[VF84Sluggo]

With my new-to-me RV-8, I've noticed a 'heavy' right wing. Need at least a 5 gallon differential for a neutral feel. Before I go squeezing ailerons (I won't even THINK about fooling with wing incidence), I was looking at the flaps. Neither one retracts flush with the fairing, and both seem to be about the same distance from their respective fairing when retracted.

I was hoping to see the left flap a bit more extended when in the "UP" position, and perhaps causing the right roll/heavy wing. And it might be, if those fairings aren't in identical positions (I assume.)

I've posted pics below. Is this gap normal when the flaps are up? Any thoughts on adjustments for this right-roll tendency?

Thanks!

 

[michjor]

The gap isn't normal, and the wing imbalance could be from many other sources. How bad is it? Something trimming out can't solve, when I fly switching fuel between left and right wing I always end up with one heavier than the other and need to trim to get level.

I'd look at the flap retraction separately.

 

[Carl Froehlich]

No, not normal.

Rigging is never “one and done”. The best process I’ve found is:
- Get the flaps all the way up, with left and right perfectly matched.
- Once the flaps are up, clamp the left aileron trailing edge with trailing edge of the flap. Now compare how the right aileron trailing edge lines up with the right flap trailing edge.
- If there is a difference, first corrective action is to adjust the aileron push tubes so they do match.
- Go fly. Take more data.

If you still have a problem you need to check:
- Any twist in a flap?
- Any twist in an aileron?
- Are the aileron symmetric with the top wing skin trailing edge (inboard and outboard)?
- Do the ailerons have the same height to an extension of the top skin (as in using a straight edge across the skin to aileron with the aileron clamped to the raise flap? Again compare the two ailerons at both inboard and outboard locations.

Whatever you do defer any aileron trailing edge squeezing until you check the more common causes for a heavy wing. Consider aileron squeezing as a very fine adjustment to a good rigging, not a fix to a bad rigging.

Carl

 

[fl-mike]

I would check the rigging first, per the manual.

Pull the wing tips
Use the end wing rib tooling holes to line up the aileron trailing edge (see plans for the tooling hole fixture (sheet 12A)),
Use the bellcrank fixture to check or set the pushrod lengths.
Once the ailerons are rigged, then you set the flaps to match the ailerons.

(and hope the wingtips line up with the ailerons!)

After that, if you still have a heavy wing, Van's has an article on the Vans website that tells how to check and correct. (for the pre-punched wings, you basically squeeze the light wing aileron TE (just a little!) as the aileron hinge brackets aren't builder drilled anymore.)

Good luck. I'm about to do this exercise with a fellow 8 owner with a heavy wing.

 

[PhatRV]

The gap at the flap/fuse intersection should be very small in the range of 1/32" measurements. You can close up the gaps by adjusting the flap pushrod length from each side. The flaps were probably removed for painting and the reassembly was probably not done correctly. This is an easy fix so do this first.

Work one thing at a time and recheck.

 

[VF84Sluggo]

The gap isn't normal, and the wing imbalance could be from many other sources. How bad is it? Something trimming out can't solve, when I fly switching fuel between left and right wing I always end up with one heavier than the other and need to trim to get level.

I'd look at the flap retraction separately.

"Need at least a 5 gallon differential for a neutral feel."

Again, need to burn at least 5 gal out of the right wing to relieve rolling tendency...maybe a bit more.

 

[VF84Sluggo]

No, not normal.

Rigging is never “one and done”. The best process I’ve found is:
- Get the flaps all the way up, with left and right perfectly matched.
- Once the flaps are up, clamp the left aileron trailing edge with trailing edge of the flap. Now compare how the right aileron trailing edge lines up with the right flap trailing edge.
- If there is a difference, first corrective action is to adjust the aileron push tubes so they do match.
- Go fly. Take more data.

If you still have a problem you need to check:
- Any twist in a flap?
- Any twist in an aileron?
- Are the aileron symmetric with the top wing skin trailing edge (inboard and outboard)?
- Do the ailerons have the same height to an extension of the top skin (as in using a straight edge across the skin to aileron with the aileron clamped to the raise flap? Again compare the two ailerons at both inboard and outboard locations.

Whatever you do defer any aileron trailing edge squeezing until you check the more common causes for a heavy wing. Consider aileron squeezing as a very fine adjustment to a good rigging, not a fix to a bad rigging.

Carl

Thanks, Carl. Very orderly approach to solving this. I really like your closing sentence.

RC

 

[71459]

Don't squeeze down the ailerons! It's not a true fix - it just adds additional out-of-trim aerodynamics into the airframe.

 

[VF84Sluggo]

Good to know. Haven't done that. In the info-gathering, troubleshooting phase.

Glad I thought to take a look at the flaps in the full-up position, see if that is a start for figuring this out. Also glad I took those pics today and post them.

Must admit, I'm a little reluctant to mess with the flap push-rods, but I can probably figure it out This big 3/8+ inch gap needs to be fixed.

 

[RV7 To Go]

I would check the rigging first, per the manual.

Pull the wing tips
Use the end wing rib tooling holes to line up the aileron trailing edge (see plans for the tooling hole fixture (sheet 12A)),
Use the bellcrank fixture to check or set the pushrod lengths.
Once the ailerons are rigged, then you set the flaps to match the ailerons.

