Ejection Charge: Hot Chunks Of Fire or Just Hot Gases

[Ez2cDave]

I would coat all body tube surfaces that will be exposed to hot gasses with thin CA.
This will provide a layer of reinforcement, and non-flammable barrier for hot particles to bounce of.

Wicking CA into a paper body tube will make it stiffer . . . Unfortunately, it also makes it brittle . . . It seems to behave like a thin-walled Phenolic tube after being soaked with CA.

My suggestion would be to thin down JB Weld with Acetone and "paint" it, thinly, into the areas that need protection from heat.

Dave F.

 

[Daddyisabar]

Got ya. Not so though on this design.

I see. But I bet the next one will have motors in the pods!

 

[rharshberger]

I have never split a compartment. That would act as a stuffer tube for each side.

I have split a tube with dual ejection charges at the same time using Estes C6-5s, it was on my SA-3/A-125 Pechora sport scale missle, I did a build thread, flight report, and damage repair thread all in one on it (it was iirc my very first build thread). Thats when I switched to using one delay that was "on the money" and the other a couple of seconds longer, it didnt seem to have much effect on kevlar shock cords as I recall, but I also put a short section of tape around the lower portion of my shock cords or shrink tube.

 

[lakeroadster]

I see. But I bet the next one will have motors in the pods!

This one could easily have plugged booster motors in the side pods... (4) Black powder motors instead of (2) composite motors.... I like that even better.

The plugged motors hold the parachutes in place.....

Back to the drawing board!

 

[Daddyisabar]

This one could easily have plugged booster motors in the side pods... (4) Black powder motors instead of (2) composite motors.... I like that even better.

The plugged motors hold the parachutes in place.....

Back to the drawing board!

What ever you end up with will be cool.

 

[BABAR]

When I do rear eject models I often downscale the central tube of the ejection pod one tube size from the motor mount. For example, a BT-20 motor mount will duct forward into a BT-5 tube pod. The upside is that it GREATLY increases the room for the recovery device. The downside is that motor ejection charges do flame for a few moments after initial charge fires, usually not a problem for same size tube or minimum diameter models, but it did tend to char the smaller tubes. I fixed this with a cut piece of aluminum can (yes it IS flammable but it doesn’t catch fire that fast) rolled up can glued inside the tube just forward of the motor.

 

[shockie]

you might want to consider a fine mesh screen that will allow the hot gases pass thru, but not the BP particles themsleves....on the outside or aft end of the baffle .....

 

[lakeroadster]

I never did update this.... when I did the bench test, using (2) D motors (1 just as a plug and one D-12-5) I used dog barf in the side pods. The ejection charge melted both chutes. Not really bad, but bad enough they wouldn't have fully opened.

But the dog barf was 42 years old and basically pretty powdery.

Plan is to use some fireproof streamer material ahead of the chutes... and maybe plug that 3rd opening I added?

Turn the speed down to 1/4 and go to the 12 second mark. Man the chutes come out of there fast!

 

[Sooner Boomer]

Ejection charges produce three things; BFBs (Burning Flying Bits), a plug of hot gas, and infrared radiation (heat energy shining up from whats left in the engine). If I remember correctly, BP produces about 30 to 1 vol/vol. (Davis? Urbanski? PATR?)

 

[Jay Rairigh]

Hope you plan on a shock cord when you fly it!
But I don't see any difference in this design over a standard ejection except the hot chunks of moving, flaming, burning fire are making a 180 degree turn. A little dog barf, a chute, a shock cord and go. As stated earlier, particles remaining in the inner parts can be shaken out.

If it was me, I would probably protect the knife edge vent holes with a thin layer of epoxy JIC for longevity.