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  #1  
Old 09-05-2017, 07:29 AM
flyenforfun's Avatar
flyenforfun flyenforfun is offline
 
Join Date: Aug 2009
Location: Wilmington DE
Posts: 320
Default Baffling heavy wing issues

Perplexing heavy left wing problems.
I finished my -8 back in 2012 and on the initial flights we had a heavy the left-wing. We tried everything that vans told us to do and more ideas from vans Air Force forum. Nothing seems to work except re-drilling and lowering the left aileron out board hinge however that caused us to have a heavy right wing but with almost full left aileron trim it flew straight and level so I've lived with that band-Aid fix for about five years. Now I have decided to revisit the problem and try to fix it properly. This weekend I raised the left hinge 1/16 of an inch hoping that I would be able to trim the plane closer to neutral position. So what's happening now is with the trim in neutral position the faster I go the more the plane wants to roll to the left and the slower I go the more it wants the rollback to the right The strange thing is that if you hold the stick in level flight both Ailerons are in line with the wingtips and flaps which makes me think that there is some kind of airflow issue going on that I can't see. I've tried all of the standard fixes like rigging, squeezing trailing edges, trim tabs and even built a brand new right the Aileron i've had various results but no eureka moments. I feel like I'm missing something and not looking at the right thing. Any ideas? I would love to find the smoking gun. I believe everything is set right i.e. Rigging, wing incidence, wheel pants and fairings. Somehow somewhere I am inducing drag and the drag increases as speed increases and vice a versa. Maybe someone on this forum can think outside the box and give me an idea of where else to look.
Thanks.
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  #2  
Old 09-05-2017, 10:52 AM
rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 6,781
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If it fly's straight when the ailerons are held aligned it is an indicator that asymmetrical aerodynamic influences on the ailerons are forcing them to displace which then makes the airplane roll.
You may be chasing the displacement influence back and forth by making small changes.
Have you done actual measurement checks of the aileron flatness, and their position relative to the wing?
The current Rev. Section 5 of the construction manual has details regarding checking for proper aileron shape.
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  #3  
Old 09-05-2017, 01:40 PM
Aluminum Aluminum is offline
 
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Location: San Jose, CA
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Default

Quote:
Originally Posted by flyenforfun View Post
Perplexing heavy left wing problems.
...
I feel like I'm missing something and not looking at the right thing. Any ideas?
Twist in rudder/vert stab?
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  #4  
Old 09-05-2017, 04:00 PM
sblack sblack is offline
 
Join Date: Dec 2009
Location: Montreal
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When you change speed, are you holding the stick so it can't move?

There are 2 things that the ailerons produce - a force vector and a hinge moment. The force vector is simply the lift on the aileron, which rolls the airplane. The hinge moment is the twisting force about the hinge line, which gets turned into a push or pull force on your aileron push rod that comes into the torque tube on which the stick is mounted. If the left and right hinge moments are well balanced then all is good. If you have something odd, like the aileron is high, or warped, or the trailing edge is poorly formed on one aileron and not the other, then the ailerons will float to some non zero deflection in order to balance the forces on each pushrod. This will change the roll trim and drive you nuts.

So, do you have an asymmetry on the aileron lift? Or do you have an asymmetry on the hinge moment? Or do you have a twisting wing or wing tip?

You can see that it can be a really difficult thing to pin down. If you want to eliminate the hinge moment, when you test hold the stick to prevent it from deflecting laterally, so even if there is asymmetric force from the aileron push rods it won't affect the aileron position. Also, any testing you do has to have the ball absolutely centered, or it is meaningless. Sideslip generates roll.

YOu say you believe that the wing twist and incidence are good - how did you measure it? Just because the ailerons align with the tips and the flaps is not telling you much - the flaps and tips can be off, by a mile. You need to make accurate templates that will sit on the wing by themselves with out falling over, level the airplane and put those templates along the wing in various places with a very accurate inclinometer and check the wing incidence at various spanwise locations. The templates should also tell you if your flaps and ailerons are aligned with the wing profile both at their inboard and outboard ends. There is something off somewhere that your current measurement methods have not identified. Assume nothing, believe nothing until you have measured it. Are the ailerons or flap TEs bowed?

