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Jet Engine

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Unread postAuthor: paaiyan » Wed May 09, 2007 3:23 pm

Haha, yea I hope this one turns out better then. That is, I hope you break the 5 mph barrier, hahahaha. But really, I think a jet boat would be pretty neat. All it'll need is rocket launchers, a video conference screen in the dash, couple machine guns...
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Unread postAuthor: super spuder » Wed May 09, 2007 3:29 pm

don't forget the James Bond "ejection seat" :D
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trying to decide on a new project, probably something small.
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Unread postAuthor: paaiyan » Wed May 09, 2007 3:40 pm

Oh yes! You really should add that one to the boat man. That one worked quite well and I guarantee you can pull it off. Hahaha. Man if we have our way, you're going to have an uber-boat!
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Unread postAuthor: zeigs spud » Wed May 09, 2007 3:51 pm

ShowNoMercy wrote:I want to make a crackbox boat, and use a jet engine vs a regualr gas engine, the power to weight ratio is a lot better.


or just make a much cheaper, valveless pulse jet engine.
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Unread postAuthor: paaiyan » Wed May 09, 2007 3:57 pm

zeigs spud wrote:
ShowNoMercy wrote:I want to make a crackbox boat, and use a jet engine vs a regualr gas engine, the power to weight ratio is a lot better.


or just make a much cheaper, valveless pulse jet engine.


Hmm, I'm not familiar with the mechanisms and workings of pulse jets. Could you give a brief rundown?
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Unread postAuthor: jjk92 » Wed May 09, 2007 5:01 pm

not trying to put down the mythbusters(i watch the show like everyday) but they suck at what they do..they overcomplicate everything (this could be for the general public to go ohh ahh) and i honestly think i could have recreated some of the myths myself and gotten better results..sorry about that rant and zeigs spuds if you know of any good sites describing valveless pulse jet engines please tell beacause i cant find any good ones through google ..thanks
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Unread postAuthor: Orpackrat » Wed May 09, 2007 5:34 pm

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Unread postAuthor: super spuder » Wed May 09, 2007 7:04 pm

jjk92 wrote: and i honestly think i could have recreated some of the myths myself and gotten better results
if you think you could have got a better result. why dont you try and recreate one of the myths?
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Unread postAuthor: turbohacker » Wed May 09, 2007 7:19 pm

I would be very interested to hear about you findings. I Tryed to find a working gas turbune a little while ago. I was going to try and build a car around it. Check out Capstone micro turbine http://www.microturbine.com/
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Unread postAuthor: jjk92 » Thu May 10, 2007 2:22 pm

i had a felling someone would say that but i would be glad to if that was my job and if i had the funding they did..not trying to sound like a cocky little smart @ss but if i did have the resources they did i know i would be able to better recreate some of the myths and i have a felling they are better able to recreate some of the myths also simply due to expierience and knowledges in certain areas ... ill just stop because i know people will give me crap and be g@y about the whole thing so what ever ..the myth busters are cool and i personally wish i had there job and ill leave it at that
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Unread postAuthor: zeigs spud » Thu May 10, 2007 2:51 pm

okay vlalveless pulse jets are VERY arguable if they are good or not. for the money, they are fine. it's liek comparing the performance of a penu cannon to a combust with the same chamber and barrel. the penu will come out victor, but overall a combust can be just as good and cost less.


this has to be the BEST jet engine forum around, it also describes how they all work with fairly good example picture. i must say some people on their are REALLY good lol.

http://www.pulse-jets.com/

here is a really good explanation to a simple pule jet.
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NOTE i copyed this off of the http://www.pulse-jets.comand am not taking any credit for this work.

The picture shows one of the possible layouts of a valveless pulsejet engine. It has a chamber with two tubular ports of unequal length and diameter. One port, curved backwards, is the inlet pipe and the other (flared at the end) is the tail pipe. In some other valveless engines, it is the exhaust pipe that is bent into the U-shape, but the important thing is that both ports point in the same direction.

Image

When the fuel-air mixture combusts in the chamber, the pressure inside rises very suddenly. To an observer it looks and sounds like an explosion. The rising pressure forces the hot gas to expand out of the chamber and pass through the two ports at high speed. As it leaves the engine, the hot gas exerts thrust.

As the gas expands, the pressure inside the chamber drops. Due to inertia, the expansion continues even after the pressure falls back to atmospheric. At the lowest point, there is partial vacuum in the chamber. At that point, the momentum of the expanding gas is spent and the expansion stops. The process reverses itself and fresh air starts rushing into the ends of the two ports to fill the vacuum.

At the intake side, it quickly passes through the short tube, enters the chamber and mixes with fuel. The tailpipe, however, is rather longer than the intake, so that it takes incoming air longer to reach the chamber that way. One of the prime reasons for the extra length is to have some hot exhaust gas remain inside the tailpipe at the moment the suction starts. This remaining hot gas will now be pushed back towards the chamber by the incoming fresh air. When it enters the chamber and mixes with the fuel/air mixture, the heat and the free radicals in the gas will cause ignition and the process will repeat itself.

It took me almost 250 words to describe it, but this cycle is actually very brief. In a small (flying model-sized) pulsejet, it happens 100 to 250 times a second. The cycle is not much different, really, from that in the conventional flap-valve pulsejet, like the Dynajet. There, the rising pressure makes the reed valves at the front of the chamber snap shut and there is only one way for the hot gas to go -- into the exhaust tube. In the J-shaped and U-shaped valveless engines, the hot gas spews out of two ports. It does not matter, because they both face in the same direction.

Some valveless engine designers have developed designs that are not bent backwards, but employ various tricks that work in a similar fashion to valves -- i.e. they allow fresh air to come in but prevent the hot gas from getting out through the intake. We shall describe some of those tricks at a later point.
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Unread postAuthor: Orpackrat » Thu May 10, 2007 2:57 pm

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Unread postAuthor: Freefall » Thu May 10, 2007 3:30 pm

What kind of 160 HP gas engine are you running that would burn through 20 gallons in an hour?!?
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Unread postAuthor: cork9 » Fri May 11, 2007 11:01 pm

ya u also would need to buy jet fual. witch a belive is carasineand its gona be way to much weight.
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Unread postAuthor: ammosmoke » Fri May 11, 2007 11:51 pm

You can just run on diesel, I have read in Popular Mechanics that it works just fine. And as you can see here, somebody has made a pulsejet powered boat already, but it has terrible fuel consumption rates. And, as you will see here, shaft driven is in some cases better than just air driven. Which, is a problem with pulsejets, as there are no moving parts. :?
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