American Fighter Aircraft Breakdown [Posted on War Clouds] - Printable Version

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Re: American Fighter Aircraft Breakdown [Posted on War Cloud - .041 Safety Wire - 06.08.2010

For the non engine savy

With a little research you will find that the Allison V-1710 supercharged powerplant was capable of attaining sea level manifold pressure at 15,000 ft MSL so this is its critical altitude. This is where the multistage and multispeed supercharger or turbosupercharged powerplant starts to gain the advantage.On a normally aspirated engine(no super or turbocharging) manifold pressure ( amount of air in the intake manifold) is always going to be lower than atmospheric. By pumping air into the manifold at a high rate it means you can add more fuel and hence gain more HP up to a point. Too much manifold pressure or over boosting will cause failures within the powerplant or cylinders to depart the engine casing in the case of radials. This is due to the excessively high pressure within the cylinder and detonation which is an uncontrolled explosion of the fuel air mixture. Most aircraft engine superchargers from WWII consisted of an impeller(rotating part of the airpump) and a diffuser ring. Both the impeller and stator ring form divergent nozzles. As the air exits these nozzles you get a step up in pressure and heat into the intake manifold. When this charge is taken into the cylinder again another pressure step as it is compressed and more heat. If it becomes so hot that it explodes or detonates rather than when the sparkplugs ignites the mixture for a smooth burn this is destructive to the engine. These superchargers were in most cases mounted between the engine case and the accessories case. In both radials and inlines with the exception of some of the German and Japanese powerplants. They were an integral part of the powerplant and required engine removal if a failure occured with the exception again being some German and Japanese ones. If the supercharger consisted of two sets of impellers of different sizes this is a multistage charger, if the speed of the impellers can be controlled through gear changes or fluid drive(engine oil) this is a multispeed charger. Allisons did not intially have any of these features. It was an impeller directly linked to crankshaft speed. This accounts for its 15,000 ft critical altitude.

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