# DIY stall warning sensor?

Discussion in 'Instruments / Avionics / Electrical System' started by cluttonfred, Apr 22, 2016.

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1. Apr 22, 2016

### cluttonfred

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I am familiar with the various DIY lift reserve/angle of attack systems, but does anyone know of a good design for a DIY blade-type stall warning sensor? Aircraft Spruce wants $300 for this one, which seems a bit silly, and$90 for this one, which is better. Still, it ought not to be too hard to gin something up with a little sheet metal, some hardware and a \$2 micro switch. The idea would be to connect it to a bright LED, a test button, maybe a buzzer or audio feed and a 9v battery to have a completely independent system. Something that could be easily adjusted after installation would be a plus. Any ideas?

2. Apr 22, 2016

### slevair

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How about a used one off of a Cessna from Ebay.

3. Apr 22, 2016

### cluttonfred

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Or maybe I could make my own air-powered one like a C150 with some plastic hose and a kazoo! ;-)

4. Apr 22, 2016

### BJC

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They are simple, and they work. Plus, they are easy to disconnect.

BJC

5. Apr 22, 2016

### gtae07

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If you lived on this continent I'd ship you the warning kit that came with my RV-7 wings (minus the access covers and ribs which you wouldn't use anyway). It's basically a pivoting tab, a microswitch, a couple of wires, and a buzzer. I'll be using the AOA on the EFIS so I don't need the buzzer.

6. Apr 22, 2016

### cluttonfred

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Thanks, but I am a long way from needing it, just doing my homework. Though, for the record and in case anyone wants to send me a non-tax-deductible donation, I am an American living and working overseas and have a U.S. domestic mailing address. ;-)

7. Apr 22, 2016

### Rockiedog2

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8. Apr 22, 2016

### cluttonfred

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Belt and suspenders, my friend, belt and suspenders....

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9. Apr 22, 2016

### gammaxy

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Pilots who thought their eyeballs, ears, and ass were good enough continue to die. Pilots transitioning to new airplanes and haven't yet developed the feel also continue to die. I applaud cluttonfred for his willingness to spend a little extra effort in an attempt to prevent himself from doing something he already knows to be wrong. Maybe his attitude already makes him less likely to need the stall warning system, but there's no way to know. In a distracted or panicked situation, we don't always know exactly how we'll act. Sometimes, during a gusty crosswind base-to-final turn pilots get deceived in unbelievable ways, but a stall warning might have given them the extra sensory input they needed. I don't think there's any way to know how many lives have been saved by stall warning systems, but I do know that most of our homebuilt airplanes have a terrible record for stall/spin accidents.

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10. Apr 22, 2016

### Floydr92

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I'd go for the tab type that sits under the leading edge and nornally is blown aft, but at stall will be pushed forward to contact a switch. Should be simple to make, maybe fly with a few tufts stuck around that area, and stall at a safe altitude to give you an idea of where to put it.

Edit: i see this is already what you've been looking at, oops.

11. Apr 22, 2016

### Rockiedog2

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"panicked" ?

by all means, whatever floats your boat
I'm gonna stick with the same one that's worked so well for me all these years; regardless of your opinion.
you get what you need; I sure got no problem with that.

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12. Apr 22, 2016

### BJC

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That is interesting. Is there data to support that?

All bets are off when a pilot panics. That is why pilots should learn to fly, not just drive around.

In an emergency, a pilot will revert to what he has practiced doing in training.

Here we go again .....

BJC

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13. Apr 22, 2016

### cluttonfred

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Folks, please take the conversation on whether or not stall warning of some kind is desirable to another thread. That's obviously a matter of opinion that will not be resolved here and a distraction from what I had asked about, which is a simple and low-cost way to include a DIY stall warning device if you choose to do so.

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14. Apr 22, 2016

### Rockiedog2

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OK Fred, I got it.

15. Apr 23, 2016

### pwood66889

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"... just doing my homework."
All one needs is an air direction indicator and a way to tell when the direction matches the criteria. Trick is calibrating that.
There is a place on the leading edge where the air stream splits. Cessna, et al, just measure wind deviation "above" that point.
Simple and easily made; just hard to calibrate. If you knew the airfoil, then the stagnation point on the leading edge would be known as a function of attack angle from the MAC.
Helped a chum on on one - he used a vane, a potentionometer and a computer for process. Display was a stack of LED's.
Percy in SE Bama

16. Apr 23, 2016

### BoKu

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FYI, that's called the "stagnation point."

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17. Apr 23, 2016

### kent Ashton

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The cheaper version you showed would be easy to make and wire to a buzzer in the cockpit but calibrating it for your airplane it would be the problem. You might install it in the leading edge and add a screw adjustor to the back end, inside the wing, so the angle of the vane (and the whole unit) can be adjusted to get an accurate stall indication.

If you know the number of your airfoil, most airfoil plots show the angle of attack for the peak of the lift curve and the stall comes a bit beyond that. It might work to mount the vane at that angle and adjust from there.

18. Apr 23, 2016

### Rockiedog2

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BoKu I think he may have dumbed it down for some of us; self included.:gig:

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19. Apr 23, 2016

### Daleandee

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Here's a crazy notion to take a gander at:

https://moderndevice.com/product/wind-sensor/

FWIW,

Dale
N319WF

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20. Apr 23, 2016

### fredoyster

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There is a not so crazy complete description of a DIY stall warner in *this month's* Kitplanes magazine. You can also see the basic patent, US 2478967 which explains it pretty clearly.