-51J, which had an aftercooler).

The two-stage Merlin engines had all of these features, which were designed to prevent detonation from charge
heating and backfire into the supercharger.

The G-series V-1710s installed on the F-82 E/F/G models had only anti-detonation injection to deal with these problems, and not surprisingly had severe reliability and maintenance problems. In one record, it was stated that the F-82
required 33 hours of maintenance for one hour of flight.

Although the early V-1710 powered P-39, P-40 and P-51A airplanes were limited to combat operations at a maximum of about 15,000 feet (4,600 m) they were available in comparatively large numbers and were the mainstay of some Allied Air Forces in all but the [Vous devez être inscrit et connecté pour voir ce lien] of war.

The engines proved to be robust and little affected by machine-gun fire.

In total, over 60 percent of the US Army Pursuit aircraft operated during WWII were powered by the V-1710.

Allison continuously improved the engine during the war.

The initial rating of 1,000 hp (750 kW) was incrementally increased; the final V-1710-143/145(G6R/L) was rated for 2,300 hp (1,700 kW).

By 1944, the [Vous devez être inscrit et connecté pour voir ce lien] rating on the P-38L was 1,600 hp (1,200 kW).

The most powerful factory variant was the V-1710-127, designed to produce 2,900 hp (2,200 kW) at low altitude and 1,550 hp (1,160 kW) at 29,000 feet (8,800 m).

This engine was static tested at 2,800 hp (2,100 kW) and was planned for installation in an XP-63H aircraft.

The end of the war ended this development, so this promising experiment never flew.

The extra power of this version was derived from using exhaust turbines, not to drive a turbosupercharger, but to return that energy to turning the crankshaft. This was called a "[Vous devez être inscrit et connecté pour voir ce lien]" arrangement.

Improvements in manufacturing brought the cost to produce each engine from $25,000 down to $8,500 and allowed the installed lifetime of the engine to be increased from 300 hours to as much as 1,000 hours for the less stressed powerplants.

Weight increases needed to accomplish this were minimal, with the result that all models were able to produce more than 1 hp/lb (1.6 kW/kg) at their takeoff rating.

Comparisons between Allison engine and the Rolls-Royce Merlin engine are inevitable.

What can be said for the Allison is that its part count was nearly half that of the Merlin engine which facilitated mass
production greatly.

The British-made Merlin engines were to a degree still reliant upon hand-crafted and fitted parts from skilled craftsmen, something which was somewhat refuted by the success of the [Vous devez être inscrit et connecté pour voir ce lien] license-produced version of it in the United States, built with American production-line techniques.

There also was a high degree of commonality of parts throughout the series.

The individual parts of the Allison series were produced to a high degree of standardization and reliability, using the best technology available at the time.

Allison employed a modular design, so that it was capable of being mated to many different styles of turbo-superchargers and various other accessories, although the variety of turbo-superchargers available for installation
was limited due to the constraints of single-engine fighter design.

Since it was produced in large numbers and was highly standardized, the engine has been used in many postwar racing designs.

Its reliability and well-mannered operation allowed it to operate at high rpm for extended periods.

Following the war, North American built 250 [Vous devez être inscrit et connecté pour voir ce lien] for air defense roles into the early 1950s.

This was the final military role for the V-1710.

Turbocharger

The Army had earlier decided to concentrate on [Vous devez être inscrit et connecté pour voir ce lien] for high altitude boost, believing that further development of turbochargers would allow their engines to outperform European rivals using superchargers.

Turbosuperchargers are powered by the engine exhaust and so do not draw power from the engine crankshaft, whereas
superchargers are connected directly by gears to the engine crankshaft.

Turbosuperchargers do increase the exhaust back-pressure and thus do cause a decrease in engine power, but the power increase due to increased induction pressures more than make up for that decrease.

Crankshaft-driven superchargers require an increasing percentage of engine power as altitude increases (the two-stage supercharger of the Merlin 60 series engines consumed some 230-280 horsepower at 30,000 ft).

General Electric was the sole source for research and production of American turbosuperchargers during this period.

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 ([Vous devez être inscrit et connecté pour voir ce lien]) 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 original XP-39 was built with a V-1710 augmented by a Type B-5 turbosupercharger as specified by Fighter Projects Officer Lieutenant [Vous devez être inscrit et connecté pour voir ce lien] and his colleague [Vous devez être inscrit et connecté pour voir ce lien].

Numerous changes were made to the design during a period of time when Kelsey's attention was focused elsewhere, and Bell engineers, [Vous devez être inscrit et connecté pour voir ce lien] aerodynamicists and the substitute fighter project officer determined that dropping the turbocharger would be among the drag reduction measures indicated by borderline wind tunnel test results; an
unnecessary step, according to aviation engineer and historian Warren M.
Bodie.

