J-3 Provisions for
Burst Tube
I got a great recommendation from Jim O'Reilly this afternoon for the blast tube. It called a blast tube or burst tube? Anyway, Jim said:
"I'd recommend that the blast tube have a slot
in its back end that is a push-fit over the rear motor anchor. If you want
to get really fancy, you can make it a 90 deg. angle slot so that you can
push it onto the rear motor anchor and then twist it a bit to hold it there
when you pull the motor out to stretch it before you start winding."
Of course, this meant that the three
modified cross members shown below had to be cut out so the blast tube would
center on the motor peg, which I did.
I'll swear, building and modifying the
construction of this rubber model is becoming a big challenge, more so than
I would have ever thought possible. I spent more than two hours this
afternoon just cutting and shaping the cut outs in the end of the PVC blast
tube to receive the 3/16" aluminum motor peg. The PVC is somewhat difficult
to work with. However, as the picture below shows, I finally accomplished
the task that Jim has recommended.
With the three modified cross members removed
from the fuselage structure, the blast tube can now be inserted into the
fuselage, slipped over the motor peg, and locked into place with a quarter
twist as shown below. As you can see, the 3/4" blast tube just barely fits
inside the fuselage sides back at the motor peg.
This picture shows the blast tube installed in
the fuselage. I still have to develop cross member structure for the top
longerons in the aft part of the fuselage. Notice the bulkhead over the
motor peg has been removed with the idea of making that bulkhead also an
integral cross member. Jim also suggested that I cut the blast tube off
about 3/4" ahead of the forward bulkhead, which I have not done yet.
Well that is about it for today. I seem to be
taking two steps forward and then one step back. This project just about has
me whipped for today.....................Tandy