Preforming D-Tube Sheeting                       MD  2 June 01
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It is very strongly recommended that you preform the curvature
in the D-tube sheeting before installing it.  This has a number
of advantages:

* The sheeting will be more resistant to cracking, since the 
outer wood surface will not be in tension.

* The installation will be much easier, with minimal clamping jigs
being needed to make sure the sheeting contacts the ribs everywhere.

* There will be less sheeting sag (yes, sheeting can sag slightly
but visibly if it's forced onto the ribs).


The main chore will be to find forms with the right curvature.
One possibility is a wide thin aluminum sheet bent into a gentle curve 
by hand over the thigh.  You can then pick spots on the aluminum 
which best match the required curve of the LE sheeting.  Another
possibility is to hot-wire the forms, covering them with something
to protect them from the heat gun.

The effort to get or make the form and do the preforming is 
very well worth it, IMO.  You'll be very glad you did it.


I originally just forced the wetted sheets onto the form and
let them dry.  This works OK, but the drying takes many many hours.
I used the new heat-gun procedure below on my new wing.  This is
tremendously faster, and allows holding down by hand which is easier.



Forming procedure:

1)  Cut sheeting close to correct dimension.  About 1/16" extra along the LE
and sides is plenty.  Sand smooth with 220 and 320 grit to minimize on-wing
sanding later.

2) Wet the sheeting with water.  Long soaking is not necessary.  Blot off excess.

3) Using a heat gun, dry off inner (to be concave) surface of sheeting until it is 
just dry to the touch.  Using intense heat is OK, but keep the gun moving 
to prevent charring once surface starts to get dry.  This takes a few minutes
at most.  Sheeting will be curved in both directions since the other wet surface
is still swelled.

4) Press sheeting against form and hold down with large piece of porous cloth 
material taped down or wrapped around form.  Holding down with oven-mitted 
extra hands is also OK and simpler.
 
5) Dry off the outer wet surface with the heat gun again.  This takes only
a little longer if using the cloth hold-down method.

6) Lift the sheeting off the form.  It will be slightly "potato-chipped" in
shape since the inner surface became damp again as the heat forced the water
through the sheeting.

7) Dry off the damp inner surface using the heat gun, more gently this time.
The spanwise curvature should disappear, and the chordwise curvature should 
increase slightly.  The curvature will likely be a little sharper than that
of the form.  Before the sheeting is completely dry, you can fine-tune the
curvature by pressing against the form one way or the other while finishing 
the drying.