Wing incidence

[lucaperazzolli]

RV8 QB Planning questions :

Do you think it's possible to drill the wing incidence with tha 'last' bottom external skin (QB Wings) only clecoed and not riveted ?

How much time do you spent for doing this process (drilling wing incidence)?

Thanks for helping

[Kevin Horton]

Sure, it should be possible to set the incidence and drill the holes without that bottom skin on, as all the measurements to set the incidence are on the upper surface. However, every wing ends up with tiny amounts of twist, no matter how careful you are. Many builders will measure the incidence at several locations along the wing span and average the results - this helps negate the effect of any wing twist. If you haven't yet riveted the lower wing skin, it is possible that the wing as riveted will have a different amount of wing twist than it had when you set the incidence. If you want the best chance for a straight aircraft, it is better to set the incidence after you have riveted all the wing skins.

When setting the incidence, I spent perhaps a half hour getting the wings installed, then about three hours messing around with plumb bobs and levels to get everything perfect. Then I stopped for the night, and measured everything again the next evening to be sure it was perfect. Then I drilled the holes. Total time - about five hours spread over two sessions. It would go much quicker if you aren't too picky.

[Norman CYYJ]

I agree with Kevin. After several planes and seeing the twist that the wings can have I always rivet the skins on before setting the angles, also a few breaks between each to make sure things are straight. You only get one chance and you can't fix it up if you screw up.

[lucaperazzolli]

Well ! Understood, I'll rivet them completely before setting the incidence.
Doing this I have to wait my next inspection so I post another question:

it's possible to set the wing incidence with the fuse on the gear (def installed) ?

if yes, there are some advice about this procedure.

Let me know and thenx in advance

Luca

[pierre smith]

Luca,
You can set and drill the rear spars for incidence with the gear on but off the floor. You need the airplane very stable with no movement possible, levelled fore and aft and sideways. We jacked the airplane under the motor mount bolts with two bottle jacks.

We used a builder's transit a few feet away from one wingtip, drilled the rear spar and while the transit was left in the same place, shot a sight across the fuselage and drilled the other wing spar.

Regards,

[lucaperazzolli]

Hi,

today I've drilled the wing incidence, everythings goes well but I have a little question.

Gus told me that the wings must have the same reference angle of incidence of my horizontal stab ( 0.1 aft up ), I did.

Both left & right wing have 0.1 aft up, horizontal stab 0.1 aft up, fuselage was level @ 0 degrees, same distance from tips to fuse center point, perfect wings allignment , left 3.4 degrees @ wing tip (dihedral angle) and 3.3 right wing, 5/8 close tollerance but in tollerance !

Opinions ?

Thanks in advance

[Jerry Cochran]

I hesitate to mention this and possibly expose ignorance, but in setting incidence and making sure wings have the same dihedral, I used water levels almost everyplace. Take that back, I borrowed a digital level for wing incidence.
However, using clear plastic tubing strung between wingtips sure is an easy way to assure level. Also, longeron fore and aft and sideways.

After a little experimenting, decided that .25 ID tube would not have enough capillary action to inhibit accuracy. It all seemed to work, my -6a is fast, flies straight and true.

Plumb bobs and water levels were used by the ancient Romans, and are only wrong if gravity is... :-)

Jerry

[Kyle Boatright]

There is no reason you can't set wing incidence without all the skins final riveted. Just make sure to have any unrivited skins cleco'd in place.

By the time I mounted the wings, measured, pulled both wings, trimmed the aft spar mounts, remounted the wings, measured, trimmed some more, remounted the wings, and finally drilled the things, it took about a day with one of my friends assistance.

At that time, the factory recommended measuring the incidence at about 2/3 span to average out any twist in the wings. Worked well for me.

Among other things, I needed 4 plumb bobs, a digital level, a water level, and a tape measure to position the wings for drilling the "big" hole.

My airplane flies very straight and true, so all the effort paid off.