Shear Pins in Interstage

[cerving]

I have a Madcow Nike-Apache, 2.6"-29mm, and I was thinking about lighting the sustainer from the booster since there's not much room in the sustainer AV bay. I'd be concerned that it might drag separate at burnout due to the differences in diameter, so I was thinking about using a couple of #2 shear pins to hold the sustainer to the interstage. Does anyone know if the sustainer blast would be enough to break the shear pins? If not, I was thinking of putting a charge in there, so that the sustainer plume lit it and blew them apart... but that might be me overthinking things again...

 

[FredT]

I've had flights where the separation charge didn't fire for one reason or another and the motor did the trick. One shear is enough, that's all I ever use.

 

[Reinhard]

I have a Madcow Nike-Apache, 2.6"-29mm, and I was thinking about lighting the sustainer from the booster since there's not much room in the sustainer AV bay. I'd be concerned that it might drag separate at burnout due to the differences in diameter, so I was thinking about using a couple of #2 shear pins to hold the sustainer to the interstage. Does anyone know if the sustainer blast would be enough to break the shear pins? If not, I was thinking of putting a charge in there, so that the sustainer plume lit it and blew them apart... but that might be me overthinking things again...

It's a bit of a function of seal vs burn speed. Compared to a BP charge you might want to pay a bit more attention how well everything is sealed. If that is the case, the motor will build up pressure until something breaks, which will be the shear pins unless you've made a design error.

The seal doesn't have to be perfect. As a rule of thumb, I'd aim for a leakage cross section that is not bigger than the nozzle throat section. The tighter the seal, the earlier the separation happens, which means less time for hot gases to damage something around the leak path.

For practical purposes, I'd expect any mechanically sound (i.e. non wobbly) staging coupler should be more than tight enough.

Reinhard

 

[Cameron Anderson]

I have a Madcow Nike-Apache, 2.6"-29mm, and I was thinking about lighting the sustainer from the booster since there's not much room in the sustainer AV bay. I'd be concerned that it might drag separate at burnout due to the differences in diameter, so I was thinking about using a couple of #2 shear pins to hold the sustainer to the interstage. Does anyone know if the sustainer blast would be enough to break the shear pins? If not, I was thinking of putting a charge in there, so that the sustainer plume lit it and blew them apart... but that might be me overthinking things again...

You every fly this?

 

[jderimig]

Older thread but one of my favorite subjects. Why would you want to prevent sustainer separation if it wants to? It will cost you altitude.

 

[cerving]

You every fly this?

Not yet, too busy doing electronics. Hopefully in the Spring... I already have a Double-Shot and a 38mm MD-38mm 29mm ready to go for the Fall launches. I've seen a few of these... one had the sustainer glued to the transition, like a big nose cone, and the other used it as a boosted dart with no motor, just a big BP charge.

 

[cerving]

Older thread but one of my favorite subjects. Why would you want to prevent sustainer separation if it wants to? It will cost you altitude.

I'm probably going to fire the sustainer from the booster, so I don't want them to separate until ignition, so it doesn't pull out the igniter. If I was going to ignite the motor from the sustainer, I'd definitely want to ditch the booster asap, especially since it's a larger diameter than the sustainer.

 

[Cameron Anderson]

I'm probably going to fire the sustainer from the booster, so I don't want them to separate until ignition, so it doesn't pull out the igniter. If I was going to ignite the motor from the sustainer, I'd definitely want to ditch the booster asap, especially since it's a larger diameter than the sustainer.

What electronics, if any, are you putting in the
Apache sustainer?
I have a 2.6" Nike Apache and I'm flying the booster with no electronics (motor recovery) and my GPS and Raven in the sustainer. I couldn't find a way to get electronics in the booster that I was happy with.

 

[cerving]

What electronics, if any, are you putting in the
Apache sustainer?
I have a 2.6" Nike Apache and I'm flying the booster with no electronics (motor recovery) and my GPS and Raven in the sustainer. I couldn't find a way to get electronics in the booster that I was happy with.

Probably a Proton in the booster and a Quantum in the sustainer, doing deployments only. I'll probably have to add a few inches to the transition-booster coupler.

 

[JamesT]

I have a Madcow Double shot that will be making it's fist flight at LDRS40 next week. I will be using a Perfectflight StratologgerCF for sustainer dual deployment and a Missile Works PET2+ timer for sustainer ignition. After some ground testing, I had to replace two 9V (in parallel) batteries for one LiPo that discharges fast enough to light the igniter. I had to 3D print a holder for my GPS tracker that fits inside the nosecone shoulder since there was no room in the e-bay. In the Booster I am also using a Missile Works PET2+ timer for booster separation and then parachute deployment. I am using 2-56 shear pins for the inter stage coupling to keep everything together. For the sustainer electronics bay, I 3D printed a sled that sits between the all-thread rails to maximize space. The first flight will be a 38mm AT J500G to a 29mm AT H250G. For the first flight I am using a motor adapter/reducer in both the booster and sustainer.