Aerotech J800 Liner

[DHays]

So today I had a Aerotech J800 spit out two burning chunks of propellant about half way through the burn. Upon motor inspection after the flight, there are two damaged spots on the liner. ( the case is fine) I don't know if this had anything to do with this or if the damaged liner is normal? Don't know if a grain collapsed during thrust or not. I did use a flashbulb for an ignitor. Any thoughts on what might of happened? I don't think that I am going to use flashbulb ignitors anymore. I did not do any grain bonding.

Thank you!

 

[n3tjm]

My guess there was a void in the propellant. This could cause the spitting, and also creates a "hot spot" in the liner. The collapsed "bubble" on the liner happens when the liner cools down.

 

[DHays]

My guess there was a void in the propellant. This could cause the spitting, and also creates a "hot spot" in the liner. The collapsed "bubble" on the liner happens when the liner cools down.

Oh ok, yes I see how that could happen. I think in the future I will take the grains out of the liner and inspect them when assembling the motor. But the void would probably be inside the grain and not visible more than likely.

Thank you for the info!

 

[Josh Anderson]

Hey Don, still was a great looking flight.
Just out of curiosity, did the nozzle have any damage to it when you disassembled the motor? Was talking to some people about this and wondered if that happened.

 

[DHays]

Hey Don, still was a great looking flight.
Just out of curiosity, did the nozzle have any damage to it when you disassembled the motor? Was talking to some people about this and wondered if that happened.

Oh hey Josh thanks!

I kept all of my used parts just in case I needed to go back and look at them at a later date. I just looked at the nozzle again and it appears normal. I didn't see any leakage around the O ring sealing areas. The inner taper of the nozzle does not have any damage, just the normal burnt propellant accumulation. The throat still looks round just by looking at it. No cracks or pieces missing from it. Going by the date on the package, it was from 2022.

By the way, you guys did a fantastic job of LCO!!

 

[n3tjm]

Got a vid of the flight?

 

[DHays]

Got a vid of the flight?

I don't. Just a still picture of it as it is leaving the pad. Looked normal.

 

[n3tjm]

I'd love to see that picture

 

[DHays]

I'd love to see that picture

This is the picture from ThunderStruck in Indiana that Justin took. It is in post #50

 

[rfjustin]

View attachment 575491
This is the picture from ThunderStruck in Indiana that Justin took. It is in post #50

So from what I saw/heard when the rocket took off, this was one spicy J-800. I've seen dozens on these fly over the years, this one seemed to be pushing more horses through the barn door at higher pressure than usual. To my "trained" eye, it appeared like the bottom most grain collapsed and got ejected out the nozzle. Or at least that is what I observed. There was some amount of propellant that was chunked out of the case and burned outside the rocket. Just sharing my observations... J

 

[DHays]

So from what I saw/heard when the rocket took off, this was one spicy J-800. I've seen dozens on these fly over the years, this one seemed to be pushing more horses through the barn door at higher pressure than usual. To my "trained" eye, it appeared like the bottom most grain collapsed and got ejected out the nozzle. Or at least that is what I observed. There was some amount of propellant that was chunked out of the case and burned outside the rocket. Just sharing my observations... J

I wonder if I should do grain bonding on any future J800 just in case? Or do you think that it would of happened anyway?

It was good to see you at the launch!

 

[rfjustin]

I wonder if I should do grain bonding on any future J800 just in case? Or do you think that it would of happened anyway?

It was good to see you at the launch!

IMO, grain bonding never hurts, only helps... But is it necessary for a J-800, I doubt it... I'm hoping AT will give some additional feedback.

 

[n3tjm]

That doesn't look like a typical J800 flame to me. Maybe because they no longer use the medusa nozzle (so sad).