On Sun, 18 Jul 2004 08:27:23 -0700, Eric Greenwell
wrote:

Perhaps we are not discussing the same thing. It sounds like you are
talking about "a stall", meaning the aircraft's behavior from the pilots
viewpoint (buffeting, loss of lift, poor control, etc), and I am talking
about the aerodynamic situation during "a stall" (high AOA leading to
flow separation and constant or diminishing lift coefficient).

I think that's partly true. I meant 'A stall' as in what happens as
the wing becomes no longer able to support the aircraft, not what
happens if you keep the stick back and the situation stabilises with a
high but constant descent rate.

I think our main disagreement is whether the aircraft really reaches
the constant Cl, increasing Cd region, let alone the diminishing Cl
region. It may do that, but the AoA would need to be very large indeed
- over 20 degrees at a guess.

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

Many aircraft have quite a high degree of flow separation during low
speed flight. In the model world we assume separation always occurs at
about 60% chord at min.sink and this would appear to be close to the
mark for sailplanes judging by Will Schumann's experiments.

I should read back more carefully before hitting SEND. I meant 80%.
Sorry 'bout that.

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.


--
martin@ : Martin Gregorie
gregorie : Harlow, UK
demon :
co : Zappa fan & glider pilot
uk :