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Homework Help: Maximum endurance at higher altitude

  1. Nov 11, 2011 #1
    As a first year aerospace engineer student I had a problem today.

    The question was :

    Does the altitude effect the endurance of an aircraft (provided that the aircraft engines can generate enough trust at this higher altitude).

    Maximum endurance is minimum fuel flow [N/s] F = Ct T

    in a steady, horizontal, symmetric flight F = Ct D

    D = Cd (1/2) rho V² S

    D: Drag
    T: Thrust
    Cd: Drag coefficient
    Cl: lift coefficient
    Rho: air denisty
    V: velocity
    S: wing area

    So higher altitude = lower density = lower drag = lower fuel flow = higher endurance.

    But also true is that F = Ct (Cd/Cl) W and none of these parameters are effected by the altitude.

    Which one is correct and why? And why is the other one wrong?

    Kind regards,
    Alex

    Edit:
    D = Cd (1/2) rho V² S
    but V is sqrt (W*2*1/(S*rho*Cl))
    so the rhos cancel eachother out.

    Is there a delete button somewhere?
     
    Last edited: Nov 11, 2011
  2. jcsd
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