And, with automatic waste gates on many models, they're easier and more foolproof to operate than ever before. Become a better pilot. Subscribe to get the latest videos, articles, and quizzes that make you a smarter, safer pilot. Colin is a Boldmethod co-founder, pilot and graphic artist. He's been a flight instructor at the University of North Dakota, an airline pilot on the CRJ, and has directed development of numerous commercial and military training systems.
You can reach him at colin boldmethod. To: Separate email addresses with commas. Now What? All Videos. Planes Careers. Colin Cutler Colin is a Boldmethod co-founder, pilot and graphic artist. Recommended Stories. How DME Works. With high ambient air temperatures, detonation could start to occur with the manifold pressure gauge reading far below the red line. A supercharger optimized for high altitudes causes the opposite problem on the intake side of the system. With the throttle retarded to avoid overboosting, air temperature in the carburetor can drop low enough to cause ice to form at the throttle plate.
In this manner, enough ice could accumulate to cause engine failure, even with the engine operating at full rated power. For this reason, many supercharged aircraft featured a carburetor air temperature gauge or warning light to alert the pilot of possible icing conditions.
Several solutions to these problems were developed: intercoolers and aftercoolers, anti-detonant injection , two-speed superchargers, and two-stage superchargers. In the s, two-speed drives were developed for superchargers. These provided more flexibility for the operation of the aircraft, although they also entailed more complexity of manufacturing and maintenance.
The gears connected the supercharger to the engine using a system of hydraulic clutches, which were manually engaged or disengaged by the pilot with a control in the cockpit. At low altitudes, the low-speed gear would be used in order to keep the manifold temperatures low. At around 12, feet 3, m , when the throttle was full forward and the manifold pressure started to drop off, the pilot would retard the throttle and switch to the higher gear, then readjust the throttle to the desired manifold pressure.
Another way to accomplish the same level of control was the use of two compressors in series. After the air was compressed in the low-pressure stage , the air flowed through an intercooler radiator where it was cooled before being compressed again by the high-pressure stage and then aftercooled in another heat exchanger.
In these systems, damper doors could be opened or closed by the pilot in order to bypass one stage as needed. The most complex systems used a two-speed, two-stage system with both an intercooler and an aftercooler, but these were found to be prohibitive in cost and complicated. In the end, it was found that, for most engines, a single-stage two-speed setup was most suitable.
A mechanically driven supercharger has to take its drive power from the engine. Taking a single-stage single-speed supercharged engine, such as the Rolls Royce Merlin , for instance, the supercharger uses up about hp kW. This is where the principal disadvantage of a supercharger becomes apparent: The engine has to burn extra fuel to provide power to turn the supercharger.
The increased charge density increases the engine's specific power and power-to-weight ratio , but also increases the engine's specific fuel consumption. This increases the cost of running the aircraft and reduces its overall range. As opposed to a supercharger driven by the engine itself, a turbocharger is driven using the exhaust gases from the engines.
The amount of power in the gas is proportional to the difference between the exhaust pressure and air pressure, and this difference increases with altitude, helping a turbocharged engine to compensate for changing altitude. The majority of WWII engines used mechanically driven superchargers, because they maintained three significant manufacturing advantages over turbochargers. The size of the piping alone was a serious issue; the Vought F4U Corsair and Republic P Thunderbolt used the same engine, but the huge barrel-like fuselage of the latter was, in part, a result of the necessary piping to and from the turbocharger in the rear of the plane.
Turbocharged piston engines are also subject to many of the same operating restrictions as gas turbine engines. Turbocharged engines also require frequent inspections of the turbocharger and exhaust systems as a result of damage due to the increased heat, thereby increasing maintenance costs. Today, most general aviation aircraft are naturally aspirated. The small number of modern aviation piston engines designed to run at high altitudes in general use a turbocharger or turbo-normalizer system rather than a supercharger driven from the crank shaft.
The change in thinking is largely due to economics. Aviation gasoline was once plentiful and cheap, favoring the simple but fuel-hungry supercharger. As the cost of fuel has increased, the supercharger has fallen out of favor. Also, depending on what monetary inflation factor one uses, fuel costs have not decreased as fast as production and maintenance costs have. Until World War II all automobile and aviation fuel was generally rated at 87 octane or less. This is the rating that was achieved by the simple distillation of "light crude" oil.
Engines from around the world were designed to work with this grade of fuel, which set a limit to the amount of boosting that could be provided by the supercharger, while maintaining a reasonable compression ratio. Octane rating boosting through additives was a line of research being explored at the time. Using these techniques, less valuable crude could still supply large amounts of useful gasoline, which made it a valuable economic process.
However, the additives were not limited to making poor-quality oil into octane gasoline; the same additives could also be used to boost the gasoline to much higher octane ratings. Higher-octane fuel resists auto ignition and detonation better than does low-octane fuel. As a result, the amount of boost supplied by the superchargers could be increased, resulting in an increase in engine output.
The development of octane aviation fuel, pioneered in the USA before the war, enabled the use of higher boost pressures to be used on high-performance aviation engines, and was used to develop extremely high-power outputs — for short periods — in several of the pre-war speed record airplanes. Learn More. I love that I can charge up while I run my errands! With my commute, those white boxes are more than just chargers, they are peace of mind. Watch Video. The user interface is just beautiful.
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