Boosted Bertha holes in boosted card stock

[laming]

I just received a BB for Christmas. Why are there holes in the boosted card stock. Are these to vent the rocket?

 

[Scott_650]

I just received a BB for Christmas. Why are there holes in the boosted card stock. Are these to vent the rocket?

Indirect staged rockets require a vent so the booster motor “burn through” can ignite the sustainer motor. Without the vents the hot particles from the booster motor might not make it up the sustainer motor’s nozzle - the cool air mass trapped between the booster and the sustainer has to be displaced so the hot gasses/particles from the booster motor can fill the space.

 

[laming]

Thank You

 

[Raythain]

They also ensure that the sustainer lights without the booster over pressurizing the interstate gap and blowing the sustainer off.