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Supercharging/turbocharging with endurance and range

  • boeing777ferdi
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boeing777ferdi created the topic: Supercharging/turbocharging with endurance and range

Hi again,

been studying the bob tait book throuroughly, which has helped with all my 4 cpl subjects so far and am a bit worried for the CPLADA exam. Came across a syllabus statement regarding the considerations to achieve max range and endurance with turbocharged and supercharged engines.

What exactly are the implications here with regard to range/endurance, I understand that it helps maintain atmospheric pressure so my assumption is for best endurance it means you may fly higher and range means higher FTH, is there anything im missing or assuming wrong? just something ive heard that CASA have asked in the past a bit nasty..

thanks,
Ferdi
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bobtait replied the topic: Supercharging/turbocharging with endurance and range

This is another example of a CASA question that is far removed from the real world. I wish they wouldn't do that. To find the recommendations for range and endurance you would simply consult the aircraft's operating handbook. However I'm pretty sure that CASA would be looking for some basic principles and the extreme case rather than the practical.

For range we need to maximize efficiency. As far as the airframe is concerned, that means flying at the best lift/drag ratio angle of attack. So you would fly at the IAS that required that angle of attack (about 4°). The height doesn't matter as long as you fly at the most efficient lift/drag ratio IAS.

However, you also need to consider the engine. The best volumetric efficiency for an internal combustion engine occurs when the throttle is wide open. So, as far as the engine is concerned, you need to fly at full throttle. Since we must satisfy the needs of both the airframe and the engine, you should fly at a height that results in the best lift/drag ratio angle of attack with the throttle fully open.

This is all airy-fairy theory and of no practical use to a pilot since the fuel used to achieve that height would probably be considerable to say nothing of the likelihood of strong winds at high altitude. In the absence of operational information from the manufacturer, I would answer a CASA question as full throttle height.

As far as endurance is concerned, the requirement would be to use the fuel at the lowest possible rate. That means to fly at minimum fuel flow. That means minimum power for a piston engine and the lower the better. Wind has no effect on endurance since all you want to do is stay airborne for the longest time - you are not trying to go anywhere. Again, none of this would be much help in practice since most aircraft at absolute minimum power are getting close to encountering control difficulties.

Again some common sense and adherence to the manufacturer's recommendations is required.
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