Calculating Force Necessary for Stage Separation?

[jmmome]

Ok- it's a goofy idea, but I'm spitballing. I have two HPR two stage rockets which carry camcorders, and I've always wanted to see the booster fall away from the upper stage before upper stage ignition. Never happened in five or so successful flights.

So I came up with the idea of putting two pods on the booster section, each carrying an Estes A, B or C motor and pointed up. A timer would ignite those motors maybe a second before the upper stage is timed to ignite.

So how would one calculate the force necessary from those Estes motors to nudge the booster section away from the upper stage? I know the mass of the booster stage and the estimated velocity at time of ignition.

Again, it's a goofy idea, but I'm not trying to set any altitude records with these two stage rockets (lol)- it just seems like an event made for capture on onboard video.

Mike Momenee
TRA#12430 L3

 

[mikec]

I have two HPR two stage rockets which carry camcorders, and I've always wanted to see the booster fall away from the upper stage before upper stage ignition. Never happened in five or so successful flights.

Are you using a BP stage separation charge? That's the standard way to do this.

 

[jmmome]

Nope- didn't even consider that. I always seem to be drawn toward the Rube Goldberg-type solutions.

 

[jmmome]

If when referring to the BP charge you were talking about the charge from the booster motor- that wouldn't be possible. For the smaller two-stage rocket, the BP charge from the booster motor deploys the booster recovery parachute. For the larger two-stage, I'm using a dual deploy altimeter to deploy the booster's drogue and main chutes, so the altimeter bay would be in the way.

 

[mikec]

If when referring to the BP charge you were talking about the charge from the booster motor- that wouldn't be possible.

No, I'm talking about a small BP charge fired by a separate altimeter channel to separate the stages prior to second-stage motor ignition. Or you can fire it at the same time as second-stage motor ignition, since it usually takes a little time for the motor to come up to pressure.

Obviously this only works if the electronics that fires the second stage is in the second stage.

 

[Nytrunner]

Sounds like you'd want to make it a slip fit interstage coupler so drag separation occurs at booster burnout.

Or as mikec suggests, use a timer or aux channel set to blow a sep charge at burnout +x seconds.

 

[jmmome]

Yup- it is a slip fit interstage coupler on both rockets, but drag separation has never occurred. My altimeters do not have a second channel, but I could use the timer on the second stage to fire a small BP charge at the same time as it fires the second stage igniter. I think I can retrofit that easily enough- thanks guys!