Any other Jet Engine builders?

Hi Al,

I dont build them, but I am very interestd in the workings, especially pulse and ram jets, so simple. I noticed on a past scrapheap challenge where the object was to build a jet dragster, that the Navy team used what they described as a ramjet, with the input as well as the output facing rearwards. The simple diagram showed a restricted pipe wih no valves in front, so it wasn't a pulse jet. I'm going quietly mad tring to figure out how it worked!.

Anyway, don't think you are any more nutty than the American scientists who've just done a couple of amazing things with scrams.

Good Luck,

Tom.

Nunce excretia in extractum est. (Appropriate this thread ?)

"Tom Jacobs" wrote

I didn't see that episode, but what you describe does sound like a type of pulse jet. Did it have a short input pipe and a long output, connected by a U-bend and both pointing rearwards?

If so, the working priciple is about as follows (I think): Fuel is injected and ignited near the bend. Initially, this only goes "whoosh" in both directions until the available oxygen in the pipe has been consumed. But because the iput/output pipes are of unequal length, the blast of hot gases will set up a draft through the pipes, as it quickly vents through the intake pipe but has some way to go in the longer output. It's kind of like a ram charger, if that makes any sense; it relies on the momentum of the blast to keep going down the pipe for a short while after combustion has ceased, thus setting up a draft that sucks fresh air in through the intake.

As fresh air then enters the combustion area and mixes with fuel, the process is repeated, and if everything is properly tuned it will start running at a steady (and very noisy) pulse with a fair amount of thrust produced.

The main problem with these, from a propulsion standpoint, is that the air intake has to point rearward in order to produce any thrust at all since it blows in both directions. As you gain speed, therefore, it will extinguish itself from lack of air. Apart from that they're brilliant machines: no moving parts, and lots of noise ;-)

The only real engineering challenge when building one is AFAIK to get the lengths and diameters of pipe just right, as it has to be in tune almost like an organ pipe. Also, the fuel to air raio must be just right if you want it to start from cold; I guess a blower could be used to get it going a bit easier though.

-- Aamund Breivik

Tom, it _was_ a pulse jet (but no reed valves!). If you want more info, go to the web site of Bruce Simpson who acted as the advisor for the pulse jet on SHC:

All the details will be revealed there...

We're involved in building large hybrid rocket motors but one of our members is working on pulse jets and liquid rocket motors too.

Chris

Whoops!.

Many thanks to both Amund, Duncan, and everybody else for information. I have been going on about that program to friends and anyone else who would listen, since I saw it. I shouldn't have to eat too much humble pie though, as I don't think very many of them were actually listening.

Thanks again, and, as I also tell everybody I know, this is THE site for informative help and assistance.

Best Regards

Tom.

Nunce excretia in extractum est.

You mean like this?

This is quite fun aswell.

Stephen

The expert on that show was Bruce Simpson, who runs a news site at

and has a pulsejet powered gokart of his very own. I wouldn't drive it... Drop him a line at editor at aardvark.co.nz. Top bloke Those jets work on a tuned pipe principle, so there is no need for valves - the harmonics do all the work. Geoff

-- Catapultam habeo. Nisi pecuniam omnem mihi dabis, ad caput tuum saxum immane mittam. I have a catapult. Give me all the money, or I will fling an enormous rock at your head

Hi Al,

Some useful links.

Do-it-yourself gasturbines:

Many (small) turbine links: 'jets'

-> select from options in blue frame to the left

You guys do know that the first turbine for RC planes, built by Kurt Schreckling and published in a German RC magazine in the mid 90's, had a compressor made out of plywood and carbon?

Met vriendelijke groet ;) Ron van Sommeren near Nijmegen, the Netherlands

----- Original Message ----- From: "Al Doyle" Newsgroups: uk.rec.models.engineering Sent: Thursday, April 08, 2004 1:25 AM Subject: Any other Jet Engine builders?

haha, you guys are funny. No offence but you dont really have a clue what you are on about. It was a pulsejet but a valveless. It was of a lockwood hiller design. It works by injecting fuel into the combustion chamber and ignighting it, this goes wish out boat ends and creas a vcaume in the combustion chamber were air is sucked in and mixed with fuel and automaticly ignights. all the exolosions make a pulsing noise hence the reason it is called a pulsejet!

Stephen H