Staging AP to Black Powder Motors
 

For a long time, I'd wondered about the possibility of staging an AP motor to a black powder motor, using the AP ejection charge to ignite the BP motor (no electronics required).
I did a ground test where I successfully lit a BP motor using an ejection charge (both motors held fixed), but I wasn't sure how representative it was of what would happen in-flight.
Well, at the OROC return to flight launch last month, I gave it a shot.
I've have an Estes PSII Mammoth that I liked to fly two-stage (F15-0 to F15-6), using the PSII booster. It was impressive to watch with that slow boost off the pad - but even using an 8 ft. rail - it didn't take much of a wind gust to cause a big weathercock. Sure enough, the last time I'd flown it, big weathercock and it impacted just as the ejection charge fired - major damage requiring the replacement of most of the body tube. So this time I decided to go F40W to F15-6. It worked beautifully! I took an F40-4W, drilled the delay down just shy of 4 seconds (I didn't want it to stage while the the booster was still thrusting), and ditched the red plastic cap for the ejection charge - instead wrapping masking tape around the top part of the forward closure and adding about twice the normal BP charge. The Aerotech 29/40-120 casing is about an inch longer than the Estes F15 so the retainer didn't work - but for proof of concept I retained the motor with lots of masking tape - allowing the extra inch to hang out the back. I was sure to give the rail an angle away from the flight line - just in case the experiment was a failure...
The flight was perfect - nice, straight boost off the pad with plenty of speed to prevent weathercocking. I'd drilled the delay grain almost perfectly - there was a slight delay between burnout and staging but it was less than a second - and then that nice, long F15 burn with ejection right at apogee. The booster tumbled back , landing in some sage roughly midway between the high power pads and the flight line.

Now that I know it can work, I'm going to make a new booster to properly accommodate the 29/40-120 casing (I plan to stick with RMS so that I can properly adjust the delay). Next time I'd like to us a G64W.

That is really cool! Aerotech made booster motors in the 80s, composite with 0 delay for staging. Your method is good if you don’t get a bonus delay or torch the closure if you drilled too far and the delay burns through while the motor is still burning.

Supposedly one can stage Quest 18mm upper stage motors with BP boosters as well.

Very nice!
What a great experiment...

Bob

That's the beauty of doing with an RMS - I can trim the delay with the delay tool - ideally leaving about a second after burnout. As long as I keep it short, even a bonus delay should still have the upper stage nearly vertical.
One thing I do worry about is finding the booster - ordinarily a lost booster is just a couple dollars of fins and body tube - now I have a pricey motor casing to worry about, and coming from much higher altitude so it's not a given it will land near the pad. OK if launching on a nice grassy field or lake bed, but our launch sites around here are mainly sage - at times you can walk a few feet from a rocket and not see it.

That sounds quite marvelous, Tim. I'll be interested to see how this develops. Thanks for sharing!

You could alter a SU delay by emptying the ejection charge and inserting the drill into the delay via the small hole, then pouring the ejection charge back into the top. It is unlikely that the single use delay formula is different from the reloadable delay slugs, so you should get similar reductions for the same depth you drill. However, you're now dipping into "modifying motors" so you are violating NAR rules. :eek: