Stall Warning in Gound Effect-Dynon AOA

[Pmerems]

Gents,

I was hoping someone much smarter then me (which is probably everyone who reads this post) when it comes to aerodynamics in ground effect and it?s effect on the Dynon AOA/Stall warning.

For those not familiar with the Dynon AOA system it basically uses the dynamic pressure port and a ?special? static pressure port which are both located on the special Dynon pitot probe. The audible stall warning is just warning tones based on the AOA. To setup the AOA Dynon has specific procedures to follow to ?calibrate? the system. I performed the setup and the AOA/Stall progressively warns of the stall prior to the full stall around 42-44 kts (at altitude). I have checked this several time and it is very consistent.

I have about 70 hours in my RV-7A and I am always trying to improve my skills every time I fly. When I return to the airport I always like to end my flight with the perfect landing, if there really is one. I have the Dynon AOA/Stall warning active and I always want to hear the first few ?beeps? from the system just as I touch down. On a few occasions I have heard a ?beep? but most of the time I don?t. I know on several landing I landed hot, but I have been working to really keep the nose up and hold it off the runway. Last week I performed several touch and goes and never heard the stall warning. However my touchdown indicated airspeeds were in the very low 50?s so I would have expected to hear the initial stall warning beep. So I stated wondering if in ground effect the stall warning doesn?t behave the same as it does at altitude. Keep in mind this system is not the same as the leading reed switch/noise generator typically found on most low end GA aircraft.

I have been reading online about low wing aircraft in ground effect and when in ground effect the indicated airspeed is faster then the actual airspeed. With this said then the Dynon AOA system may not sense the near stall in ground effect if the Dynon ?thinks? the airspeed is higher then I really is. Does this make sense?

Any experts out there with some knowledge in this area?

Thanks

[Sam Buchanan]

Originally Posted by Pmerems

Gents,

I was hoping someone much smarter then me (which is probably everyone who reads this post) when it comes to aerodynamics in ground effect and it’s effect on the Dynon AOA/Stall warning.

For those not familiar with the Dynon AOA system it basically uses the dynamic pressure port and a “special” static pressure port which are both located on the special Dynon pitot probe. The audible stall warning is just warning tones based on the AOA. To setup the AOA Dynon has specific procedures to follow to “calibrate” the system. I performed the setup and the AOA/Stall progressively warns of the stall prior to the full stall around 42-44 kts (at altitude). I have checked this several time and it is very consistent.

I have about 70 hours in my RV-7A and I am always trying to improve my skills every time I fly. When I return to the airport I always like to end my flight with the perfect landing, if there really is one. I have the Dynon AOA/Stall warning active and I always want to hear the first few “beeps” from the system just as I touch down. On a few occasions I have heard a “beep” but most of the time I don’t. I know on several landing I landed hot, but I have been working to really keep the nose up and hold it off the runway. Last week I performed several touch and goes and never heard the stall warning. However my touchdown indicated airspeeds were in the very low 50’s so I would have expected to hear the initial stall warning beep. So I stated wondering if in ground effect the stall warning doesn’t behave the same as it does at altitude. Keep in mind this system is not the same as the leading reed switch/noise generator typically found on most low end GA aircraft.

I have been reading online about low wing aircraft in ground effect and when in ground effect the indicated airspeed is faster then the actual airspeed. With this said then the Dynon AOA system may not sense the near stall in ground effect if the Dynon “thinks” the airspeed is higher then I really is. Does this make sense?

Any experts out there with some knowledge in this area?

Thanks

Paul,

I fly the Dynon AOA in tandem with an LRI. The LRI probe and indicator is used but the Dynon provides the aural warning.

I suspect your AOA is calibrated to a lower speed than you are using for landing. A full-stall landing in your plane would have the tail nearly dragging the ground.

I can't address the ground effect "effect" on indicated airspeed, that is too technical for me.

I nearly always get an audible warning on landings but my RV-6 is probably seeing greater AOA than your -7A.