29 April 2014

Empennage: Elevators. Trim tab piano hinge wire bent and inserted.

The piano hinge wire has to be bent properly so it butts up against the elevator rear spar.  This, when tied down with safety wire, prevents the wire from working out in flight.

The more you push the wire into the hinge, the more friction there is, so it becomes harder to push it in further.  Eventually, even after greasing with lithium grease, I could not get the wire through the last 3 eyelets of the hinge.  A former United and (original) Frontier A&P suggested chucking the wire into a drill and slowly driving it through.  Sure enough, that sucker slipped right on in to the end.  With the wire inserted, I could mark off where to make the first bend, then reinsert to mark off the second bend.  The A&P also suggested to file the end of the wire down so it becomes self-centering in the eyelets as you drive it through.

Here's the bending process prior to snipping the extraneous length off.

And the hinge wire in its final location.  It didn't seem feasible to have the part of the wire running aft-to-fore to seat up against the rear spar flange (see bottom picture):  The inboard hinge eyelet is in the way.  But since the up-down part of the wire seats nicely against the rear spar web, I'm happy with this. Just need to trim the end of the pin down so it doesn't dig into the spar.

Incidentally, on the top picture you can see an AN470AD4 where an AN470AD3 should be on the top-most inboard spar rivet.  When I originally squeezed the AD3 that should have been there, it clenched on me.  In removing it, I messed up the hole and had to upsize the rivet to an AD4.

After the slight trimming of the pin, all that remains is threading some safety wire in the 1/16" hole between the inboard spar rivets.  The hole isn't visible because it's behind the hinge wire in the image.

The trim tab has some added friction when it deflects upwards.  It's due to each half of the hinge not quite lining up.  One of the halves probably has a minor curve to it.  It's far from binding during travel, so let's just say it adds to the uniqueness of my airplane.