Tuesday, August 19, 2014

31B-10 wing pin sensors

This was a fun page to do.  Although kind of silly, the plane is designed to tell you that the wings aren’t installed and it will not let you start the engine if they aren’t there.  The way it is designed is that the wings are held in place with some very strong steel pins that go through the F-1204 bulk head and wing spars.  Those pins have a protruding handle that has a magnet installed in them.  The magnets then close reed switches and provide a confirmation that they are in place.  This is wonderful, except for the fact that you can install the pins without the wings, so it’s pretty easy to confuse the plane.  Anyway, on to the installation of the reed switches.  (The magnets have already been installed, back in chapter 30.)

Anyway, these magnets are housed in epoxy, which is housed in an aluminum bullet, which is then housed inside the steel barrel attached to the main pin, which is rotated to bring the barrel into proximity of the magnetic reed switch.  Do you see a problem here?  The magnets are shielded inside the steel barrels. I couldn’t get the switches to close anywhere near their installation position, although they closed just fine out in front of the assembly where the steel wasn’t shorting out the magnetic field.  The book said that the tubes could be shortened 1/32” at a time, up to 1/8” but I ended up shortening them by 1/4” to get them to work.    

Shortening the tubes was yet another learning experience.  I used a grinder to abrade the tubes to the desired length, but then discovered I could place neither the springs nor bullets into the tube any more.  Although I couldn’t see it, I deduced that there was a rounded lip inside the barrel.  That came off with a dremel bit and things went back together again. 

Lastly, I had to twist the bullets 180° to find the best position for the respective reed switches.  The pin assemblies are now marked with red & green tape for port & starboard.  Finally, it was unbelievably challenging to start the nut on the screw that held the reed switch on the left.  Just wanted to let you know that it wasn’t fun.

IMG 3556

Starboard Wing Pin

IMG 3557

Port Wing Pin


The epilogue to this page was that I lost my 1st part out of the kit.  I couldn’t find the 4 little snap bushings that channel the sensor wires through some sheet metal to the conduit.  I had to wait a few days to get $0.48 in parts from Van’s for $5.  <sigh>.  To salvage the embarrassment of ordering such a tiny amount, I ordered some caterpillar grommets to line the sharp edges of the access holes while I work on them. That should make things a bit more comfortable on my arms. 

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