Magnum II

BDB said:

Thanks for the input. The engines were taped together, but it is a bit difficult to do because they are two different sizes. The original Magnum worked great because the 18 mm sustainer engine fit perfectly inside the 29 mm booster engine, so you could overlap the two motors by ~1/16". But that isn't the case with the 24/29 mm combination. However, I should mention that I used masking tape instead of cellophane. I forgot that cellophane is recommended for staging. (It's only been 25 years since I last did this.) Do you guys know why we friction fit with masking tape but join stages with cellophane?

I started repairing the sustainer yesterday. It is actually a very quick fix. I'm just waiting on a BT60 payload bay from Estes, and I'll be ready to repaint.

For the booster, I'm going to try all of the above. I think I will sand the crud out of the aft end of the 24 mm sustainer engine casing next time, so it nests into the booster engine a little better, tape well and combine all of that with 3 x 1/8" vent holes in the centering rings and at the top of the booster engine casing.

Click to expand...

Cellophane is thin, easy to break once started, and burns/melts through quickly, masking tape is thicker so it builds friction fits faster, is not slick on the outside, but it would take longer to burn through and might not do so cleanly.

It worked!!! (and then it didn't)

Last month, I finally had a chance to test my hypothesis about the need for venting when staging with 29 mm BP motors. The idea was that there is so much empty space inside a E16-0 and an F15-0 that the pressure build up caused by the burning booster separates the stages before the sustainer ignites. I experienced this twice in a single day in December (vide supra).

I modified my booster by drilling three small holes through both centering rings (not shown), so pressure could be vented out the aft end of the rocket. I also shortened the front end of the motor mount ~1/4" and cut grooves into the motor casing to allow gasses to escape.



I then sanded the aft end of the C11-7 sustainer motor so ~1/16" of it seated into the F15-0 booster motor and then taped them together with two strips of cellophane, being sure to not cover the vent grooves in the booster motor.

Besides the unintended rod whip (I really need 1/4" launch lugs.), the flight was great. Staging happened at least 1000' up, which caused the RSO to exclaim "What were you thinking!" Luckily I had cut a large vent hole in the chute and the sustainer landed safely on the field.

...the issue was the booster recovery. The motor casing must have been ejected during the staging event. To all of our surprise, it was stable! It just floated like a glider into the woods, never to be seen again.

Excellent! (aside from booster loss)

The motor must have broke free if it came down like that. The booster for mine came down quick and landed with a thump with just a D12 casing in it. Well at least they're simple and cheap to rebuild...

Regarding the rest of the flight: What kind of altitude did you get? How far was the recovery?