19th September 2011, 03:26 AM
3 fins and a nose cone...
hi everyone, i'm new here, (not to rocketry) and i am about to start on my "3fnc" build. a quick check with openrocket says its a go, but im not so sure, and dont know what to do about the recovery system in the small amount of space. help would be great, especially if you have done something similar. thanks
19th September 2011, 04:10 AM
19th September 2011, 05:43 AM
I'm thinking rear ejection with a streamer or chute wrapped around the motor tube. Change the parameters of your fins to 3/32 rounded balsa and that will lighten up the rear a bit. That should help the CG some. Check your parameters on the nose cone and tubes as well. The overall weight seems a little bit high to me. Move your LL to about 14 degrees radial. I would also add a forward centering ring. You may still need a 1/4 ounce of clay in the tip.
Very cool design. I've done a few of these in MMX scale for spot landing comp.
19th September 2011, 06:27 AM
Here's just a thought here. Still in the spirit of a very short rocket, but considerably more stable and higher flying.
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19th September 2011, 01:26 PM
It looks to me like you just need to add a 1/2 ounce of nose weight to it.
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19th September 2011, 06:14 PM
In my experience, it's a little light in the nose. OR says about .5 calibers stability. What I would do, is to glue a spent engine casing in the nose. The "inner tube" (as OR calls it) would slide over this. I would use a (flame-proof) streamer wrapped around the base of the inner tube as recovery. The engine casing in the nose (maybe a little extra epoxy...) will add weight and serve as a piston and protect the inside of the nose cone. I did something like this with my egg rocket (casing acrually fit *over* engine tube in egg). Also - you may experience tumbling just after thrust ends. I've seen several "odd ball" rockets that were stable under thrust, but tumbled before ejection (examples are the egg rocket, and some spools). Here's the insides of the egg...
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20th September 2011, 12:11 AM
Wow, thanks for all the help. I did plan on adding a bit of weight to the nose, and now I just have to figure out some type of ejection method, probably piston/ streamer as sooner.boomer suggested. Will post pictures when finished.
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