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Model Rocket Engine Failure - Advice Requested

Ultimate Steve

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So, I have a bit of a problem. A few days ago I was flying a model rocket (which was my first launch of an "E" engine) and, well, it sort of exploded.

Details: It was an Estes E9-6 engine. The rocket was an Estes Magician. When it launched, the propellant, cap, and nozzle separated from the cardboard engine casing and blasted up through the rocket, breaking it in two and melting the paratrooper I had stuffed inside. This was not an engine mount failure, the mount was perfectly fine and the empty (no nozzle or anything) cardboard engine casing was still in the rocket after the failure. The clay cap in the rocket engine may have been partially cracked, the other two in the package are sort of cracked (although it is hard to tell if this is normal - this was my first "E" engine launch) and that may have contributed to the breakup of the engine. As far as I know, I stored the engines properly. They were stored in my basement, which can get a bit chilly but is usually at a constant temperature. Not sure about humidity, but if it helps I live in Iowa. The engines are less that two years old, and I have successfully fired engines stored in these same conditions for around three years, although they were not "E" size. The temperature at the time of launch was cold, but above freezing. I also flew another rocket that day, but it wasn't an "E" and the engine did not fail (although the rocket sort of did). I can provide more details, pictures of the empty casing and other two engines, and two separate camera angles of the failure if necessary.



My question is this - is it safe to use the other two engines that came in the package? And if not, would adding some glue to reinforce the clay cap fix the problem?

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54 minutes ago, Ultimate Steve said:

My question is this - is it safe to use the other two engines that came in the package? And if not, would adding some glue to reinforce the clay cap fix the problem?

Failure is part of flying rockets. There is only one way to find out whether the remaining engines can be fired safely :) However, I would not modify any rocket engine unless you are sure about what you are doing. They are carefully constructed objects that contain a lot of energy, so tampering with them might quickly lead to danger. If you are unsure, dispose of the motors in a responsible fashion and get new ones.

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Any launch should be conducted in such a way that nobody would be endangered in the event of a CATO, so I'd say go ahead with the other motors, if you have enough spare rockets [and infantrymen] to risk!

I would say no to modifying the engines in any way though, the only difference between a motor and a bomb is confinement, and it can be a fine line. You may be increasing the minimum safe distance - which would be fine if you knew by how much, but I dont think you could.

It may be that the propellant is cracked, in which case reinforcing the end cap could significantly increase its explosive effect.

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Ahhh!  Cato... something I have MUCH experience with.  You should see what 4x E15-4s did to an Estes Patriot kit about 20 years ago (this was the Pro-Series kit that could fly on four Ds or Es).  All four blew at the same time, and I even got it on video.  Sent a nice letter to Estes and a copy of the video (not really necessary), including a slo-mo frame-by-frame segment, and they were nice enough to send me a new kit and a new pack of Es.  I WILL say though that this was one of the first batches of E motors they sold, and there were... problems.  They may have sent me the new kit due to that, but it couldn't hurt to send them a nice email/letter/whatever, or call customer service, and maybe they'll replace the kit and/or motor(s) for you.

Found a pic of an Exocet kit from The Launch Pad that I launched around the same time as the Patriot I mentioned above: http://www.the-launch-pad.com/blank-cnmc.  It experienced the same thing you did.  Pics were taken by two different people from different angles.  Turns out the pair of E motors were from the same bad batch.  I didn't bother trying to get anything for them, as the damage was minimal, and easily repaired:


With that said, there are some things I picked up over the 30-odd years I spent building and flying rockets.  You mentioned they were stored in a basement that gets chilly in the winter.  They really should be stored in a constant temperature, as temp fluctuations can contribute to expansion of the paper casing.  This leads to separation of the propellant from the casing, causing gaps.  Once you ignite the engine, the flame front will propagate around to the gaps, and start burning more propellant than it's supposed to, leading to overpressure, blowing out both ends of the motor.

You also mentioned the temp you flew in was above freezing, but still cold.  Where were the engines stored prior to use, and for how long, and in what kind of temperature?  Sudden temp changes can also do Bad Things™ to rocket motors.

I agree with the others that you absolutely should NOT do anything with the motors.  Any tampering with them will void any chance you have of getting anything for them, and will definitely make YOU responsible for any injuries and/or property damage that comes from it.  I might also suggest joining the National Association of Rocketry ( www.NAR.org ) and finding a local section to fly with.  The best things that the NAR can provide is information, a $1,000,000 insurance policy covering you for damage/injuries from defective rockets (provided you've followed the safety code) and Sport Rocketry magazine (or whatever they're calling it nowadays).  AFAIK, the insurance has never had to be used, although there have been attempts, but they ended up turned down because they violated the safety code in one way or the other.

The last bit of advice I can give you is to check out The Rocketry Forum: http://www.rocketryforum.com

I haven't been there in a long time, but it's still very active, and you might get better help there, as well as seeing stuff that just might make you want to get some power tools and start saving money for BIG projects.  Like this (yeah, that's me, and that's also my Pershing 1A model sitting on the table):



There's also this display and talk I did for fifth and sixth graders a couple years before I quit rocketry (no money, space, or time):


That red metallic cylinder in the top right image?  That's a composite reloadable J-motor.  The largest Patriot model in the bottom center image is the replacement Estes sent me.  The other two Patriots are scratch-built by me and also use a four motor cluster.  The smallest one I'm holding uses four mini motors, and the mid-sized one uses four B or C motors, or Aerotech reloadable Ds.

Edited by MaxxQ
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  • 1 year later...

Hello Guys,

I am reviving this thread to ask for some assistance. Not because of a CATO, but because I have a website and forum where one of the sub-forums deals with gathering information on CATO's. 


Since the NAR only gather's the data with their MESS reports, the Sagitta Cantina  has come up with the S.A.M.E. (Survey of Anecdotal Malfunctioning Engines) Sub-Forum.


The Survey of Anecdotal Malfunctioning Engines is kind of like that other survey done by the NAR, but this one allows anyone to see the information. While all reports are from witness reports, we can not verify the accuracy of any reports. This information is given here to let you be informed and decide if that beautiful newly built rocket should take a chance.

We're looking to give Model rocketeers information so they can make an informed choice on whether to use an engine in a new (or old) rocket.

You can view the information here. Any help is appreciated.




Edited by Bernomatic
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