Aerotech RMS Failure

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Swissyhawk

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I had a failure this weekend using an Aerotech G53-7FJ in an Aerotech ARCAS. There was some burning, maybe weak thrust, definitely not a normal thrust. I don't remember if there was an explosion sound; it happened so quickly. After a few more seconds, there was an ejection charge pop and the chute deployed like it should. The rocket never left the pad.

The motor liner was split and one grain was still inside of it unburned. The aft closure was completely missing. The forward closure was still attached to the case. I had an Estes Motor retainer on the rocket. The part that is glued to the MMT was still attached but a little bit angled. The screw on part was still screwed on, but the lip that holds the motor in had been blown off. The MMT appears intact. The baffling blew off the end of the MMT. There were two charge containers stuck in the baffling. Obviously one was from a previous flight. I'll have to watch that. Lastly, the forward centering ring completely burst apart and the body tube was buckled where the center ring was attached.

Can anyone tell me what might have gone wrong? I'm worried that I assembled something incorrectly and I don't want to repeat that mistake.

Thanks.

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Unless you remember exactly how you assembled it, we will not know if that was the issue or not. Did you use the igniter that was supplied with the load?
 
I used a First Fire Jr. Igniter. I was kind of hoping someone could say this kind of failure is typically caused by ..... Anyway, I'm a little concerned by the aft closure being missing. I just don't see how that thing could come off.
 
They're actually made to fail in that manner, to keep the case from rupturing. Did it come with the Firstfire igniter? There's too many variables to diagnose the problem with the info you've shared so far, especially with it being a reload.
 
It came with a different igniter. The first launch I went to, it was suggested that I not use the igniters that come with the motor kit.

I secured the igniter by bending it over the nozzle and then putting that little red plastic cap over the nozzle.
 
first fire jr or 1st fire jr 3"? did you use a launcher stand off(elevate the rocket off the blast deflector)? my 1st impressions are that the igniter wasn't installed properly(at the top of the slot, which is easy to do if you overlooked taping the grains together), and you had a real hard chuff. w/o the aft closure and nozzle tis hard to figure out what else might be a cause.
Rex
 
I can't find the nozzle info for the G53, but I don't think that's the issue. The motor overpressurized for some reason, I'd guess it was one or all of the things Rex suggested above.
 
Definitely looks like a overpressure event. I say that because the motor retainer, aft closure and nozzle are missing. Also the liner is split, Plus the baffle has been pushed out of the motor tube and through the centering ring with a lot more force than a standard ejection charge would have. I would definitely try to find the missing parts if you can because that would really help determine what happened. If possible you need to check to make sure it had the correct nozzle (0.141") and that the First Fire Jr. Igniter didn't block the nozzle.
 
It was a first fire jr 8". There was a block sticking out of the rail that the rocket rested on. I'm very positive I taped the two grains together. This was my first time where you weren't allowed to put the igniter in before going to the pad. (This was only my 5th or 6th launch). I was nervous about installing the igniter on the pad. I found it kind of awkward. Maybe I didn't get it all the way in. What's a chuff?


Unfortunately I won't be recovering the missing parts. That was at Red Glare and I live a couple of hours away.
 
Never be nervous about installing the igniter at the pad...it's a safer procedure and it's pretty much mandatory for flying HPR. Could have clogged the nozzle but there's no way to say for sure. If you are uncertain you didn't get it all the way in that's a big potential clue. You could have lit the bottom of the grain and it didn't have the pressure to 'spit' the igniter out and it was all bunched in the nozzle when it tried to pressurize.

A chuff is when the motor doesn't fully pressurize and the propellant is trying to ignite and keeps extinguishing and re-igniting. As the word implies it's when the motor 'chuffs and puffs' before lighting.

Not using the supplied igniter could be an issue too. Don't be afraid of Copperheads, they work pretty well...and FJ propellant is really easy to light too. If you don't know how to make them two lead igniters all you do is put a lighter to the leads (NOT the pyrogen end of course) and it will burn away the insulation between the copper strips making two leads.
 
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I did vent the red cap. I cut a notch out of it with a razor blade.

Its a 29 mm. I haven't really looked at the threads closely. I guess I could try putting my other aft closure on it and seeing if it screws on ok or not. I do think I only hand tightened it. I believe that because later I came across the wrench for the aft closure and I remember using the wrench on the second motor I put together but not the first one.
 
Hand tightened should have been sufficient. The wrench just makes it easier on the hands, especially for the 24mm case.

Adrian
 
Did you vent the cap?

It came with a different igniter. The first launch I went to, it was suggested that I not use the igniters that come with the motor kit.

I secured the igniter by bending it over the nozzle and then putting that little red plastic cap over the nozzle.
 
Venting is one thing you do to allow gasses to escape as the igniter burns and allow the propellant to start burning over enough surface area to fully ignite and pressurize. if the igniter was to pop out with no venting the ignition process can be interrupted or altered in a bad way.


BUT, if the red cap is on too tight, the vent hole allows the motor to come up to pressure but the cap will never pop off. If you used an absurdly larger igniter with very thick wires, the red cap will stay on and the wires will either not pop out of the nozzle properly (clog and bad failure mode) or they will pop out and remain attached and flailing around in the exhaust stream causing strange variable thrust deflection as the wires interact with the exhaust.

That is why, if using the red cap for the igniter retention, you do not install it all the way (super tight = BAD), you barely plug it onto the tip of the nozzle. The vent hole will allow the gasses out, but once the motor really ignites, it will blow the cap off and spit the igniter wires out. Unless the igniter wires are absurdly too large for the nozzle and can bend and clog the nozzle if they are held on with a too-tight red cap or an absurd amount of masking tape. Rubber bands usually work best at popping off at the correct time, but I'm sure someone could use way too large of a rubber band....


I did vent the red cap. I cut a notch out of it with a razor blade.

Its a 29 mm. I haven't really looked at the threads closely. I guess I could try putting my other aft closure on it and seeing if it screws on ok or not. I do think I only hand tightened it. I believe that because later I came across the wrench for the aft closure and I remember using the wrench on the second motor I put together but not the first one.
 
I pretty much gave up on the supplied Copperhead igniters anywhere I’m not allowed to actually build the motor with the Copperhead installed as the instructions state.

I believe AeroTech is discontinuing the Copperheads and are now supplying some other type, perhaps the FirstFire, with new reloads. I haven’t built one of these new reloads and thus haven’t read the instructions with regards to the use of the “Red Cap”

I do know that when using ignites that have wires I toss that cap and just tape the igniter in place. I’ve never had a problem doing it this way.

I have to agree with previous observations, you didn’t tape the grains together and the slot for the upper grain was misaligned thus the igniter wasn’t completely inserted resulting in “Bad things happening” though that begs the question as to how the delay grain ignited.
 
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