G74 - WARNING

Wanted to share this with you all and hopefully save a rocket or two. Some may be aware of the WAC Corporal I built earlier this year. The one that met its end on its very first flight due to the failed ejection charge of a G74. Aerotech replaced that motor with a G77 and I then proceeded to analyze the failed motor.

First there was BP in the well so that wasn’t the issue

Cut that sucker open and found that the delay was completely burned.



Took out my trusty xacto and scratched the area between the delay housing and the charge well and, a, Houston...




The gap in the well is completely covers / plugged with epoxy!

I contacted aerotech and Karl tells me that this is new to them. I checked my remaining G74s (popped off the red cap, dumped the BP and made sure the gap in the well was clear) they were good

Let this be a word of warning. Check your SU motors, it just may save your project!

-Sean

Oh dang, that ain't cool.

Sorry to hear it!

Please make sure to log a report of the failure at motorcato.org.

What is the motor lot code?

Yikes. Ummmm...

Check em out. It will take a bit but it’s worth it!

Theory said:

Check em out. It will take a bit but it’s worth it!

Click to expand...

And if any more are found with epoxy blocking the touchhole please report it to motorcato.org.

"Aerotech replaced that motor with a G77 and I then proceeded to analyze the failed motor."

I believe that motor failure analysis should be standard operating procedure for the manufacturer. Unless there is some danger of some post office "sniffer" (assuming they even exist) false alarming for some reason on combustion products, the manufacturer should request the motor be mailed to them for analysis, making that a requirement for a replacement motor and including a coupon to compensate for return postage.

Thanks for the info.