Posted: Mon Mar 10, 2008 2:36 pm Post subject: Q: Deployment of #2 receovery device w/o explosive charge?
Rockets that fly high need two systems for recovery, since it doesn't make sense to deploy the main parachute at a 3000 feet, it will get carried away and lost by even a gentle breeze. At apogee the motor's ejection charge could deploy a streamer or drogue parachute, then I would like the rocket to fall to earth rapidly until a reasonable drop in altitude is rached, when the #2 or main parachute should deploy. But I'm not attracted to a mthod that uses electric matches & a black powder charge ignited by a timer or altimeter - or is that the only way to deploy the second parachute? Is there no spring-based mechanical ejection system? For example, one could conceive of a timer that is activated when the primary ejection charge separates the lower body tube from the upper body tube or nose cone, then when the time runs out it triggers a spring-activated ejection of the main parachute from a tube. Is anything like that available?
I've seen that type of method discussed before. The general approach is this...
Build the recovery system such that it's spring loaded. On one end of the system is a piece of threaded rod, or some other similar device, which is held in place by rotating a captured nut.
To "arm" the system, the recovery system is held in place and a servo is advanced such that the threaded piece is pulled down by the nut. When deployment is desired, the electronics advance the servo in the opposite direction, releasing the spring.
Joined: Jul 01, 2007 Posts: 543 Location: Fullerton, CA
Posted: Mon Mar 10, 2008 9:38 pm Post subject:
I don't by any means want to discourage anyone from thinking outside the box, but keep in mind, that using electronics, and "explosive" (rather, rapidly burning under pressure) devices for deployment is very widely used, and with VERY high reliability, and safety, so long as you do it right.
Of course, you _could_ utilize standard electronics, and with a little ingenuity, utilize servos, relays, electro-magnets, motors, solenoids, air/CO^2 Pressure and the like to compose a device that it pyro-free. I'd be interested to hear your thoughts.
There are a small number of ready-made devices that use CO^2 pressure for deployment, though typically with very high altitude flights, but within reason, I don't see why a device like that would not suffice for lower altitudes, other than lack of expansion, and low ejection pressures, but with small dia rockets, I'd have to think it could fairly easily be made to work. Of course, the larger the chute chamber, the more pressure you would need, just as 1g of BP doesn't always do it, perhaps a second CO^2 cartridge could be used. _________________ RD
There's another issue at stake when one begins to suggest mechanizing a recovery system; weight!!!
Think about it. Although it would be kinda cool to say your recovery is system designed with absolutely no avionics or explosive charges of any kind, you have to admit that the added weight in springs, threaded rods, servos, CO2 cartridges or what have you would surely prompt you to select a much bigger, and thusly, more expensive motor. In addition to that, you may even have to lengthen your body tube (adding more wieght) or enlarging your fins (adding more weight AND drag), as stability tests may later reveal that your CG is too far back or too near to your CP.
And of course, like Rubr_Duky (cool name btw) mentioned, you'de be compromising some reliability.
If you've got something that's of reasonable weight and of even greater reliability than the traditional avionic/explosive-charge combo, I'd say go for it! Otherwise stick with the programable alitimeter. It's your safest bet, and there really isn't any significant performance/economic advantage to go any other way.
This may be a dead thread but i read this knowing i have the exact same situation infact my final year project at uni is to develop a non pyrotechnic recovery system by exploring of the possible concepts for deploying the chute.
The reasoning is not just the low pressures of high altitude flights but the legal one also. Here in UK the laws on high powered motors have been relaxed, so there is no need for a license for the use of them. Black powder however still does under the Explosives Act. A system like this would be beneficial that sense also. Less paperwork and cost of the license.
Anyone who's worked on any like this or has anything to add your reply will not go unoticed.
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