Full Stick Deflection in ROLL, feels like its fighting back!

I have heard this is normal for RV's but figured I'd ask anyway and see if there is a way to get rid of it. When I do a full deflection aileron roll, you can feel the ailerons shutter. Its hard to explain it. Not really a vibration, more of like the stick is bouncing in my hand.

I heard it is due to the leading edge on the up aileron being exposed to the air stream (its like a big block out there). Is this true? Anything that can be done? I'm thinking the only thing would be a total aileron redesign.

carrollcw said:

I have heard this is normal for RV's but figured I'd ask anyway and see if there is a way to get rid of it. When I do a full deflection aileron roll, you can feel the ailerons shutter. Its hard to explain it. Not really a vibration, more of like the stick is bouncing in my hand.

I heard it is due to the leading edge on the up aileron being exposed to the air stream (its like a big block out there). Is this true? Anything that can be done? I'm thinking the only thing would be a total aileron redesign.

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Every RV I have ever rolled does that Clark - it is just letting you know that you are at the end of travel.....

Aileron stall

My 8 does it along with the 7 I've flown , I believe it's the ailerons "stalling " for a brief moment .

g zero said:

My 8 does it along with the 7 I've flown , I believe it's the ailerons "stalling " for a brief moment .

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It is the downward pointing leading edge of the "up" aileron tripping the airflow and burbling. Van's tried VG's on that aileron leading edge years ago to see if they could solve the problem. They never published the results, so they must not have succeeded.

carrollcw said:

Anything that can be done?

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I find that it happens more if my entry speed is higher. At a lower entry speed, I can do a full-deflection roll with no burbling.

My experience has been that the quicker the roll the more pronounced the snatch. As the others say, it's the norm for an RV. But it helps to know that going in. Try rolling more slowly and see if there's a difference.

Chris

Thanks everyone for the feedback. Although not a big deal, it would be nice to have ailerons without all that drag during full deflection maneuvers!

Frise Ailerons

Previous posts are correct that it is caused by flow separation from the nose of the up-aileron projecting down into the airstream, and it has a rather sharp nose radius on that side so the flow separates.

You should be thankful and grateful though - This style of aileron, called a Frise aileron, provides very light stick forces because of the flow around the nose providing an aerodynamic counterbalance.

Changing to a center-hinged aileron would eliminate this buffet at large deflection, but instead, you would have heavier aileron forces all the time. There are other somewhat successful types of aerodynamic counterbalance with curtain seals and blunt trailing edges, but none provide the delightfully light stick forces we all appreciate on the RV's.

If you reduce the aileron deflection just a bit, the buffet will go away, and you will see about the same roll rate - just don't push the stick all the way to the stop, try 3/4 deflection or so.

Easy fix

The Sport wing version of the F1 uses the same aileron shape, and has a similar problem. One ambitious builder decided to fix this problem by curving the bottom of the ribs and skin fwd of the spar - in the same manner as was done on the Bearcat. I'll have to check if this project ever got into the air, but I do recall the builder said the change was easy to incorporate. I think he raised the counterweight tube 3/8"? It could have been 1/4" - it wasn't much. The aileron had a better looking airfoil when finished.

If you are interested in this change,let me know and I'll see if I can find the pictures of the finished product.

The Evo uses center higed ailerons, and these have camber on the bottom. At low speeds, these do have a bit more resistance, but they don't load up nearly as much as the std RV aileron does at higher speeds. Of course, the 'feel' is very different, so a comparison is difficult.

Carry on!
Mark

They all do that. It's not a problem.

chrispratt said:

My experience has been that the quicker the roll the more pronounced the snatch.

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This is not "aileron snatch". That's something else altogether.

My -7A exhibits this same shuddering effect at higher entry speeds, as well...an interesting but not disconcerting phenomenon. Rather interesting, and it would cool to see some sort of fluid dynamics simulation of what's happening (does the airflow exhibit some sort Von Karman Street type of flow aft of the aileron or something like that?).

RV7A Flyer said:

This is not "aileron snatch". That's something else altogether.

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Yeah I think some may be using aileron "snatch" and "buffet" as interchangeable terms. True snatch is when aerodynamic forces move/keep the ailerons in a deflected position irrespective of pilot input. The only airplane I've ever flown that exhibited true snatch was a Giles 202. Actually required slight stick force to return the ailerons to neutral from full deflection. But I understand this can be corrected by adjusting the depth of the aileron hinges by a few mm. Some say all RVs display aileron buffet. Never noticed it in my RV-3 through full deflection.