Hawk37,
Originally Posted by Hawk37
It is dangerous to use the terms "max range" and "best L/D" in the same sentence. A jet at an IAS for max range is not at the speed for best L/D.
Point taken. Will not use L/D in jet discussion any more!
Nevertheless, the answer to Capt NK Airbus' question in post 8:
Why does Indicated Mach No. reduce if weight reduces, even if Flight Level is the same. I tried hard to find out the reason. No good.
is related, is it not? As the weight reduces, the lift required reduces and so the drag for any particular speed also reduces (given we're on the front side of the drag curve) and we would normally accelerate. Therefore, we can reduce the thrust to match that reduced drag. The issue is whether the speed value for max range reduces as weight reduces. Airbus says it does, in that earlier reference I gave.
Where does the curve go as weight reduces? That is the crux of the issue (with thanks to DP Davies
) because that will determine where the tangent line is, speedwise.
Do you have a reference for the AoA not being constant at the Max Range Speed for various weights? I was always under the impression that Max Range speed at any weight was at the same AoA.
Found a Boeing document that talks about the subject:
Aero 12 - Angle of Attack
What I don't get is that "It can be seen that the optimal long-range cruise Mach number does not vary significantly as gross weight (hence, lift and AOA) changes." seems to be counter to those Airbus figures which show a max-range speed change of .67 to .73 over a 40t weight change. I would have thought that that
was significant (although a 40 tonne burn is almost more than my aeroplane weighs!).
