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Heavy wing experience

griffg

Active Member
I thought I would share my experience with the heavy wing on my RV-7A.

It began when Van’s shipped two right hand ailerons in my Quickbuild wing kit. When I advised Van’s they then shipped my left hand aileron some months later. But more of that later.

On the first flight Glenn advised that, even with full R/H aileron trim, the aircraft would roll to the left when he let go of the control stick. It especially became very noticeable at speeds approaching 150 Kts. These two photographs show the misaligned aileron trail.

https://flic.kr/p/2onV3bT

https://flic.kr/p/2onSgWk

Subsequently, we downloaded the Van’s “How to diagnose and fix a heavy wing” and worked our way through this document.

The following is what we found and the actions taken initially.

1. The ball in the PFD was centred in cruise flight.

2. The angle of incidence of both wings is 1 degree.

3. The flaps and ailerons on both wings are aligned as per the wing template.

4. I measured the depth from the top of the aileron to the top of the hinge point bolts. The variation between the measurements was 0.012”.

5. We reduced the trailing edge radius of the right aileron and found no observable difference on the flight performed after this was accomplished.

6. Manufactured a trim tab as per Chapter 15 of the Construction Manual and attached it to the right aileron with duct tape. We found no observable difference on the flight performed after this was accomplished.
 
Heavy wing continued

After this we placed a straight edge across between the top wing skin and the aileron top skin and found that they were nicely aligned and found the same result with the wing bottom skin and aileron bottom skin.

One observation from performing this check was that the left ailerons A-802PP bottom skin forward of the spar was concave right from the counterweight back to the spar. It was uniform right across the width of the aileron except where it came up at both ends to attach to the A-704 ribs. View the photo below to see the depth and shape.

https://flic.kr/p/2onSia2

I checked the A-801-1PP rear skin of both ailerons and they were flat on the top and the bottom. View the photo of the bottom skin on the left aileron which is typical of both ailerons.

https://flic.kr/p/2onV64S
At this point we were unsure what the next step should be so we borrowed a L/H aileron (which had a flat bottom in the location where mine was concave) from another builder and installed it to my aircraft. We then went flying and it flew straight and level hands free with a small amount of right aileron trim. To say we were absolutely blown away is an understatement.

Following this astounding outcome I removed all the CS4-4 rivets from the lower surface of the A-802PP Leading Edge Skin and the spar plus the rivets at the A-704 Nose Ribs on the left aileron. View the photo.

https://flic.kr/p/2onWi3T

I reworked the A-802PP skin aft of the A-409 Counterbalance and removed the concave surface so that the skin is flat and in line with the aft skin. View the photo.

https://flic.kr/p/2onWjAx

I rivetted the A-802PP back to the spar and the nose ribs, reinstalled the hinge brackets and installed and aligned the aileron.

We then went flying again and we found nearly a 50% reduction in the heavy wing (i.e. the aileron misalignment in the trail was significantly less).
 
Heavy wing continued

I then removed the A-406 hinge bracket from the left aileron and made slots in the attachment holes and dropped the aileron down by a 1/16 inch. After reinstalling the bracket and aileron we went flying again. This change made another significant improvement but not enough.

I then repeated the above step and increased the slot in the A-406 so that the aileron then sat 1/8 inch lower than originally. After reassembly we went flying again which resulted in about 95 to 98% removal of the heavy wing but still requiring some right aileron trim.

This time I removed the A-406 from the right aileron and made slots in the attachment holes which raised the height of the aileron by 1/16 inch. After reassembly we went flying again which resulted in removal of the heavy wing effect and no aerobatics initiation due to the ailerons being in neutral trail.

We have arrived at a configuration that has neutralised the aerodynamic forces that were causing the ailerons to be misaligned in trail and which made the aircraft want to roll left into an aerobatic manoeuvre.

View the photographs for the height and alignment of the L/H aileron.

https://flic.kr/p/2onShRg

https://flic.kr/p/2onShuK

View the photographs for the height and alignment of the R/H aileron.

https://flic.kr/p/2onWiDs

https://flic.kr/p/2onX7Bw

What have I learnt from this.

1. The loan aileron was almost identical in shape to my R/H aileron. This made the aerodynamic forces act equally on both ailerons.

2. I have checked my son’s ailerons on the RV-8 he is building and they were identical in shape to each other and you could probably call them a matched pair.

3. My two ailerons were not a matched pair, even after my careful rework, so I had to make unusual adjustments to accommodate and neutralise the aerodynamic forces.

I hope you have found this interesting and informative.
 
Excellent work.
I assume you had a loaded passenger seat?
A well balanced side by side will want to fall to the left due to the weight imbalance when flying solo.
I only mention this as I have seen folks chase a heavy wing that wasn’t.
 
Super interesting. That was a lot of work for you. I’m hoping that this doesn’t happen to me but I’m glad that there is a solution if so.
 
Excellent work.
I assume you had a loaded passenger seat?
A well balanced side by side will want to fall to the left due to the weight imbalance when flying solo.
I only mention this as I have seen folks chase a heavy wing that wasn’t.

Hi Jon,

The passenger seat wasn’t occupied, but this was a heavy wing way beyond the ability of the aileron trim to correct. It was a head-scratcher on such an immaculate build.

The big symptom was the deflection of the ailerons, as shown in the photos. This imparted a roll, which naturally became stronger as speed increased. The aircraft couldn’t be flown hands-off. I hadn’t yet encountered an RV that was so far out.

Thanks to Gordon’s systematic changes, particularly to the hinge heights, the aileron asymmetry is now gone and a fine tweak of roll trim is all it needs in flight. The aircraft now flies as well as it looks, so we can continue with Phase 1.

Glenn
 
Thanks for the detailed posting of your journey. I had a significant heavy wing on my 7 and went through the vans document. I did look at the aileron flatness aft of the spar but not ahead.

I changed the aileron pivot bracket(s) positions to effect the desired balance but am still not satisfied that the airfoil profile is true.

I found an RV6 (I suppose it could be early 7) drawing from vans where they recommend making a plywood template. The instructions indicate using it to identify any aileron pivot placement errors that will offset the aileron relative to the airfoil profile. This template is currently being constructed with some alacrity as the plane does fly nicely balanced inspire of my lack of confidence in the correctness of my "fix".

You are commended for a description is an outstanding example of reporting.
 
T
I found an RV6 (I suppose it could be early 7) drawing from vans where they recommend making a plywood template. The instructions indicate using it to identify any aileron pivot placement errors that will offset the aileron relative to the airfoil profile. This template is currently being constructed with some alacrity as the plane does fly nicely balanced inspire of my lack of confidence in the correctness of my "fix".

You are commended for a description is an outstanding example of reporting.

If I recall correctly, Vans sent a full scale template drawing with the intent to make the template out of the crating. Seemed to work very well.
 
Thanks for posting Gordon, and glad to hear you have it sorted.

(You had me run out the back to recheck mine with a straightedge! 😬)
 
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