Thorp Air Command - T18.net

My question pertains to the SDR listed below. Should a person choose to drill out a rivet as described below, I assume a pop rivet would be used to replace the rivet you drilled out for inspection, but what pop rivet would be used?

1. Horizontal Tail Spar Doubler- Refer to T-18 drawing B-502, Newsletters# 27 and 39. The original horizontal tail main spar as shown on drawing A-502 (obsolete) was made up of a single 2.0" X 0.083" 2024 T3 aluminum tube. Referring to drawing B-502 (current), the main spar tube was changed to .049" wall thickness, and calls for a second tube (B-502-7) with a 0.71" wall thickness to be inserted inside the main tube, and to extend 17.5 inches each side of center (BL 0). There are two ways to verify that this SDR mod has been completed. The first way is to drill out one rivet on the underside of the horizontal tail assembly about 10 inches from the center line. Using a piece of safety wire or similar material, with a 90 degree bend on one end … insert the bent end into the rivet hole and pull the bend so it contacts the inside surface of the tail spar tube. Mark the wire even with the outer skin surface, then remove the wire and measure the distance from the mark to the bend surface on the wire. This will be the combined thickness of the stabilator skin and the spar. If the modification has been completed you should measure a total thickness of .145 inches (.025 skin thickness + .049 tube wall + .071 inner tube wall) If you measure only .108 inches then you have the original spar without the SDR Modification.

Cherry Max rivet . You can also remove one horizontal tip and remove the end cap from the spar tube and sight down the tube to see if the doubler is in there . It would also be possible in my opinion to drill a #30 hole in the end cap and fish in a piece of wire to feel for the doubler . If you remove the rivet a Cherry Max rivet depth gauge would do the same thing as the wire gauge .

RB

I like the idea of the drill hole in the end cap. that's a good idea.