Worlds simplest valveless?

[Mike Everman]

I've been trying to come up with simple ways to try a number of valveless configurations easily, still mimicing SNECMA/Lockwood or Kentfield proportions. I stumbled on the notion that you could make any length and change in volume by squeezing down a piece of tubing just right. When closing it down, there is a width increase, but it makes for the smoothest transitions, and maybe some hidden benefits??

I'm still trying to get my software to blend this properly, some transitions look sharp, but a real tube would not be. I'm thinking of bolting a collar on the combustion chamber area to maintain it's diameter and length while forming everything else in a press or vise. Once the geometry is nailed, that is, (a miracle happens and) the engine runs well, I can make a one-shot press die set pretty easily for mass production.

[Bruce]

While it's true that you can change the cross-section by squashing a tube, you don't alter the surface-area -- in fact you increase the surface-area to cross-sectional area in a manner that is significantly disproportionate to the use of a cone or smaller diameter tube.

This could cause some problems insomuch as your losses due to drag will be much higher with a crimped pipe than they will be if a proper cone were used.

Also remember that in many valveless engines a smooth transition between the various sections is not necessarily ideal for best performance.

In the LH designs for example, the transitional cones at each end of the combustion chamber are designed to induce significant turbulence within the gases that enter the chamber. If that transition were smoother then the turbulence produced would be lower and you'd get inferior air/fuel mixing on the intake side and slower ignition when the exhaust gases re-enter on the tailpipe side.

However, there's an even bigger reason why this idea is not a good one.

If you distort the cross-section of almost any part of an LH engine from a nice round circle, the engine will collapse unless very strong (thick) materials are used for its construction.

Quite coincidentally, this is exactly what just happened with the 200lbs-lockwood and I've also had it happen with the smaller 55-lbs engine.

I'll post pictures on my website shortly but you must remember one important thing -- Mr Bernoulli was right.

When you reduce the cross-sectional area of a conduit, the gasflow through the narrower section will increase in velocity. Mr Bernoulli tells us that the higher the velocity, the lower the pressure.

Now a perfectly round tube will withstand a reasonable amount of external pressure -- but if you oval that tube it can be easily crushed by atmospheric pressure if the pressure inside is reduced.

The pictures I'll pust represent a *very* graphic demonstration of Mr Bernoulli's theory at work and I'd wager that the same problem would beset a "squashed cross-section" engine if it were made of reasonably lightweight (aka: practical) material.

[Mike Everman]

Sorry to hear about the Lockwood, Bruce. Yeah, while I did plan on rather thicker material, and on pressure induced flex, I did not consider the intake or the flow derived vacuum! Hmmm. I had considered the constant surface area, but though that might be a good thing.

[Bruno Ogorelec]

Mike,

I'm a sucker for this kind of approach. I think it would work well in a number of cases. However, Bruce is right in warning about form stability.

may I suggest that you make the approach just a mite more sophisticated. Instead of squashing a tube flat, squash it from two or more directions -- say, into a cross-shaped or shamrock-shaped section.

That way, it will keep its shape better. You can also use the corrugations in a number of nifty ways. For instance, adding a thrust augmenter onto a cross-shaped duct allows you to keep its diameter small for lower drag.

Just don't make your engines small, or the poor surface-to volume ratio will start bothering you.

You can shape such ducts with hydroforming. That's one of the greatest ways of shaping metal I have seen. Simple, cheap and cheerful.

Bruno.

[Mike Everman]

OK, now my real work is really suffering... This was fun! Thanks for the spark, Bruno, I'm starting to like this idea. Now I have to consider what I need for hydroforming!!

[hinote]

OK, now my real work is really suffering... This was fun! Thanks for the spark, Bruno, I'm starting to like this idea. Now I have to consider what I need for hydroforming!!

OK, NOW you're talkin MY language!

Just bell the ends of the intakes (or they won't work)(also looks like they are too long in the rendering), and make as much of the assembly round as you can--and you've got yourself something that should be successful.

Bill H.

[Mike Everman]

Just bell the ends of the intakes (or they won't work)(also looks like they are too long in the rendering), and make as much of the assembly round as you can--and you've got yourself something that should be successful.

Here's some flares, Bill. I can't wait to see what it looks like when I make sure it has the proper lengths, areas, etc! Oh, yeah, and that any section has roughly the same area of tubing material(!) It'll stretch or compress some in hydroforming. My software is really not made to do this, so it's going to be laborious but fun.

Now, that's torn it, I really must get back to work!

[Bruno Ogorelec]

Mike, ask Our Man in Avon and Somerset Police, Nick Ibbitson, about hydroforming. He built one or two BCVP prototypes that way.

