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AlphaHybrids

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A long time ago in another epoch of HPR, there was an article on something called the Z-Pard. Essentially an aluminum piston recover device using BP. Advantages were very reliable operation, less BP used, you don't have to pressurize the entire recovery compartment and positive deployment. I've been using them for a bit, but don't really see them in other rockets. I think it is because recovery is the least thought out, though most important, part of HPR people stuff a parachute in a rocket and 'blow it up or blow it out'.

Here is an animated GIF of a test today. The piston was 3/4" tube with a 1/2" tube inside it. The stroke was 15 inches.

https://imgflip.com/gifgenerator

I was going for the tree but missed. Some statistics about the nosecone. 6" diameter, prototype nosecone that was rejected because of concentric alignment issues. Wood/Foam/Tube construction. Weight of the nosecone was approximately 2 pounds.

The nosecone really gets up and goes. The best part is that to get this effect it took 0.8 grams of 4FFFF BP. I don't have a calculator handy but I know it would take much, much more to get the same effect if I was pressurizing the 24" long x 6" diameter parachute compartment.

Edward

1dfvzn.jpg
 

ttabbal

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I remember reading something about those a long time ago. It seemed like the design was intended for very high altitude flights. The idea being to contain the BP charge and pressurize a smaller area. I don't think I've ever seen one used before, so thanks for that.

I like the idea, it seems like it would be more reliable than trying to pressurize the whole compartment, particularly for larger HPR projects. Amusingly, sort of, searching on google for it right now, finds an old post of yours as the first interesting result. I did find this sample from Rockets magazine that has some info..

http://www.rocketsmagazine.com/RocketsMagazine/Issue0007/sample.pdf

I might have to try building one, I don't have a lathe so cutting a grove for an o-ring wouldn't work. However, it seems like I could treat it a little like a muzzleloader. BP, dog barf, piston. If the piston is sized so that it seals decently against the tube, it should work. Perhaps include a patch or similar to tighten up the seal.. I'm not going for very high altitude, but I have been lax in my recovery systems in the past, and had problems as a result. I also would like to have less BP residue all over everything. I think I'll try setting something up in a smaller rocket for some ground tests and later, test flights.
 

markkoelsch

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Edward, how do you keep the piston/ejection portion from cocking in the tube?

Could you snap a few pictures of your setup?
 

AlphaHybrids

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If you mean the tube, you mean the airframe I attach the piston to centering rings on both ends. This keeps it positioned correctly.

Edward
 

markkoelsch

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That was kind of what I was getting at. It is a piston of sorts with something underneath that plugs into the z-pard.

I would love to see a pictures of the whole deal if you can/would.

I assume you use shear pins to hold the nosecone? If so, any issues shearing the pins ( I doubt it looking at the test)
 

AlphaHybrids

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It has no problem with 3 #6-32 nylon shear pins. Typically I z-fold all my recovery harness and put in the area occupied by the Z-Pard piston. That way you are just popping the parachute out and then the recovery harness comes next.

Edward
 
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