Martin Gregorie wrote:


I've not played with calibrated AoA indicators. If you have, what AoA
was reached at the stall? I'm curious.

I haven't used calibrated ones either, so I don't know.


I think our modern airfoils have very little separation at minimum sink,
and certainly far aft of the 60% point. Instead of "separation", perhaps
you mean the transition from laminar flow to turbulent flow? That does
occur somewhere around the 60% point (maybe 70% or so) on modern airfoils.


Depends on the surface texture and Re number: the turbulent transition
is just behind the hi-point with a paper covered surface and Re =
50,000. I'd guess the separation point was about at the aileron hinge
line on a Discus 1 - otherwise why put the turbulator there? Its job
is to increase the boundary layer energy by forcing a transition from
laminar to turbulent and hence causing separation to be delayed.
Without measuring the wing, that must be in the 80% ballpark.

I was talking about the separation on the top surface at high AOA
during a "stall situation". I now realize you were talking about laminar
flow separation on the bottom surface, which isn't related to the stall
situation.

For the modern laminar airfoils, the transition (from laminar flow to
turbulent flow on the bottom of the airfoil) is at least 80% or more. On
my ASH 26 E, the turbulators are on the flaps and ailerons at about 95%.

The transition from laminar flow to turbulent flow on the top of the
airfoil is sooner, perhaps in the 60%-80% range. There is rarely a
laminar flow separation, though the Speed Astir is a well-known example.

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Eric Greenwell
Washington State
USA