Complex Estes Cluster 3 stage

[Lucas]

I am designing an estes sized rocket. In the booster it will use 4 estes C6-0s in 18 mm pods and in the central tube a D12-0. 2 of those outer pods will have nosecones on 2 of the tubes. The second stage has another D120 in the center and 2 outboard C motors. They are lite by the outboard C6-0s in the booster. The final stage will have an E9-8 in it. I will post some pictures soon of the start of the rocket. It should be cool. 4 C motors and a D staging to 2 C motors and a D. then staging to an E motor.

 

[powderburner]

An ambitious plan--

Do you have any info on the burn time of your first stage C6-0s and the D12-0? One of these is going to burn through sooner than the other. Even with the 1.68 second burn time for the C6 (catalog data) and the 1.70 second burn for the D12, that may not be close enough.

Add to that the variation you will have at first stage ignition (on the pad), where these motors may ignite at different times (ignition time will be a function of motor age, igniter age, igniter electrical conductivity, igniter head size, igniter head placement, ignition clip connection, and a few others) and your five first stage motors are almost guaranteed not to light at the same instant. Which means they will not burn out at the same time.

At that moment, one of your second stage motors will be lit (hopefully this will always be the central motor?), the stages will begin to separate, and there will be a significant chance that the other second stage motors will not ignite.

Oops.

You may want to start experimenting with three-on-three and see how well that works, before investing in a bigger design.

 

[Lucas]

The D-12 has a 1.70 second burn and the C6 has a 1.68 second burn which are very close. I believe that it will work. There is moderate chance that some of the motors will not light in the second stage, but I am fairly confident that they will. Also all of the motors are very close to the center of the rocket If one of the C motors does not fire then I am not sure if the rockets trajectory will change that much. do you know if it would? We have a cluster of a K in the center and 4 Js surounding it, one of the Js did not light but the rocket flew relativly strait. This was not close to a minimum diameter rocket either. The central motor mount is in a 4 in tube and it is 54 the outboard motors are in 54mm pods and are 38mm MMs.

 

[shreadvector]

Add the total propellant mass. I think you exceed the limits of "Model Rocket", but I have not pulled out my calculator. correct masses are on the NAR website.

https://nar.org/SandT/NARenglist.shtml

C6-0,3,5,7C 10.8 grams

D12-0,3,5,7C 21.1 grams

E9-4,6,8,PC 35.8 grams

 

[jflis]

Originally posted by Lucas
The D-12 has a 1.70 second burn and the C6 has a 1.68 second burn which are very close. I believe that it will work. There is moderate chance that some of the motors will not light in the second stage, but I am fairly confident that they will. Also all of the motors are very close to the center of the rocket If one of the C motors does not fire then I am not sure if the rockets trajectory will change that much. do you know if it would? We have a cluster of a K in the center and 4 Js surounding it, one of the Js did not light but the rocket flew relativly strait. This was not close to a minimum diameter rocket either. The central motor mount is in a 4 in tube and it is 54 the outboard motors are in 54mm pods and are 38mm MMs.

Well, there are other concerns. You have to be CERTAIN that the D motor is the one that lights, if only one does light. Because it is the D motor that will light the top stage E motor. Without that burn she's going to come down hard.

Also, a 1.7 vrs 1.68 second burn is not as close as you think. If you had a 3 motor cluster with ALL C6 motors, you would have a very high probability of ignition failure because there are so many other factors in the timing:

1) How fast do the motors ignite. They will NOT all light at the same time.

2) how fast will the motors burn. The 1.7 seconds is just a spec number based on some random test data. The actual burn could be quite a bit off from that and I assure you that each motor will have a different actual burn time

3) At what time during the burn does the fuel slug break through to light the next stage. This will also be different for each motor even if they are all C motors. It is a function of chamber pressure and the resiliancy of the fuel slug and a dozen other factors

4) After the fuel slug breaks through to light the next stage, how long does it take to light that next stage?

Just some more things to think about

jim

 

[Lucas]

Thanks for the sugggestions! It is very helpfull!