Few Quick Questions...

[larry cottrill]

Eh at http://pulse-jets.com/ramjet/ramjet.htm it shows that the flameholder should be [, conflicting with your attached document (which states it should be ] direction)

There's a lot of good information there. Even in this article, he points out that there are a LOT of different ways to make working flameholders! There are benefits and drawbacks to each design. Some are better for higher speeds, some for lower. Some easier to build, some not so easy. My original idea was to have the flameholder the other way round, but I decided it took too much volume out of the rear of the diffuser "cone" I was using. It would probably work that way, and would probably help reduce heating of the front end of the chamber wall.

L Cottrill

[larry cottrill]

Guys I got an idea. Is it possible to have a powerful fan that forces air in, and one it starts the fan will keep on spinning (faster and faster every second) due to the thrust? What I plan to do is:

Have a long heat-resistant rod to go through the center of the ramjet, connecting two fans: One to blast air in and one at the back (obviously it gotta be heat-resistant). Run the fan off a battery until the ramjet starts, once it starts up the battery can be disconnected. Air will enter the ramjet at x velocity and exit at x+y velocity (due to the fuel exploding and creating a faster-velocity stream of air). The x+y velocity thrust will spin the fan at the back which will in turn increase the RPM of the one in front (because they're connected by the rod).

Will it work?

Well, that's a primitive turbojet. It probably won't work because of the inefficiencies of simple sheet metal fans. You won't get enough power from the turbine (rear fan) to drive the compressor (front fan) hard enough to mean anything. Amateurs can make their own turbojets, but it takes a LOT of engineering skill to design, and a LOT of technical skill to build. Just browse the Turbojet Forum (EDIT: I mean, the Gas Turbine Forum, of course ;-) a while and take a look at how it's done. Anything much simpler than that just won't work well (and maybe not at all), because it's so hard to get the necessary efficiencies. The "losses" have to be extremely low, and you cannot get by without high precision machining, not to mention many other potential problems that come up along the way.

If such an idea was easy and effective, everyone would be doing it.

Please understand, I'm not trying to discourage you from inventing. Just trying to frame this particular question in some harsh realities ;-)

L Cottrill

[fterh]

Hi guys,

will two of these work? http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... %26ps%3D54

I just got my JB Weld, and damn it was HUGE. I thought it'll be those tiny epoxy tubes sold in singapore, haha. So naturally I'm kind of eager, though I got 3 tests this week and 3 tests next week (school sucks )

Or is this better? http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... %26otn%3D2

I think the first one should be better because it is smoother and the handle is easier to remove? But I think I'll try hunting one down locally so I can make sure the flameholder will fit it

[larry cottrill]

will two of these work? http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... %26ps%3D54

Yes, that looks like the very one. You could use one full length for the combustion chamber / nozzle, and cut another one short for the diffuser. That would actually be a much better diffuser than the stubbier mug I used. You will find that the stainless is paper thin -- thinner than a business card -- if they're just like the ones I got.

Good luck!

L Cottrill

[fterh]

Okay I'll try to hunt one like that down in singapore. The shipping is almost $60 USD, what the $@#!#!%!#%$!

Btw if I'm starting the ramjet by throwing a sparkler down the diffuser, should the flame holder be [ or ] (say the air flow is from the left to right).

[larry cottrill]

The shipping is almost $60 USD

That is outrageous. It probably says "Made in China" right on the box ;-) Yes, there's GOT to be someplace local that you can get something just as usable.

Btw if I'm starting the ramjet by throwing a sparkler down the diffuser, should the flame holder be [ or ] (say the air flow is from the left to right).

If you must use a sparkler, use it in the tail end and just let it blow out (don't start any brush fires, though !!!) Whatever you do, I'd still say the [ orientation is better, even though it's opposite to what I did on the original.

L Cottrill

[fterh]

The shipping is almost $60 USD

That is outrageous. It probably says "Made in China" right on the box Yes, there's GOT to be someplace local that you can get something just as usable.

Btw if I'm starting the ramjet by throwing a sparkler down the diffuser, should the flame holder be [ or ] (say the air flow is from the left to right).

If you must use a sparkler, use it in the tail end and just let it blow out (don't start any brush fires, though !!!) Whatever you do, I'd still say the [ orientation is better, even though it's opposite to what I did on the original.

L Cottrill

Another anti-china products? Same here.

Oh my god there aren't any bush in Singapore to set fire to , LOL

[fterh]

I think I'm going to try my "primitive pulsejet" if I can find aluminium fans at my PC store and aren't too expensive.

Oh by the way, is a ramjet loud compared to a pulsejet? I don't want police treating me drinks in a station just for testing out my ramjet :X

[larry cottrill]

If you actually get it to work well, it will be plenty loud. However, it will be nothing like a pulsejet of the same size, and it won't be the kind of noise that carries very far. The sound is not nearly as obnoxious as a pulsejet roar, because it is not "explosive" noise like the pulsejet. It is closer to the character of "white noise".

L Cottrill

[fterh]

Will this work? Can't find the deep one, will a shallow one work?

[larry cottrill]

That will work, though you have a LOT of "rim" to trim off! It will be even better if you drill out the holes a little bigger, so there's more hole than steel.

Good luck!

L Cottrill

[fterh]

That will work, though you have a LOT of "rim" to trim off! It will be even better if you drill out the holes a little bigger, so there's more hole than steel.

Good luck!

L Cottrill

Trim off? If it fits, no need for trimming right? And for the drilling, what I think is that if the holes are too numerous/large there won't be enough resistance to slow down air flow to allow fuel/air to mix sufficiently, no?

[larry cottrill]

Trim off? If it fits, no need for trimming right? And for the drilling, what I think is that if the holes are too numerous/large there won't be enough resistance to slow down air flow to allow fuel/air to mix sufficiently, no?

If the big rim stays on, the perforated part will be an awfully restricted area. You want mostly free space for the air to move through.

If the holes are too small a fraction of the total area, you won't get enough flow to take advantage of the pressure gain achieved. It should be the diffuser, NOT the flameholder, that slows the air and boosts pressure. In the classic "textbook" ramjet, the flameholder area is VERY minimal. If you don't minimize it reasonably, you will have a thrustless burner, though it will probably run fine.

L Cottrill

[fterh]

Hey guys I finally found a stainless steel mug in the shape of Maggie Mugg's design..

But it's double-walled with insulation in between, will it work? o.O

Btw larry can you add me on skype? Mine is fabianterh.. So I can ask you questions asap It's good to make more friends too

[fterh]

Im thinking of using a straw with pin-sized hole to spray the fuel mist into the combustion chamber... If the front of the diffuser is STILL too hot for the straw maybe I'll place the straw in FRONT of the fan which sucks air (and now fuel) and blast them in ...