I have (actually, it’s my daughter’s) an Estes Cosmic Cobra. I figure it’s probably about as simple as helicopter recovery can be, with the nose being the helicopter and the rest descending on parachute. That’s the theory anyway...it has yet to have a 100% successful flight. It’s been repaired/rebuilt after every attempt. Basically, we haven’t had any luck with getting the parachute to come out. The nose has come down occasionally by helicopter blade successfully. But the rocket body itself has either lawn darted or core sampled with every attempt as I can’t seem to pack the chute and blades together tight enough so that they can both deploy with the ejection charge.
Last night it hit me…why can’t I make the Cosmic Cobra come down together and eliminate the parachute all together. I’ve seen a few posts in here where the builders wanted their rockets to descend nose first, or flat to protect fins on landing. And I remembered at least one or two descriptions of the shock cord actually running along the outside of the rocket. And with that I had my idea.
It took me all of five minutes to do it. I drilled a hole in the tip of the nose cone. Then I took some Kevlar cord and threaded it through the hole, pulling the end out through the shoulder so I could tie a knot into it to keep it from slipping back through the hole. I tied a swivel to the other end of the cord and attached the swivel to the shock cord in the rocket’s airframe. Then, I cut a small rectangular section off the front end of the body tube, wide enough for the Kevlar and bit longer than the nose cone’s shoulder. Boom…I was done.
The idea, is that when I prep the rocket, most of the shock cord is inside the airframe, but a section comes out along the cutout section, pulled tight up to the tip of the nose cone. No parachute, and the rocket launches normally. At ejection, the nose cone separates from the body, its blades deploy and it starts spinning but stays connected by the shock cord, and the entire rocket descends under the spinning nose. I didn't take any pictures last night when I did the work, but have attached a basic drawing showing how the rocket should look on ascent and descent.
I have two concerns, one being that the blades were designed to only bring down the nose, and with the full rocket, it may not actually be able to slow the descent enough for a landing with no damage. I figure that the rocket has landed with no slowing for every launch of its career, so even not slowed enough is better than not slowed at all. Assuming everything works correctly, I’ll know after one launch how well the entire rocket is slowed by this design.
The second concern is that the shock cord gets tangled up with the blades during deployment. I haven’t come up with a way to prevent this, I’m just hoping that the nose separates from the body fast enough that the cord is pulled tight before it starts spinning, thereby minimizing the chances. But again, with the blades out, even if they can’t spin properly because of a tangle, I’ll end up with at least tumble recovery, which probably won’t be enough to prevent damage, but it’ll be better than what we’ve had to date with it.
Through my searches here on TRF, it seems that the better design is for a solid connection with the blades, as opposed to a flexible cord. But I think it's worth a try to see how it works. Aside from the two problems I've already thought of, are there other things I'm missing that I should address prior to the first launch?