Bill,
My (early) fuselage bottom moulding also had a twisted rear end. Mine
required an anticlockwise correction (looking forward). Also the
diameter at bottom of the the fin close-out seemed too large by several
millimetres to allow straight lines through the 78mm datum at the top of
the bottom moulding (page 18-2) and the diameter at the top of the fin
close-out. I did a trial fit of the top moulding and the fin before
fitting the rear bulkhead (but with a tie rod holding 255mm on the
torque tube centre line). I also compared the width of the rudder
(quite difficult to measure correctly) with the expected close-out
widths passing through the 78mm datum and concluded that the bottom
diameter should be 86.5mm i.e.:
Dia. at bottom of fin Width top of bottom moulding Dia. at top of
fin
0f fin bottom moulding
86.5mm 78mm 57.5mm
In a small workshop it is almost impossible to gauge accurately a
vertical at the rear or the fuselage because of the sweep of the rudder
hinge line. So I made a fixture out of 6mm plywood. This has two panels
fixed accurately at 90degs to each other with the first panel on the
diagonal of the the second. The first panel is about 27ins long and has
an elongated horseshoe slot on its centre line with dimensions derived
---From a plot of the figures above. ( allow an extra mm for irregularities
and add a chamfer to fit the fuselage taper) The first panel was clamped
on the rudder hinge line on the bottom moulding and then glued on with
bondo. Having made sure the wing spar pins were horizontal, it was easy
to apply corrections to the rear of the bottom moulding and make sure it
was vertical by fixing a plumb line close to the second panel. I then
carried on and completed the rear bulkhead layup, and fitted the rear
plywood close-out ( determining the right position without the fin in
position is another story), mod 43 - the new tailwheel and the tailplane
torque tube. Even so the rear end will not be completely rigid until the
top moulding has been glued on and I will have to keep the fixture in
place until that stage is completed. I will not know if my 86.5mm is
right until I come to fit the rudder. The top 6ins of the ply close-out
is removable so that I can glass the rear bulkhead to the top moulding
when the time comes.
I also found that I had to be very careful when opening up the holes for
the tailplane torque tube - the centres marked on the moulding were not
on the same level.
Hope this helps,
Gerry (121 - Classic)
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