The Great Ramjet Challenge!!!

[Irvine.J]

One of the biggest problems facing the ramjeteers who wish to use the aerospike (IMO) is where the gas injection should occure and the easiest way to accomplish this on one simple fuel line.
WHY?
Well... One must try not to let their fuel lines disrupt incoming airflow, however normally (without aerospike) one can have the fuel line enter the jet infront of the flameholder and give a nice even spray from the centreline. Howeve in a small jet such as this one, its damn near impossible to get a small enough quad or T juntion into that aerospike infront of the flame holder, and simply coming through the inlet diffuser wall would not give proper mixing... this engine is so small it does not warrant the use of 4 gas lines or the time it takes to rig it up. I guess I will use the little aerospike, as this engine will be a gift for someone...

I believe you'll get a much nicer, bigger, and more consistent burn from having the fuel injected right before the flameholder... any ideas as a few of us are trying out these new aerospikes, lets get some fuel set ups for them on the table? Out of the way of incoming airflow in a nice tidy arrangement. Larry your assistance here is most appreciated.

[Irvine.J]

Well, its 4:20 am, and i just completely stuffed my last T junction with the fuel nozzles, hence, i'm about to do them again, just having a quick break. Shown front aspect is the flameholder config (smaller as it goes out) the T junction inside the spike, and 2 slightly protruding fuel nozzles. The blue lines indicate gasflow and should rapidly spread as it makes high speed contact with the walls right before the flameholder... photo shortly.

[Zippiot]

I think 1 line entering the spike 1/2 way down then splitting to 4 lines, each shoot up right in the middle of the flow by area of the flameholder. It would mix with the turbulent air and be almost totally hidden!

[Irvine.J]

Yeah I think using my sodabulb trick would do well, the line in going into the inlet part, however the spike is about the width of my thumb so its not going to happen...

This was a total mongrel of a job, finally finished at 6 am after a totally botched attempt. Finally it looks good, is neat and tidy, the guy is gonna love it. My only concern would be over gasing it, with 6 holes, its got merely 2 less the same size as my monster jet. It was REALLY darn hard trying to get the silver solder to properly flow around without melting the solder holding in the nozzle etc.

Micro-lance fuel line below...

[Zippiot]

That should work fine!
Ok you've done it, I am getting to work on my jet right now!!!!!!

I spend like 4 bux on the steel to make one and 10-20 on welding supplies...
Damn flux core wires stupid welding shop needs to fix my tank or give me a new one (I rented it and they are out at the moment).

[Irvine.J]

BRING IT!!!! *Draws his ramjet*
LOL Can't wait to see it mate, can't wait to see what your beast can do :D
Flux cored wire aint so bad, I used it for this 1mm stuff and I'm surprised it worked so well. Anyway, the challenge has begun! Lets kick this pig...or ramjet...or something, not the anvil...

[Irvine.J]

Well, I have to run this yet to see how it goes, might catch a quick nap first. Do you think he will like this little jet, I think it looks allright, what do you guys think? If it runs really well i might just keep it for myself, I NEVER want to try that fuel setup again...it had better work!

[Zippiot]

That looks really good, cant wait to see the video!

I cut out my steel, cept the flameholder but I am getting there. Might actually finish this by the end of the day, the 1 day ramjet!

[Eric]

For the aerospike style engines I found the best way to make fuel holes is to use the spike itself as the fuel injector, and use a plasma cutter to pierce many many holes in it. For the 8.5" engine I have 60 holes that come out to just under 1/16" of an inch which works quite nice, and would otherwise be ridiculous to drill that many holes in stainless.

You could also do various arrays of holes at different increments to play around with mixing.

If you inject the liquid propane in the back cone, it will give you free cooling and preheat the fuel quite nicely.

Eric

[Zippiot]

Eric you better be building that thing!!!!!!

If I had a lathe (which I might by the end of the year) something like that could be built...I want a lathe!!!

Beautiful drawing, any idea if the plug nozzle (or aerospike in the tail whatever you wanna call it) works well at subsonic speeds?

[Eric]

The nozzle forms a CD tail, the effectiveness depends entirely on the inlet pressure.

If the engine is a decent size I just roll the cones and tubes from stainless and weld together, cuts down on the weight greatly and makes it easy to use the core as an injector.

Eric

[Zippiot]

I am just having a hard time rolling nice cones...how do you guys do them?

Takes me 10 minutes to make a lumpy pos cone and many hours of hammering later it starts to resemble what I want it to...

[Zippiot]

Eric I was also under the impression that the plug should "bend" inwards like a teardrop. That supposedly forces the hot fluids to bend with it, also it should have a blunt end. But this is just from examples I have seen...

[Mike Everman]

RE: cones, I just clamp a rod to the bench on some shims and bend it up. Bill had a similar setup in the tools forum.
You guys are really making me want to make a ramjet!

[Zippiot]

I have a bench, I have a bar, sweet!

You should make the jet, costs very little b/c it barely uses any materials. They are fun to run as they are loud and pretty fire shoots out the back. All we have to do is get everything just right to make them useable in some field, whether it be rocketry, r/c planes or uav type things. Also manned vehicles, but I wouldn't strap myself into anything I built meant to go more than 20 mph.