Discussion in 'Propulsion' started by ATGM, May 16, 2015.
Was that you at Bama Blastoff?
We spoke after, you showed me the case. Either you or Chris S. said that the case would be replaced. Very glad to hear it was, but I was not sure with whose (AT/CTI) case.
Curious, how long did it take for your to receive the replacement case and reload? Days, weeks, months?
ANYTHING that beats CTI's YEAR PLUS replacement cycle is $$$$$$$$$
Got the motor a month later from Chris at a launch in Georgia. Think it took about 2-3 months for the case which came direct from Aerotech.
That does not sound too bad given the hardware availability problem reported on this thread.
I had my first CATO today on an Aerotech 29/40-120 G76-7G. The motor discharged thrust out the nozzle at launch, and within a second, out the forward closure through the ejection charge well. The inside of the rocket was toasted pretty well and took a nose first landing. That crushed anything that hadn't been scorched. I gave the motor enough time to cool off and took it apart to see where I went wrong. All of the o rings and the forward insulator were intact with the exception of the delay o ring. That, as well as the delay liner and spacer were completely gone. The charge well hole was also burned open to about 1/4" diameter. The inside of the casing is still in good shape and all of the threads stayed clean and undamaged. It looks as though the delay burned through in a second or less instead of the 7 seconds it was set for. I've looked at the Aerotech warrantee, and this appears to fall under one of their exceptions for coverage. I'm okay with owning my own mistakes, but I'm not sure where this one went wrong. I'm open to suggestions from people with more experience than me on where I might have made my mistake. Thanks for helping out a new guy.
This failure is almost always the delay spacer not being installed towards the propellant grain, but instead being put forward into the closure.
This is how I CATO'd a G-64W. A lesson I won't soon forget.
Another possibility is an overdrilled delay, though at 7s that's somewhat less likely.
Good to know. My daughter had the same thing happen a couple years ago on some F motor in that’s hobby case. I was always going to see about getting a new fwd closure for it but never have.
I appreciate the replies. I took another look at the inside of the forward closure and there is a residue on the inside face that would have needed an air gap to be deposited. I think that is a clear indicator I had the spacer on the wrong side. Tough lesson, but at least I shouldn't have to repeat it. Thanks all.
I had the same thing happen to both my cases on the same 2 motor cluster flight. They were G53FJ. Everything was assembled correctly including the delay grain spacer and the delays were not drilled. These were a brand new batch and what I noticed about them was the delay liner was very loose in the forward closure. If I tipped it upright the delay and liner fell right out. I didn't think it would matter. It seems that it did.
I started wrapping each delay liner with a layer of masking tape after that and didn't have another failure.
BTW, I sent photos of the parts to Aerotech and received two new forward closures and two reloads.
+1 Beat me to it! The delay liners lately supplied with the reloads have been very loose. In the last 2 G-64's I used this year I had to tape the delay liners to get a snug fit in the delay well. I use cellophane tape. The flights were nominal. I had to tape other loads previously also. There has been discussion about this in other threads or earlier in this thread. Make sure the delay liners fit snugly in the well.
Had the pleasure of working with a 98-15360 case and N-2200 Dark Matter reload. Easy to assemble and everything fit like a glove. Looking forward to letting this baby rip at LDRS!
Initial check and preparation.
Greased O-rings and assembled forward bulkhead.
You're gonna love that motor!
i had the same issue with a J350 that spelled disaster for my cert 2 flight back in 98'. ever since then i put a good coat of Dow 111 grease around the delay insulator. no problems since.
I saw the M2200X pics from LDRS 38 on your Facebook page. Any estimate when this will be available?
I'm really looking forward to seeing the thrust curve too... How does it compare with the M1297 for total impulse?
Here is what they posted about it. 5498 total impulse
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