I just completed the LA mod this weekend. I had put this mod off as long
as I could. I sat in the plane with the top on telling myself I have
enough room, I don't need to perform the mod. Who was I kidding? I
just didn't what to do the lay up in the tunnel or cut out all that foam.
Well I am happy to say I developed the following technique that worked
perfectly!!! Here it is for those of you that are thinking of performing
the mod but dread the task at hand.
First, make the inside molding as described below. The molding when
cured, is trimmed and then covered with a thin layer (1/8"-1/4") of
expanding polyurethane foam (available at most building supply houses)
and sanded to match the contour of the inside molding. The molding is
then reduxed into place on the inside of the tunnel. Once the redux is
cured the exposed foam (outside of the tunnel / inside of the cockpit) is
then covered with two plys of bid, lapping onto the sides of the cockpit
module to finish of the mod. What could be easier?
To make the inside molding follow the directions below.
1) Cut out the side of the tunnel leaving the corners. There is no need
to cut any part of the top of the tunnel on the side.
2) Rotate fuselage onto it's side so that the port side is facing up.
This was done using an engine stand bolted to the landing gear frame.
3) With the side of the tunnel positioned horizontally, loosely tape a
piece of plastic film (I used a plastic trash bag) over the cut out.
4) Using zip lock baggies filled with water (get the good ones that don't
leak) lay them on to the plastic film. They will cause a natural
depression in the film. Adjust the baggies weight and volume so that you
get the desired depression. You may have to let out some of the plastic
film.
5) With the landing gear up verify that there is at least 1/4" to 3/8"
clearance between the bottom of the plastic film and the tire.
6) On your workbench, ay up two plys of bid on plastic film and roughly
cut to shape.
7) Remove the zip lock baggies and place the bid directly onto the
plastic film taped to the tunnel. Leave the film which is on the back
side of the bid in tacked. You should end up with a layer of plastic
(taped to the fuselage), a two ply layer of bid and finally a layer of
plastic film on top.
8) Place the zip lock baggies directly onto the film which is on the back
side (now the top side) of the bid. Position baggies to obtain desired
depression and leave to cure.
9) Upon cure remove lay up and trim all around leaving a 1" flange.
Cover flange with masking tape. The flange of the fiberglass molding
will be reduxed to the inside of the tunnel (step 12).
10) Using expanding polyurethane foam that comes in a spray can cover
the inside of the lay up with a thin layer of foam. The idea here is to
form an 1/8"-1/4" thick layer of foam which will only require minimal
sanding.
11) Once the foam is fully cured, sand to obtain the contour of the
molding.
12) Redux the molding to the inside of the tunnel using clecos to hold in
place.
13) Upon cure cover the exposed foam with two plys of bid, lapping on to
the sides of the fuselage by 1".
Well that's it. More time is spent waiting for the epoxy to cure than
anything else. No fuss no mess. Hope this helps anyone who is thinking
of doing the mod. Best of luck.
Erich Trombley
A028
Tucson, AZ
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