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Power Off - 1-G vs. "Controllable" stall

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undean

Active Member
Joined
Jun 30, 2019
Messages
34
I've been looking at available Part 103 aircraft, AC 103-7 and the appendices, Other FAA documents, this and other forums, and am attempting to reconcile what appears in AC 103-7 (appendix 2 Stall Speed graph) to be a reference to 1-G "stall" and a number of designs which appear to have been designed to critical AoA stall.

Using the oft referenced stall calculation [ V = √( 2 m g / ( ρ S Clmax ) ) ] and even using the over-predictive 2-D Cl_max at appropriate Re I've noticed some airplanes list a much lower Vs0 than what that stall calculation would predict. However, making a simplified/idealized version of the plane in xflr5 appears to show controllable flight below the formula predicted velocity (e.g. it will close on a solution with W > L).

For one popular UL (to my knowledge) the above formula indicates the need for a CLmax of ~2.15 at Re = ~1,100,000 without the use of flaps, slats, or other high-lift devices on what is roughly a Clark Y to meet the 24 knot stall which is above its listed Vs0.

All of this being said, I am having difficulty with what appears to be finding a velocity (x) with, maybe, sink rank (y), just prior to the point where it will presumably nose down as opposed to just entering deep-stall as the latter, if "controllable", would mean it could be argued its not in "stall".

Perhaps I am misunderstanding something or it's one of those winked at things but at a minimum I cannot reconcile a stall calculation which over predicts stall onset despite using CLmax. I've found some interesting discussions on this topic here and elsewhere but at this time I would rather not officially inquire about this but if I have missed something obvious to someone else I would like to hear that as well.
 
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