Roll to the right - thump thump thump

RBD · #1 01-14-2011, 08:30 AM

Until I get more training, the only acro I'll do is wingovers and aileron rolls....at altitude. I've noticed that when I roll right, there is a pronounced "thumping" or buffeting on the the stick. My guess is that is has something to do with the prop wash. Anyone else experiencing this? Is it common? Concerning?

bkthomps · #2 01-14-2011, 08:34 AM

ailerons are stalled, this is normal

I've been doing acro training recently and that was one of the things that surprised me as well

F1Boss · #3 01-14-2011, 08:46 AM

I'm told this is the LE of the aileron, sticking into the airstream. Back off about 10% of deflection, and no more shakey.

Carry on!
Mark

DanH · #4 01-14-2011, 08:52 AM

Normal, although for some reason it is less evident in my new -8 than the last one I flew.

Capflyer · #5 01-14-2011, 09:00 AM

Anyone experience stalls in a tight loop in the RV4? Pulled a tight one and had a couple of bumps over the top.

JonJay · #6 01-14-2011, 09:01 AM

You have nothing to worry about in my opinion but this has been brought up before. I suspect you are using full aileron deflection, that was where I got my "bumps". Technically, according to Van's, full contol input should be limited to less than Manuevering Speed, which for a 4 I believe is 115Kt?
(check your manual or POH). Most people do their rolls at something considerably higher. The real concern is full deflection of elevator above these speeds but I do not believe the manual distinguishes what kind of control input. I will have to go back and check.
I now execute my aileron rolls as mentioned with a touch less than full although if you pull gently rather than snap to full deflection you may find the "bump" is not present even at full deflection.

RBD · #7 01-14-2011, 10:13 AM

Though I don't ever get full deflection to the right (my right hand/wrist hits my knee,) I'll back of the aileron input a little bit and see how she responds.

And good point, JonJay, Va is 115kts (133mph) and I usually pitch up for rolls somewhere around 150mph.

Snowflake · #8 01-14-2011, 12:41 PM

I find that the thumping is speed dependent as well. If I enter the pull-up at 160mph vs. 140mph indicated, the thumping is felt with less deflection at the higher speed. At 140 I can get almost full aileron without feeling it.

But as has already been pointed out, full travel isn't necessary to do a roll in an RV anyway, even at 140.

sandifer · #9 01-14-2011, 01:05 PM

Quote:

Originally Posted by JonJay

...although if you pull gently rather than snap to full deflection you may find the "bump" is not present even at full deflection.

This is a good suggestion - accelerate into the roll input smoothly (but quickly) rather than banging the stick over. Not making any judgments on your technique, but many do have a tendency to bang the stick around. My RV did not exhibit this aileron buffet, but I've heard others mention this technique can minimize the problem. It's also just good smooth technique in general.

Kevin Horton · #10 01-14-2011, 06:32 PM

Quote:

Originally Posted by Capflyer

Anyone experience stalls in a tight loop in the RV4? Pulled a tight one and had a couple of bumps over the top.

Yeah, I've managed to stall over the top of a loop before, especially one day when I was experimenting to see how slow an entry speed I could have and still get around an ugly loop (the answer for my aircraft is 100 kt, if the gross weight isn't too high). Pull too hard, and the angle of attack gets too high and the wing stalls.