Saw an interesting motor failure at yesterday's NIRA launch. Motor was an Estes E9-4 in a Big Daddy. At ignition it went bang, then continued to burn like a safety flare. Burned a while, then slowed down for the delay, followed by a big puff from the ejection charge.

Examination after the "flight" showed the nozzle spit out. OK, I've seen that before. But the interesting part was that this time we found the ENTIRE NOZZLE, still intact, with the plug still in and the igniter in place. Never seen that before.

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I fought the law, and the law LOST!

That is weird. Especially considering that the E9 has been a remarkably reliable motor.

Definitely a case for a MESS form, and a call to Estes. Let them know the date code, etc.

I wonder what could cause that. Badly pounded clay? Insufficiently wet clay?

Poor bond between clay plug and casing wall.

How that could have happened remains for someone with more knowledge of how Estes makes their motors.

N

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N - "Born - Again Rocketeer"

I've seen the nozzle spit out with the loud "PING" off the deflector on the E9, D12 and C11. I've never found the nozzle, so I've never seen if the igniter was still plugged in.

Obviously, each and every thime this has happened, there is virtually no bond of the nozzle to the casing. If there was any kind of bond, the motor would build some small amount of thrust and the pressure would build inside and then when the nozzle spit it would be a loud POP sound. The only sound associated with these failures in the PING of the nozzle hitting the deflector.

Oh yes, and the classic D12 failure mode of blowthrough and sometimes simultaneaously ejecting the nozzle is very loud and is clearly a result of propellant/casing interface mechanical bond failure and the nozzle is ejected with enough force to dent the deflector and break the plastic leg of an Estes pad.

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-Fred Shecter NAR 20117 (L2)
Southern California Rocket Association, NAR Section 430

After I made my initial post, I remembered a little detail that somehow didn't register yesterday. I'm still checking to confirm this, but my recollection when showed the remains is that the igniter plug was WHITE instead of BLACK.

I've accidentally tried to use the wrong plug myself, and just couldn't get the thing in. I don't know how this person did.

And I don't know why this caused the nozzle to blow. I can't believe the plug nozzle-bond was tighter than the nozzle-casing bond.

Regardless, it's strange.

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I fought the law, and the law LOST!

Your instincts are correct. No known form of igniter retention plug (regular plug, oversized plug, wadding ball crammed in with massive force, etc.) will allow an overpressure that can overcome the normal nozzle to casing bond. I think if you poured epoxy ove a wadding ball crammed in it wouold still pop right out of the nozzle - it might take a tiny bit of surface clay, but it will pop out.

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-Fred Shecter NAR 20117 (L2)
Southern California Rocket Association, NAR Section 430

I've captured this failure mode in two high-speed videos. Coincidently, both times it was a boost glider being launched. In both cases, the nozzle seems to have failed.

The first time was actually the very first "high-speed" video I created with my new EX-F1 camera. It was the launch (or attempted launch) of an Estes Eagle:

http://www.payloadbay.com/video-7927.html

That would have been an 18mm motor.

The second time was the launch of a beautiful radio-controlled boost glider. It was a 24mm motor, but I'm not sure if it was a D12 or E9. You can see the failure at about 30 seconds into the video at:

http://www.payloadbay.com/video-7933.html

Fortunately, the glider wasn't badly damaged. You can see a successful flight later in the video.

I don't think anyone found the nozzle intact in either of the cases. I would have found it interesting if someone had. I wish the videos were higher-resolution so that we could see the nozzle failing instead of just the result.

I sometimes take close-ups of motors firing in slow-motion. Maybe I'll get lucky (unlucky?) enough to catch one of these failures. :-)

I wonder if temperature cycling or rough handling of a motor would make it more likely to suffer this failure. In addition to the couple of times I caught this on video, I've seen it a few other times at our launches. The rate of occurrence is a fraction of 1%, but I wonder if it's more likely to happen here in Florida where the motors may have been subjected to storage in hot and humid areas.

-- Roger

Over the years I've seen over ten E9 motors fail in just that way (though Bob's right about the intact nozzle being weird). I've seen five or six do a roman candle cato and one do a split casing cato.

Them's just the hazards of bigger black powder motors.

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Roy
nar12605

Yup, that's what was weird. I too have seen many a blown nozzle over the years, but none that ever spit out the entire intact nozzle, especially not complete with igniter & plug. Most unusual.

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I fought the law, and the law LOST!

I would rather eject a nozzle than the roman candle type. The one I had last year with my Nike X scared the crap out of us!