Discussion in 'Hangar Flying' started by Aerowerx, Jul 14, 2019.
Betz was right about propellers...please read the paper.
Red, I believe you might be in a good position to address some of the questions raised earlier in this thread, pertaining to whether Al's Prandtl twist is only valid for one Cl, or one fight condition? Knowing Al I would bet that he considered this during his research, but I think you're closer to being able to verify that factually than myself and most of the others here. I hope to see you in Tehachapi,
Bill / VB
To piggyback on this question a little, maybe the problem should be attacked from the other direction. What kind of configuration and mission profile would result in the least amount of Cl change during flight?
Flying really, really high.
Or maybe really, really slow, like, you know, in a Cub.
But that's for Cubs!
Do you mean Coefficient of lift (lower case letters) or Coefficient of Lift (upper case letters)????
Coefficient of lift (lower case) depends only on the AoA at each wing station, and the airfoil used.
Coefficient of Lift (upper case) depends on the gross weight of the aircraft and the wing area.
To clarify, in the context of the discussion, if there is a large penalty for the off design condition, what kinds of configurations and missions could this be practically applied to.
Not sure I have a good answer for that, except for a touring/sight seeing/cross country mission you would be spending 90% of your time in cruise.
Also, in the book "Tailless Aircraft" they give the example of a sailplane. Low speed/high Cl when in thermals, and high speed/low Cl between thermals.
If any of you are REALLY interested in flying wings, buy, borrow, or steal a copy of Nickel's "Tailless Aircraft in Theory and Practice". It covers many of these topics. Although they treat elliptical as the ideal, IMHO the same arguments could be applied to the Prandtl-D bell shape.
Well, you either work out how to use a point design, or work out how to minimise the penalty.
For a long distance mile eater, flying really high keeps the Cl high and increases ground speed. The bad is that you need a engine that can put out enough power while breathing a partial vacuum. After that, the Armstrong limit gets in the way. A lot of additional weight is needed to safely get past that one...
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