Hello,

I will be attempting a two-stage flight this weekend using a PML Quantum Leap. Most likely using Js for both stages. Does anyone have experience with using shear pins to secure the two stages? I used them successfully for general recovery, but not sure on the using them for the inter-stage coupler.

Any thoughts are most welcome.

Fred Hower

I'd recommend a friction fit. What advantage do you think the shear pins would provide? Maybe I'm missing something.

I think it depends on how you plan on igniting your upper stage. if you have the ignition on the upper stage then a loose friction fit with a planned drag separation would be optimal. If you are relying on ignition from your booster then you really dont want them separating early - so shear pins, in my opinion is a great, reliable way to go. Friction is such a ubiquitous quantity to try to guess on what is enough to prevent drag separation and what is not too much to prevent boost separation. At Balls last year we staged a M to an L and we used a timer in the booster to ignite the upper stage. We went with shear pins to keep them coupled - the Majority of people at Balls thought we were nuts and that the coupler would explode when the engine ignited. If I remember correctly it was a mid thrust CTI L-730 so not a really high impulse motor - but end story our transition/ coupler with the shear pins worked perfectly and we hit 38k+ on the flight. No damage to the coupler from the boost. My comment is if you watch most rockets light they have an initial flare from the ignitor before the motor really comes up to pressure so that is what should shear the pins. It worked for us. I have also 2-stage flights with a timer in the booster with a friction fit which also worked so I guess go with your gut feeling. Either way it can work. -Sean

The QL has the timer in the booster if I remember right. I never got to try mine so.... I look forward to seeing it. However you decide.

The 98mm two stage I have been working on has the timers in the sustainer, and timers and ejection charges in the booster section, to say goodbye to the booster right after burnout. Still a work in progress though.

Decided to build a smaller version to experiment with, as 98mm motors cost more money than say......Js . 😯