Page 30-02: Fuselage pin stopper assembly

The fuselage pins are the heavy-duty steel cylinders which secure the wing spars to the fuselage in a fashion similar to that of glider wings, allowing easy and quick removal of the wings.  The fuselage pin stopper is the mechanism which keeps these pins from backing out in flight, an important task in

my estimation.  The stopper is a spring-loaded aluminum cylinder which must fit within the small steel tube welded to the main pin.  The spring is inserted, followed by the stopper, a hole within which has been tapped to allow the machine screw assembly to be threaded in, holding the whole thing together.  Problem was, the stopper was not even close to being able to fit into the said tube, the OD of the stopper being significantly larger than the ID of the tube.

I first tried fixing this by using  a pistol bore cleaning rod with a strip of ScotchBrite inserted in the slot rather than a cleaning pad.  The rod was turned in the ID of the tube with a drill.  This didn't remove anywhere near enough metal to make it fit.  I next created a poor-man's reamer by cutting the head off a 4-inch-long 5/16 bolt, then cutting a 2-inch-long lengthwise slot in the bolt

(shown in the third pic).  Into the slot I threaded a length of fine-grit 2-inch-wide sandpaper from my belt sander, wrapping enough around the bolt to make a tight fit in the ID of the tube (shown in the second pic).  I chucked the bolt in the drill.  The sandpaper looks too big in the picture because it unrolls when you're not holding it.  After lots of trial fitting and reaming it fits perfectly.  I cleaned the ID with the bore-cleaning rod (to the left in the picture) and swabs, then applied some Boelube and assembled the whole thing.

All of the other builder blogs I could find which discussed this spoke about the earlier system which required that a magnet be inserted in the stopper and it then be filled with epoxy.  The magnet was somehow used to tell the Skyview that the pins were secure.  That system apparently proved

problematic and was replaced.  Not sure how this new arrangement lets the Skyview know that everything is secure.  I suppose I'll find out in the near future.

The finished assembly is shown at left.  When the wings are installed, the machine screws allow the stoppers to be retracted and then snapped into a hole in a plate in the fuselage.  I doubt the pins would ever back out in flight even without the stoppers, but it would ruin my whole day if they did.