clustering question

[nohup]

Hi, I've been thinking about building a 3 engine cluster, w/ engines inline, 1 24mm D in the center flanked by a pair of 18mm B or C engines. The intent is to be able to fly it w/ either the 2 18mm, the single 24mm, or all 3 engines.

I guess the first question is do all 3 engines need the same burn times or delay times? Obviously the 2 18mm engines need to match, but I am thinking it would probably work if I had a shorter delay on the D engine to blow the chute and the 2 others would just blow into an open body tube. Or should I use booster type 18mm engines w/ no ejection charge & a shorter burn time than the D engine?

Any suggestions on what engines to use would be greatly appreciated, as well as any other comments, advice or warnings. Has anyone else here tried this?
Thanks

 

[KenParker]

Although I have not personally tried it, I think that the design you are proposing is fairly common.

If you want to post the dimensions of your design, there are several people on the forum with RockSim and I'm sure that one of them would be willing to run your design through it with various engine combinations.

I think what most people do with a design like yours when it is flown with all three engines is to use booster engines in the 18mm tubes and use an engine with delay and ejection in the 24mm tube. You probably want to plug the tops of the booster engines so that they will not leak the ejection charge, because they are likely to burn out quicker than the 24mm. The length of the delay you should use will depend on the weight and configuration of the rocket. Again, if you post the specs RockSim will produce a suggested optimum delay.

If you fly it with only the 24mm, don't forget to plug the two 18mm tubes so that they won't leak your ejection charge. And, of course, the same would be true if you fly it on the 18mm's alone - plug the 24mm tube.

If the rocket is kept pretty light, the choice of engines could be quite broad. Again, RockSim can check out various engine combinations.

One suggestion: you might want to make the engine mount for the 24mm tube capable of handling the new longer Estes "E" engines. I have used a number of them now with good results. It would be a cool launch to have 2 C 18mm engines with a central 24mm E engine. The E's have a burn time of about 2.8 seconds, so you would get a great boost off the pad with all three, then burnout of the C's with the E providing another second plus of sustainer thrust.

You have a lot of fun potential in the design you are proposing. Good luck.

 

[jflis]

A close up of the tail of my Maxi-Orbital Transport shows just this configuration...

outboard 18mm and a center 24mm. This model is fairly heavy, so in this configuration I used a D12-3 in the center and the outboards were C6-7. I had differnent recovery chambers and the D12 would kick out a small droge chute and kick off the glider. After another 5 seconds, the outboards would kick out a pair of large (24") chutes.

worked great *S*

jim

 

[jflis]

whoops! would have helped if i actually included the link ot the picture, wouldn't it....

https://jflis.com/hobbies/rocketry/photos/13-mar-01/xport13.jpg

jim