On Monday, February 15, 2016 at 7:13:43 PM UTC+3, Tango Whisky wrote:
Le lundi 15 février 2016 16:32:27 UTC+1, Bruce Hoult a écrit*:

I don't agree.

As I've already said once in this thread, you're going to get a certain amount of drag from the fuselage anyway. If the presentation to the airflow for minimum drag generates zero lift then, by the calculus definition of "minimum" of a continuous function, the first little bit of lift will not add any drag. The optimum thing to do is to use it. It might be *very* little, and a very small AoA, but it's nonzero.

If the presentation to the airflow for minimum drag generates non-zero lift ... then of course you'll take it!

Yes, the fuse has a low L/D. But that's better than the 0.0 L/D if you don't take what lift you can from it...

Why do you assume that the fuselage has zero lift in a perfect airflow?

I don't. I present the argument for both cases: zero and non-zero lift at minimum drag.


Why do you assume that the increase of drag is zero for small slip angles?

Follows directly from the definition of "minimum" for a continuous function..

The minimum is, by definition, at the point at which the function (the drag) has zero change for small changes in the input (the AoA or slip angle).