Help with Mini-Cobra

[bcdlr]

I'm building a Mini-Cobra from Jim Z's plans. The plans call for .05 card for the fins. Can I use 1/16" balsa without affecting the weight too much.?
---
I'm also planning on using a balsa nose. Going to do the shock cord like a Semroc or Quest with a piece of kevlar around the motor mount and a piece of elastic. Sound good / comments?
This will be my first 'scratch' built and first two stage.
---
And yes, I have some 13 mm booster motors. Got most of my stuff from BRS Hobbies and the motors from Countdown Hobbies. Countdown has a good deal of OOP stuff.

 

[powderburner]

Yes, you can safely substitute 1/16 balsa sheet for the cardboard fin material (it is probably even lighter than the cardboard) if you are using the same size fins. You could also use some tablet-backer cardboard, or doubled-over notecard cardboard, but these will be a little weaker than the balsa approach.

The kevlar/elastic combo is a good idea. I use it often myself. I like having a tether that reaches out the front of the rocket so I can replace the shock cord if it ever needs it. The only way I have found that is better than this is to use an external mount for the tether. Anyway, you should be fine with your improved shock system as long as you can get all that stuff packed back into the front of the rocket.

I hope you have a really big field to fly that thing. Or else, I hope you are not too attached to it?

 

[bcdlr]

Originally posted by powderburner
I hope you have a really big field to fly that thing. Or else, I hope you are not too attached to it?

You think it will be that bad?
I may wait to take it to where the local club shoots (not a member yet).
I have some 1/2 A-0T's I was going to start out with...

 

[powderburner]

Many of those little "minimum diameter" designs will really get up and go. And the small ones are hard(er) to see at apogee---well, at least they are for my old eyeballs.

You may want to try flying your rocket with only the upper stage for a first shot. You may also want to swap out any 'chute that you might be using, and go with a small streamer or with nothing at all. A recovery system called Nose-Blow is one where you just pop the NC at ejection (you still use a tether and/or shock cord) and let the thing tumble down. You get a faster descent but you may get more landing damage unless your field has lots of nice grass.

When I started launching rockets as a kid, the two-stagers (and some of the single stage rockets) were lost on the first flight. I think I went through three Estes Apogee II rockets before I gave up on recovering both stages. I hope you have much better luck, but don't say I didn't warn you-----

 

[BobH48]

I think I went through three Estes Apogee II rockets before I gave up on recovering both stages

Does that ever sound familiar

I had quite a collection of Apogee II booster stages after a while. I don't know what happened to them.

I have been contemplating building a Mini-Cobra also because I have about 25 A10-0T's to use up but I don't feel like making 25 upper stages

I think I need to make something more substantial if I expect to have a chance to recover the upper stage

bcdlr, Take it to a club launch. You may actually see it again. A lot of times, if you can't find it, someone else will find it while they are looking for their rocket.