3 fins and a nose cone...

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Ta.anders

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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

View attachment original.ork
 
Well, It certainly is interesting! Kudo's for originality! :)

I did a simulation with Altitude/total Velocity/vertical orientation and it did some "interesting" things: It appears to go into a tumble after about 4 seconds from Engine Burnout.

My simulation parameters:

Wind: 7.2 km/hr
Wind deviation:1.2 km/hr
Launch site elevation from sea level: 670 metres
Launch rod length: 1.3 metres
Launch rod angle: 1 degree
Direction of launch rod in relation to wind: 180 degrees (tilted with the wind)

Original Flight simulation.jpg
 
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.
 
It looks to me like you just need to add a 1/2 ounce of nose weight to it.
 
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...

egg1.jpg
 
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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