Aug 9-10, 2020
Installed both wings for the first time. We took our time and did it one at a time on the first day to make sure nothing would go wrong when we installed them to set the incidence and sweep. Hardware store bolts with a tapered end and some wheel bearing grease and the bolts went right in with no problems. This was more or less to make sure that we could get the wings on and off easily before we set out to drill for incidence.
Aug 10th – Got an early start and put both wings on the plane. Had to turn the plane sideways in the garage and leave one wing hanging out a few feet. This means that we were limited to a single day to get the rear mounts drilled because we couldn’t close the garage. A bar across the longerons was set until the level read 0.0 degrees one direction and 0.1 degrees when the level was reversed. We couldn’t get it anymore accurate than that since the level only reads out the 0.1 degree. We double checked the levelness by putting the level on the main spar center section and the readings were identical. We then leveled front to back on the right longeron until the level read within 0.1 degree when it was flipped around. Since incidence has some allowable play we decided to take all the measurements from the right longeron. As long as left and right wings were the same we’ll be good to go.
First attempt with the 4 plumb-bobs draped over the leading edges showed a bit of forward sweep. We had to remove the wings and grind off some more of the rear mount on the wings to pull the backwards. After this the left wing seemed good, but the right wing had to be removed again for a bit more sanding down. Once the sweep was good we started measuring to make sure things were square to the fuselage. We picked a few repeatable points on the tail and wing tips and got the measurements within 1/16″. Vans website says anything within 1/2″ is acceptable, so we’re more than happy with 1/16″ difference between left and right measurements over ~168″. After that was set, we moved on to the incidence angle. We set the left wing so that the flap skin sat flush against the bottom of the fuselage with the flap in trail with the neutral aileron. This required installing the aileron and flap to make sure everything lined up well. Turns out that the incidence was 0.9 degrees (instead of the recommended 1 degree) for the skin to sit flush. Once this was set, we set the right wing to the same incidence. The skin doesn’t sit exactly flush on the right wing, so during final assembly I’ll put a little bend into the right flap lower skin to make up for the minor differences.
After a bunch of fine tuning we ended up with zero sweep, 1/16″ difference off square, and identical incidence angles for left and right wing. The amount of extra room given on the rear mount to maintain 5/8″ edge distance is extremely small. We ended up with maybe 3/32″ of margin for the bolt placement on each side. Before you take off too much from the rear wing mount, it might be worthwhile to remove the rivet that interferes with the rear wing mount and replace it with a countersunk version. This will get you ~1/16 of an inch of additional movement. I drove a punch right in the middle though and we met all edge distance requirements without too much worry. I made a drill guide out the old, non-usable center rudder pedal brace and started drilling the holes. The final hole was drilled undersized and reamed to final size for a tight fit. Afterwards we removed the right wing and put it back into storage so we could close the garage again.
-Paul
(Total Build Hours 528.6)