Originally posted by JStarStar
Both good points, I don't know if any currently available kits feature engine-ejection recovery. I think fire codes would be extremely dubious of the idea. Ejecting still-smoking loose engine casings into grass, etc. probably ain't a good idea.
A few current manufacturers sell kits that feature engine-ejection. Estes and the 220 Swift (do they still make the Quark? if so, throw it in there) being a primary example.
Also the Blink rockets from RocketHead rockets.
Starlight rockets has one or two like this as well.
I also wanted to throw my 2 cents in on this tumble vs. featherweight recovery thing.
If a rocket kicks the motor, it is featherweight recovery. Very basic rule of thumb. Think about it.
The rocket would *have* to be SOOOOOOOOOO marginally stable for the engine itself to put the CG ahead of the CP that even minor nuances in finishing techniques would throw the whole ball of wax out of whack. Particularly in *small* models where "featherweight" recovery is employed, thus reducing the weight, the distances, and the margin for such error.
For a rocket to become unstable upon ejection of the motor casing, the CG would have to move *rearward* significantly enough for the rocket to become significantly unstable after losing only a handful of *grams* at the location of the engine (mind you, the rocket must still be stable after the propellant is spent. This instabilty must occur after losing the weight of only the casing, any spent BP residue, and the ejection charge and clay cap.)
Am I getting through now? I'll be *EXTREMELY* suprised if anyone here can
kit a rocket that will become unstable after kicking the weight of the casing of an Estes SU A3-4T. yet the rocket was still stable under coast. And that rocket must fly to a respectable height, be easy to build (be no more than 3 or 4 FNC) and be at *most* a skill level 1. Oh, and there must be *zero* restrictions on how I finish the rocket, and no warnings necessary about acheiving proper balance prior to launch.
If we're speaking the same language now - who here has seen an Estes Mosquito, Quark, or 220 Swift come down in a "tumbling" motion? The thing was stable when it went *up*, it got *MORE* stable when it spent the propellant AND kicked the engine. It lawndarted. Light enough that no harm was done, but be honest - that's what happened.
For "Tumble" recovery, lets refer to the Estes Astron Scout. This is *still* one of my favorite rockets. With all due respect, Jim, I have not seen nor read a review of your Tumbleweed. I trust that it follows similar principles.
On the Scout, the engine is forward in the body tube an inch or so during launch and/or boost-coast. The ejection charge fires, and the motor casing is kicked back to the end of the engine hook (which extends more than an inch beyond the base of the body tube). The casing is *retained* in a position behind the position that it was during boost - coast. In this design, the weight of the engine itself helps to keep the CG ahead of the CP during boost - but then, as the CG dissipates as the propellant is spent, and then the ejection charge throws the remaining mass rearward (and then it is held, not lost) finally tipping the scale of the CG/CP relationship. The Scout comes "tumbling" back to earth. In this design, the rocket actually becomes *less* stable as the propellant is spent (which is untrue for most rockets out there.)
I hope this makes sense. I feel like I'm rambling now.....