(and hope the wingtips line up with the ailerons!)

After that, if you still have a heavy wing, Van's has an article on the Vans website that tells how to check and correct. (for the pre-punched wings, you basically squeeze the light wing aileron TE (just a little!) as the aileron hinge brackets aren't builder drilled anymore.)

Good luck. I'm about to do this exercise with a fellow 8 owner with a heavy wing.

You can purchase undrilled A-406 aileron hinge brackets from Vans. Had to do this on friends RV a little while ago. Slot the drilled ones first to find the location needed to correct the heaviness then drill the undrilled bracket to the new hole location.

 

[rv8ch]

Is this gap normal when the flaps are up? Any thoughts on adjustments for this right-roll tendency?

That is very very far from normal. I recommend a call to the factory and to find a good local RV-aware mechanic. I would fix the flaps before looking at the wing imbalance.

 

[VF84Sluggo]

I would fix the flaps before looking at the wing imbalance.

My thoughts at this point exactly. This flap mis-adjustment could be the wing-heavy cause.

 

[VF84Sluggo]

Next time I go to my hangar, I want to look at something I didn't pay close enough attention to yesterday:

I'm curious if the aileron/flap/wintip trailing edges are all lined up with the flaps adjusted in the current slightly extended position.

If so, just trying to visualize it sitting here, that'll mean that with the flap-up postion being readjusted, and the ailerons adjusted to align, then the aileron trailing edges might be slightly above the wingtip trailing edges. Hmmmm.....

 

[PhatRV]

The ailerons should be aligned using the tool holes drilled in the outer ribs. There is a drawing for this particular item.
On my RV8, after the ailerons are mounted and aligned, I fitted the flap and aligned it to the trailing edge of the aileron. Then the flap/fuse intersection plates are fitted and riveted to the fuselage. When the flaps are remounted after moving or reassembly, the flap/fuse intersection plates should serve as the alignment guide to ensure everything is back to where it was. This assumes all the parts are straight at the start.

 

[Carl Froehlich]

The ailerons should be aligned using the tool holes drilled in the outer ribs. There is a drawing for this particular item.
On my RV8, after the ailerons are mounted and aligned, I fitted the flap and aligned it to the trailing edge of the aileron. Then the flap/fuse intersection plates are fitted and riveted to the fuselage. When the flaps are remounted after moving or reassembly, the flap/fuse intersection plates should serve as the alignment guide to ensure everything is back to where it was. This assumes all the parts are straight at the start.

Yep - this is what Van’s says to do, however….

The “align with the tool holes” or “use the aileron bell crank jig” to set the ailerons is, in my opinion, a good starting point. I do not consider this to be a complete rigging process.

In particular, I would not be surprised if the current flap low problem reported by the OP is a result of setting the ailerons rigging then aligning the flap trailing edge to the aileron trailing edge, but never doing final checks. I recommend always rigging the flaps fully up (and identical left and right) then working out from that. I personally know of one RV that had a heavy wing for years. One flap was 1/4” lower than the other. Once properly rigged the heavy wing was gone.

I offer careful measurement using straight edges the wings to determine flap and aileron mounting height should not be overlooked. This is how you find the notorious “one end of the aileron is lower in the breeze than the other”. I refer back to the post on no hole aileron brackets as the cure.

Side note. Back before prepunched everything Van’s wing shipping crate came with a full size wing cross section drawing on the crate plywood. Careful cutting transformed this drawing into a very good aileron and flap rigging jigs. I kept these from my first build and still find use for them on other RVs.

Carl

 

[Mikeyb]

Next time I go to my hangar, I want to look at something I didn't pay close enough attention to yesterday:

I'm curious if the aileron/flap/wintip trailing edges are all lined up with the flaps adjusted in the current slightly extended position.

If so, just trying to visualize it sitting here, that'll mean that with the flap-up postion being readjusted, and the ailerons adjusted to align, then the aileron trailing edges might be slightly above the wingtip trailing edges. Hmmmm.....

Believe it or not you don’t have to fret about the wing tip alignment. The consensus is it doesn’t have much effect. It’s seems like it is almost always related to the aileron alignment to the wing. Check the aileron alignment to the wing tooling holes and the hinge alignment first.

 

[Scott Hersha]

I would follow the company advice on how to fix a heavy wing, in the order described:

How to Diagnose and Fix a Heavy Wing - Van's Aircraft Total Performance RV Kit Planes

If there is one question that requires a lot of time answering at Van’s it is the ” I just did my first flight and a wing is heavy, what do I do?” question. It usually is followed by the corollary “which aileron am I supposed to squash?” There turns out to be a bit […] Read More

www.vansaircraft.com

If all of that doesn’t fix it, then you’ll have to get creative, but I would follow the Vans directions first.

 

[VF84Sluggo]

Yeah, I read that missive from Van's. Most beyond what I want to tackle. Not gonna make new brackets and start drilling and riveting. The plane's likely been like this since it was built.

I'll adjust that flap gap and fly. Maybe leave one a tad more down than the other and see if that helps. Otherwise, just easier to just burn out of the right tank and live with it.

Thanks for the inputs. I do appreciate it.