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autorowt8

I'm New Here
My father has an RV-4 160hp fixed pitch. With the aircraft trimmed for cruise at 70% power (he's typically between 2000-5000ft) the control forces become rather heavy and even minor pitch changes result in a what he describes as elevator buffeting until stick pressure is released. Is this normal and if not, what could be the cause?
 
Long Shot

Check the trailing edges of the elevators and make sure:
1. They line up with each other so one is not higher than the other.
2. Make sure there is not a twist in the trailing edges of the elevators.
3. If he is getting buffeting, I wouldnt fly it until it is fixed.
 
Could his elevator hinges be offset in a vertical direction?

This could screw up the shape of the horizontal stab. airfoil.

And, if you disconnect the elev. drive at the horns, do the elevators move freely?
 
Is this a new thing or has it always been there (and how many hours)?
What do the wing root fairings look like (both shape/style and condition)?
 
Check the trailing edge of the elevators and see if they are pinched down too much. My previous elevator trailing edges were so I replaced them with new elevators. Took away the heavy control forces that I experienced. With my previous elevators even taxing on the ground it took a lot of control pressure to hold the stick back.
 
Not normal

What you are describing is definately not normal. I have same set up, 160hp and fixed pitch prop, which should be irrelivant anyway. I have flown several different RV's and never is there any buffet in pitch,and stick pressures are light and proportional to speed. It is common to get buffet in full aileron deflection due to "stalling" (feels like a series of bumps)because of its angle of attack, but your situation is far different. I would fully inspect everything in the tail, and verify the elevators are actually balanced. How long has this been occuring? I would have to assume this is either a new aircraft or newly aquired aircraft, and not something that has just started happening.
 
autorowt8 said:
My father has an RV-4 160hp fixed pitch. With the aircraft trimmed for cruise at Is this normal and if not, what could be the cause?
Click to expand...

No and I have had a friend with an RV-4 that encountered this and it was because one of his elevators was oil-canning. He filled an area with expanding foam and that stopped it but he ended up building a new elevator.
 
Response to answers

There's a lot of good information here and I apologize for the delay, my flight instructor (the old man) is on a trip and can't fly his own plane while he's flying other peoples airplanes. Don't be surprised if he responds under my "nom de guerre".
 
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