Stall Warning - AofA

On Sun, 01 Mar 2009 11:12:59 -0600, Brian Whatcott
wrote:

One of the design features of the Cessna 150 that I admired most is the
stall warning. It is a small aperture in the lower curve of the leading
edge guarded by a wire screen (those pesky flies!) The cavity connects
to a tube leading to the wing root in the cabin. There, covering the
other end of the tube is a mouth organ reed, arrange to be silent when
blown, and to whine when sucked. That's three components and just one
moving part if you could call a vibrating reed, a moving part.....
The most bang from the least buck - it seems to me.

It was pre flight checkable - with a wipeoff of fly squash and a mouth
applied suck. Wonderful!
It was not everyone's cup of tea, I don't suppose: in particular, that
mouth to wing actvity was eliminated by a small vane on a microswitch,
which howled when the vane pushed up at high AofA. I think that was a
C172 mod wasn't it? It needed power to work though.

Anyway, for something a little fancier yet, a kind of lift reserve or
AofA indicator that takes two pitot tubes to a differential pressure
gage, shown he about $`125

http://www.pipcom.com/~cowcam/AOAr.htm

I am prejudiced in favor of red sector in right, not in left but that's
just my feeling.

[No financial interest]

Brian Whatcott
Altus OK

my stall warning has cost me $1.25 and has performed faultlessly for
20 years, then again for 8 years. :-) (I accidently glued it up with
epoxy)

yea it is on a wooden wing.

a small microswitch is imbeded in the wing skin.
contacting that is a small aloominum vane held to the wing loosely by
two brass countersink screws. the middle of the vane is cut away so
that it looks like two postage stamp sized areas separated by two
pieces of aluminium about 10 mm wide. (think of a rectangle with a
square hole in the middle) the screws provide a hinge in the middle of
one end rectangle.
the two parallels are curved around the wing leading edge profile and
the end area bends up perpendicular to the leading edge at that point.
the exact position of the bend is found experimentally so that the
vane lifts and the microswitch is triggered on about 5 knots before
the stall.
the microswitch has two wires back to a light on the panel.
the circuit is of course powered from the aircraft battery and sits
normally open circuit until the microswitch closes when the red light
illuminates.
this requires no power at all unless the stall warning is activated.
stall warning light and aircraft wiring of course cost more than the
$1.25 I spent at tandy replacing the microswitch I glued solid but
that is all it has cost me.

it is chugger simple and it works to 160 knots.

$125 buys more envy though :-)

Stealth Pilot