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Aileron "snatch"--buffett

petersb

Well Known Member
After searching the forum there are two suggested reasons published.

1: Aileron leading edge causing flow separation

2: Trailing edge radius.

Which is it ?

I have aileron buffet in a right roll and none in a left roll, strange.

Ailerons look identical in trailing edge roundness, vertical alignment, bell crank position.

Of course I know it is not critical, however, being an experimental aircraft I would like to experiment and identify the cause for my own satisfaction
 
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Could it be that you aren't getting the same amount of aileron deflation?

I can see your left leg restricting your stick movement when rolling left. When rolling right, you have more room to move your right leg out of the way.

Just a thought.
 
I get the buffet both ways if my entry speed is too high. Try dropping 5mph and doing it again?
 
Could it be that you aren't getting the same amount of aileron deflation?

I can see your left leg restricting your stick movement when rolling left. When rolling right, you have more room to move your right leg out of the way.

Just a thought.

Good thought, but I think I was applying equal stick deflection. Infact, my impression is the right roll buffet occurred with just over half stick deflection, it seemed to be much less deflection than my previous RV6 required before it buffeted
 
I get the buffet both ways if my entry speed is too high. Try dropping 5mph and doing it again?

I was doing 140 mph

My real interest was to determine why is there a difference between the left and right roll in regards to buffet and no buffet
 
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Isn't "aileron snatch" different than the aileron buffet felt during rolls at higher entry speeds? (Just FYI...I'm certainly not an expert in *anything* related to aerobatics :) ).
 
Isn't "aileron snatch" different than the aileron buffet felt during rolls at higher entry speeds? (Just FYI...I'm certainly not an expert in *anything* related to aerobatics :) ).

Yes, I used both "snatch" and "buffet" in the heading as many people are using either word to describe the same condition. It is really buffet
 
I get the buffet either way I roll. I'm not sure why you only get it one way. It's possible you may be deflecting the stick more in a right roll if you are using your left hand on the stick. If you are rolling with your left hand on the stick, your arm muscles work better for a right roll, it takes a lot less effort to push away to the right than to pull left on the stick, especially against the air pressure on the ailerons at speed. Try rolling with your right hand and see if the opposite happens. The aircraft doesn't seem to roll any faster if I give it full aileron anyway, so I just do about half as others have mentioned.
 
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Aileron snatch is when aerodynamic forces move the aileron against your command. It feels like someone grabbed the aileron and applied force. If you are holding the stick lightly it will move. Buffet is an oscillation in the airflow that creates a vibration or shaking that doesn't really displace the overall deflection of the aileron.
 
Aileron snatch is when aerodynamic forces move the aileron against your command. It feels like someone grabbed the aileron and applied force. If you are holding the stick lightly it will move. Buffet is an oscillation in the airflow that creates a vibration or shaking that doesn't really displace the overall deflection of the aileron.

Yes you are correct, I used "snatch" as it seems to be the generic term used in the forum
 
Tuft Testing

You could try tufting the underside of the outboard wing and aileron, and mounting a GoPro camera under the wing to record the tuft activity during aileron deflection. I suspect the aileron leading edge trips the boundary layer and causes turbulence on the underside of the aileron.
 
Ah, yes, at 140mph you should be good... I agree with others who suggest you may not be getting the same deflection on each side. The airflow over the aileron is separating and re-attaching in quick succession, which is what gives the buffet. The question is what's making it separate in the first place.

Slight differences in rigging from side to side could have your aileron higher or lower relative to the main body of the wing... That could subtly affect the point at which it trips.

Another thing to try is just bringing the stick back a few degrees towards center when you feel the buffet... You don't really need full aileron to do a nice roll.
 
I have noticed the same issue, buffeting with full right aileron but not with the left. I'm thinking the ailerons are positioned slightly different on the wing, which could also be causing my heavy left wing. I've followed Van's checklist for diagnosing and fixing a heavy wing as far as rigging is concerned and everything seems correct.
Possibly my right aileron is 1/32 lower causing a buffet and heavy left wing. I've installed a foam wedge (3 inches long 1/4 inch tall) under the right aileron to temporarily fix the heavy wing until I get all of the fairings installed.
 
I have noticed the same issue, buffeting with full right aileron but not with the left. I'm thinking the ailerons are positioned slightly different on the wing, which could also be causing my heavy left wing. I've followed Van's checklist for diagnosing and fixing a heavy wing as far as rigging is concerned and everything seems correct.
Possibly my right aileron is 1/32 lower causing a buffet and heavy left wing. I've installed a foam wedge (3 inches long 1/4 inch tall) under the right aileron to temporarily fix the heavy wing until I get all of the fairings installed.

Yes, that was my thought. However, they look pretty close in vertical alignment
 
Mine appear to be spaced vertically the same referencing the aileron jig and tooling holes. (At least as far as I can measure) I'm hoping for some decent weather (6-8 inches of snow and ice tonight) so I can make my intersection fairings- test fly-possibly lower/raise an aileron soon!
 
Mine appear to be spaced vertically the same referencing the aileron jig and tooling holes. (At least as far as I can measure) I'm hoping for some decent weather (6-8 inches of snow and ice tonight) so I can make my intersection fairings- test fly-possibly lower/raise an aileron soon!

Yes, weather her in Toronto is also bad. I checked my vertical alignment ny placing a straight edge on top of the wing and over the aileron, they look very close
 
I have had this issue for a while, and was uncomfortable rolling because of it. This past Saturday I spend 1.5 doing rolls and perfecting my control inputs... No more buffeting. I was not applying the proper amount of rudder, and was pulling back ever so slightly on the stick while upside down. Depending on your arm positioning you could be doing the same one side VS the other.
 
A bunch of years ago we were flying competition in a 6 and 4. We decided we needed more roll rate, so we designed new bell cranks that would give us more down aileron. As I recall our deflections were 32 up and 25 down. Guess what! Faster roll and the buffeting was gone . Explain that to me. Aerodynamics are highly over rated. :)

Terry Burch
RV7 IO-375
 
I have had this issue for a while, and was uncomfortable rolling because of it. This past Saturday I spend 1.5 doing rolls and perfecting my control inputs... No more buffeting. I was not applying the proper amount of rudder, and was pulling back ever so slightly on the stick while upside down. Depending on your arm positioning you could be doing the same one side VS the other.

I do have aileron buffet in both sides, and I do had a heavy wing issue that was "fixed" by the builder. But I did not know I need to use rudder in rolls with the RV7 I did not use rudder with my first plane that was a RV9. My impression is that this my new plane a RV7 rolls slower than my old 9 what to me is a disappointment.
A bunch of years ago we were flying competition in a 6 and 4. We decided we needed more roll rate, so we designed new bell cranks that would give us more down aileron. As I recall our deflections were 32 up and 25 down. Guess what! Faster roll and the buffeting was gone . Explain that to me. Aerodynamics are highly over rated. :)

Terry Burch
RV7 IO-375

Terry do you have any blue prints , plans or comments on how could I do this mod in a RV7, mine seems to roll pretty slowly (even compared to a 9) and is giving a buffet rolling either side.

I'd really want to fix this roll rate (increase it) and stop the buffeting. Anyone had it and got it improved/fixed could instruct me how would be of most help.
 
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