This is a preliminary report on an idea I had for a science-olympiad-legal chute release, it still needs lots of refining. It's a "self-cocking" design: there's no tension in the rubber band as the rocket sits on the pad, which is what makes it legal (the rubber band tension in the standard airspeed flap design disqualifies it from SO competitions). In this case, the launch itself "cocks" the release.
Here's the idea: there are two flaps. One is hinged to the bottle just underneath the nose cone, and a thin rubber band holds it out flat, sticking out perpendicular to the bottle. This flap also has a "ledge" sticking out from its surface near the bottom edge. A second slightly longer flap is hinged to the nose cone, and swings freely from it. On the launch pad, the nose flap rests on top of the body flap, like this:
(By the way, this is a nice way to make a quickie nose cone: use the neck portion of a bottle, cut off the neck itself, then glue or tape a piece of a ping pong ball over the hole.)
At launch, both flaps are pushed down by air pressure and/or inertia, so they lie closely along the body of the rocket. As is usual with airspeed flaps, as long as the rocket is traveling through the air fast enough, the flaps will stay against the rocket. With the flaps closed, the bottom edge of the nose flap is just above the ledge in the body flap. Now, when the rocket reaches apogee and the airspeed is low enough for the rubber band to pull the body flap back out, the nose flap gets caught by the ledge on the body flap, like this:
And as the body flap is pulled open by the rubber band, the nose cone gets pushed partially off the rocket, like this:
The idea is to destabilize the nose so it will fall off easily in the chaotic moments when the rocket stops rising, turns over, and begins to fall.
I did some preliminary testing, and the mechanism itself worked very well, effectively destabilizing the nose at or near apogee every time. But the chute ejection isn't very positive, and with all the flaps hanging off the thing, the potential for chute tangling is great, so some refinements are in order to get better reliability.
One chute packing method I tried shows promise: instead of the usual string, I used a strip of plastic cut from a shopping bag, about 2 inches wide and 18 inches long, to connect the nose and rocket. I placed the packed chute in the center of it, then rolled the plastic around the chute, jso that when the nose and rocket separated, the plastic unrolled and the chute was ejected halfway between the nose and rocket. This seemed to mostly eliminate tanglng problems, but delayed the chute release slightly.
Although I haven't tried it yet, I think that two of these flap arrangements, on opposite sides of the bottle, will more effectively eject the nose cone, actually lifting it off the bottle instead of just pushing it to the side. But more flaps also means even more potential for tangling. It would be ideal to figure out a way to also cock a chute ejection mechanism with the launch energy, or to get the nose to actually spring away from the rocket with some force. Put on your thinking caps...
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