Will this work...

[flying_silverad]

While building the new "Smoke and Fire" I have run into an issue I hope someone can help me with. This is a 3 engine cluster rocket that I need to channel ejection gases through a 3/4" hole inside a Balsa TA6080, about ten inchs away, in a Bt80 tube. Question:
1.) Is the hole through the transition large enough to handle that amount of gas.
2.) And, will the inside wall of the bored out transition smolder/burn even though it's 10 inches away from the motor? (Thinking about coating inside with glue.)

See pics for ref.
BT80, TA8060, Respective tubes and motor mount.

Triple Cluster Engine Mount

 

[sandman]

John,

I wouldn't worry about the transition burning.

A single coat of Elmers on the inside should be more than enough to protect it.

The thing I would be concerned with is the transition getting "blown off" by the force of 3 ejection charges going off at once.

sandman

 

[Fore Check]

Nice engine mount - BMS does a good job on those centering rings, eh?

What are they made of (material) and what cluster radius did you use? I am about to order some 3x24mm BT80 cluster rings myself - I can't decide between 1/8" lite ply or 3/16 basswood. on RSim, the 3x24mm motors fit very nicely and evenly on a cluster radius of 0.6 inches, however that places them a tad further apart than yours and a tad closer to the host tube (it appears that way, anyhow)

Regarding your question: I agree with Sandman regarding the possibility of blowing off that transition with three ejection charges. This might be solved in two different ways: use a 0 delay booster on 2 of the three engines (which presents a separate host of problems) or use longer delays on 2 of the three engines.

For the latter, say the optimum delay on your cluster is 3xD12-5. I'd use one D12-5 and 2 x D12-7's. Just make sure that you put a couple of thick pieces of wadding on top of the 7's. The 5 delay should deploy your recovery system. Then the 7 delays go off 2 seconds later. The hole through the transition will be vented to atmosphere (imparting less back pressure) and the d12-5 carcass will now be a hollow tube to provide additional venting of the 7 second delay charges through the rear. Just make sure that all of the engines fit nice and snug and that your hooks hold everything securely in place.

 

[flying_silverad]

I used 1/8 Birch ply. I basically had him set it up so that all of the motor tubes are together. In a BT80, that's the most practical method for what I needed. I basically filled out the BMS spread sheet and e-mailed it. 4 days later, a bag full of rings!

I used Space Cad for this which, as far as centering rings are concerned....stunk. It does not take into account the motor mount tube around each motor! Luckily, BMS always listens to what you want, then give you what you need!

Since this may end up being kitted, I may just opt to have it recover into 2 sections. I don't know how a buyer would feel about having to use either plugged engines or mixing delays. I wouldn't mind, but that's me. I may just opt for dual recovery.

 

[Vance in AK]

Hi John.
Just a question from a guy that still has ALOT to learn.
Why would you go to dual recovery rather than a single chute with the transition being the seperation point?
If I was scratch building using engines with different delays wouldn't bother me, but I think if I was looking at a kit to purchase I would expect the designer to have worked it out so I could use matching engines.
Just my .02.
Vance in AK.

 

[Fore Check]

Originally posted by Vance in AK
Hi John.
Just a question from a guy that still has ALOT to learn.
Why would you go to dual recovery rather than a single chute with the transition being the seperation point?
If I was scratch building using engines with different delays wouldn't bother me, but I think if I was looking at a kit to purchase I would expect the designer to have worked it out so I could use matching engines.
Just my .02.
Vance in AK.

I don't mean to answer for John, but....

I believe his intention is to sell this design in kit form - hence the desire to have all the delays worked out as you describe.

You can check out his neat clones and other designs at www.thrustaero.com

Be sure to get some of his ripstop nylon 'chutes. I HIGHLY recommend them. The BEST performing chute I've ever used - bar none.

 

[Vance in AK]

Understood Fore Check.
My question was why dual recovery with seperation at the transition rather than a single chute with seperation at the transition.
I have one of John's chutes & am very impressed with the workmanship too. When it comes time to order chutes or clones he'll get my business.
Thanks, Vance in AK.

 

[flying_silverad]

"Why would you go with dual recovery instead of a single parachute at the transition seperation point"

I can't say for sure that I'll go with dual deployment (split vehicles) I just have a hard time (in my mind) with the size of this upper payload section dangling and banging around. You see, the upper section, including the transition will be somehwere around 20-22 inches long! Longer than the aft portion for sure. When I design a rocket, I like to visulize everything...that means how it looks statically, during launch and recovery.

But...I wonder if I could use two chutes and still have them tied together??....hmmmm

 

[flying_silverad]

Originally posted by sandman
John,

I wouldn't worry about the transition burning.

A single coat of Elmers on the inside should be more than enough to protect it.

The thing I would be concerned with is the transition getting "blown off" by the force of 3 ejection charges going off at once.

sandman

That's what I thought. Might do 2 coats. The first a little diluted so it seeps in and then another coat of full strength.