PART 3: BUILDING A MODIFIED AEROTECH ASTROBEE
D KIT
1. THE PARACHUTE BRIDLE:
The kit is constructed per instructions, with the following
modifications. One modification is the parachute bridle attachment to the
forward end of the motor mount. Half inch wide, 550 lb. kevlar tape is used
for the parachute bridle. A 3.75 inch length of tape is threaded through
the screw eye and folded over on itself with a 3 inch length of nylon binding
tape secured between the two layers. The same dimensions for the loop at
the opposite end of the bridle is used and secured in the same manner. Make
the length of the parachute bridle at 5 feet, so it will extend 2.5 feet
out of the booster tube. For one continuous length of kevlar bridle, make
to length from motor mount attachment to opposite end at 10 feet. Parachute
bridle consists of 5 foot length of kevlar and 5 foot length of 400 lb.
flat braided dacron line, joined by a no. 4 rapide link. Tape overlap is
secured with E thread using 2-point cross stitch.
Figure 2: Strong and lightweight kevlar parachute bridle motor tube anchor
plate/ejection baffle.
Make a fourth centering ring from 1/16 inch pylwood or
basswood traced out from a kit centering ring before motor mount tube assembly.
Prior to motor tube mounting, the kevlar bridle is threaded
through the forward end of the booster tube. For 29mm H motors, the engine
retaining hook isn't installed on the motor tube, and is epoxied in place
with the exception of the motor tube end being flush with the end of the
booster tube.
Mark other tubing section at 6-5/8 inch from one end. Use a sheet of paper
as a marking guide and carefully score tube using a sharp hobby knife. Clean
cut ends using sandpaper on a flat surface. The purpose of doing this is
to build the kit so the payload section will separate at its scale location
as on the real sounding rocket.
Cut the 6 inch long coupler at 2.25 inches from one end and mark in the
middle. The other length of the remaining coupler section should be 3.75
inches long. Use this section for payload construction. Short coupler section
is epoxied to motor mount tube and long piece of other cut tubing section.
Secure two sections of booster tubing together with epoxy. Sand booster
tube between coats of white primer to eliminate evidence of the coupler
joint.
A 6 inch felt sleeve is slid over the end of the kevlar bridle and tacked
in place extending 3 inches beyond the tube to protect bridle and booster
tube from180 degree pulls over booster tube lip during parachute inflation.
Figure 3: Felt pad sleeve tacked to kevlar parachute bridle with straight
stitching at one end with horizontal zig-zag stitching.
Figure 4: 5 foot kevlar bridle connected to 5 feet of 400 lb flat
braided dacron line with a no. 4 rapide link.
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D Rocket Project