J

JohnF

Well Known Member
Each time I fly I have in mind to resolve or otherwise adjust something. I have flown 10-times this month. Most things are now set properly, but one thing that I keep having 'troiuble' with is the stall warning 'horn.' Initial setting sounded the warning tone only a few MPH from actual stall. Adjustments to the exterior vave have been frustrating because minor bending results either in no warning upon stall or not much change from the 2 or 3 mph above stall. The micoswitch is so awkward to get at through the inspection hole that I have not been able to to do much with it except to try trial and error bending which hasn't worked well at all. When I get my hand up in near the microswitch it blocks my view and the attempt at adjustment is just a shot in the dark...not very scientific or precise at best.

Have you been able to make some sort of reasonable adjustment of the switch, and if so how did you do it?

Otherwise the -12 is doing just fine.
 
Sounds right to me

In my humble opinion, it sounds as though your initial setup of 2 to 3 kts above stall is correct. Anything greater would be a nuisance. Steve
 
Thanks for your views. Maybe I'll just leave it (easiest fix I can think of !)

I was looking for around 5-mph alarm prior to stall, but unless my reactions slow down a lot it does give me enough time to push down.

Thanks folks !
 
14 CFR 205.207 says the stall warning should be 5 kits or 5% above stall, which ever is greater. I'm don't think we have to follow this, but it does give a good guyed.I've been having problems getting mine adjusted as well.
 
Yes, Larry, I also adjusted mine according to the plans but it doesn't produce the 5-kts I was looking for. Trying to set the vane at 90-degrees to a curved surface such as the leading edge of the wing is, at best, a wild guess as to what is or is not 90-degrees.

I wish the inspection hole were placed differently so you could get at it.

JohnF
 
Dick, is it hanging up anywhere? Should be free, and not touching the sides.

I'm sure you have checked this, just trying to think of any possibility. :D
 
Angle of Attack

Hey John,

If you're like those ex-carrier pilots and really appreciate an AOA, you could put one in pretty easily. Just mount it in your wing and run the tube to your Dynon. The Dynon is already set up for it. Then you never have to worry about the horn. In fact someone on here has already done it to their RV12 I know.
 
Stall and AOA

Yes, I saw that posting and was waiting and hoping for some photos. I would like to install a Lift Reserve Indicator which I had in my RV6A and really liked it. The 'inspection' plate near the stall microswitch would make a good installation plate for the LRI...and the two plastic tubes from the LRI could be routed through the tunnel up to the instrument panel for it. A future project.
 
Stall warning switch

My stall warning alarm would not sound until the stall occurred no matter how I adjusted the vane. It was a not a stall warning, but rather a "stall-has-occurred" alarm. The vane was not binding and fell freely by gravity. The vane seemed to require too much force to operate. So I stuck a piece of tape on the vane to increase its area and make it easier for the air to move it. The stall warning worked fine after that. I wanted a permanent fix instead of tape. So I bought a new switch that requires less force to operate, Cherry part number E22-50KL. It is basically the same switch as the original except that the roller arm is moved forward to give a better mechanical advantage. Since the little roller is farther forward, I was concerned that it might contact the wing skin, but it does not. Now the stall warning works fine.
Joe Gores
 
Hey Joe - -

The angle the vane is relative to the opening is very important. Mine worked well first time. Have not changed it. I'm sure you did that. Did it seem to bind any ? Mine is rather loose, which seems fine.

John Bender
 
John,

Adjusting the vane will not change the speed that activates the stall warning. Since stall is bases on AoA,Vans determined the point on the leading edge where the flow separates around the wing at the stall AoA. Bending the switch only changes the amount of force required to move the switch. In order to change the warning speed, the tab will need to be moved forward or back on the wing. This is not an easy task since the switch is riveted in place and holes are already cut into the wing. The easiest solution would be use an AoA probe. This also eliminates the variability of stall speed due to weight.

Brian
 
Sorry Brian - -

I trust you are not building a 12. The instructions said to bend the tab as needed to afffect when it comes on. I believe it. Angle is a factor.

