Mounting snap ring cases to test stand

[dvdsnyd]

When testing motors in snap ring cases, what part of the motor should take the load, the forward closure or the case?
Thanks,
Dave

 

[0011001100]

I have my motors clamped to a sled and the whole sled moves but the force on the load cell is from the forward closure (actually from a pipe elbow because I also use a pressure transducer). Since my liners are still intact at the end of the burn I see no reason it wouldn't be accurate.

 

[Kelly]

It shouldn't matter. I've seen some people here talk about commercial motors that they say are more prone to CATO (in flight) if the forward closure is the point of thrust transfer, buy I can think of no reason why this should be so.

 

[rharshberger]

It shouldn't matter. I've seen some people here talk about commercial motors that they say are more prone to CATO (in flight) if the forward closure is the point of thrust transfer, buy I can think of no reason why this should be so.

possibly it could occur if the forward closure is taking the entire load and the liner gets damaged (snap ring or CTI style 24-54mm cases). Not sure if that is a issue, but with pressure inside the motor being higher than out side the motor it would be hard to move a forward closure backwards in the case during the burn phase.

 

[eggplant]

possibly it could occur if the forward closure is taking the entire load and the liner gets damaged (snap ring or CTI style 24-54mm cases). Not sure if that is a issue, but with pressure inside the motor being higher than out side the motor it would be hard to move a forward closure backwards in the case during the burn phase.

For a hypothetical 3" motor (2.75" ID) running at 1000 PSI you'd have about pi*(2.75/2)^2 * 1000 ~= 6000 lbf of force keeping the FC against the retention ring or snap ring. I don't care how long your 3" motor is, it isn't producing close to 6000 lbf of thrust. You see the same result for any diameter, where the motor would have to be quite high thrust for the diameter and running at a low chamber pressure for these figures to get at all close.

 

[rharshberger]

For a hypothetical 3" motor (2.75" ID) running at 1000 PSI you'd have about pi*(2.75/2)^2 * 1000 ~= 6000 lbf of force keeping the FC against the retention ring or snap ring. I don't care how long your 3" motor is, it isn't producing close to 6000 lbf of thrust. You see the same result for any diameter, where the motor would have to be quite high thrust for the diameter and running at a low chamber pressure for these figures to get at all close.

I was figuring something like that but didn't know how the numbers would play out.

 

[dvdsnyd]

@eggplant
Andrew,
Thanks for quick gut-check. That's what I was initially thinking, but I appreciate your explanation.
I'm also looking forward to RTMS, hoping supply chains start to gain some robustness. I'm hoping to get in on your next run.
Thanks again,
Dave

 

[AdAstraPerAspera]

For a hypothetical 3" motor (2.75" ID) running at 1000 PSI you'd have about pi*(2.75/2)^2 * 1000 ~= 6000 lbf of force keeping the FC against the retention ring or snap ring. I don't care how long your 3" motor is, it isn't producing close to 6000 lbf of thrust. You see the same result for any diameter, where the motor would have to be quite high thrust for the diameter and running at a low chamber pressure for these figures to get at all close.

I could see a sudden impact changing that, however. If the closure wasn't firm against the bulkhead before flight, then shifted and impacted against it, then I could see a problem...