FWE - The Next Generation

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larry cottrill
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FWE - The Next Generation

Post by larry cottrill » Thu Feb 10, 2005 7:41 pm

Here's how I'm going to build my second FWE, unless someone can show good reasons why this layout won't work. Of course, I now realize that Eric and Steve are having the best results from the linear version they developed, but I still like the rear-facing intake, so here goes:

I'll use 1.25-inch [32 mm] tubing to form the intake, same material as the tailpipe - that sounds huge, but I'll only be using half the area! The idea is to flare and 'split' the tube so a flared 'half tube' forms a 'low profile' tunnel into the chamber. Since I still feel that nozzling into the chamber is good, the half-tube will be carefully carved to lie with its top edge parallel to the engine centerline, letting the 'ramp' of the upper surface of the chamber cone form a long nozzle section. The port into the chamber will be a 'rounded rectangle' 36mm long and something less than 30mm wide. Again, this sounds gigantic, but the flow in will be at a steep angle through it, directly toward the front dome of the chamber.

The drawing should show it a lot better than my description, especially if you bother to print it out. I figure the intake area will be similar to 3/4-inch conduit squeezed down to about 1/4 inch wide at the chamber end, roughly. The plan is to trim the overall engine length to 22 inches / 560 mm. The finished engine should fit in virtually any model originally designed for the Dynajet.

Comments? Any traps here that might be 'show stoppers'?

L Cottrill
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focus_wave_head_detail_new.jpg
Low-profile half-tube intake on the 'traditional' FWE chamber. Copyright 2005 Larry Cottrill
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Dave
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Re: FWE - The Next Generation

Post by Dave » Fri Feb 11, 2005 12:32 am

Larry
The only down side I can see is that you will be transferring a lot of heat to your intake air as it moves along the hot combustion chamber wall toward the inlet.
Dave

larry cottrill
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Re: FWE - The Next Generation

Post by larry cottrill » Fri Feb 11, 2005 1:16 am

Dave wrote:Larry
The only down side I can see is that you will be transferring a lot of heat to your intake air as it moves along the hot combustion chamber wall toward the inlet.
YES - but not as much as those [apparently successful] engines which wrap their intake completely around the tailpipe, concentrically!

L Cottrill

larry cottrill
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Re: FWE - The Next Generation

Post by larry cottrill » Fri Feb 11, 2005 2:19 am

Ben wrote:Which engines are those? I'm to the point of assuming no success unless an engine has been built after 1980 or had a paper published on it. (I don't count a patent as "a paper")
Ben -

Like this one from SNECMA ...

L Cottrill
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snecma_turbine_pulsejet_389_618.jpg
SNECMA valveless, for turbine drive studies. The dimensions are not mm, they are pixels from a jpeg rendering, so the proportions could be seen. Copyright 2004 Larry Cotttrill
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Mark
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Re: FWE - The Next Generation

Post by Mark » Fri Feb 11, 2005 2:44 am

Here's another view of "it."
Mark
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Presentation is Everything

larry cottrill
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Re: FWE - The Next Generation

Post by larry cottrill » Fri Feb 11, 2005 4:22 am

It still breathes ;-)

I think it was Bruno who once made a case for the pre-heating of intake air in pulsejets, or at least put forth a convincing argument that it isn't a bad thing to allow. Of course, if the average temperature in the intake stack is unusually high, it might have to be lengthened to phase properly with the engine frequency and harmonics.

L cottrill

Eric
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Re: FWE - The Next Generation

Post by Eric » Fri Feb 11, 2005 5:03 am

Maybe when I get some free time I will post some of the stuff that I have been working on as of late. Its basically the fwe i proposed back a while ago with the intake wraped around the tailpipe like those engines you pictured.

The one engine actually got hot enought to destroy the stainless steel. As many know when you weld stainless without sheilding gas it likes to suck in air and form a nasty foamy oxide, which is what the combustion chamber basically turned into from being majorly overheated :( Luckily the rest was recycleable.

One big thing that I would recomend if you have a large portion covered is to have the intake on the bottom when you are running the engine, It seems ridiculous how much more heat is transfered to the top of engine under those speeds, but there could be enough of a difference to keep the engine from hurting itself.

Eric
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Re: FWE - The Next Generation

Post by Stephen H » Fri Feb 11, 2005 11:58 am

hey larry after your last fre jets you must be very emotionally attached to your file by now!!! just seems to be a lot of filing work involved, but looks interesting!

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Re: FWE - The Next Generation

Post by Eric » Fri Feb 11, 2005 4:42 pm

Eric, that doesn't surprise me at all, and it certianly shouldn't surprise Larry after our fun experiments. I have a design for that kind of coaxial chinese/fwe that would not have that problem, but I'm not yet sure I want to give it away.
Me too, its a very simple mod, however its being developed in my "skunkworks" project.

Stephen I think if Larry had to remove a pound of material from something and was given an angle grinder and a file, he would still probably pick the file ;) His faithful use of those damn files makes me kringe sometimes, but then again I have been known to make a japanese katana or two from anealed bar stock with nothing but a file and a rasp, I just dont like getting blisters from it.

Eric
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Re: FWE - The Next Generation

Post by mk » Sat Feb 12, 2005 10:42 am

Larry Cottrill wrote:
Dave wrote:Larry
The only down side I can see is that you will be transferring a lot of heat to your intake air as it moves along the hot combustion chamber wall toward the inlet.
YES - but not as much as those [apparently successful] engines which wrap their intake completely around the tailpipe, concentrically!
I'd support intake air pre-heating, too, Because of the following, being more related to the "tools and construction" part. Maybe there are disadvantages in "over-heating", but who knows? At least a bit of pre-heating shouldn't be too bad.

Before the heating element of my "hot air gun" -- I did and do mostly use it for starting my engines -- broke down, the whole torch starting methode was a lot easier. The heated air could be regulated from about 300deg Celcius to 500deg Celsius. Heating up the "guns" stainless steel shaft and the engines intake pipe with a torch lets me still get better results than I'd get with cold air only.

For me, rather building smaller engines in a range from 50mm to 120mm comb. chamber ID, the main advantages using an hot air gun compared to a compressor are:
- relatively low air velocity, but accleration with different nozzles is possible,
- relatively large amounts of air can be delivered, maybe equal to a compressor and
- it delivers air over a relatively large area -- nozzle-shape related -- not only spot-source like.

All these points support the "blowing-the-flame-into-the-engine" methode, also known as (propane) torch starting methode.

For further information about such a little starting air device just ask me. Perhaps you can get a low price unit somewhere.
The original parts do not resist too long -- my experience -- but by doing some easy replacements and changes that shouldn't be the problem later on.
mk

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