Chute Cannon for 38mm (re)build thread

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Adrian A

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A chute cannon is the way I like to handle recovery on high-performance minimum-diameter rockets, especially ones that are designed to be used as a sustainer on a multi-stage rocket.

A diagram of a version of this for a 3" rocket is here:
https://www.rocketryforum.com/threa...ign-and-build-thread.26383/page-4#post-238112

I killed my chute cannon I had in my 38mm rocket at LDRS this year because of a dud apogee charge, so it's time to rebuild, this time stronger and simpler than before.

In the past I have tried bonding the cannon directly to a Featherweight 38mm active bulkhead, but the deployment charge shock was too much for some of the electronic components. Recently I have bolted the cannon to the 4 rods of the 38mm av-bay, but this is a pain because of a lack of clearance to get a nut driver to install the nuts.

This time, I'm going to bolt the cannon to the front of the rocket with a single central bolt, and an adapter plate that connects to the 4 threaded rods of the Featherweight 38mm av-bay. More on this later.

So I bought some hardware from McMaster: A nice low-profile 10-32 bolt, a pronged T-nut, and some long tools so that I can screw the bolt down when it's on the inside of the bottom of the cannon.

IMG_5080.JPG


And I bought some parts from Apogee: A nice, thin-wall 24mm tube and some bulkheads (too many airframe bulkheads and not enough coupler bulkheads)

I have been using a14" hemispherical chute of my own design that packs really small. This last 600 ft/second deployment may have been the nail in the coffin, but I guess I could always just sew the tears back together (again)

IMG_5072.JPG
One of my daughters is thinking of getting into the rocketry chute business, so I'll be a customer for a 14" chute if that comes together.

But at least the above chute is still usable as a placeholder for sizing the tube. First I did it from one end of the 4' tube I got from Apogee:

IMG_5073.JPG

which tells me it needs to be about 7.5" long to hold everything, which includes a piston, a protective end cap, and a small charge.
But after cutting it and putting a little pressure on both ends, it squishes down small enough so that a hex driver can reach the bolt down the length of the cannon:

IMG_5076.JPG


Note that the 14" chute fits into a 24mm tube about 3.5" long. That's just about exactly the size of an Estes E motor. Shortening the tube to this size will also let me make the front end of the airframe a little smaller for more performance, so I cut the tube down to the blue tape edge. Next up in this thread will be attaching and reinforcing the tube. I think I want to get a couple more coupler-sized bulkheads before I start that, though.
 
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