CTI liner burnthrough

[iter]

Today's flight of the Vulcan glider is my first use of CTI motors.

I wonder if this is the normal result on CTI motors in general, if this is typical of moonburners like G54 in particular, or if this is just a freaky occurrence.

Ari.

 

[fyrwrxz]

Ari-Yup! Mine looked almost exactly like that-awesome motor tho' love 'em! And no- not typical of all. Flew an H255 two days ago and the entire liner was intact-no cleanup! How did your flight go? Love that bird- you did an awesome job on it!

 

[iter]

Thanks! Check out the flight video in the glider thread: https://www.rocketryforum.com/showthread.php?41888-Vulcan-L1-cert-glider&p=408177#post408177

Ari.

 

[fyrwrxz]

OMG-How COOL was that! You are my hero! Hey- Pm your addy-you deserve this book I have about Vulcans in the Falklands dustup. I was so impressed with these as a teenager in Britain- they were so sleek and powerful and to have one come by at treetop level where you could wave at the pilot was just thrilling. Made me a die hard fan.

 

[iter]

Thank you for your kind words! You have PM.

Ari.

 

[Jeroen_at_CTI]

The liner burn-through is pretty typical for the longburn (moonburner) motors. Nothing to worry about. I like to squirt some silicone spray in the case before inserting the reloads. It prevents the liner from sticking.

Awesome built and video.

Jeroen

 

[neond7]

I just recently started using CTI, so far I've only flown J453W 6XL loads - its burned through every time.

I've got a CTI 54mm 3 grain J760W ready to go whenever the weather cooperates. Hopefully it won't burn through, its a mess to clean. The plastic "goop" from the liner really sticks to the inside of the casing (and it smells!!!).

 

[G_T]

Most CTI 38 that I've flown have burn-thru somewhere around the middle. I don't like seeing it, as aluminum won't take much temperature rise before losing its strength, but I haven't seen evidence that enough heat got to the casing to damage it. If I saw a change in the anodizing, or warpage, I'd discard the case for safety reasons, but I haven't seen it yet. However, Jeff, your burn-thru looks worse than any I've had. I mostly do EX now and there it is the same thing. Either an expensive liner, or a cheap one that burns thru, or something like a treated liner or making your own, which is more time consuming. Ya picks yer poisn and takes yer chances! The bigger the motor and the longer the burn, the more attention I pay to the liner. YMMV.

Gerald

 

[Jeroen_at_CTI]

The plastic "goop" from the liner really sticks to the inside of the casing (and it smells!!!).

Use some silicone spray (see post #6 above). It really helps with the sticking. Longer loads to tend to 'cook' the liner. Most of this actually happens during the burning of the delay.

Jeroen

 

[iter]

Most of this actually happens during the burning of the delay.
Jeroen

I was wondering about that. The glider uses plugged loads, and I was wondering if failing to vent at the front is contributing to the burnthrough.

Ari.

 

[MasonH]

Every single one of my CTI reloads does that, and I don't give it any second thought. It seems to happen the most on the G125 Reds, or at least from my experience. That's the motor I fly the most (probably half a dozen) and it happens every time.

 

[neond7]

Most CTI 38 that I've flown have burn-thru somewhere around the middle. I don't like seeing it, as aluminum won't take much temperature rise before losing its strength, but I haven't seen evidence that enough heat got to the casing to damage it. If I saw a change in the anodizing, or warpage, I'd discard the case for safety reasons, but I haven't seen it yet. However, Jeff, your burn-thru looks worse than any I've had. I mostly do EX now and there it is the same thing. Either an expensive liner, or a cheap one that burns thru, or something like a treated liner or making your own, which is more time consuming. Ya picks yer poisn and takes yer chances! The bigger the motor and the longer the burn, the more attention I pay to the liner. YMMV.

Gerald

As for losing its strength, I don't think the burn through is occurring during the action phase of the motor - which is 2.24 seconds for the J453. The motor is too hot to remove even 10 minutes after being fired, it seems to be the residual heat melting it.

 

[CarVac]

If you are flying it without an ejection charge, would it be best to drill the delay to the minimum time so it doesn't cook the liner?

 

[Wingarcher]

If you are flying it without an ejection charge, would it be best to drill the delay to the minimum time so it doesn't cook the liner?

Won't make much difference. The drilling doesn't shave the whole grain down, full diameter, it creates a hole up the middle.

N

 

[CarVac]

But during the motor burn, it'll eat outwards from the drilled hole. That's how drilling reduces the total time the delay burns.

 

[New Ocean]

Common enough in CTI motors... Aluminum is an excellent heatsink so short duration heating in one spot is not going to instantly weaken the case, particularly since this happens near the end of motor burn, and the case no longer has to withstand pressure.

 

[iter]

Won't make much difference. The drilling doesn't shave the whole grain down, full diameter, it creates a hole up the middle.

N

What Nat says, plus I like the smoke trail behind the glider. On at least one occasion I recall the smoke saving a glider. I fly into the sun and lose track of it, and the smoke helps me locate it again.

Drilling probably does little to the heat. If you drill a delay a lot, you can see it continue to smoke after ejection, while your rocket is under the parachute.

Ari.

 

[iter]

But during the motor burn, it'll eat outwards from the drilled hole. That's how drilling reduces the total time the delay burns.

My understanding is that drilling does little to total burn time. It does a lot to how quickly flame reaches the ejection charge. The delay charge can happily continue to smolder from the center outwards after the ejection.

Ari.