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Bob Kaplow
09-21-2009, 01:48 PM
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.

stefanj
09-21-2009, 02:38 PM
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?

rangerstl
09-21-2009, 02:47 PM
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

Shreadvector
09-21-2009, 02:49 PM
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.

Bob Kaplow
09-21-2009, 03:04 PM
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.

Shreadvector
09-21-2009, 03:18 PM
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.

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.

jadebox
09-21-2009, 04:06 PM
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 (http://www.payloadbay.com/article-using-the-ex-f1-to-photograph-rocket-launches.html) 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

Royatl
09-21-2009, 05:58 PM
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?

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.

Bob Kaplow
09-22-2009, 07:39 AM
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). .

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.

mycrofte
09-22-2009, 12:41 PM
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!

shockwaveriderz
09-22-2009, 03:22 PM
Bob, exact same thing happened to me with the exact same engine(?) a few years back. The nozzle plug and igniter stayed in the spit out nozzle!. Iused a white nozzle plug too. I have a pic of it around here some wherer, I'll try to find it but it may have been zapped in one of my 2-3 disk head crashes I've had over the past few years.


EDIT Found the pics!

1st pic shows the white nozzle plug with the estes solar igniter still in place on the spit out nozzle.

2nd pic shows the roman candle exhaust on my Big Daddy. Never left the pad

3rs pic shows inside nozzle looking back into it.

Pic 4 shows the clay cap still in place on the engine although the propellant/delay train/ejection charge all seemed to burn out from the engine end.

Based upon what I remember seeing and now looking at these pics, I used a white not a black engine plug and froced it in. Evidently the igniter ignited, starting the propellant burning inside the nozzle and the nozzle/propellant grain interface let go. You can clearly see the curved concave nozzle section that touched the propellant grain. Normaly these two interafces are pressed into each other with such force that if you were to take an engine apart and look at this interface you will see that the grain structure is larger grained than the rest of the proeplllant grain. Its bumply looking and feeling. This is because you are pressing granular BP against an already smooth and pressed nozzle, and these grains at the concave nozzle/propellant grain interface are embedded into one another.

Its entirely possible that through either temperatre/humidity cycling or perhaps rough handling, these motors developed a grain/propellant interface debonding. This would allow the propellant grain to ignite, the pressure would be much greater than the nozzle/paper casing bond pressure and it would release/blow out much easier with the wrong plug in the nozzle still?

I beleive that Fred et al described just this in his seminal 1978(?) work on temperature cycling of D12 motors.

Terry Dean

georgegassaway
09-22-2009, 06:23 PM
I have seen this happen too, but only the last few years. Usually with E9’s. Sometimes with D12’s. Have not seen it happen with anything less than 18mm motors.

Edit - have not seen it happen with anything less than *24mm* motors.

Usually when it happens, there is a small “crack” or not very loud “pop” sound. I have not seen intact nozzles, but we fly from grass and nobody thought to try to look for possibly intact nozzles.

What is very strange here is that usually when there is a de-bond failure, it has been the propellant, not the nozzle. Something must be very different for the nozzles to be blowing instead.

Now maybe it is not a bad thing. That is, if the motor was going to have a de-bond failure, it is better to pop out the nozzle than to have the propellant fireball thru the model (or blow apart). The nozzle blow-out might cause some damage to the back end of the model (Flames swirling around, esp. from flat deflectors), but that tends to be cosmetic. While a blow-thru can badly damage and even destroy some models.

Best of all of course is that for there never to be any failure.

As to why this is happening now, nozzles blowing out as opposed to propellant blow-thrus or “kabooms”, it could be many things. Could it be an intentional change so the nozzle is a “Safety valve” in case the motor was likely going to fail by blow-thru or blowing apart? Could it be the clay nozzle composition is different, with unintended consequences to its characteristics. Possibly shrinking over time? Not tending to “stick” to the casing as well as before? Or not being compressed as much as before. Or possibly a change in casing material properties, if the casing “stretched” a tiny amount over time.

Larger and larger BP motors have always tended to have more of a problem with reliability.

- George Gassaway

Shreadvector
09-23-2009, 07:20 AM
George is (as always) correct in his observations.

Terry's last post had some confusing wording ("motors developed a grain/propellant interface debonding"). The grain is the propellant, so it would not debond from itself. I've attached the usual file that has the typed out explanation of how the normal failures occur. It also contains the info on the nozzle to propellant interface and how a crack on this interface will result in a *LOWER* peak pressure iniside the motor.

Also, when I refer to a "Roman Candle", I mean the fireball shooting upward into the air - and through the rocket body. If the nozzle is spit out and the propellant burns out the open lower end of the casing with virtually no thrust, that is more like a highway flare.

The motors that spit nozzles at the instant of ignition obviously have virtually no mechanical bond between the nozzle clay and the casing, while the propellant, delay, ejection charge and upper clay cap maintain a good mechanical bond. Result: pop goes the nozzle.

Feel free to save the attached file and repost it whenever necessary. Or share it with others who need the phenomenon explained. Thanks!

jetlag
09-23-2009, 10:48 AM
Also, when I refer to a "Roman Candle", I mean the fireball shooting upward into the air - and through the rocket body. If the nozzle is spit out and the propellant burns out the open lower end of the casing with virtually no thrust, that is more like a highway flare.

You mean like this?

D12-3 'roman candle.' Lander has since been fixed and flown. Blowtorched the inner BT, which I was able to replace.
Allen

luke strawwalker
09-24-2009, 01:11 PM
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.

Yeah, we had one do that... my club buddy Dave came out for a 'test fly' one day and we sent up a few, and his vintage FSI Maverick had the E9 spit the nozzle out of the casing-- PING! right off the blast deflector into the grass, fully intact. It held long enough for the ignitor and plug to spit and the rocket had JUST started to move, then right back down and sat in it's own fire and roasted the bottom of it, and burned a fin off... he repaired it though...

First time I've seen it but I've heard about it before... :) OL JR :)

tbzep
09-24-2009, 02:24 PM
You mean like this?

D12-3 'roman candle.' Lander has since been fixed and flown. Blowtorched the inner BT, which I was able to replace.
Allen

Ouch....that's sickening to look at. The potential for that is why I probably will build another ML with less detail for flying and keep the current one for hanger queen duty.

Most of the few motor failures I've had have been more violent, ripping up body tubes in addition to annihilating motor mounts and stuffer tubes. A cato blew the whole rear end of my Centuri Saturn 1B off once. That was probably my most depressing moment in rocketry.

mycrofte
09-24-2009, 03:47 PM
Tell me about it. I almost cried looking at the top of that rocket...

So, does mine from last year count as a roman candle?

CaninoBD
10-03-2009, 06:37 PM
I have seen this happen too, but only the last few years. Usually with E9’s. Sometimes with D12’s. Have not seen it happen with anything less than 18mm motors.

Edit - have not seen it happen with anything less than *24mm* motors.

...

- George Gassaway

This summer we had a new person show up to our club launch. His first model had a Estes C6-3 and it did Crack ... Road Flare. First time I seen it on a 18mm motor. He put another C6-3 and tried again, and it did the same thing. I asked if the two motors came from the same package. He show me a new Estes Blast Off Flight Box. He said he bought it in the last week and those were the first to motors from it. The box didn't look like it was old stock. He flew more motors from the box without problems.

Mikus
10-05-2009, 02:29 PM
That is weird. Especially considering that the E9 has been a remarkably reliable motor.

Hmm, you say that but I've seen 2 spit nozzles in the last 2 years - once on one of my flights.

And I've seen zero instances of that with other motors. :confused: