Personally I wouldn't put my electronics in a piston and still use it as a piston. Just the thought of shooting it out of the rocket and all the jostling doesn't seem that great. Just my opinion. Also - are you using your pistons with the bulkhead next to the charge - like "|_|" and not the other way?

Edward

Both sides of a piston are subject to pressure changes due to deployment and therefore wouldn't be an appropriate location for altimeters and other electronics.

Warren

I had thought about the ejection part too, so I was trying to figure an alternate way to add the altimeter. But, not knowing much about ways to do it, I couldn't come up with anything better. I had thought about using some expanding foam with a molded area in the center for the RRC2 to sit, the vent is a problem though. When it discharges from the tube, it will get a sudden blast of pressure if the vent is on top. If it's on the side, I would have to use a sheer pin that is drilled through the center to keep the bay in line with the hole and gasses out. The sheer pin is Jeremiah’s idea, I thought of drilling it.

This is more of a temporary thing unless it works well. I have one of the Pico P1 altimeters coming that I can mount in the nose cone on the BB. The Sumo is destined to become a dual deploy and then the problem is solved.

I was going to run the piston with the bulkhead on top, that was the way both PML and Aerotech showed it. Is there alternate thinking on doing it this way? I'm all ears..... 🙂

The way on the bottom is actually the correct method. The other method results in an unstable piston.

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

Edward

The way on the bottom is actually the correct method. The other method results in an unstable piston.

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

Sorry to disagree with you Edward but I've seen that site before and his theory, analysis and "tests" are all flawed. I think it's a prime example of how misinformation can easily spread. Now I don't put the bulkhead plate in my pistons at the top, but I do try to put them forward of the center point of the coupler tube.

Doug

8) One good reason for putting the plate on the bottom is space. Often the space is limited and the plate on the bottom give you more room for shockcords and chutes. 8)

8) One good reason for putting the plate on the bottom is space. Often the space is limited and the plate on the bottom give you more room for shockcords and chutes. 8)

Good point, however I think the bulkhead pulling the piston scurt, instead of pushing, would be the way to go.

Space on the Sumo may be an issue, but the Brant has more than enough room. Both pistons have the bulkhead set in about 1/4" but hardly anything close to being centered.

I was talking to Jeremiah about something along these lines....

I feel it would be helpful to have some construction techniques stickeys on each of these "topical" threads. I don't know how basic it would need to be, but something that walks a new builder through some "tips/tricks" that you guys use for builds. I know my way around a shop and have built about anything you can think of, but, ideas like this w/ the piston would never come to mind..... Kind of like using a spoon to mold the epoxy on a fillet.....

Personally, I put the piston bulkhead right about the 1/2 way point in the piston. Additionally, my pistons are about 10% longer than the diameter of the airframe so that they can't cock and jam in the airframe. Pistons are great and I use them on everything from 38mm up to 3". Above 3" I've never bothered with them although I know folks who use them up to at least 6" airframes.

Warren

A clarifying question for you all...I am finishing up my scratch built L1 cert rocket for Oktoberfest and would hate to be embarrassed.

Should the piston sit all the way towards the bottom of the airframe "on" the ejection charge/top of motor or should a centering ring with a very wide mouth be used to hold it higher up? My thinking is to use the CR approach to shorten the distance the piston has to travel reducing the chance for a jam and making the piston last longer.

This is a straight forward rocket, no bays. Just a 34" x 3" airframe with motor mount, nosecone, and recovery system. Thanks for the help!

John

I always put the piston right against the charge. They travel just fine when you keep it clean. What airframe material is used. I also have my piston sitting in my rocket so that it looks like a drinking glass - bulkhead on the bottom and open on top.

Edward

Thanks Edward! This is almost all LOC components (paper tube), piston using nylon webbing with a nomex sleeve attached via a metal D-ring to piton bulkhead. The webbing is epoxied to the 10" motor mount through 2 of 3 centering rings. I haven't actually attached the piston to the webbing yet or epoxied the bulkhead into the piston so your options are open to me. The "cup" shaped piston seems very counter-intuitive to me though I'll admit while certainly not denying your experience of which I have none! 😉

Assuming this L1 attempt is good I plan to pick up my first G10 kit at the event.

There is a site that says it is the better way because of stability but I believe Doug G. says it is bunk (I can't confirm/deny if it is, but I'll go with Doug). It works for me mainly because it give me extra room to pack everything in. The other way eats up some space. This way I have a 'cup' shape to start packing everything in. I also make sure that I ground test with my pistons. I like to get the piston out and about 5-6 from the end of the rocket put a 'stop' on the shock cord so that the piston stops and the momentum from the parachute keeps going throwing it out. Has worked every time for me since I've started doing it. I also like to size my charges so that all the shock cord gets straightened out.

Edward