F62 Ejection at Burnout

[FlyAwaySam]

Hello!

I launched a TARC rocket with the 24mm Aerotech F62 today where it failed at launch. The launch went normally up until burnout when the ejection charge fired, causing the rocket to end its flight well short of a normal flight (the rocket itself was fine). As far as I can tell during the motor cleaning, nothing looked out of place although everything was black so I did not notice if there was anything missing. Is there anything that cause the motor to behave like this or just an unlucky launch?

Thank you.

 

[bjphoenix]

If the ejection charge went off at propellant burnout then this was a defective motor. Other things could happen to cause premature deployment such as a loose nose cone that comes off early.

 

[Buzzard]

In a reloadable motor if the delay insulator assembly is loose in the forward closure, hot gases from the propellant can leak around and set off the ejection charge. If it happened at burnout, as bjphoenix noted, it could have been a loose nose cone or payload section. With TARC you have the egg weight to consider. The model deccelerates, but the payload section continues on its way. We saw that happen at a recent DARS TARC launch.

Chas

 

[FlyAwaySam]

If the ejection charge went off at propellant burnout then this was a defective motor. Other things could happen to cause premature deployment such as a loose nose cone that comes off early.

In a reloadable motor if the delay insulator assembly is loose in the forward closure, hot gases from the propellant can leak around and set off the ejection charge. If it happened at burnout, as bjphoenix noted, it could have been a loose nose cone or payload section. With TARC you have the egg weight to consider. The model deccelerates, but the payload section continues on its way. We saw that happen at a recent DARS TARC launch.

Chas

Thank you. I was able to get a video of that launch. The video showed that the ejection charge did go off and not the payload section falling off as it was on the ascent stage of a normal flight so it was the motor.

 

[dpower]

As far as I can tell during the motor cleaning, nothing looked out of place although everything was black so I did not notice if there was anything missing.

When disassembling a motor like this, to diagnose the problem you need to carefully take all the pieces apart to verify they were all in place. Even though everything was black, you'll still be able to tell if anything was missing or in the wrong place. Were all 3 O-rings in the right place, and intact? Was the forward insulator installed, and in the correct place? Was there any black on the outside of the delay insulator? When you removed the delay O-Ring, did you see a nice clean surface where the O-Ring was? When AT RMS motors fail like this, it's usually due to assembly, not luck, as there's not much to be defective (though it's possible the wrong parts were in the package). Common assembly issues include parts missing, in the wrong place, O-Rings damaged during assembly, or as Chas mentioned, a loose delay insulator - if the delay insulator is too loose, grease needs to be added on the outside to improve sealing.