The production P-39 was thus stuck with poor high-altitude performance and proved unsuitable for the air war in Western Europe which was largely conducted at high altitudes.

The P-39 was rejected by the British, but used by the U.S. in the Mediterranean and the early Pacific air war, as well as shipped to the Soviet Union in large numbers under the [Vous devez être inscrit et connecté pour voir ce lien].

The Soviets were able to make good use of P-39s because of its excellent maneuverability and because the air war on the Eastern Front in Europe was primarily short ranged, tactical, and conducted at lower altitudes.

In the P-39, Soviet pilots scored the highest number of individual kills made on any American fighter type.

The P-40, which also had only the single-stage, single-speed-supercharged V-1710, had similar problems with
high-altitude performance.

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 (9,100 m) – 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 [Vous devez être inscrit et connecté pour voir ce lien], 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 [Vous devez être inscrit et connecté pour voir ce lien] by October 1944.

A few P-38s would remain in the European theater as the F-5 for photo reconnaissance.

The P-38 had fewer engine failures in the Pacific Theater, where operating techniques were better developed (such as those recommended by[Vous devez être inscrit et connecté pour voir ce lien] during his [Vous devez être inscrit et connecté pour voir ce lien] in the PTO,) the fuel quality was consistently superior and the Japanese did not operate at such high altitudes.

Using the same P-38Gs which were proving difficult to maintain in England, Pacific-based pilots were able to use the aircraft to good advantage including, in April 1943, [Vous devez être inscrit et connecté pour voir ce lien], the interception and downing of the Japanese bomber that was carrying Admiral [Vous devez être inscrit et connecté pour voir ce lien].

New P-38 models with ever-increasing power from more advanced Allisons were eagerly accepted by Pacific air groups.

When Packard started building Merlin V-1650 engines in America, certain American fighter designs using the Allison V-1710 were changed to use the Merlin.

The P-40F, a Lend Lease export to Britain, was one of the first American fighters to be converted to a Packard-Merlin engine.

However, the installed engine was the V-1650-1 with a slightly improved single-stage, two-speed supercharger, yielding only modest gains in performance.

The first production P-51A had the Allison V-1710 without turbosupercharger and thus, poor high altitude performance.

At low altitudes, the P-51A was substantially faster than the Spitfire, which very much impressed the British when they first received the plane; they quickly realized the P-51 had an outstanding low-drag airframe and the airplane could become one of the best of the war if the Allison V-1710 engine were replaced by the two-stage-supercharged Merlin.

Conversion proceeded on both sides of the Atlantic, with North American Aviation engineers making the definitive changes to the airframe to fully integrate the Packard-Merlin V-1650-3 into the P-51B.

Ironically, because the P-51 was not originally developed for the USAAF, this was allowed to proceed rapidly with no Army input (or interference).

A similar attempt to cure the problems of the P-38 by replacing its Allisons with Merlins was quashed by the USAAF, after protests from Allison.

Starting with the V-1710-45 around 1943, Allison attached an auxiliary supercharger to some of its engines in an effort to improve high-altitude performance, with limited success.

Although described as a two-stage supercharger, it was essentially an afterthought and did not have the full refinements of the two-stage Merlin, such as the pressure-altitude governed two-speed gearbox and the intercooling system.

Various configurations of this auxiliary supercharger were used in production versions of the V-1710 that powered aircraft such as the [Vous devez être inscrit et connecté pour voir ce lien] and [Vous devez être inscrit et connecté pour voir ce lien]E/F/G series.

In addition, it was tried or studied as the powerplant for many experimental and test aircraft such as variants of the Boeing [Vous devez être inscrit et connecté pour voir ce lien], [Vous devez être inscrit et connecté pour voir ce lien], both with turbo-superchargers (AP-10), Curtiss [Vous devez être inscrit et connecté pour voir ce lien], and Douglas [Vous devez être inscrit et connecté pour voir ce lien].

F-82 use

The F-82 did see brief action in the Korean War, but the type was completely withdrawn from Korea by the end of 1950.

It had a short service life that was probably due to a combination of factors: poor reliability from the G-series V-1710 engines, low numbers of F-82s produced, and the arrival of jet fighters.

The initial production P-82B had Merlin engines, but North American was forced to use the Allison V-1710 for the E/F/G models.

In total, over 70,000 V-1710s were built by Allison during the war, all in [Vous devez être inscrit et connecté pour voir ce lien].