Spitting the liner...does that affect performance?

[DAllen]

So NDRT had their first test flight this past weekend and it looked like about 2/3 of the way through the flight it spat some of the liner. The reload was a I435 and the white liner around the grains is what appears to have been ejected. While I am not entirely sure that this is exactly what happened I can say there was significantly less debris inside the main black liner than normal. Does this affect overall performance? They were expecting 2k but only managed 1600. This doesn't sound like a lot but when you're doing a competition details like this are important.

 

[David Schwantz]

Just a quick guess, but could the nozzle have been plugged partially?

 

[DAllen]

Just a quick guess, but could the nozzle have been plugged partially?

I loaded it and am 100% nothing plugged it. If there was it was after ignition.

 

[Theory]

No, wouldn’t affect performance of the motor.

Have had many AT motors do that and the performance was “within the noise.” H250s seem to do this on the regular

 

[tfish]

Did you go look at the pieces of casting tube? Often there is still propellant stuck to it. I would say ..yes it does affect performance...

Tony

 

[Theory]

@tfish are you saying that a casting tube with chunks of propellant on it was spit through that nozzle?

 

[eggplant]

@tfish are you saying that a casting tube with chunks of propellant on it was spit through that nozzle?

Seen it before. Depends on a lot of factors, but usually it'll be on high L/D, high pressure motors and the web of the grain will be down to a tiny fraction of the original, like <0.125" thick. I glue grains in just about any motor that uses casting tubes, and prefer to cast directly into the liner in part for that reason.

 

[tfish]

@tfish are you saying that a casting tube with chunks of propellant on it was spit through that nozzle?

no...
I'm asking him if he found and looked at the casting tubes spit from his motor.

I see and find casting tubes..often still have propellant on them.

Tony

 

[tfish]

Usually it's the bottom 2 grain's.. casting tubes... that can get spit out...before their time. I just did a burn sim..one grain similar to those in a I435.. One grain with just .125 coating of propellant..each side is is actually .250" worth. That's about 42 n/S roughly a 5% F44 worth.

Tony

 

[kjhambrick]

So NDRT had their first test flight this past weekend and it looked like about 2/3 of the way through the flight it spat some of the liner. The reload was a I435 and the white liner around the grains is what appears to have been ejected. While I am not entirely sure that this is exactly what happened I can say there was significantly less debris inside the main black liner than normal. Does this affect overall performance? They were expecting 2k but only managed 1600. This doesn't sound like a lot but when you're doing a competition details like this are important.

Interesting Thread @DAllen ...

Do you have any pictures of the flight and the post-flight motor debris ?

-- kjh

 

[Theory]

All I know is I have had several motors spit casting tubes and the performance of the flight (maximum altitude as recorded by the on-board electronics) was what I would expect, and within normal motor/flight variation.

 

[DAllen]

Since getting the right alt is so important maybe I'll glue the grains in for the next flight...hmmmm. Can't hurt can it?

 

[ECayemberg]

Spitting casting tubes isn't uncommon, especially in longer motors, those with tapered cores, higher mass flux, etc. Gluing grains to their respective liner is indeed the fix and won't change the performance of the motor so long as excess glue doesn't creep out and onto the grain faces.

 

[kjhambrick]

@DAllen --

1600 ft -vs- 2000 ft isn't a whole lot of difference when comparing actual to sim'd altitude ...

So one other Q is what were the specs of the rocket ( at least the diameter, length and mass ) so I can play along at home ?

Thanks

-- kjh

 

[Theory]

Finish is also a big deal when it comes to sims. Also, let’s not forget there is an appreciable variance in motor performance from motor to motor.