Old 26th Nov 2012, 13:39
  #116 (permalink)  
Owain Glyndwr
Join Date: Jun 2011
Location: West of Offa's dyke
Age: 83
Posts: 474

I thought a bit about it and I deem that the heavy at 226kt is above max L/D AoA while the lighter one, at that speed is below it, and they happen to be the same L/D. Is that right?
Yes, that's right. If you look at the graphs I posted (#48) you will see that at 226 kts the high weight aircraft is flying below minimum drag speed (AoA above that for max L/D) and the light weight above its minimum drag speed (AoA below that for max L/D). I guess that if one had the time and the inclination one might be able to derive some sort of formula to tell you what that speed might be for any given set of coefficients, but to be honest I can't be bothered

Of course if one is thinking about how long it takes for aircraft with different weights to slow down then the drag/weight will vary with airspeed differently for each aircraft so the fact that at one particular speed the values of D/W i.e.1/(L/D) are the same is unimportant, particularly since that speed is going to be pretty close to the lower limit of authorised airspeeds (1.25~1.3 Vs?)

Last edited by Owain Glyndwr; 26th Nov 2012 at 13:50.
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