Wing incidence

For those who built their plane, what would be an accepted maximum degree of positive incidence in order to maintain the bolt edge distance? On our rebuild project, in order to match both wings and still have proper bolt edge distance our digital level shows .04 positive. We had to replace the rear spar carry through due to mis-aligned and extra holes, so I have no idea what it was before we took the wings off for transport.

The builders manual indicates that 0.5 positive is "desired" If you're within acceptable edge distance, I'd say bolt it on.

Incidence measurement ?

I did not find a spec in my plans for -3B rebuild. What does .4 or .5 mean and how is it measured ? In the absence of this information, I installed the ( used ) wings to the NEW fuse assuring edge distance & equal incidence on both wings. Obviously, the precision of rear spar bolt holes in the used wings is significant.

Thanks Joe. I have a second hand builders manual and must have overlooked the incidence specs. I was under the assumption it was zero or level with the fuse. All I found was the section that has a drawing on the setup which shows how to make the block for the wing level. The illustration also shows a level on the fuse top longeron and a level on the wing. When we set both to zero the wing attach brace sticks up above the carry through bar over a 1/4" and the gap between the fuse skin and bottom of the wing is worse than that. When the attach point on the wing is down in the carry through where it should be and clamped in place, all the old wing fairing rivet holes seem to line up almost perfectly. This gives us .04 positive incidence and the required 5/8" bolt edge distance.

in the end, the it is the relative incidence angles of the wing and HS that are the most critical.

Ensure that the two wings have identical incidence, then adjust the HS according to the instructions. I measured the wing incidence at each rib station, then averaged it. Both wings should have the same average. This helps to remove the aerodynamic effects of any minor wing twist.

Wing Incidence

Arlie -

If you are referring to SK-51 Setting Wing Incidence Level, the 2.8" block sitting on the aft spar "sets" the wing incidence to 1/2*+ to the fuselage when the level that spans the two spars is indicating level.

As noted above, if you can't get the design incidence (for whatever reason), you can fudge a bit one way or the other. But if the F-404 bulkhead (spar carry through) was installed correctly, it is also at 1/2*+, and aligning the wing at some other incidence introduces torsional stress in the main spar at the wing root where it enters the fuselage.

The Horizontal Stab is set at 0* to the fuselage, as shown in SK-48 Leveling of Horizontal Stabilizer. So the stab is set at 1/2*- to the wing. I don't know how old your airframe is, but, if checked, you might find the stab set at the wing incidence or slightly above. Way back when, John Harmon recommended to local builders to shim the stab to wing incidence - before internet, so we all got updates by word of mouth.

As Vern says, as long as the incidences are in their correct relative position AND not too much torsional correction is required you will probably be fine. Your fuselage will "fly" at a slightly different angle than designed, but most likely will be unnoticeable.

David Howe
HR II S/N 002

Good information. When I replaced the rear carry through spar all I did was copy the old one exactly and match drilled the holes. So the old one may very well have been wrong. as for the rear Hoizontal stab it was already shimmed 1/4" so Im going back with the same setup.
One note though, I did have to tweak the wing brace and rear spar slightly to get it to line up, but everything I have read so far says this is normal on the -4.

Arlie,
All the well known RV builders have told me to match up the wing and horizontal angle of incidence. You can easilly make a bigger spacer at this point in your build. If you adjust the angle of horizontal incidence later, you will have to modify the empenage fairing.

Hope to seeyou in the air soon.

+1 for vlittle's comment.

If it's not too late, match the wing to the belly skin (and rear spar, of course), then set the tail incidence to what it needs to be to correspond to whatever the wing is. Nothing else is likely to matter.

Psssshhhhhhh... quickbuilds are for sissies.

Update

We finally got reattach the wings to drill the rear spar. The best we could do to match both wings and still be within the 5/8" bolt edge distance was .09+ on the digital level. So if I am reading the plans correctly that gives us 1.4+ incidence due to the built in .05+ Using the 2.8" block and set to level.
So for the tail, we had to shim the left side almost 1/4" due to fuslage twist and we set the horizontal at .09+. I didn't feel comfortable going any higher with the front shims (built from aluminum flat bar) Does this give me a difference of .05 from the wing to tail? I think I can live with a half degree difference.
Being that a hanger "I" beam fell on the tail and crushed it, this is probably the best I could hope for on a repair job.