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Stall Warning - AofA
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 |
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Stall Warning - AofA
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 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 |
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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... 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... |
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Stall Warning - AofA
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 he 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. |
#5
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Stall Warning - AofA
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 he 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 |
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Stall Warning - AofA
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 he 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 |
#7
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Stall Warning - AofA
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 |
#8
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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 |
#9
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Stall Warning - AofA
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 |
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