How small can jets get?

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benzo
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How small can jets get?

Post by benzo » Tue Sep 07, 2004 3:56 am

Hay all!

Im new here and have a question.
How small can you build a jet?

turbojet, pulsejet, ramjet.. whatever..

Does anyone know of a miniture turbojet engine project?

I know about simjets engines.. but i mean small like a banana? :)

A mini radialCompressor turbojet can't be too expensive to build?

Bruno Ogorelec
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Re: How small can jets get?

Post by Bruno Ogorelec » Tue Sep 07, 2004 7:37 am

benzo wrote:How small can you build a jet?
Not much smaller than the smallest in existence right now. It is not so much a matter of technology as of physics. In a jet engine, you have cool air enter the engine, get mixed with fuel, burn, and exit the engine. All those stages in the process require space -- most of all length. Don't expect ever to see a proper jet engine shorter than about a foot long, and even that is achieved so that the gas paths get convoluted rather than straight and it is achieved at the cost of performance.

The faster a fuel burns, the shorter the engine can be, meaning that the shortest engine you can build will run on hydrogen -- but it brings with it big new technological problems, because hydrogen is expensive and very awkward to handle.
benzo wrote:A mini radialCompressor turbojet can't be too expensive to build?
You're wrong. Making it small saves only the amount of material used, which is the least of your worries. The technology remains as expensive as it was and the production procedures for small parts are often more expensive than for big ones. Smaller engines are less efficient, so the cost per pound of thrust goes up as you scale the engine down.

benzo
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Re: How small can jets get?

Post by benzo » Tue Sep 07, 2004 9:19 am

Oh ok..
thanx for you quick reply!

Stephen H
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Re: How small can jets get?

Post by Stephen H » Tue Sep 07, 2004 9:39 am

how small you want it... heres a nice small turbine for ya http://www-mtl.mit.edu/mtlhome/6Res/AR2 ... ilicon.pdf

yipster
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Re: How small can jets get?

Post by yipster » Tue Sep 07, 2004 9:51 am

read mini/micro engines at: http://www.grc.nasa.gov/WWW/AERO/base/rac.htm still in a rush but remember they can be as smal as a button

steve
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Re: How small can jets get?

Post by steve » Tue Sep 07, 2004 6:58 pm

check out these:

http://www.mech.kuleuven.ac.be/pma/rese ... t_en.phtml

http://www.aip.org/tip/INPHFA/vol-7/iss-6/p20.pdf

pulsejet engines can not be made too small but turbojets can be made extremely small if designed correctly. Also these micro turbines don't necessarily have to be fueled by hydrogen; the newest versions of the silicon turbine will be made to run on hydrocarbon-based fuels.
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Bruno Ogorelec
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Re: How small can jets get?

Post by Bruno Ogorelec » Tue Sep 07, 2004 7:04 pm

steve wrote: turbojets can be made extremely small if designed correctly.
So I see, though I must say the physics of this baffles me. Everything I know about fluid mechanics and gas thermodynamics (which is admittedly not much) says this should not be possible. There are so many problems, starting with the length of the flame path, the viscosity of gases etc. that I would never have thought it possible, much less efficient. Those guys are claiming some startling efficiency figures.

Tom
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Re: How small can jets get?

Post by Tom » Tue Sep 07, 2004 7:20 pm

Perhaps a much more down to earth project for the experimenters, these silicon chip turbines are a tad beyond any of us i think : o)

http://www.technologie-entwicklung.de/G ... kp31_.html

Tom
Experience speaks more then hypothesizing ever can. More-so in chemistry.

Bruno Ogorelec
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Re: How small can jets get?

Post by Bruno Ogorelec » Tue Sep 07, 2004 7:30 pm

Oh, it's a great website; one of my favorites. What do you say to Andreas Petzoldt's 'Monocopter'?

Tom
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Re: How small can jets get?

Post by Tom » Tue Sep 07, 2004 7:33 pm

Some amazing work, i am really hoping it flys in the end, it would be something to see : oD
Experience speaks more then hypothesizing ever can. More-so in chemistry.

Al Belli
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Re: How small can jets get?

Post by Al Belli » Tue Sep 07, 2004 11:19 pm

Hi,

Go to http://www.memagazine.org/backissues/fe ... msize.html for an interesting article on a small ( very small ) conventional turbine engine.

Al Belli

benzo
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Re: How small can jets get?

Post by benzo » Wed Sep 08, 2004 9:20 pm

Thanx for all replys!
Im blown away by some of the links!

Absolutly cool ! ;D

Tom
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Re: How small can jets get?

Post by Tom » Wed Sep 08, 2004 10:30 pm

Also, see Wren Turbines for smallish turbines available to the hobbyist.

Tom
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Mike Everman
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Re: How small can jets get?

Post by Mike Everman » Wed Sep 08, 2004 11:13 pm

Those are so cool, Tom. As a manufacturer, I have to say they're a bargain, too.
Mike
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