What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Tail buffet at stall?

catmandu

Well Known Member
Uncharacteristically, after reading a few threads and not finding a similar situation, I am going to shoot from the hip with less than total information available. Please be gentle.

I flew an RV-9a with a relatively dirty aerodynamic snapshot: less than streamlined but secure cowl, rough paint, no fairings or pants on the gear, yet to be calibrated (by me, anyway) pitot static system. When I stalled it with full flaps at altitude to set my indicated airspeed for landing, it was an as advertised docile stall, but enough noise behind me to take a look. Seemed as if the upward deflected trailing edge of the elevator was rather, ahem, excited. Not much feedback in the stick.

Typical for the configuration?
 
No mine

I?ve never experienced this on my -9.
Scott may comment more precisely on the factory model.
 
I haven't had my 9 very long but have done at least 20 stalls and have not experienced what you describe. Docile stall characteristic requiring just a slight bit of rudder to raise the left wing.
 
I have a bit of time in a friends 9A and spent much of it exploring the stall. This airplane behaved just as you describe. With the stick held full back and floating down, the tail shakes like a wet dog. The -8 and the Rocket are similar, but not as bad as the 9.
 
Uncharacteristically, after reading a few threads and not finding a similar situation, I am going to shoot from the hip with less than total information available. Please be gentle.

I flew an RV-9a with a relatively dirty aerodynamic snapshot: less than streamlined but secure cowl, rough paint, no fairings or pants on the gear, yet to be calibrated (by me, anyway) pitot static system. When I stalled it with full flaps at altitude to set my indicated airspeed for landing, it was an as advertised docile stall, but enough noise behind me to take a look. Seemed as if the upward deflected trailing edge of the elevator was rather, ahem, excited. Not much feedback in the stick.

Typical for the configuration?


Hi Mike nice meeting you today, this is Bill with Davis Aviation. I just remembered the last RV9A I finished a few months ago that we rebuilt the tail section on also had a loud noise in the lower speed range. It was loud enough to have me concerned. It was found to be the rear skirt on the sliding canopy. The owner Added a piece of weather stripping and the noise is gone. It definitely wasn’t a sound I would have attributed to the canopy. It was a loud buffeting sound just as you describe. Perhaps when you come down next week to pick the plane up we will experiment with the weather stripping.

Take care
Bill
 
Last edited:
Thanks, folks. It was probably noise coming in through the skirt as Bill said which first got my attention. And I do tend to go deeper into stalls due to spending a lot of time at 35* AOA back in the day, so the wet dog theory may apply. I will put this in the "look further into it but probably nothing" brain file for now, maybe set up some video on it later.

Always nice to get a warm fuzzy from the VAF collective. :)
 
Thanks, folks. It was probably noise coming in through the skirt as Bill said which first got my attention. And I do tend to go deeper into stalls due to spending a lot of time at 35* AOA back in the day, so the wet dog theory may apply. I will put this in the "look further into it but probably nothing" brain file for now, maybe set up some video on it later.

Always nice to get a warm fuzzy from the VAF collective. :)

If you deeply stall an RV-9 (easy to do because it is very docile... depending on C.G. position) you can ride the stall down hill with the stick full back with the nose bobing up and down as the wing flow attaches and detaches.
This disturbed airflow will cause a lot of dirty flow over the tail making it shake a lot. With no gear leg or wheel fairings the flow over the tail is probably even dirtier making what you are seeing, even worse.
 
If you deeply stall an RV-9 (easy to do because it is very docile... depending on C.G. position) you can ride the stall down hill with the stick full back with the nose bobing up and down as the wing flow attaches and detaches.
This disturbed airflow will cause a lot of dirty flow over the tail making it shake a lot. With no gear leg or wheel fairings the flow over the tail is probably even dirtier making what you are seeing, even worse.

ditto this
 
Curiosity

I was intrigued by this thread. I?d heard of stall buffet being caused by the tail but never investigated it. My 9A has a noticeable buffet just as it breaks in the stall. Today I went out to investigate and sure enough the buffet is from the tail. I watched the tail over my shoulder during the stalls and it definitely shakes and is causing the buffet. It was more pronounced with the flaps up, but present either way.

-Andy
 
I was intrigued by this thread. I?d heard of stall buffet being caused by the tail but never investigated it. My 9A has a noticeable buffet just as it breaks in the stall. Today I went out to investigate and sure enough the buffet is from the tail. I watched the tail over my shoulder during the stalls and it definitely shakes and is causing the buffet. It was more pronounced with the flaps up, but present either way.

-Andy

The stall induced buffet felt in the stick and airframe is generally caused by the disturbed flow rolling off the wing and striking the tail.

That is why it can be different between different airplanes depending on the relative vertical position of the horizontal tail surfaces to the wing.

It is also why the buffet can be different depending on flaps up or flaps down... the physical angle of attack of the aircraft will differ between the two which will result in the wake of the wing striking the tail differently.

I think this is also why the trim change (nose up vs nose down) with flap deployment is typically different between low wing airplanes and high wing airplanes because the wake of the wing is in a different position and thus has a different influence on the horizontal tail.
 
Back
Top