Stall Warning - AofA

[Brian Whatcott]

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 here: 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

[Dan[_12_]]

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 here: 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

It's a rather nice system.

What is the purpose of the zip tie around the tube? It's not tight
enough to secure anything.

Dan, U.S. Air Force, retired

[Dana M. Hague[_2_]]

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...

Hah!

Many years ago I took my then recent bride for her first small
airplane ride in a 150 borrowed from a friend (since my T-Craft had
been down for work for some time). Being young and foolish and a
showoff, I decided to do a spin, which is, of course, preceded by a
stall... to this day she tells of the flight, "Oh my goodness, we were
flying along and all the sudden a SIREN went off and I thought we were
going to die..."

-Dana
--
I can see clearly now, the brain is gone...

[Paul Tomblin]

In a previous article, said:
>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 here: about $`125
>
>http://www.pipcom.com/~cowcam/AOAr.htm

Our club bought a plane that had a Lift Reserve Indicator. Everybody
hated it, because it was in the way, and so we had it ripped out. I never
got a chance to see it in action.

--
Paul Tomblin > http://blog.xcski.com/
"What we obtain too cheap we esteem too lightly; it is dearness only that
gives everything its value." - Thomas Paine.

[Brian Whatcott]

Dan wrote:
....
>>
>> 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 here: about $`125
>>
>> http://www.pipcom.com/~cowcam/AOAr.htm
....
>> Brian Whatcott
>> Altus OK
>
> It's a rather nice system.
>
> What is the purpose of the zip tie around the tube? It's not tight
> enough to secure anything.
>
> Dan, U.S. Air Force, retired

I have no great insight into operating this system, but my guess is the
usual one about things on struts - they tend to oscillate in the wind -
and this might damp it out???

Brian W

[Dan[_12_]]

Brian Whatcott wrote:
> Dan wrote:
> ...
>>>
>>> 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 here: about $`125
>>>
>>> http://www.pipcom.com/~cowcam/AOAr.htm
> ...
>>> Brian Whatcott
>>> Altus OK
>>
>> It's a rather nice system.
>>
>> What is the purpose of the zip tie around the tube? It's not tight
>> enough to secure anything.
>>
>> Dan, U.S. Air Force, retired
>
> I have no great insight into operating this system, but my guess is the
> usual one about things on struts - they tend to oscillate in the wind -
> and this might damp it out???
>
> Brian W

I would think it would be better served to strap it securely to the
strut.

My pet peeve with some who use tie wraps is they don't cut the tail
flush with the lock. It's a safety issue since the tail can scratch or
cut ones skin. Depending on where that strut is the tail could catch an
unwary person in the eye.

Dan, U.S. Air Force, retired

[Morgans[_2_]]

>
> What is the purpose of the zip tie around the tube? It's not tight
> enough to secure anything.
>
It looks to me like the tie is loose enough, but at the midpoint of the
lines, so that when exposed to airspeed, the tie holds the lines more or
less straight.
--
Jim in NC

[Stealth Pilot[_2_]]

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 here: 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

[[email protected]]

On Mar 1, 10:12 am, Brian Whatcott > wrote:

> 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.

The 172's also used the sucker horn. The microswitch was a earlier
iteration on smaller Cessnas and was used much later on faster
singles.
The reed for the horn is one of the cheapest parts you can buy from
Cessna. Last batch I bought were something like 47 cents apiece. But
then, some of them didn't work and took a little dorking with the reed
to get them to squeak properly.
If there are ANY leaks in that system it won't work. Common leakage
is at the wing's leading edge skin-to-hose fitting interface, where
there's a small plate (with the slot in it) sandwiched between the two
that's adjustable for stagnation point so the 5-10 kt thing can be
adjusted. The hose fitting is plastic and cracks, too, and Cessna more
than makes up for the low reed price by charging bigtime for the
fitting.

Dan