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Most efficient cruise altitude

Asked by: 1158 views Aerodynamics, Aircraft Systems, General Aviation, Private Pilot, Student Pilot

Hi Gentlemen,
 

Is flying at low or high altitudes more efficient , and why ?

Thanks in advance ,
P.G.

 

 

4 Answers

  1. Best Answer


    Christopher Arndt on Mar 15, 2013

    Assuming standard temperature and pressure, no wind, higher altitudes provide a more efficient way of flying.

    Because gravity affects air molecules as they do everything else, air is much more dense at lower altitudes. This denser air provides better performance for takeoffs and landings, however at cruise it creates a disproportionately higher amount of drag as more air molecules are interacting with the aircraft surfaces for a given volume of air.

    The higher you go, the less friction the aircraft encounters and the faster the aircraft can go if thrust remains consistent. This is limited, obviously, because aircraft engines operate better with denser air (more O2 to burn) and every aircraft reaches a point where it can not maintain a given amount of thrust to maintain airspeed.

    This is also expressed in the difference between True Airspeed and Indicated Airspeed. Indicated airspeed is increase in pressure exerted by fast moving air molecules in the pitot system. Is it NOT a measure of the absolute speed those air molecules are moving, only the pressure they exert. At sea level, TAS/IAS are the same on a standard day. TAS can be thought of as the absolute speed an air molecule is moving in relation to the aircraft, and is a function of temperature and pressure. TAS increases the higher you go.

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  2. Prodromos Galaktidis on Mar 17, 2013

    Thank you sir.

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  3. Prodromos Galaktidis on Mar 17, 2013

    Thank you sir

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  4. jacob conell on Mar 17, 2013

    Looking a the winds are important. If you have a 20kts cross wind at 3000ft it might be a 40kts tail wind at 7000ft.

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