High-speed video of A8-3 motor

[Steve Golson]

View attachment 3357851620235384205pro_mo_c001h001s0001.mov

High-speed video of A8-3 motor.

• 1,000 fps
• Fastcam SA-X2 camera
• 512x512 px
• playback at 30fps, 1/33x speed

Posted with permission of the original author, who is a PhD student at Colorado School of Mines. This was not part of a research project, but rather a one-off test in an explosives research lab. Don't try this at home…

Things I find most interesting:

1. Flame jet wanders off-axis during the burn. How does this affect the thrust vector?
2. It takes a while before the delay charge really starts to generate smoke.
3. Sparks are lovely.
4. Wow that ejection charge is powerful!

 

[jmasterj]

That's really cool to watch. I was interested by the same things as you - the delay between burnout and the delay smoking seemed very weird to me. I'll have to watch my LPR launches more carefully to see if I can notice that.

 

[shockie]

I've seen a number of these off center thrust before in other slo-mo videos with different Estes motors.

Per #1, that offset thrust line has to affect the trajectory. I can only assume that is caused by nozzle erosion. Can you tell at what time period that is happening after initial ignition?

I also wonder if the Estes plug which pushes the ignitor up against one side of the nozzle may be causing that?

It'd be interesting to redo this with a MJG BP igniter and see if there are any differences.

Perhaps the clay nozzle needs a little graphene nanopowder in it to strength it and make it more erosion resistant.

Notice how the thrust line goes back and forth,

 

[Steve Golson]

Per #1, that offset thrust line has to affect the trajectory. I can only assume that is caused by nozzle erosion. Can you tell at what time period that is happening after initial ignition?

Well, it's 1000 frames per second. I think you could identify the moment of ignition in the video, and compare this against the published time vs thrust curves. An exercise for the reader
You think the offset thrust is due to nozzle erosion, or an irregular burn front?

 

[waltr]

I have seen on most BP nozzles after burn deposits.
I think the offset thrust seen in the video is due to a build-up of slag on the nozzle. Not nozzle erosion.

 

[Steve Golson]

I think the offset thrust seen in the video is due to a build-up of slag on the nozzle. Not nozzle erosion.

Is the slag affected by gravity? Do you think the effect would be different if the motor was pointing down?

 

[Delta V]

Is the slag affected by gravity? Do you think the effect would be different if the motor was pointing down?

Maybe! Say that a small chunk of the nozzle broke off into the motor while burning, it would effect the plume more than if gravity was pulling it out of the motor. if it was upside down then the only thing pushing it out of the motor is the combustion gases