Ahh, how nice it is to be an American who's allowed to stall without
warning--one of the unsuspected benefits of wiping Geo. III's eye about
this time a few years ago...
But seriously folks, a few years ago there was a product on the market
here--even STC'd in quite a few production airplanes--called a "lift
reserve indicator" and sold by a gentleman called Morgan Huntington, who
I believe is since deceased (of natural, i.e. nonaviation, causes). The
way this thing worked was via a rather sensitive differential manometer,
apparently available over the counter from specialists supplying the
heating and air conditioning industries, hooked up to a rather
odd-looking probe with ports at 45 degrees above and below its
stagnation point. Later research indicates that you could do just as
well, and much less draggily, with a couple of holes equally spaced fore
and aft of the wing leading edge outboard of the prop blast.
The way you were supposed to calibrate the thing was to stall the
airplane once and note where the pointer indicated. Since lift is based
on the pressure differential above and below the wing, this should
indicate the same regardless of weight or G-load--in other words, while
the thing doesn'te quite read angle of attack directly, it does provide
a consistent indication of "available lift margin before the stall." I
flew with the production version, and it worked a treat.
I gather the placement of the upper and lower holes isn't terribly
critical as long as they're roughly equidistant from the stagnation
point. Any small errors are taken into account by the flight
calibration procedure.
The manometer Huntington used cost around $100, was nicely damped, and
fit exactly into a normal 3.125" instrument hole.
Good luck!
psl
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