Trammeling

To All:

Every now & then you run into a repair that involves turning two
airplanes into one. Typical case is mating a tail-less airframe to the
aft fuselage of an identical airframe which lost its nose.

Doing so is fairly straight-forward but tends to be easier with steel
tube than aluminum. Basic chore is maintaining alignment of the parts
while you rebuild /re-attach the mating portion.

To facilitate that alignment you often use the floor of the hangar.
With steel tube, close enough was good enough. Using Bondo as a
temporary adhesive, you triangulate supports to keep the pieces of the
fuselage(s) well enough aligned to get your splices tacked. Depending
on how much of the original structure you have to work with, the repair
may involve some ugly -- but strong -- splices. Fortunately, with rag
& tube the finished appearance depends more on the stringers & fabric
than on the welded structure. But trying to mate monocoque
airframes, if you want your repair to be invisible, your positioning
fixtures will have to approach the accuracy of the factory jigs.

One method of achieving such accuracy is to make up a welded steel
fixture into which the fore- and aft- portions of the fuselages are
installed. The jig itself is usually portable and if you ask around,
you can generally track one down for the particular airframe of
interest. Coupla phone calls later, it falls off the back of a truck
outside the hangar and you're good to go... as soon as you figure out
how to secure the jig to the floor of the hangar.

Yep. The jig want's these humungous anchor-bolts.

Well... okay. (But Bondo would prolly work too.)

Hammar-drill zips through the concrete. That is, the sonofabitch zips
right THROUGH the concrete! Hangar floor is supposed to be 6" thick
but turns out to be about 3-3/4" And of course, the anchors are
about 4-1/2".

Okay, we could have started over; come up with a different anchoring
system. Except we've been planning this particular campaign for a
while, there's already six holes in the floor and pieces of Cherokees
are starting to arrive and we've got about three days to get them glued
back together and vanish before the Citation returns to its roost.

So that's what I used. Urethane glue. (Hint: Urethane expands as it
cures.) Squirted a healthy dollop of the stuff down into the holes --
and into the dirt -- then smeared it all over the anchors and drove
them into the holes. (Tight fit!)

I don't know if it's legal, moral or politically correct but it worked
okay. Jig got trammelled zero-zero on all three axies and things lined
up so nice that some of the holes even matched. After that it was
'round the clock assholes & elbows for a couple of days turning
write-offs into flying machines.

You know, given enough hurricanes a guy could earn a living fixin'
aeroplanes...

-R.S.Hoover