J-3 Provisions for
Burst Tube
I received an e-mail from Ed DeLoach recommending
that I make provisions for a 3/4" burst tube so if the rubber motor breaks
while I am winding it, the fuselage will not be destroyed by the energy
release. Mike MidKiff told me to go to Lowes and buy a length of 3/4" thin
wall PVC tubing. I bought a 2' length of PVC and learned that #40 is thick
wall PVC and # 20 is thin wall! After I got back home, I careful cut out an
oversize circular hole in the front bulkhead as shown below so that the PVC
tube would slide into the fuselage easily. Question
(1): Should I make this opening in the front bulkhead, say square on the
bottom, to act as a key to always position the nose block on the front
bulkhead in same way?
The picture below shows the 3/4" PVC burst tube
inserted through the hole in the front bulkhead and running all of the way
back to the rubber motor pin (Duke
Horn told me it is peg, which I shall call it from now on).
As you can see, the arched cross members keep the PVC burst tube from
centering on the rubber motor peg in the back, which will be shown more
clearly in the next picture. Question (2): How far
should the PVC burst tube extend out in front of the fuselage's front
bulkhead?
This view looking forward shows how far off
center the PVC burst tube is relative to the rubber motor peg. Question: If
this is going to cause a problem when winding the rubber motor, then
I should once again cut out the two arched cross members that are holding
the burst tube down and provide new cross members that will allow the burst
tube to center on the rubber motor peg. However, back this far, it may not
matter. Please advise at your earliest opportunity..................Tandy
Notice in the picture above that a 3/16" O.D.
aluminum tube has replaced the 3/16" wooden dowel for the rubber motor peg.
Duke Horn recommended this in order to be able to wind the rubber motor on a
stooge. He suggested I flare one side of the aluminum tube and drill a small
hole in the other side for a wire to retain the motor peg, which I will
do..........................Tandy