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Might it matter how much of a gap (if any) was between the nozzle and the blast plate, to the extent it could not expel the ignition wire and the nozzle plugged, etc.? Just guessing. Two occurrences seems to indicate something in common between the two, in an unusual firing configuration.
 
looking at how clean the blast deflector appears...I'm going to ask the question, how much space did you leave between the nozzle cap and the deflector when you clamped the rocket to the pad? if the cap was prevented from moving etc. you got an excessive amount of pressure inside the motor.
Rex
 
After 2 failures I’d be worried that the case is somehow either faulty or damaged.

Two questions come to mind:
1. Did you over tighten the closure? It should only be done by hand.
2. How hard did you clamp the motor? Could you have warped to motor case or was the aft closure (which has a larger diameter) be clamped against a price of metal?

Alternatively as Rex said if the cap was right up against the metal then this would cause an over pressurisation issue.

Another possibility is that first failure damaged the case. Guess the question is how did the first failure happen?
 
Last edited:
Worsaer said:
Might it matter how much of a gap (if any) was between the nozzle and the blast plate, to the extent it could not expel the ignition wire and the nozzle plugged, etc.? Just guessing. Two occurrences seems to indicate something in common between the two, in an unusual firing configuration.
Click to expand...

Yes, Bill, that kind of obstruction definitely could cause this, but only if constrained from moving (as it was). Good thought! You may be exactly right.
That would reinforce Timbucktoo’s point also.
 
On the 38mm CTI cases, it's possible to cross thread the soft plastic aft closure resulting in a similar looking failure. Still my guess is as Steve suggested, a smaller or blocked nozzle.

As to they naysayers, fight it all you want but CTI motors in the 24-38mm range are disposable motors placed in a reusable case. It's not a knock against you manhood, not a knock against the product, it's not a knock at all, it's just how I see it.
 
Here’s one helluva theory, could the exhaust gas plume itself cause a choked nozzle condition at the throat of NoZZLE if the plate is placed too close to the motor exit diffuser? It would take a CFD to visualize it or destructively testing more products experimentally. It’s been about few months since I had compressible gas dynamics. I do know shocks can clog in supersonic flow when holes and back pressure isn't quite nominal. But that excuse in theory only explains the first not second failure the OP had. I’d just file a MESS and be done with it. Still struggling conceptually but the plate may be raising the nozzle back pressure beyond design spec for hole size at worst due to flow issues if placed way too close but not exactly clogging NoZZLE. Maybe I need a beer and just simmer down.
 
Yeah, have a beer! [emoji16]
I really think Timbucktoo and Worsaer nailed it. I suspect the yellow cap just couldn’t be ejected because the nozzle was too close to the plate. Once a motor started pressurizing the rate of combustion went up, resulting in even more pressure, and higher yet combustion rate, etc in a chain reaction.
 
BTW Andrew, holly lube there buddy. Those O-Rings only need to be "wet". Yours look like they just came from a German fetish party.
 
anthony domzalski said:
I did my best, noting the instructions to shove it all the way up and the make a single loop coil to prevent the igniter from backing out, using the yellow cap provided to secure the firing system.
Click to expand...

Where did you put the igniter loop? It should be between the red cap and the nozzle, not beyond the nozzle inside the motor. That's the only thing I can think of that could explain why they both blew up in the same unusual way.
 
Steve Shannon said:
Anthony,
Thank you very much for your service.
That’s a failure of the aft closure. It appears that the nozzle somehow plugged causing excess pressure, which in turn caused the plastic aft closure to separate above the thrust ring., The thrust ring and the nozzle were ejected downward and through the blast plate. It looks like the forward half of the aft closure stayed in the case.
Nozzle plugging can happen as a result of an overly large igniter but it could simply be that CTI built the motor with too small of a nozzle or that there was a problem with the grains in both motors (less likely but possible). I assume you used the igniter you received with the motor from CTI. Did you do anything to hold the igniter in place?
It’s not technically a “detonation”, but it was certainly an explosive release of high pressure gases. If it had been a detonation the case would have shattered and the propellant would have been consumed. As you can see, very little of the propellant actually was consumed. If our propellants truly detonated you can imagine how much more damage would have been done. That failure you had was much safer because the ejection happened in a safe direction, although it probably was not good for stress.
I think your dealer should replace both of those motors under warranty. You should also submit what is called a MESS report for each motor. It’s a fairly simple online process (although not perfect) that’s available here:
https://www.motorcato.org
If you have any questions or want any help, I’d be happy to help.
Click to expand...
 
