I have just done Mod 74 and you may be interested in our experience.
To remove the pins we simply cut a piece of the foil covered insulating material
about 8" in diameter and made a hole in the center the same size as the pin
- with that in place, a short blast with a heat gun on the pin soon made the
glue
soft enough so that mole-grips on the pin would make it move - work it back
and forward a few times and it will come unscrewed. The surrounding structure
was barely warm.
I was helped by someone who is very experienced in composite construction/repair
(he repairs seriously broken gliders for a living) and he was unhappy with the
mod as described due to the placement of the hole so near to the flap plate
and the rather short taper of the skin in that region. So we moved the hole 10mm
further outboard and used a smaller hole (less than 2" dia).
We didn't use locktite to fix the pins but, instead, bonded the pin/washer/nut
assemblies in in one operation with the wings rigged. We thought that this would
remove the possibility of a pin becoming un-aligned if done as per the
instructions.
As this is the third set of pins to be installed in my aircraft, they
were a bit loose in the threads and so we thought that this was the safest
option
to ensure perfect alignment.
Apart from the final tweaking of the nuts, the job can be done with the wings
off
and then rig, put all the pins in and then tighten the nuts down (not too
tight).
To tighten the nuts we used a socket with universal joint drive. That worked
fine
but if you try the same thing and it won't fit, it's OK to open up the hole
in the outboard and forward directions - don't make the hole bigger towards the
root or trailing edges. Take care to not damage the original foam under the
edge of the hole.
We actually used two-part foam to fill the cavity - it was very quick and
produced
a perfect job. If you want to do the same, make sure that the expanding foam
you have is compatible with the blue foam and doesn't eat it!
The layups were completely symetrical around the hole and round in shape. The
layups
did not quite reach either the flap bracket or the trailing edge.
After the layups cured, we made good with filler and then, finally, put white
Fablon(tm)
patches over the top and it doesn't look too ugly at all. Perhaps, sometime
in the future, I will re-gel those areas.
I don't know how easy the job would be going through the flap closeout but as we
did it, it was very straightforward and I believe the end result to be
structurally
more sound than if we had carried out the instructions to the letter.
Obviously, if you want to stray from the official guidelines you have to have
expert advice.
Cheers,
Mark
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