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[airforce]

I'm creating a multi-engine rocket for under $20. I will use 2 Estes B or C and 1 D. I'm sorry I can't provide a picture but here goes. I'm using an Estes Super Nova 'D' power for the main body and 2 Banshees fixed to each side. I only want chute deployment from the main body but I don't want to be bothered buying non-ejection motors for the Banshee boosters. I was thinking that I could exhaust the ejection charge using ports on the outer side of each Banshee. Finally my question, how much pressure does a B or C Estes create? How many exhaust holes will I need to keep it from exploding?
I think it will be really neat even if it only launches once but I would just as well have it back.
Thanks for any help.
Randy

 

[sandman]

Try this, use a reasonable delay on the main body with the "D" engine say a D12-5 depending on wt. Then, use a very long delay, like a C6-7, on the two outboard engines and rig them so that they just deploy their respective nose cones at ejection.

You will need shock cords in the outboards.

And be sure to check it for stability with all those engines in the rear!

sandman

 

[airforce]

Thanks sandman that would probably work. I was concerned with the burn time as well as the ejection delay. B, C and D engines have different burn duration don't they?

 

[jflis]

Here's a thought...

Let's take a lesson from history (for us oldsters anyway... ) and look at models like the Estes Scout, Sprite and the FlisKits Tumbleweed

These models were not much longer (the body tube) than the motor they held. There were designed such that the ejection charge would kick the motor back, to catch a hook, then stop. The remainder of the ejection gasses were then directed out a small (1/4" - 5/16" diameter) port hole in the side of the body tube.

With the motor kicked all the way back, that left a cavity of about 1" long and the diameter of the body tube to contain the expanding gas and push it out the port hole. In all my years of flying these models, i have never seen one "blow up"

So, while there *is* a bit of pressure, I would say that the risk is minimal.

With all of that said (sorry to drone on so...), I would consider this approach:

Take a stage coupler to fit the body tube of the Banshees and glue it in place at about the mid point of the model. Cut a port hole in the body (i would say that 1/4" would be enough) at the MIDDLE of the stage coupler. This will give you a port (vent) hole, but one that is re-inforced with the strength of the phenolic stage coupler for long life.

Further, I would set it up so that the port holes on each banshee were pointed in opposite directions, tangent to the Super Nova body. Select motors such that the outboard ejection charges go off AFTER the main motor burned out, but BEFORE the main motor ejected...

This would have the effect of putting the model into a gentle spin just before deployment....

If I wasn't clear on what I mean, let me know and I will sketch it up and post it.

jim

 

[airforce]

Thanks Jim,
I think I know what you mean but a drawing, like a map, would certainly confirm ones thoughts. I'm old but not an oldierocketguy. I was thinking more about sandmans ideas, I could shoot some streamers out of the Banshee tubes just for looks. Originally I was thinking, fixed nose cones with exhaust on the Banshee and like you I thought a 1/4 inch hole might work and the Banshee tube already has one for the external shock cord attachment. I guess part of the fun and originality is to choose one way and try it.
Thanks again for the ideas. By the way, how can you determine the burn time on B, C and D motors? I know some burn longer then others. I suppose a B6 burns longer then a B4 ???
Randy

I can't wait until you let us buy your new offerings. I feel like a kid waiting for Christmas.

 

[Stymye]

I like the ejection spin gas idea alot Jim!


sounds like a fun project
...keep in mind the possibility of tangeling chute and streamers
as well when you design the recovery set-up.

 

[jflis]

The burn time of the motors (and actual ejection times) can be found in a number of places on the web.

most notably, at the NAR site https://www.nar.org/

You will also find the burn time in the catalog and on the motor data sheet that comes wiht the motors.

i'll post a figure this afternoon when I get home.
jim

 

[Micromeister]

Simpler yet, don't use the motor hook, perssure fit the outboards and kick the motors a ejection, If your worried about free falling b or C motor caseings tape 2 or 3 inches of streamer to each motor near the nozzle end. Works Great.
You could also vent the longer delayed outboards into the main body with a slot 3/16" wide by about an inch long. I usually use 4 card stock "mounting plates" over the slots then epoxy to seal. Sorta like the mounts on the deep space transport. excellant way to prevent the Oops! if your center motor fails to ignite. Check out the clustering the classics thread..in the lowpower section.. Good pic of a 3-C6 clustered SR-71 in this situation

 

[loopy]

Okay, not sure how you would do this, but it would be killer if you could! Have you thought about using the Banshee's like strap on boosters? I think there's some thoughts on this on EMRR, but there could be other examples on the web. Just a thought...

Mark

 

[jflis]

First, careful on kicking the motor... I had a question on that particular issue with the NAR and the official ruling is that kicking a motor withOUT a streamer attached is a violation of the safety code.

Aside from that, here is the sketch I promised on cutting a port hole.

let me know if it helps.

jim

 

[airforce]

Thanks Jim for the drawing, a very neat drawing. How clear it all becomes when its that obvious.
Loopy, your idea about strap on boosters, you mean have them actually depart from the main body like real boosters? now wouldn't that be so cool.
I would be willing to bet, that if it can be done, someone on this Forum will have the needed steps with pictures and comments.
I will be waiting for the knowledge to pour in.
Randy

 

[Micromeister]

Jim:
Tell it to Estes, Quest and just about ever other manufacturer that has and is making model rockets. Mosquitos, quarks, several B/gs the list goes on and on of models that kick the casing by design.
I just pulled out my copy of the Model Rocket Safety Code and reread all 14 points, there is absolutely nothing in it about free falling motor casings or any reference to kicked motors.
It is only a violation of the Sporting code (Pink Book), during contests,.. Why I do not know, but as I said in the previous post, 2" of streamer material make for a nice fit, and fill the bill if your worried about the contest code.
Kicking a motor casing is not a voilation of the SAFETY CODE.
Just to keep everything in proper prospective.