John Bender
 
bscycleman said:
John,

Adjusting the vane will not change the speed that activates the stall warning. Since stall is bases on AoA,Vans determined the point on the leading edge where the flow separates around the wing at the stall AoA. Bending the switch only changes the amount of force required to move the switch. In order to change the warning speed, the tab will need to be moved forward or back on the wing. This is not an easy task since the switch is riveted in place and holes are already cut into the wing. The easiest solution would be use an AoA probe. This also eliminates the variability of stall speed due to weight.

Brian
Click to expand...

JBPILOT said:
I trust you are not building a 12. The instructions said to bend the tab as needed to afffect when it comes on. I believe it. Angle is a factor.

John Bender
Click to expand...

John is right.

The angle of the vane has everything to do with when the switch trips and indicates a stall.

In simple terms, you are adjusting for the angle of attack where the relative wind changes from hitting the vane on the top (holding it down) to hitting it on the bottom (lifting the vane and closing the switch).

What can occure when bending the vane is that its adjustment relative to the micro switch changes and it no longer moves far enough to activate the switch. If this happens, you need to get inside teh wing and re-adjust the position of the entire assembly.
 
John Bender,

You are correct, I am building a 7.

RVBuilder2002,

The directions for the stall system on the 7 are very specific as to the agle of the stall tab. It should be normal, 90 degrees, to the leading edge. The directions say to remove the tab and bed it as needed to ensure it is 90 degrees. By doing this, it eliminates the tabs AoA influence and relies upon the separation point moving behind to tab to trip the sensor. I have not seen the directions for the 12, but assumed they were the same for both aircraft. I stand corrected.

Brian
 
In simple terms, you are adjusting for the angle of attack where the relative wind changes from hitting the vane on the top (holding it down) to hitting it on the bottom (lifting the vane and closing the switch).
Click to expand...
Reminds me of holding my hand outside of a car window and making my hand "fly" up or down by moving my fingers.
Joe Gores
 
Mich48041 said:
Reminds me of holding my hand outside of a car window and making my hand "fly" up or down by moving my fingers.
Joe Gores
Click to expand...

Reminds me of all the RV's that were built prior to the 12 without any stall warning system. Most likely because the best warning system is the "burbles," the wing drop, the very low number on the A/S indicator in some instances. LSA rules require it, but really...! How many gear horns prevent gear ups?
 
The stall warning vane and alarm works a bit differently (knots to the buffet) when lightly loaded compared to near or at gross weight. (With the ball centered, the stall is so gentle it is hard to ascertain a stall speed!!)

Do not know why.
 
Last edited:
You should be able to physically recognize a stall (without a horn) on any aircraft at any configuration. If you become horn dependent and stall it on base or final, don't bet you'll ever hear it. The first thing most test pilots on new aircraft (including homebuilts) do is to find that envelope. AND to teach themselves what characteristics the airplane exhibits so that your muscle memory is prepared for that low altitude possibility. Unless you fly an F-16, it is ridiculous to expect that you can power your way from behind the curve. Too slow is too slow, regardless of the ball position.
 
So why don't we all just hook up the AOA like Joe did and solve the stall warning problem that some are experiencing? I fortunately have no problem with the warning function (about 6 to 7 kts above stall), but the AOA seems to me a good idea with or without the above mentioned problem.
Dick Seiders
 
Peterk said:
Reminds me of all the RV's that were built prior to the 12 without any stall warning system. Most likely because the best warning system is the "burbles," the wing drop, the very low number on the A/S indicator in some instances. LSA rules require it, but really...! How many gear horns prevent gear ups?
Click to expand...

Peterk,

You state that LSA rules require a stall warning. Is that new? My CTSW does not have one.
 
Bend the arm Inside

Once you have the external tab set to 90 deg, you have to bend the actuating arm inside the wing (the one with the contact) to change the position where the tab actuates the stall warner. I laid a small flashlight inside the wing, then used two small screwdrivers to bend the arm up or down until I got a tone (you can hear it while under the wing) with "minimum travel" of the tab. Mine comes on somewhere near 5 knots above, usually before the airplane tells me it's ready to quit flying.

Wayne 120241/143WM
 
You must log in or register to reply here.