Stability of rocket with flyaway pods.
 

I'm working on a clone of the Estes Titan IIIe. I'm planning on making the boosters powered and flyaway.

To do that, I'm planning on clear fins on core and boosters. I'm thinking that if I make each part stable, I should be okay when they are put together.

So I've put the core and boosters in separate OpenRocket files. The boosters take a little noseweight. And I'll build them with just two fins, though I simmed the single one with four.

Does this sound like a reasonable approach?

It would seem that you are on the right track. CMR used to sell single fin add-on pods for existing "normal" rockets that do the same thing you are trying to accomplish. However, I have no direct experience with it and I don't know personally if there are any "gotchas" with this type of parallel staging and recovery.

Considering another thread I've posted in, this may seem ironic for me to do, but....

George Gassaway has been online here today and I'm sure will drop back in soon. He will know something about your project if nobody else has direct experience with it. If he hasn't done it himself, he's seen it done in competition at various levels. There was a finless Titan 3 or 34E at one of the Rocket City Classics in Huntsville several years ago. At the very least, he's probably familiar with that one. Compared to a finless Titan, one with fins should be a cakewalk.

Im trying to stay away from that thread. Too many old dogs chewing favorite old bones :-)

Lol :) I added a link to your thread so George would see it when I replied earlier. You can PM him if you are in a hurry to move ahead with the project.

I'm patient. Still need to fly my big Vigilante successfully.

I could always ask over on TRF. But I'm trying to contribute some rocketry content here :)

These are the CMR pods I was talking about.
http://www.ninfinger.org/rockets/ca...87/87cmr25.html

You know, I've seen that print somewhere else before. I've come across it before. Thanks for the reminder - that's very much like my plan.

Yes. Except that I would not put noseweight in the boosters. If the entire stack needs forward weight, it is better to put a little less in the top of the core - you know, that long lever thing.

A booster does not need be stable on its own unless you intend for it to separate and continue for a bit longer under power. As long as you have enough fin area on the core and the boosters combined to make up for the added weight of the boosters, you should be fine.

It goes without saying that the core should have enough fin area to remain stable after the boosters are gone...


Bill

The CMR pods and the USR Sentra SRB pods are not "flyaway". They both eject from motor ejection and "fall" away. Not sure if you are munging terms or not.

http://v-serv.com/usr/kits/sentrasrb2.7.htm

To answer your question, two fins should be sufficient and there is likely to be coning.

I do mean fall away. And the Sentra SRB is one of the midels I've been looking at for ideas.