Recovery Charge sizing, not usual question [Result]

[Tonimus]

The payload bay on my 4" Patriot is 8" long. And it is full. Very. There's only the 1.5" or so inside the nosecone shoulder that is air space. Considering this, how does one size an ejection charge?

 

[GregGleason]

I have my own calculator.

Assuming 8" of empty volume, no sheer pins, and 100 N of force to remove the nose cone (guessing at that one), I would start with 0.75 grams of BP for your first test. It will probably be +/- 0.15 grams of that initial value.

Greg

 

[tim cubbedge]

Here's a link to a calculator.

https://www.rockethead.net/black_powder_calculator.htm

 

[jmmome]

I would definitely recommend a ground test before you launch.

Mike Momenee
TRA #12430 L3

 

[Tonimus]

I am definitely going to ground test. The starting point is like black magic. I think I'll start at .75 grams. I've got 2 #2 shear pins, due to doing dual deploy.

 

[Tonimus]

I settled on .6 grams of 3Fg BP for the main 'chute compartment. I did not note it before, but there are 2 #2 shear pins.
[video=youtube;CfsrGtF2AVI]https://www.youtube.com/watch?v=CfsrGtF2AVI[/video]

And here's the reason we ground test. Drogue gets hung up in the body tube, taking the sustainer for a ride.
[video=youtube;PNfhuY_ohaE]https://www.youtube.com/watch?v=PNfhuY_ohaE&feature=youtu.be&t=15s[/video]

And the successful drogue test:
[video=youtube;mM9JiCOBA0Y]https://www.youtube.com/watch?v=mM9JiCOBA0Y[/video]