Why can't there be an adjustment of aft Wing Spar attach?

People: I think there should be a better way then to permanently drill the aft spar before the first flight. You are fixing the incidence angle and if you end up with a heavy wing, you are resorted to moving the ailerons around or worst yet a tab.
Production aircraft have cam eccentrics which allow adjustment. My temptation is to fix the one wing with the standard AN5 bolt and use an AN3 or 4 on the other side just to get the airplane in the air to check how close one is to being in rig with the other wing. Granted this is beyond the scope of this forum to do the engineering analysis of such a practice, or the associated hazard, but would like to open it up for discussion if someone out there has a better method and or idea.

There is very little wiggle room on the rear spar and maintain bolt hole edge distance. With the main spar secured in the centersection, aligning the rear spar to the edges of the rear spar "box" puts a fair amount of twist on the mainspar, and you can feel it when moving the rear spar up and down.

I think the more opportunities you give an amateur builder to "change" a proven design, they'll screw it up.

I found aligning the rear spar to the middle of "box" fully met the alignment criteria in the plans. If a person finds a heavy wing during flight, the root of the problem is something other than wing incidence. Most likely heavy wing is related to miss positioned/twisted flaps or twisted wingtip. It doesn't take much misalignment of the wingtip to create a roll force. Aligning/attaching the wingtips is kind of a precarious process. People pinch aileron edges to compensate for roll issues, but I think that simply masks the root cause.

I had no heavy wing out of the gate.
Just my observations and experience.

Eccentrics

Cessna uses eccentrics. Note they also sweep the wing forward and aft so much that the inboard wing fairings are adjustable. I considered this for an RV but figure it's not worth the effort as the wings are not likely to ever come off, and easy to build true. I imagine it's possible to drop a flap, aileron and wing tip to fix a heavy wing, if you had to, and no one would be able to spot it without careful measuring.

wingtip alignment causing heavy wing

rv9av8tr said:

... Most likely heavy wing is related to miss positioned/twisted flaps or twisted wingtip. It doesn't take much misalignment of the wingtip to create a roll force. Aligning/attaching the wingtips is kind of a precarious process. People pinch aileron edges to compensate for roll issues, ...

Click to expand...

I agree with this, it takes care to get the floppy glass tips aligned with no droop, which in this case, the droop equates to effective twist and rolls the airplane.

A friend of mine drilled the rear spar for an AN4 bolt for the first flight. It was left wing heavy. With a 1/32" adjustment and redrilling with a drill bushing then final reaming for an AN5 bolt, it became right wing heavy. It took that little of a difference in incidence to make a difference. Wingtip alignment makes little difference since its been proven that wingtip trim tabs don't work.

scsmith said:

I agree with this, it takes care to get the floppy glass tips aligned with no droop, which in this case, the droop equates to effective twist and rolls the airplane.

Click to expand...

rocketbob said:

A friend of mine drilled the rear spar for an AN4 bolt for the first flight. It was left wing heavy. With a 1/32" adjustment and redrilling with a drill bushing then final reaming for an AN5 bolt, it became right wing heavy. It took that little of a difference in incidence to make a difference. Wingtip alignment makes little difference since its been proven that wingtip trim tabs don't work.

Click to expand...

Just a data point FWIW.... I have had a heavy left wing since day one. It's the one thing that really annoys me about my plane. I had to slot BOTH ailerons to get it right. I've always been curious about the tips and how much affect they have on the problem. A good friend of mine said to take the tips off and go fly it. He's retired Navy with an Aeronautical engineering degree and said it wouldn't make any difference. I did this recently (after 8 years of flying) and he was right! Go figure. The plane still had a heavy left wing.... The main thing I noticed was stiffer than normal control inputs, but the heavy left wing was still there. At least in my case the tips are NOT the problem.

Regards,

Drill Bushing

Rocket Bob:

You mentioned above your buddy redrilled the AN4 to an AN5 with a drill bushing. Help me out here please as to what this process entailed? For I have never used a "Drill Bushing".

Thank you.

I know of two local RV's where one had rigged the flaps to match the aileron, which when you put a straight edge on the top of the wing, the two flaps were not in the same relation to the wing. The other had a twisted wing tip which was hard to detect by just eyeballing it back and forth. You have to use straight edges to compare. He split the trailing edge of one wingtip and re-glassed it. Both cases of heavy wing solved.

I think the key to drilling the aft spar hole is to just make sure they are both in the same position. Using the plans method for checking with a level across the top of the wing seemed to me to have far more variability than just placing the the rear spar in the middle of the drilling "box". Just doing that met the level criteria.

There are so many places in a build to create rigging issues but the key is ensuring what ever you do is watching symmetry.

I think the instructions are a little vague on where exactly to measure from on the wings to set the incidence. When I first started it appeared the the skin joint (9A) was the place with a specific height spacer centered on the line of rivets at the aft end. In other words it seems that it would be very hard to get both sides exactly the same.

I ended up with some help (thanks Al and Tim) and we used a transit to set the incidence and I can say with certainty that it is set the same to +/- something less than .015". And I ended up almost EXACTLY in the center of the rear spar.

I know the cases of wing heaviness isn't as pronounced in the 9's as it is the others, but mine exhibits no heavy wing when balanced side to side on the weight.

I followed the pdf instructions that supplement the manual to set wing incidence/ drill rear spar hole and used the end rib tool holes to align aileron and flap. No heavy wing.

I went to a lot of trouble to insure that my RV6 wings, flaps & ailerons, and tips, were in exact alignment. I didn't want the possibility of adjustments for rigging problems, which create drag, as well as opposite roll, depending on air speeds.

I ended up with a heavy right wing. The left aileron trailing edge, which is bent in a brake for the RV6 had just a bit more radius than the right. After a bit of minor flattening, the wings are perfect, symmetrical, and you can see just how even everything matches, in cruise, and usually the climb as well.

I wouldn't want Cessna type adjustments, when a good alignment solves the issue to start with.

I agree

L.Adamson said:

I wouldn't want Cessna type adjustments, when a good alignment solves the issue to start with.

Click to expand...

The purpose for the cessna type adjustment is to "fix" manufacturing tolerance build up issues and repairs that aren't quite right. We get to control both as the labor involved doesn't cost us extra.

Outboard Aileron hinge

I had a heavy right wing, I ran through van's trouble guide and after lots of measuring, I determined my right outboard aileron hinge sat up too high. I plan to write this up on my log but you can measure the plans, they are full scale.

You will see that with a straight edge along the top of the wing, and sitting on top of the curved part of the aileron there is about 1/32 of daylight between the wing skin and the straight edge laying the top at the trailing edge of the wing skin. My left aileron hinge was perfect the right sat high. I slotted the right hinge bolt holes some to lower it but did not want to over do it, it still sat a bit high. It helped but did not take the heaviness out. After 20 hours flying like that I finally got around to slotting it some more, this time shooting for 1/32 daylight in the spot I mentioned above. Took her flying and now no heavy wing. The heaviness was worse with increasing airspeed, but after matching the ailerons I flew up to 180 knots plus and no heaviness.

My ailerons are QB, and they looked identical, the only variable was me riveting the aileron hinge bracket, the one with he bearing in it, onto the wing rear spar. There must be some way to drill that off to cause this issue was also seen on a new flying RV-7 here had a heavy wing, the heavy wing aileron sits high compared to the other side and compared to the drawing

Food for thought

Cheers

I'm certain that our wing alignment is spot on... we check ... double checked ... triple checked and then re double tripple checked every measurement for two weeks before we drilled the holes to 1/8 then re checked every double check again as we stepped the hole up to final size.

We were so careful with every measurement we were rather suprised when our right wing was a little heavy.

We double check every thing as were a little perplexed as to what we did wrong. At that point one may have considered adjusting one of the wings ... because that must be the problem.

So were sitting there one night looking at the amazing machine we built and it kinda smacks ya in the head.

Well DUH ... there is a heavy auto pilot servo sitting 15 feet out on the right wing well that explains a lot! Tweaking one of the wings would have been a bad solution to that problem.

A few inch strip on the left aileron to make up for the heavy weight in the right ... flies poerfect

Levels sold in hardware stores are not accurate enough for building airplanes. I use a machinist level that is far more accurate. They cost more but are well worth it. Any place selling machine tools will have them for a couple hundred dollars.