SIdea - Inverted Piston (To creat a small ejection charge cavity):
Pistons are a great way to separate the hot gases from the recovery
equipment. Pistons are located near the ejection charge at the bottom of
the body tube. So, pistons can sometimes bind within the long tube due
to temperature differences and grime that will cause friction. The main
purpose of the ejection charge is to separate the two halves and to also
push the upper part away to pull out the parachute. So, what if you
inverted the piston and put it at the top of the body tube rather than
at the bottom. The piston would be stopped from going down into the tube
by resting the piston on top of a small coupler that has been glued down
inside of the tube. The avionics bay would go on top of the inverted
piston and slid into the body tube as normally done. When the ejection
charge goes off the two halves are separated and the piston is also
pulled out with the shock cord from the ejection force. The advantage of
this method is now you only have a small volume to expand, using smaller
charges. The piston will still separate the hot gases from the recovery
equipment. Also, you should be able to retrofit most rockets with this
idea. I might not have explained this very well so I will build a
prototype and post some pictures.
Initial body tube
Pieces for the inverted piston.
Assembling the inverted piston. A metal ring or a knot will normally be
added to the shock cord loop to make it much stronger.
Coupler tube that will be mounted inside the body tube. Edge that is
exposed to the recovery equipment is beveled to make a smooth surface
for the recovery equipment to slide across.
Coupler or stop piece mounted down inside the body tube. The inverted
piston will rest on top of the coupler.
Body tube and inverted piston assembly. Parachute will be attached to
loop.
Body tube, inverted piston, and avionics bay (Shock cord length is just
for demo. purposes). Shock cord will be just long enough to separate the
tubes and pull out the piston. Charge will be mounted at the bottom of
the avionics bay.
Inverted piston inside of body tube.
Inverted piston inside of body tube and the avionics bay is ready to be
installed.
Tubes assembled together.