New ramjet experiments

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Bill Lubarsky
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re: New ramjet experiments

Post by Bill Lubarsky » Sun Dec 10, 2006 10:55 pm

I have been checking up on what is actually needed to build a basic
ramjet and what design parameters have values that can looked up.
You need an inlet, diffuser, flame holder, combustion chamber and exhaust nozzle.

For anything operating below Mach1 the inlet actually needs to be nothing more than the front opening of the diffuser. A Bellmouth fitting from a
HVAC supplier can be optionally used as a Mach0 inlet.

The diffuser included angle can range from 10 to 15 degrees, this is necessary to prevent the flow from separating from the wall.

The region of maximum static pressure begins at the exit of the diffuser.
This is one place to position the flame holder. Alternatively you can
build a can-type combustor, designed like those used in a turbojet and inject the fuel at the top end.

Bill Lubarsky

Bill Lubarsky
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re: New ramjet experiments

Post by Bill Lubarsky » Sun Dec 10, 2006 11:03 pm

Rats!

No picture. Maybe this time?

WEL
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GENERAL RAMJET.jpg
GENERAL RAMJET.jpg (13.92 KiB) Viewed 5914 times

Zippiot
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re: New ramjet experiments

Post by Zippiot » Sun Dec 10, 2006 11:46 pm

Here is a neat picture of a few different styles of ramjet

http://www.erkenntnishorizont.de/images ... ramjet.jpg

top appears to be subsonic, middle supersonic and bottom hypersonic (scramjet). But I'm not sure about that.
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Bill Lubarsky
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re: New ramjet experiments

Post by Bill Lubarsky » Mon Dec 11, 2006 12:35 am

Yup.

Though even the subsonic design shown would be working at a much higher free stream velocity than anything you can test with a garden or workshop blower. The included angles for the diffuser given are for an essentially
Mach0 design. With enough ram-compression you can build something
with lorger include angles and gain far higher values of pressure recovery.

So many people seem wedded to designs using hard to make conical
components. A ramjet will work quite well with a rectangular cross-section
and simple tapered boxes and wedges. Adding hinges, the inlet and exhaust
can be adjusted during operation.

WEL

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re: New ramjet experiments

Post by Zippiot » Mon Dec 11, 2006 12:40 am

I always wanted to see if a "semicircle" ramjet would work. Like a ramjet cut down the middle from front to back then welded to a flat plate.

Next project is for sure a square jet, rolling cones is a pain!
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re: New ramjet experiments

Post by Bill Lubarsky » Mon Dec 11, 2006 3:47 am

I have scanned a couple of ramjet diagrams from old NACA
reports. The quality isn't good buy it illustrated some points.

WEL
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General Ramjet_1.jpg
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RECTANGULAR RAMJET.jpg
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Mike Everman
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re: New ramjet experiments

Post by Mike Everman » Mon Dec 11, 2006 4:40 am

Thanks, Bill. Those were keepers.
Mike
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Zippiot
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re: New ramjet experiments

Post by Zippiot » Mon Dec 11, 2006 7:00 am

Very cool, I wish more views were drawn in though...
Sailing Student- How do I know if my life jacket is tight enough?
Me- Can you breathe?
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