Speaking of pistons…

[Anonymous]

The problem with a fit that is too loose is that the very wispy, thin parachute material could theoretically get pinched between the wall of the airframe and the piston — which could indeed cause it to jam. Too much gap there is potentially problematic.

I’ve never used Nomex with a piston, just the piston by iteself…. i.e. I use a piston both for expulsion of the laundry + protection from the heat of the charge.

[edwardModerator]

Flip the piston so that the bulkhead is down and is open upward. It is actually the stable design for one. I don’t have the website handy but a guy did a study and found that flipping it is the best way. I’ve used it on 54 to 98mm rockets and it has worked great. Saved a bird once in a 75mm design when the motor had an anomaly. The chute came out and inflated in abou 25′ from 150′ altitude.

Edward

[Warren B. MusselmanModerator]

I always place my bulkheads either midway in the piston or on the side AWAY from the charge.

Warren

[edwardModerator]

Here is the link for the research – bulkhead closest to the charge.

Edward

http://www.deltavrocketry.com/piston.htm

[Doug GerrardParticipant]

Thanks for the link Edward, I had not seen that site. Not only do I think his analysis and assumptions are full of Cr*p even his so called test video is misleading. He states

Note the rattling that the unstable piston undergoes as it moves up the tube.

I could only hear the rattling on the way down when the piston is bulkhead down (from the direction of flow)!

I’m going to continue to use the pistons that have been working every time for me.

Doug

[Chris LaPanse]

I have used pistons both ways, for various reasons (the upside down one, the way that the website promotes as “stable” was actually an accident), and I can say that regardless of orientation, I have never had any problems with pistons.

[Kenneth ReillyParticipant]

Whether the bulkhead is toward or away from the charge or somewhere in the middle, I don’t think matters nearly as much as 1) the skirt is long enough to preclude any significant twisting and 2) keep the tube and skirt reasonably clean. Some lubricant might also help, although I have not tried any yet. Plausible suggestions I have geard are baby powder, dry soap and maybe graphite powder.

[Bruce R. Schaefer]

For my L3, I’m using a piston in the upper dual deployment section, with an option to use a second one in the section above the booster. The other alternative for the booster is the zipperless, blow-the-section-off-the-booster-exposing-the-harness-attachment method. Either way, I feel safe… though I haven’t ground tested yet. That’ll be a blast… literally. The rocket sims from 8k to just under 19k depending on the flight configuration and/or motor (obviously). I’ll try putting the piston in both ways, and let you know which way appears more reliable. Never used pistons before, so this will be fun. 8)

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