Bob and Alan have expanded on an interesting topic. I have no doubt that the
'judder' (that's what it used to be) serves a useful purpose in avoiding
unwanted wing stall. Being warned of impending stall would have saved
several lives of Yale pilots who also flew Harvards, because of the history
of cantilever wing development.
HOWEVER in them days we were always taught that 'stall' strips were that -
made to stall the wing.
Why? ....because the early wings (beacuse of structural considerations)
could not acquire the 'washout' necessary to permit the tips to keep flying
while the root area stalled. This was thought necessary so that bank control
kept the wing level while stall progressed. That's why the 'vicious' wing
drop suffered from the total stall of the wing.
The STALL strips produced wing stall in the area of the root BEFORE the tips
stalled. They had nothing to do with judder initially. That is a by-product
of their installation.
If warning of impending stall is the target, then rather than reduce the
effectiveness of the wing approaching stall why not select another form of
warning? Stall Warning vanes, stall strings, tufts, and Angle of Attack
indicators, perhaps others. The advantage of AoA is that it progressively
indicates approach to the stall in every mode - G, turbulence, mis-trim all
effect the airspeed at which the stall occurs. The vane in spamcans often
confirms too late. The need for AoA is too present the approaching threat
primarily as a visual adjunct to the windshield view - and a dial down under
the panel coaming don't cut the cake, or tufts and string aren't where you
should be looking. That's why the US Navy puts primary stress on the AoA for
landing - you can see the stall approaching on descent and landing - and air
turbulence is readable in terms of range and depth - right where you're
looking at it.
Just a thought.
Ferg
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