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Stall Warning Failure

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ledson

Joined: 29 Apr 2009
Posts: 62

Posted: Mon Jul 30, 2012 6:37 am Post subject: Stall Warning Failure

I'm trying to find out if anyone else is have this problem with the Stall Warning system on their Allegro 2000.  

Last Saturday during cruise flight, the stall warning horn started sounding.  I was at approximately 95 mph.  The stall warning light did not come on and there was not any changes in the AOA.  Upon landing, the stall warning horn stopped sounding and the stall warning light came on like it normally does when landing.  I checked the feed tube to ensure that there wasn't anything blocking it and then tried several more takeoff and landings with the same results.  I'm assuming that it is either a failure of the stall warning control board or the ASI. Right now I'm at a loss on how to proceed.  I don't have a wiring schematic of the stall warning system and without one I'm not sure what's next.  So if anyone has any experience with this system I would certainly appreciate your advise. 



Thanks, 



Larry Edson

N4362C

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brad(at)vision-technology
Guest

Posted: Mon Jul 30, 2012 6:45 am Post subject: Stall Warning Failure

I wouldnt think the ASI is involved unless we have a really unusual system.  Maybe whatever control board it has or a wiring short to the horn?   

 

 Brad N221FA.  Bismarck ND

 

 P.s. was good to see the allegro folks with a display at OSH

 

 Brad Kramer / VisionTech

 (701) 222-3009 



ledson <ledson(at)oneil.com> wrote:[quote] [quote]--> Allegro-List message posted by: "ledson" <ledson(at)oneil.com>I'm trying to find out if anyone else is have this problem with the Stall Warning system on their Allegro 2000.  Last Saturday during cruise flight, the stall warning horn started sounding.  I was at approximately 95 mph.  The stall warning light did not come on and there was not any changes in the AOA.  Upon landing, the stall warning horn stopped sounding and the stall warning light came on like it normally does when landing.  I checked the feed tube to ensure that there wasn't anything blocking it and then tried several more takeoff and landings with the same results.  I'm assuming that it is either a failure of the stall warning control board or the ASI. Right now I'm at a loss on how to proceed.  I don't have a wiring schematic of the stall warning system and without one I'm not sure what's next.  So !    if  [quote][b]

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ledson

Joined: 29 Apr 2009
Posts: 62

Posted: Tue Jul 31, 2012 5:50 am Post subject: Re: Stall Warning Failure

I received the following response from an e-mail that I sent to Allegro USA: 



That alarm is controlled by an small pressure switch near the airspeed indicator under the dash.  I would start by removing the pitot line from the switch and make sure that the line is clear throughout the system. ( you should be able to blow air through the tube and out the hole in the wing)   it is not likely but possible that the line has been pinched inside the wing. If you find resistance in the line, then trace it back through the wing and find and repair.   If all is clear you can try adjusting the pressure switch, this will require a small screw driver and I few flights, to get it to were its only alarming  about 5 miles an hour before stall.   This can be tricky but doable.   If this does not fix the problem then you would need to try replacing the pressure switch. But the likelihood of it being bad is slim 



Hope this helps, if your still having problems and you have tried all the above, let me know will look into it further.



Thanks 

Kyle Lawler

Production Manager

LSA America Inc.



I'll give this a try this weekend and see if I'm successful. 



Thanks, 



Larry

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jkgcpa(at)ix.netcom.com
Guest

Posted: Thu Aug 02, 2012 8:47 am Post subject: Stall Warning Failure

We do have an unusual stall warning system.  The ASI has a stall warning

electrical connection.  A pressure switch interfaces between the static

system and the control board.  It causes the green light to light & powers

the system.  When stall setting approaches, the ASI sends a signal to the

board to change the light to red & sound the horn.



Your problem sounds like either the static connection to the pressure switch

is bad, the pressure switch itself is bad, or the ASI setting mechanism has

failed.  The pressure switch is available through suppliers, its number is

printed on the side.  Trouble shoot it to see it is closing with a meter.

Check your ASI connections in the back to see they are clean.  If it's the

internal ASI or the board, no one can fix it.  So you would have to get a

separate stall warning system.



Let us know how it goes.



Thanks,



Jerry Goldberg

N44456

X09

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brad(at)vision-technology
Guest

Posted: Thu Aug 02, 2012 1:02 pm Post subject: Stall Warning Failure

I don't understand how the airspeed indicator would play a role in determining when to sound a stall warning.  It can't sense angle of attack,

Any ideas?

I'm curious now to peek behind my panel and see exactly how this all works.  (which I really should know anyway)

Brad / N221FA

 

 [quote]--

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ledson

Joined: 29 Apr 2009
Posts: 62

Posted: Sun Aug 19, 2012 2:23 pm Post subject: Re: Stall Warning Failure

Brad,



From what I can gather, the ASI activates the stall warning system at around 30 mph plus it activates stall warning light at about 5 mph above stall.  The pressure switch activates the stall warning horn when the pressure that it senses drops below the setting.  



I'm still trying to get a wiring schematic for the control board.  I do have the wiring diagram that shows how the system is wired, but without understanding the logic that is on the board I'm at a loss.  I've tried everything that has been suggested with no change.  I would like to know the measured pressure that activates the pressure switch.  That would allow me to adjust the pressure prior to flight without the trial and error method that has been suggested.  



If anyone out there has any suggestions,  I'm certainly open to them.



Thanks,



Larry

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ledson

Joined: 29 Apr 2009
Posts: 62

Posted: Sun Oct 07, 2012 5:11 pm Post subject: Re: Stall Warning Failure

The stall warning system is repaired.  Follow the guidance that was provided by Doug Hempstead, we performed diagnostics by parts replacement.  Not my preferred approach, but without and understanding of the wiring and the board logic, it was the only way to go.  We started by replacing the circuit board and then test flying the airplane.  No change. We then ordered the pressure switch from Allegro USA.  When we received the new pressure switch, we replaced the new circuit board with the old one. (Doug was good enough to take it back with no charge). We replaced the pressure switch, test flew the airplane and the stall warning system performed just like it should.  It required no adjustments.  Stall warning was about 5 MPH above stall.   



I'm thankful that it is repaired so I can enjoy the wonderful fall colors here in Ohio.  



Thanks to everyone that provided suggestions and assistance during this repair. 



Larry



N4362C

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ledson

Joined: 29 Apr 2009
Posts: 62

Posted: Sun Oct 07, 2012 5:12 pm Post subject: Re: Stall Warning Failure

The stall warning system is repaired.  Follow the guidance that was provided by Doug Hempstead, we performed diagnostics by parts replacement.  Not my preferred approach, but without and understanding of the wiring and the board logic, it was the only way to go.  We started by replacing the circuit board and then test flying the airplane.  No change. We then ordered the pressure switch from Allegro USA.  When we received the new pressure switch, we replaced the new circuit board with the old one. (Doug was good enough to take it back with no charge). We replaced the pressure switch, test flew the airplane and the stall warning system performed just like it should.  It required no adjustments.  Stall warning was about 5 MPH above stall.   



I'm thankful that it is repaired so I can enjoy the wonderful fall colors here in Ohio.  



Thanks to everyone that provided suggestions and assistance during this repair. 



Larry



N4362C

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