Queston on staging - gap between motors

[JRobinsonUSAF]

What would be considered the largest acceptable gap between the top end of a “D” booster motor and the nozzle of a “D” sustainer nozzle to ensure ignition. I am looking at a scale/semi-scale two stager that, if built to specs, would leave a 3 inch gap between the two motors. Is this wishful thinking, or would I be able to get second stage ignition?

 

[tsai]

I have a rocket with an 8" gap between. Use a small vent hole near the second stage to prevent separation from the pressure. 3" should be no problem.

 

[rharshberger]

What would be considered the largest acceptable gap between the top end of a “D” booster motor and the nozzle of a “D” sustainer nozzle to ensure ignition. I am looking at a scale/semi-scale two stager that, if built to specs, would leave a 3 inch gap between the two motors. Is this wishful thinking, or would I be able to get second stage ignition?

Gap staging can be reliably done up to 10", its a good idea to put a vent port near the upper motor to prevent early seperation. I have successfully gap staged 8" with zero failures over the 10 or so flights with my rocket that uses it.

 

[kjohnson]

Are you talking about a 3" gap with nothing in between, or a 3" gap that allows for some sort of tubing to direct the hot gas and particles from the booster to the sustainer?
What's the prototype?

kj

 

[JRobinsonUSAF]

Are you talking about a 3" gap with nothing in between, or a 3" gap that allows for some sort of tubing to direct the hot gas and particles from the booster to the sustainer?
What's the prototype?

kj

The gap would be within a tube the same size as the motor (BT-50), between the top of the booster and the nozzle of the sustainer.

JR

 

[kjohnson]

Yes that will work fine. As others have said, put a hole in the top of the connecting tube, just below the bottom of the upper stage motor.

kj