As a first year aerospace engineer student I had a problem today.(adsbygoogle = window.adsbygoogle || []).push({});

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?

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# Homework Help: Maximum endurance at higher altitude

Can you offer guidance or do you also need help?

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