On the Edge

Sunday 24th Feb 6 hours

Re-assembled the left and right elevators, match-drilled left and right trailing edge wedges and countersunk them.

The wedge for the rudder is pre-punched but those for the elevators are not. To ensure accuracy, I assembled the elevators one at a time. I cut a straight piece of 4 X 2 into which I could drill and cleco the trailing edges. I left each elevator resting on the clecos, which raises the piece 2 inches off the bench. the depth of the elevator at the leading edge is 3.25 inches so I cut the timber to 3 and 5 eights (2" for the clecos plus half the depth at the leading edge) This meant that the chord of the elevator was horizontal and I could drill perpendicular to the chord by simply holding the drill in the vertical. This method of drilling the trailing edge into a timber is demonstrated by George Orndorff in his video and differs from the method in the Vans plans, which call for a length of aluminium angle to be match-drilled and clecoed to the upper skin trailing edge to keep it straight. As long as the timber is perfectly straight (mine is), the Orndorff method is certainly easier. I found that you need to be careful about alignment of the top and bottom skins for this drilling stage. There is still quite a lot of flexibility in the structures even with all the other parts clecoed together. This flexibility dissapears when the trailing edges of the skins are fixed together but any twist in the structure at the time the trailing edge is match-drilled will be made permanent when it is riveted. From this point of view, it might be better to have the elevator skins rivetted to the bottom of the spar and ribs and lying flat on a flat table (preferably weighted) as the Vans instructions suggest. However, I am afraid that some of the flexibility would already be lost by the riveting up to that point, resulting in stresses being fixed into the structure when the trailing edge is pulled into place. By matchdrilling while the elevators are assembled with clecos, all the joints can still move to allow the skin trailing edes to assume their correct position. I felt the elevators looked perfectly happy resting on their clecos and the whole structure seemed straight and well-aligned so I think this method is better.

I removed the wedges after this process and deburred and countersunk them on both sides to take the dimples in the skins. To make this easier, I planed an angle into the edge of a piece of scrap timber to match the angle of the wedge. I then drilled and clecoed the wedge to this edge so that the top surface of the wedge was horizontal. This makes it easier to countersink the holes perfectly. As the timber was quite short, I moved the wedges along, replacing the clecos and doing about 6 holes at a time. I also deburred and dimpled the trailing edges of the skins. The wedges are supposed to be bonded in place with tank sealer before being rivetted as a means of ensuring a straight edge that won't distort during riveting. I have now realised that I forgot to mask off the area where the wedges go so these areas have primer on them. It's back to the Dremel to clean the primer off these areas. I will have to clamp a metal straight edge in place to mask off the primer that needs to stay undisturbed.