Stall warning horn

[Graham]

Hello all-can anyone assist. I fly a Bristell NG5 with Dynon HDX. The stall warning inhibit is set to 35knts. On take off the stall warning sounds despite not being close to the stall - it continues for around 10 ear blistering minutes even when in level flight doing 85 knots until the green bars on the stall warning display start appearing. No idea what’s causing it because in straight and level it shouldn’t be sounding at all. I’ve tried recalibrating and the same thing happens. It’s as though something needs to “warm” up first….Anyone have an ideas please? Many thanks Graham

 

[PhatRV]

When you did the stall calibration, what was the stall speed. My Dynon’s beep will start to sound at around 40kts but it stopped when I am at take off speed

 

[Graham]

When you did the stall calibration, what was the stall speed. My Dynon’s beep will start to sound at around 40kts but it stopped when I am at take off speed

Around 46 knts- we cannot do a full stall in the Bristell due to potential severe wing drop so that's as far as I am comfortable with. However, the issue isn't that as such. During ground roll - no stall warning, immediately after take off stall warning even when the nose is lowered to get the benefit of ground effect. Then I accelerate to 67knts climb speed - there should be no stall warn at this point but it remains on. I level out in the cruise after a couple of minutes (max) at 90 knts - the stall warning continues for another 3 or 4 minutes until the bar indicators on the dynon screen start turning green. After 5 minutes the calabration display is fully green as it should be. Basically its as though something is warming up for it to work properly. Those 3 to 4 minutes straight and level flight should have sorted any stall warning out but it continues for 3 or 4 mins then stops - its really weird!

 

[PhatRV]

If you cannot perform a full stall than the system will be confused when the stall occurs. You should get a CFI to do a full stall calibration if you are uncomfortable with a wing drop. I suggest you delete all of the stall data from the Dynon HDX EFIS because you should not fly with bad stall horn data. Lots of airplanes will drop a wing at stall so you should be comfortable flying and performing these maneuvers . I am surprised you don’t do this at your flight reviews

 

[Graham]

I have done several full stalls and the wing drop is very severe. The problem persisted but after the full stalls I was told by someone experienced with Bristells not to perform them as they have caused fatalities. I’ve 2000 hours on various aircraft and I have to say I can understand what this person said-it was not a pleasant experience. In any event it didn’t cure the problem-it’s always been as I’ve explained and I therefore tried again at a little above the stall. Having said that-calibrating the stall prior to the actual stall (albeit not that much difference) shouldn’t cause the horn to sound in level flight for a few minutes then stop-if it were calibrated erroneously then the stall warn would stay on full time not for a short period in level flight then stop after 4 or 5 minutes. It’s really weird. I really appreciate the reply but I don’t think my calibration is the issue because the stall warn would stay on and not disappear after 4 mins straight and level. Any other ideas would be much appreciated! Thank you

 

[PhatRV]

Sorry to hear the airplane has such severe wing drop. Have you check the rigging of your Bristell?
I found this Youtube showing the stall behavior of his Bristell. It was like stalls on most hershey bar wing airplane. A bit of yaw to the left near stall in the video.

 

[Stevec]

Are you talking about the AOA warning or a separate stall warning. The RV12 has two different systems one from the AOA sensor and the other from a stall vane in the leading edge. The warning speed inhibit only works on the AOA derived warning as far as I am aware. If you have a stall warning vane I suggest that has worked loose and is causing your issue.

 

[airguy]

Around 46 knts- we cannot do a full stall in the Bristell due to potential severe wing drop so that's as far as I am comfortable with. However, the issue isn't that as such. During ground roll - no stall warning, immediately after take off stall warning even when the nose is lowered to get the benefit of ground effect. Then I accelerate to 67knts climb speed - there should be no stall warn at this point but it remains on. I level out in the cruise after a couple of minutes (max) at 90 knts - the stall warning continues for another 3 or 4 minutes until the bar indicators on the dynon screen start turning green. After 5 minutes the calabration display is fully green as it should be. Basically its as though something is warming up for it to work properly. Those 3 to 4 minutes straight and level flight should have sorted any stall warning out but it continues for 3 or 4 mins then stops - its really weird!

I would suspect you have a bug or some kind of blockage in the second line sensing AOA, not the main pitot tube line. It would give exactly the symptoms you describe.

 

[Graham]

The stall warning derives from the Pitot. It’s one system with a tube running to the ADAHRS. I’ve applied compressed air down the tube at the ADAHRS end recalibrated on the ground before recalibrating in the air-still the same issue. I’ve had the aircraft (kit build) from new and it’s always been like this for 3 years now. Without meaning to be complacent it’s more of an annoyance than something that bothers me because I’m always aware of the attitude of the aircraft so a stall is highly unlikely unless I’m unconscious of course! Equally though I appreciate that pilot error (and therefore my own) can lead to circumstances leading to a stall however experienced a pilot is so I would like it to work. It’s odd it’s only on take off (with no bearing on the AOA) and thereafter level flight for 4 mins or so. After that it works as it should. That’s what’s confusing (and annoying with the warning on for the first 5 ear splitting mins!)