A question about homemade ramjets

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Arman_awn
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A question about homemade ramjets

Post by Arman_awn » Thu Jul 20, 2006 1:29 pm

Hello guys,

the first time I came to this forum to read about home made gas turbines,
I saw a club named "Ramjets". Now I wanna ask you that is it possible to build and run a ramjet engine at home (surely I don't mean I do this at home, I mean is it possible to build such an engine by using the materials found easily)?

You know that the operational speed of a ramjet starts at about mach 0.7, so how can I make a ramjet engine and run it? Probably you want me to get my hand out of the window of a flying airplane with my engine to run it!

I will be thankful if you provide me some information about the home-made ramjets and their operational possibilities.

Thanks

Arman.
What every man really wants is a Jet to fly...

larry cottrill
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re: A question about homemade ramjets

Post by larry cottrill » Fri Jul 21, 2006 2:14 pm

Arman -

On this forum, go to the thread called Steve's TLAR Ramjet:
http://www.pulse-jets.com/phpbb2/viewtopic.php?t=1881
Scroll down a little ways to see the picture of his engine in action. BE SURE you download the ZIP file and WATCH THE VIDEO WITH YOUR HEADPHONES ON!!!

Notice how Steve uses a high-speed blower to drive air into the jet. Also notice how nicely this little engine runs!!! NOTE that this is way LESS velocity than the Mach 0.7 that all the textbooks claim you need!

You don't need a fast vehicle to run a small ramjet - you just need some fast-moving air. How much speed you need depends entirely on the design of your engine, not on what some textbook author says.

L Cottrill

mk
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re: A question about homemade ramjets

Post by mk » Fri Jul 21, 2006 2:33 pm

While you could of course run such a small ramjet at fairly low air-velocities, do not expect it to be a propulsive device. Rather take it as an illustrating model or something.

You also would not need to throw your textbooks away, because I'm sure the author(s) reffered to ramjets, which were used as real propulsive devices. Therefore, there is no need to doubt they are likely choices for larger vehicle velocities.
Last edited by mk on Fri Jul 21, 2006 6:57 pm, edited 1 time in total.
mk

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Re: re: A question about homemade ramjets

Post by larry cottrill » Fri Jul 21, 2006 3:06 pm

mk wrote:While you could of course run such a small ramjet at fairly low air-velocities, do not expect it to be a propulsive device. Rather take it as an illustrating model or something.
Well, that depends on what you're trying to propel, and how skillfully you can build. If you create an engine that weighs a few ounces, and has thrust even a single kg greater than the value of its internal drag, you can certainly propel something with it! You just have to build very light and smart. AND, of course, you need to design a way to get it up to its operating speed.
You also would not need to throw your textbooks away, because I'm almost sure the author(s) reffered to ramjets to be used as real propulsive devices. Therefore, there is no need to doubt they are likely choices for larger vehicle velocities.
Quite right, Marten!

The reason the textbook examples are written up and illustrated the way they are is that the authors naturally think you're only interested in high speed / high efficiency ramjets. We, on the other hand, can't build a model airplane that will do 0.7 Mach, no matter how good an engine we can build !!! So, what we need to concentrate on is getting engines that will work at more moderate speeds - say, 150 km/hr or something. We will certainly not get an engine that anyone would describe as "efficient" for propulsion. But we CAN get an engine that will work - IF we can figure out how to get it moving before the ramjet is expected to kick in. OR, use it as a "motorjet" behind an efficient high-speed fan (which I personally think is the way to go).

There is NO "pure jet" solution that gives truly efficient propulsion at low speeds. This is why "hybrid" solutions such as fanjets and turboprop engines are important.

L Cottrill

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re: A question about homemade ramjets

Post by Najm » Fri Jul 21, 2006 3:17 pm

I have made ramjets from bodies of aerosol cans and they run as good as any other homemade ramjet as far as I can tell.
I recently made a ramjet out of two aerosol cans and aluminium(sheet), used epoxy and some tape to join it all together and it ran perfectly with an 800 W leafblower.

Arman_awn
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re: A question about homemade ramjets

Post by Arman_awn » Fri Jul 21, 2006 8:05 pm

Do you think if there is a good design, the engine can deliver acceptable thrust? of course when it is stationary?

What do you think about the designing? How can I design an efficient ramjet?
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re: A question about homemade ramjets

Post by Zippiot » Fri Jul 21, 2006 8:21 pm

Rams are tricky at subsonic speeds. There are so many different designs, but primarily they have a few key parts:
intake
expansion area
flame holder
exhaust (nozzle of sorts)

Larry has a grea intro to ramjets, google maggie muggs :)
You can build the muggs ramjet for less than 20 dollars, it doesn't usually make much thrust but there is no better into to subsonic ramjet design than glueing some cups together!

There are also multitudes of subsonic ramjet flameholders, which is one of the most improtant parts of the design.
A fingered flameholder works very well, and are quite easy to make.

