Flash pan ignition of BP motors, started by composite motor

[plkap74]

I've been kit bashing together a cluster that is a bit too heavy to use only BP motors (29mm core, 2x 18mm boosters). I'd like to be able to use Estes BP motors on the boosters because of the option to get 0 delay ones for fall-away boosters in flight. But I know I can't just wire together and ignite composite and BP at the same time because of different ignition speeds. I was thinking of making a flash pan that is initiated by the flame of the composite motor. One other complexity is that the boosters are displaced vertically and horizontally somewhat far from the core. I saw this "spider" contraption that has brass flame guides from a central BP pan. http://meatballrocketry.com/wp-content/gallery/articles/spider/spiderdwgnew1.pdf, and was thinking of making something like that out of brass tubes, with an open central pan and tiny hole, then more BP inside the larger tube. It would be secured to and kept upright by the the launch rail, before putting the rocket on. Any thoughts on this?

I know airstart is also an option, as is using all composites, but I am curious about if this approach seems feasible.

 

[SolarYellow]

Use four boosters and go all BP.

 

[Antares JS]

It doesn't sound like it would be all that reliable. How quickly is your rocket taking off the pad? Is there a possibility it would leave the flash pan behind too quickly for it to light the boosters? I would suggest getting your hands on some fuse, put a piece of fuse in the BP motors, and position the ends of the fuse such that they will be lit by the composite motor.

 

[heada]

Build/Use a spider which is like flash pan but the foil is shaped so that the loose BP is directed into the nozzles of the BP motors. More contained and more reliable that open pan.

Another option is to use fast paper fuse. Fuse from Skylighter. It's NOT quick-fuse (regulated!!) Burns at 0.1 sec/ft up to 0.4 sec/ft. Open the fuse some to expose the BP coated strands to the exhaust of the APCP motor and place the other end in the nozzle of the BP motors. I use cotton string (kite string) to bundle the fuse together and have used it on a 7 motor cluster (1x APCP and 6x BP)

 

[plkap74]

I 3d printed this U shaped spider with an opening in the middle to let the exhaust from the composite motor ignite a small amount of BP inside the U. I tested with an e-match and about 0.25g of black powder, seemed to spit flames the right direction! Hopefully that is enough to ignite the two BP booster motors mounted higher up on the sides of the rocket. I'll put a metal plate or some foil with an opening to make sure it doesn't just melt the U on the first attempt.