Shear Pins in Interstage

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cerving

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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

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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

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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
 
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