Dual deploy w/ motor eject backup to the altimeter

[Dave S.]

I was working on my 1st dual deploy rocket and was wondering something about the drogue chute and the nomex blanket.

I use the Aerojet DMS motors, so I was thinking I would have the motor eject set to go a couple seconds after the simulation predicted apogee as a backup to the altimeter in case that malfunctions.

Usually I use a nomex blanket and dog barf for my motor eject flights w/ DMS motors. I was thinking that the chute could get hit with a blast of fire from either the motor below it or the altimeter charge on top. Question is - should I just use a large nomex blanket that can fully wrap up the chute top and bottom in case either one goes off first?

That is very probably the case, but wanted to ask what others do.

EDIT - Forgot to mention I have a One Bad Hawk 3 loop kevlar harness that was going into this rocket for the connection between the booster section and the altimeter bay.

 

[Kane]

Using the motor ejection charge as a backup is definitely a useful strategy. Of course, you want to be relatively certain of your flight profile so you can trim the charge to where you want it. Be sure that your actual fully loaded weight, CG, and CP match what's in your sim. The drag coefficient can be the tricky variable. I am usually able to get my simulated drag dialed in after a few real flights by comparing the actual flight altitudes and velocities with the simulated ones. For a first flight, I'd leave as much time after your predicted apogee as possible for the motor backup.
As far as the nomex, best practice IMO is to burrito wrap your chute in the blanket so it's fully protected. I would do this whether I had motor backup or not.

 

[David Schwantz]

No matter type of BP charge, I always fully wrap chute in nomex blanket.

 

[cerving]

Just burrito-wrap the chute in the Nomex and you'll be fine.

 

[Dave S.]

Thinks to all of you. I figured I was on the right track.

 

[thzero]

Yes