Clear Rocket Motor Shows Combustion Taking Place

[r12ski]

Note to Mods: This is not intended as a source for making any type of model rocket propulsion system, it is simply a scientific demonstration to show what is happening inside a rocket motor when it is fired.

[video=youtube_share;TLPWqCMb7DE]https://youtu.be/TLPWqCMb7DE[/video]

Makes it easy to see why it takes a second for composites to build up pressure.

 

[Cyril's Scribe]

Someone's been browsing reddit, just saw that this morning, very cool, I did not think the acrylic would hold up to the pressures be it looks like the builder used a pretty thick piece.

 

[troj]

Yep, that's a pretty common motor demonstration -- at home, I have a grain from a demonstration at MSFC.

The acrylic works, as long as you don't run the motor for too long. You don't want to let the walls get too thin.

-Kevin

 

[mdoering]

You don't want to let the walls get too thin.

As an example, in this video if you watch the right side of the combustion chamber closely you can see it thin considerably as the burn progresses...

[video=youtube;p-iAyp88qb4]https://www.youtube.com/watch?v=p-iAyp88qb4[/video]

 

[rstaff3]

I've seen these before but don't remember seeing a better example. Very nice.

 

[r12ski]

Someone's been browsing reddit

Guilty as charged.

 

[Cyril's Scribe]

Someone's been browsing reddit.

Guilty as charged.

We really need to build up the amateur rocketry page there...

 

[rocketguy101]

Hah this brought back memories! In 1972 I attended a ModRoc Conference at the Air Force Academy. They took us on a tour of some small wind tunnels, and demo'd a "Plexiglas" (acrylic) rocket engine, using a spark plug to light it. They also fired a regular BP motor and produced a thrust curve on an oscilloscope. Here are pics I took--they are scans of very old slides, so the color shifted significantly. It was very cool, though!

 

[JStitz]

I'm glad rocketguy dug out his old pics as this has been done before by both the PRS and the RRS. I am between PC's so I can't watch the vids till I download the upgrades.

RRS (Reaction Research Society) had a LOX Acrylic Hybrid with approximately a 2" solid tube with a 1/4" core.
If I remember it had a simple 1/4 turn ball valve for the Lox. It would perform that classic "Hour-glass" shape from the Lox burning hotter near the source.Impingement from the forward injector? (and the gasses starting to diverge and exit faster than near the front closure.) it was just bolted together and made in one weekend.

 

[Issus]

I wonder if a cast epoxy "grain" would be be better for demonstrations. It should burn through slower and be stronger so as to resist burning through.

Cool demo though, wish I had something like that shown to me as a kid!

 

[JStitz]

Issus, if you did this ..the Gougeon Brothers of West Systems Epoxy fame would be bugging you to submit this to their twice a year publication "Epoxyworks"

If anyone is interested E-mail them at [email protected] or call 1-866-937-8797 If you use West Systems and don't read their mag you are missing out.

 

[Issus]

Could be fun I was thinking - the other advantage of epoxy is that it doesnt melt as readily as acrylic, so you wouldnt get the soggy end that was shown in the first video.

Could be a fun project - I wonder how safe epoxy would be though.

 

[troj]

Epoxy, by itself, likely wouldn't contain the pressure -- you'd need to thicken it with fibers. Once you do that, you'll lose the transparency that makes acrylic so good for this.

You also need an epoxy with a Tg high enough to handle the internal temperature as the motor burns.

For West Systems, that's around 140F
For AeroPoxy, it's at 196F
For FibreGlast System 2000, it's in the 180 - 195 range (depending on the hardener used)

This is for their laminating resins, which tend to be more transparent (though none are as clear as acrylic).

-Kevin

 

[Issus]

Hmm i'm not so sure that it wouldnt contain the pressure as well. Epoxy has longer chains which crosslink better than acrylic. I'm not sure how well it burns, but a long chain olefin would be good - even a polycarbonate would be better than acrylic.

 

[mdoering]

I assume you could also use large acrylic rod like these guys use and bore it out significantly and make an epoxy propellant grain that would go inside of that to address the pressure concern... It only takes a quick hit with a torch through the bore hole on acrylic to polish the surface and remove the "frosted" appearance.

I think this thread is bordering on EX now...

 

[Issus]

Thats a pretty good idea. I wonder if a CO2 bulb could be mounted on the gas inlet to extinguish the motor so it stays shiney and doesnt get the soot inside. Would make it look much nicer after a demo.

I don't think it's EX, you wouldn't ever launch a rocket with a motor build like this, using a gaseous O2 as an oxidiser source would you?

 

[cjl]

I was part of a team which made one of these as a school project - ours was a self contained nitrous hybrid though, not GOX. We got some really cool video too.

Here's a video of one of our test firings:

[youtube]gQ2AlG2r5Ws[/youtube]

And here's the ignition and first part of the burn of a later test firing taken with a high speed camera - I believe it was 1000FPS, but I could be wrong:

[youtube]K3Cuey-isuw[/youtube]

 

[Issus]

That high speed footage is pretty cool, near the end there being able to see the exhaust plume lit up with shock diamonds. Very nice.