The intake expansion area and exhaust are all designed around the ram's "design speed". How fast you want it to go, starting speed also. The flameholder is also a vital speed design issue, but many flameholders are interchangeable at the same design speed.


Mess around with stuff, the roar of your first ramjet coming to life is quite incredible.
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Najm
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re: A question about homemade ramjets

Post by Najm » Sat Jul 22, 2006 6:36 am

The only problem with a ramjet is that it needs some air flowing into it to work, when a ramjet is stationary no air is flowing into it so it will not produce any thrust but if you are blowing some air into it when it is stationary it will produce some thrust.
Here's a program that helps in designing a ramjet
http://www.alt-accel.com/rjsc.zip

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re: A question about homemade ramjets

Post by Arman_awn » Sat Jul 22, 2006 7:01 pm

Thank you all my dear friends,

I have a very interesting idea, to build a ramjet that can start when it is stationary (by using a leaf blower) and then disengage the leaf blower and the engien (the RAMJET engine, you heard right) will sustain.

The idea is under some improvments, if this will be possible, it will be a revolutionary design in ramjet engines, because such an engine can start an sustain and reach high speeds without using any booster....

I'll talk about this new design soon, stand by.
Be sure that the engine has still no moving parts...
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re: A question about homemade ramjets

Post by Mark » Sat Jul 22, 2006 10:53 pm

This brings to mind a couple of things. One is the account of small ramjet tipped helicopter blades. Apparently you could get them up to speed by merely spinning the blades with your hands, does anyone recall the burning rag technique? In this case it takes but a little forward velocity to start the ramjet.
Another thing is the valveless pulsejet that transitions into a ramjet. In the distant past, there was some mention that such technology was taboo or technology transfer in this area is guarded information, something you couldn't trade with certain nations. Of course anyone can own a ramjet I suppose and pulsejets too, so I wonder just how interesting/hazardous a hybrid would be. Maybe a variable forward intake Gluhareff would be an avenue to supersonic speeds. Certainly it would take a bit of effort to perfect/harness all the variables.
Mark
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Zippiot
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re: A question about homemade ramjets

Post by Zippiot » Sat Jul 22, 2006 11:28 pm

I recall that messerschmidt (i must have butchered that) had a valveless pj, inline with a cone in the intake. At no airspeed flame came out of both ends like all valveless linear pj's, but once it got some forward momentum the flame bent backwards and started to produce thrust only in the direction of the exhaust. Also once up to speed it could sustain ram-operation.

I do remember the gas soaked rag technique.
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Re: re: A question about homemade ramjets

Post by tufty » Sun Jul 23, 2006 7:36 am

Zippiot wrote:I recall that messerschmidt (i must have butchered that) had a valveless pj, inline with a cone in the intake. At no airspeed flame came out of both ends like all valveless linear pj's, but once it got some forward momentum the flame bent backwards and started to produce thrust only in the direction of the exhaust. Also once up to speed it could sustain ram-operation.
It was "slightly" more complex than a conventional pulsejet - it had 2 combustion chambers, one for "pulsejet" operation and a second for "ramjet" operation, with a variable geometry ramp between the two, they also tried a variable geometry tailpipe and a whole bunch of other stuff.

The cone in the intake was nothing (directly) to do with ramjet operation.

I really should finish translating the damn document.

Picture and performance graph attached...

Simon
Attachments
performance.jpg
Messerschmidt pulse-ramjet performance graphs
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picture.jpg
Messerschmidt puse-ramjet photo and explanatory cutaway
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Bo Danerius
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Re: re: A question about homemade ramjets

Post by Bo Danerius » Sun Jul 23, 2006 7:40 am

Zippiot wrote: I do remember the gas soaked rag technique.
Never heard of it. Any links or other explanation is greatly appriciated. /Bo

Arman_awn
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re: A question about homemade ramjets

Post by Arman_awn » Sun Jul 23, 2006 9:13 am

I think you've got a little surprised....

I'm not working on a pulsejet-ramjet design, I'm talking about some kinda ramjet engine that is not surely a pulsejet engine, even not a helicpoter ramjet...

I will talk about the main design, that I'm sure it will surprises you a lot more, soon.
________________________________________________
I have a question, How fast does the air coming out from the nozzle of a home made ramjet(by using a leaf blower to keep it running) travels?

Give me some information about the speed of the out coming air from that kinda ramjet engien.
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Re: re: A question about homemade ramjets

Post by leo » Sun Jul 23, 2006 9:44 am

Arman_awn wrote:and then disengage the leaf blower and the engien (the RAMJET engine, you heard right) will sustain.
I have thought about that too, creating some sort of cyclone inside a ramjet, and transferring some of the energy of the exhaust gasses to the intake air, without mixing them to much, like in a vortextube, so taking over the function of the compressor and turbine from a normal jet.

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