After that, start looking at any difference in the aileron cove - the space between the rear spar and the aileron that has that bent piece of sheet that fills in the space. Same with the flap. Something has to be off somewhere, but you have not been picky enough to find it. My bet is that if you search long and hard enough, you will find it on the ground.

A final thought, though it is a long shot - do you have a massive lateral imbalance in the airplane? A horrendously heavy landing light on one side? That would give you a roll trim requirement that would change with speed. Just a thought - hard to image that you have something like that. But I wouldn't take anything for granted.
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  #5  
Old 09-05-2017, 10:28 PM
PilotjohnS PilotjohnS is offline
 
Join Date: Jan 2016
Location: Los Angeles
Posts: 301
Default Rudder trim

Are you sure the plane is flying straight? With the main section of each wing at the same angle of attack?
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  #6  
Old 09-06-2017, 03:51 AM
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swisseagle swisseagle is offline
 
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Location: 20km outside of Zurich, Switzerland
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What does the Inklinometer shows? Ball always in the center at the different speeds?
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  #7  
Old 09-07-2017, 06:21 AM
Capt Capt is offline
 
Join Date: Feb 2017
Location: Australia
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As we all know an increase in speed will change an aircrafts balanced trim position and require retrimming. Eliminating aileron control position by having them both streamlined, fuel tanks equal quantity, ensuring wing tips are both accurately placed and the fin/rudder are aligned correctly I would be looking closely at the empennage specifically the tailplane and each elevator, this area is often overlooked if a plane wants to roll when speed is increased.
Keep researching -
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  #8  
Old 09-07-2017, 09:12 AM
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az_gila az_gila is offline
 
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Location: 57AZ - NW Tucson area
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Smile

Set the controls to neutral, take a digital level and measure left and right control surfaces, flaps, ailerons and elevators every 6 inches along their span.

This will identify any left/right imbalance and any control surface twist.
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  #9  
Old 09-08-2017, 06:29 AM
John-G John-G is offline
 
Join Date: Jan 2012
Location: Northeast Ohio
Posts: 442
Default Check wing skin aft of rear spar

I'm not sure if this will help you .... but I'll throw it out there for you to consider. My RV-12 had a slightly heavy left wing which was solved by tweaking the wing skin aft of the rear spar. A straight edge placed parallel to the ribs was used to insure the metal aft of the rear spar was in alignment with the wing skin.

On my RV-12, some areas aft of the rear wing spar were a little low and others were a little high on both wings ... after using a small block of wood to bring the metal into alignment with the wing skin forward of the rear spar, the heavy left wing was gone.

Happy flying,
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  #10  
Old 09-08-2017, 01:04 PM
N999BT N999BT is offline
 
Join Date: May 2005
Posts: 189
Default I have the same issue

My airplane started out with a heavy right wing, with the forces increasing the faster I went. I squeezed the left aileron, and it helped but didn't fully solve the problem. In normal cruise, which for me is 8 gph and about 174 KTAS, I have a nice neutral stick. In the pattern, at slow speed, my plane rolls left, but forces are low, so no real issue. The problem is that when I race, the right roll becomes very pronounced and takes a lot of stick force, especially at the end of the race when you are diving for the finish.

I talked to Burt Rutan about it, since he has taken up residence at my home airport. He said, "If it bugs you, put a trim tab on it." Not really the answer I was looking for. For the last several years, I have taped a trim tab on using 230 mph tape, and it works for racing, but I don't really consider this a satisfactory answer.

I have measured my wings several times, and they appear to be straight. I know that my rudder has a trim tab, that is great for cruise, but I also have to use some rudder pressure to keep the ball centered when going fast. I have thought about repositioning the rudder to center the ball at high speed to see what that would do, but I can't see it really solving the roll problem.

I have been thinking about modifying the aileron location up or down, probably down, on the right side thus helping the aileron deflect down, with a higher lift component.

I do agree with a previous post that the issue has to be related to wing, tip, or aileron geometry. For me, I have changed the tips when I race, and no appreciable change, so I think I have eliminated that. I have done the template thing with my wings, and am not able to identify anything. I have not closely looked at the slot between the ailerons and wing, so I will do that.

Very interesting thread, I will keep watching.
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