2 Stage Scratch Rocket

[Lancecrafter]

Hello again. I'm building a 2 stage rocket with a D boost and a C 2nd stage. The boost stage is going to utilize vent holes, so the colder air can escape. The boost tube is 4 inches and is the same size as a D engine mount. Any tips or suggestion? Short of buying Semroc simulation program.

[Doug Sams]

Hello again. I'm building a 2 stage rocket with a D boost and a C 2nd stage. The boost stage is going to utilize vent holes, so the colder air can escape. The boost tube is 4 inches and is the same size as a D engine mount. Any tips or suggestion? What you describe is very similar to the 1st-to-2nd stage operation of the Estes Comanche, which uses a D12-0 booster to a C6-0 (or B6-0) 2nd stage. Most everyone modifies it by adding vent holes to the 1st stage.

Below is a close-up shot of mine showing one of the two vents. The aft end of the staging coupler, outlined by the dashed pink line, functions as the motor block for the D12-0.

(The kit was old when I got it, and the decals were very brittle - hence the chips in the green band :( )
http://www.doug79.com/comanche/com-boost1-2.jpg

Positive motor retention is a must in boosters. It ensures the booster stage separates with the motor.

On mine, I added an external motor hook which you can see in the pic below. It's not one of my better implementations - it coulda used another round of filler - but it shows the key details such as the C-bend which keeps it from twisting. A wrap of tape around the aft end of the hook secures the motor.

Also notice the length of masking take on the coupler. This is used to friction fit the coupler into the next stage. This keeps the 1st stage attached to the 2nd for just a hair longer at staging to ensure the 2nd stage motor lights. This gets adjusted each flight to make sure it's not too loose nor too tight.

HTH. Doug.

http://www.doug79.com/comanche/com-boost2-2.jpg

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[Lancecrafter]

So is the airframe of this booster shown the same size as the D engine or does it have a motor mount? If the coupler is doing a double duty as coupler/motor block, it makes me think it is, but i just want to make sure.

The only other ? I have. Have you ever tried attaching side tubing, like on the Renegade, but cut the side tubing so it is attached to the booster and the main airframe, and they just line up, not connected with couplers, so the booster can come down with chute/streamer?

[Intruder]

Since your booster is short, you don't HAVE to have vent holes, but using them anyway won't hurt anything. Since your rocket is minimal diameter, I would suggest that you put the vent holes in the coupler so that it can't be seen.

As far as using streamer/parachute recovery, I wouldn't recommend it. The way you described it would make the streamer/parachute get caught in the sustainer's exhaust which could damage it beyond use. Besides, the booster your describe will tumble on the way down which will make it fall plenty slow to land without damage.