Guys, thank you all very much for the analysis. There are 2 things I'm questioning myself about: In my ignorance of being a novice,
1.) I shoved the factory igniter as far up as it would go.
2.) I may have clamp the rocket (i know, not a brilliant idea) too close to the base plate

these two things could have cause perfectly good motors to try and do something they weren't designed to do....
 
Shoving the igniter up as far as it will go is what you're supposed to do. CTI motors like the one you used have a mall black powder pellet in the top of the top propellant grain. The ematch needs to be as close to this as possible in order to get consistent, fast ignition.

The issue here may have come from the fact that the igniter was unable to be pulled out of the motor since everything was clamped down.
 
anthony domzalski said:
Guys, thank you all very much for the analysis. There are 2 things I'm questioning myself about: In my ignorance of being a novice,
1.) I shoved the factory igniter as far up as it would go.
2.) I may have clamp the rocket (i know, not a brilliant idea) too close to the base plate

these two things could have cause perfectly good motors to try and do something they weren't designed to do....
Click to expand...

1. The factory igniter should almost always be inserted all the way. There are a very few motors whose instructions require the igniter to be inserted and then pulled back a little, so always follow the instructions.
2. I don’t know how you clamped the rocket, but there must be room beneath the motor to allow the igniter and cap to be ejected. If they couldn’t move out of the nozzle, then the motor would almost certainly be destroyed in the way it was.
 
for what it's worth:
All rockets on the pad should be spaced are a few inches above the blast plate. All pads should have a stand-off of some sort, to ensure this. An old motor casing is common for LPR & MPR. A mechanical stop, or a chunk of something on HPR pads

We have a stop, and a block of wood, both in the 10"-12" range to ensure the [HPR] rocket isn't sitting on or close to the blast deflector. (Use whichever you want..)
 
I get that you wanted to do a full-up ground test, but that's really not something that's generally done. There's just too many things that can go wrong (as you unfortunately found out). You'll just have to take on faith that if you build the rocket and the motor properly that it's going to work... the rocketry vendors spend a lot of time and money making sure that they're all as reliable as can be expected for rocketry.

Hopefully you won't let this experience discourage you, repair the damage and take it out to your local club launch. Don't be afraid to ask questions... we were all newbies once.
 
I guess all the motors we use are single use. Case involved or not they won't work again once used. I would say where an aluminum case is used, that would be a reloadable, all others are disposables.
 
anthony domzalski said:
put together my first 38 mm "wildman punisher". decided to ground test it. , make sure the parachute deploys etc... 38 mm Cesaroni engines. the engines blew up????did I do something wrong??? could use some help

So, I built a couple of rockets with my son, all are 38mm. I thought it would be a good idea to test them on the ground to ensure the engines didn't fall out, and the nose cones, parachutes would deploy. So, I loaded up a rocket with a 01 grain cesaroni casing and ignited it with the rocket locked down to the launch rail with household clamps; didn't change or alter the delay, just loaded it and fire. The motors didn't burn, they blew up. tried it twice. 02 one grain motors, same results.....
Click to expand...

Assuming the motors were built correctly, this is NOT what should have happened.

I do remember reading about 1-grain 38mm Cesaroni motor over-pressurizing and blowing off the the aft (plastic) closure.

Is that what happened to you?
Can you elaborate on "blew up"?

a
 
CTI said:
If they're single use motors, what is function of the case then?
Click to expand...

rcktnut said:
I guess all the motors we use are single use. Case involved or not they won't work again once used. I would say where an aluminum case is used, that would be a reloadable, all others are disposables.
Click to expand...

This has become a pointless argument in semantics.

The casing is a required part of a system. When that part is absent, the system fails. Can we move on?
 
Not sure why you are being difficult. I'm not knocking your product. I'm just pointing out that they are different. I use you motors as much as I use other options but can change that if you wish. Just let me know ok?
 
grouch said:
Not sure why you are being difficult. I'm not knocking your product. I'm just pointing out that they are different. I use you motors as much as I use other options but can change that if you wish. Just let me know ok?
Click to expand...
An unsuccessful attempt at humor on my part. Sorry about that.
 
All good in the hood. FYI, my 29mm 3 grain case is easily my most flown. It's the first case I purchased when I started flying HP and got my L1 with a H410. I've flown a ton of CTI over the years and the ease of "building" the motors was why I chose that system to start out with. I think ease of use of the system is probably the primary reason AT started making the DMS line. Of course that's just my opinion. Same as me not seeing the CTI motors as reloadables.
 

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