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Tinker

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Tthis rocket is a design testbed for a rocket I have been thinking about since I was a kid. I moved to Colorado and was driving out near Hartsel (which is just down the road) and thought I have to get back into rocketry and design my masterpiece! Who new they launched HPR in Hartsel......
So Apogee is just down the road (along with Estes) and I got a copy of Rocksim and built my big bad super duper rocket in Rocksim. After some long hours of mixing and matching it is basically done. (3 stage with clustered first, E&F Black powder motors)

Rocksim says it will fly 5600ft and 600fps! But this brought some issues, first of which being I need a level 1 cert for 210grams of black powder.
Second of which is I want to see this rocket again so this means dual deployment from a BT-60 rocket, so this got me thinking about aft ejection for the drogue shoot but then there is the problem of drag separation......

So, I won't be ready to buy all the stuff I need for a level 1 cert before winter sets in up here at 9400ft, so I thought I would build a test rocket to work on the aft ejection issues. Aft ejection would seem silly in this rocket as front is so much easier but I would rather blow the side out of this rocket then my big one. So here I am. I need in this case to be able to eject the aft end without blowing up the rocket. (Assume it must overcome ~13 newtons of internal restraint against drag separation) This rocket will be 24mm Estes engines, but the big one will be 29mm. I am afraid if I don't deal with the ejection charge elegantly, that it will fail critically somewhere before it pushes the tail off the rocket (and drag on the released aft pulls the shoot out of its sealed container). So here we are at baffles and aluminum foil.......

Current design has the MM tube at 5.75 inches to allow for 2" of brillo at the top of the tube. 1" space from top of MM tube to bottom of baffle 2-3" of baffle and then entering a 1" space below the parachute container. (From top of MM tube to bottom of chute container is double walled) The rocket will separate at this space. I am not sure 4-5" in a BT-60 tube is enough room for those gases in that short amount of time before separation, so I was thinking of venting some out the bottom, but then this will be extra force I will have to overcome as it will work against separation.

I need to understand how much pressure a BT-60 tube can take. Current calculations I think have the pressure at ejection at ~27 PSI in the pressure area of the tail. Is this too much? Secondly I need to understand how much force I need to counteract to prevent drag separation.

The baffle works like this. Each bulkhead is separated by a double 24mm MM ring. This ring has 'tail' that connects it to the wall of the BT-60(c) tube. Next to this 'tail' are holes drilled in the bulkhead so that high pressure gas come up through these holes and travels around the outside of the 24mm ring until it comes to the other side of the tail where there are holes up through the next bulkhead. This repeats 2 more times with the gas traveling ~4.5" in 2" of height. I will probably line the entire thing with aluminum to absorb more heat.

When the gas come out of the baffle, it hopefully will separate the rocket there, and as the tail pulls away, it pulls open the canister holding the parachute and pulls out the main shock cord and chute.

Here is the Rocksim file. Any help would be appreciated.

View attachment Super Alpha 24 (Rear Mod).rkt
 

BEC

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Just an FYI - the Jolly Logic Chute Release fits in a BT-60 model fairly easily.....so that's another option to have the effect of dual deployment.

Not as interesting, perhaps, as what you're describing, but it could do what you need.

....just a thought.
 

Tinker

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Just an FYI - the Jolly Logic Chute Release fits in a BT-60 model fairly easily.....so that's another option to have the effect of dual deployment.

Not as interesting, perhaps, as what you're describing, but it could do what you need.

....just a thought.
Cool, I hadn't thought of that. In the big project for next year, I was going to use a RRC3, so that both aft and noses ejections are on program, while the built in estes ejection would be the redundant one for the drogue chute and the programable event would be the redundant for the main. This is a good thought though.

My only worry about this baffle design is that it might make too much back pressure, and thus cause either some bad failure OR could it vent the pressure back out the motor and not put enough gas in the separation section...

Tinker
 
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