Cato

[rocketcharlie]

Hi everyone. I went to a launch last weekend and had a motor mishap that really baffles me. I was flying a Binder Design California Kid on a CTI J195 19. It is a 2 grain motor. I had it in a 3 grain case with a spacer. Everything seemed normal, after the countdown, it seemed to start to ignite, then boom the upper half of this dual-deploy airframe shot 20 some feet into the air, while the lower half stayed on the launch rail. When I went to inspect I found that the forward end of the motor casing had expanded so that the motor spacer had shot out of the casing. The lower body tube was torn into pieces. The aft end of the E-bay had crumpled, but, neither deployment charge had exploded. You are probably thinking the motor over pressurized, but the thing that doesn't make sense is that the propellant did not burn at all. Both grains looked brand new. I wish I had taken pics, but the vender took the motor back to return it to CTI. Any ideas Rocketry Forum?

 

[Dwatkins]

Most likely over pressurization. AP a lot of times when it experiences rapid depressurization it snuffs out and the grains appear to have never been ignited.

 

[fyrfytr310]

Deleted. Saw the answer to my question in the OP.

 

[markkoelsch]

A J195- never heard of this motor. CTI does not list it, nor is it on Thrustcurve. I assume 54mm?

Sounds like a massive overpressurization, which blew the forward closure, and snuffed the grains. What igniter was used? Was it augmented? Is this a motor with a molded plastic forward closure?

Importantly, did you enter it on motorcato.org

 

[mikec]

A J195- never heard of this motor. CTI does not list it, nor is it on Thrustcurve. I assume 54mm?

Presumably he meant Pro54 J145 2G longburn Skidmark.

 

[rocketcharlie]

Presumably he meant Pro54 J145 2G longburn Skidmark.

Yes, pro 54 J145 longburn skidmark, a fairly new motor, sorry about the typo.

 

[blackjack2564]

That motor has an incredibly small nozzle throat & a BP starter pellet.
It's possible there was nozzle blockage at ignition from match wire causing the overpressure.
Pellet causes a "spike"at ignition, by design, increasing the max thrust to 113 from 56lbs. , literally doubling it for a few milliseconds. Thus allowing an otherwise wimpy motor ability to lift 8-9lb rocket.

 

[markkoelsch]

That is possible Jim. That said, if the wire is enough to plug the nozzle and cause this then that is a potential design issue in my estimation. Wires are only going to be so small for an ematch, and they should not cause this.

Again, I ask the op if the motor data was entered on motorcato.org?

 

[BDB]

I had the same thing happen to me last week with a Loki G66. I tried to light it with a sonic igniter because that is about all that will fit through the small nozzle. It didn't light, so I used a small thermite-augmented igniter that a friend gave me. This is what ensued.



My grains are mostly unburned too. The blast blew a hole in my forward closure (blue). Fortunately, the rocket has minimal damage.



Does anyone think the extra oomph from the thermite may have caused this?

 

[markkoelsch]

I had the same thing happen to me last week with a Loki G66. I tried to light it with a sonic igniter because that is about all that will fit through the small nozzle. It didn't light, so I used a small thermite-augmented igniter that a friend gave me. This is what ensued.

View attachment 320902

My grains are mostly unburned too. The blast blew a hole in my forward closure (blue). Fortunately, the rocket has minimal damage.

View attachment 320903

Does anyone think the extra oomph from the thermite may have caused this?

How much thermite, and how many newtons seconds is this motor?

 

[rocketcharlie]

How much thermite, and how many newtons seconds is this motor?

OP here Mark. I did not know about motorcato.org, I will post about this.

 

[tim cubbedge]

I had the same thing happen to me last week with a Loki G66. I tried to light it with a sonic igniter because that is about all that will fit through the small nozzle. It didn't light, so I used a small thermite-augmented igniter that a friend gave me. This is what ensued.

My grains are mostly unburned too. The blast blew a hole in my forward closure (blue). Fortunately, the rocket has minimal damage.

Does anyone think the extra oomph from the thermite may have caused this?

Quickburst & Chris Short sell initiators that will fit that motor.

 

[BDB]

How much thermite, and how many newtons seconds is this motor?

The G66 has 134 Ns of impulse.



I don't know the specifics on the igniter because I got it from a friend.

 

[markkoelsch]

Thermite is potent stuff. Common rule of thumb is a gram per thousand newton seconds. You easily could have too much for such a small motor to the point I would question ever using thermite for something this size.

 

[markkoelsch]

OP here Mark. I did not know about motorcato.org, I will post about this.

This is motor failure that looks a lot like failures that many have had with CTI 38 mm motors with faulty forward closures.

 

[boatgeek]

This is motor failure that looks a lot like failures that many have had with CTI 38 mm motors with faulty forward closures.

I saw several o fthe 38mm CATOs last year, and they don't sound like this. On the ones I saw, the rocket ignited, got 20-40 feet off the pad, then blew the nose off and fell to the ground with fire coming out both ends. In all cases, the fuel burned completely. I don't know enough to diagnose the OP's failure, though.