I'd show a photo, but the Albion Propulsion would be onto me like a ton of bricks.

It's a lot of fun and if you're inventive about cutting your patterns, you can produce some weird shapes. You do a lot of ridiculous-looking stuff before you learn, though.

Bruno
The Singing Pig Propulsion Inc.

[Mark]

Mike, ask Our Man in Avon and Somerset Police, Nick Ibbitson, about hydroforming. He built one or two BCVP prototypes that way.

I'd show a photo, but the Albion Propulsion would be onto me like a ton of bricks.

It's a lot of fun and if you're inventive about cutting your patterns, you can produce some weird shapes. You do a lot of ridiculous-looking stuff before you learn, though.

Bruno
The Singing Pig Propulsion Inc.

Maybe you could do some vacuum forming, look how well it works for crunching the Lockwood.
If you just crimp either side of a straight duct , you can form a typical pulsejet shape. You might use the excess flange to mount the pulsejet or integrate in a fuel tank of sorts. My brother toyed with a smallish brass prototype formed this way. If you didn't care about weight, you could prototype a shape with 2 sheets of thin steel and shape a form with flat rods that clamp the 2 sheets together.
I wonder if ice forming has ever been used, using the tremendous expansive power of the change of state of water to ice to press fit or indent some object?
Mark

[Mike Kirney]

Not to belittle your work Mike, but that first pic you posted in this thread (tube1.jpg) looks just like a big kazoo. If you built a kazoo jet with a noise-making reed and everything, I would idolize you. If you made six of them and tuned them so they sounded like an intergalactic freight train horn or something I would happily PayPal you $9.95 for some digital movie footage.

[Mike Everman]

Not to belittle your work Mike, but that first pic you posted in this thread (tube1.jpg) looks just like a big kazoo. If you built a kazoo jet with a noise-making reed and everything, I would idolize you. If you made six of them and tuned them so they sounded like an intergalactic freight train horn or something I would happily PayPal you $9.95 for some digital movie footage.

oh, it's "go time" :-D Brace yourself, I'll have your $9.95 one way or another...

Maybe you could do some vacuum forming, look how well it works for crunching the Lockwood.
If you just crimp either side of a straight duct , you can form a typical pulsejet shape. You might use the excess flange to mount the pulsejet or integrate in a fuel tank of sorts....

Yeah, now I'm looking at forming quadrants out of sheet rather than deal with 10,000 psi fluid and all that tooling. I can make tools to form 1/4 or 1/3 of this thing and spot or edge weld. If I spot weld, how to you think ceramic bonding compound would be for sealing?

[Viv]

Just bell the ends of the intakes (or they won't work)(also looks like they are too long in the rendering), and make as much of the assembly round as you can--and you've got yourself something that should be successful.

Here's some flares, Bill. I can't wait to see what it looks like when I make sure it has the proper lengths, areas, etc! Oh, yeah, and that any section has roughly the same area of tubing material(!) It'll stretch or compress some in hydroforming. My software is really not made to do this, so it's going to be laborious but fun.

Now, that's torn it, I really must get back to work!

OK now I hate you! that one works no problem, all we need now is a few K$ to make the dies.

But what about the recuperators:-)

Viv

[Mike Everman]

OK now I hate you! that one works no problem, all we need now is a few K$ to make the dies.

But what about the recuperators:-)

Yeah, I'm daydreaming about the recuperators now, and also realizing that the ribs are not going to form like that in hydro since the area that would force them radially outward diminishes to nothing. maybe I'll design dies so that I can press this from sheet in quadrants, but then I've got welding and such and we'll have to change the name to "world's kinda simple idea that went horribly wrong and expensive just to find out it doesn't work"
I'll be thinking of gentler material movement to get it back to tube hydroforming.

[Viv]

OK now I hate you! that one works no problem, all we need now is a few K$ to make the dies.

But what about the recuperators:-)

Yeah, I'm daydreaming about the recuperators now, and also realizing that the ribs are not going to form like that in hydro since the area that would force them radially outward diminishes to nothing. maybe I'll design dies so that I can press this from sheet in quadrants, but then I've got welding and such and we'll have to change the name to "world's kinda simple idea that went horribly wrong and expensive just to find out it doesn't work"
I'll be thinking of gentler material movement to get it back to tube hydroforming.

They produce some surprisingly complex shapes, the front beam axles for a lot of cars are now made this way, Mercedes use it to make the engine mounting frame for one of their cars.

The tube is bent in to a U shape first, after forming it is a very complex shape and squire with holes punched during forming.

Viv

[Nick]

further to the interesting stuff already mentioned here i would just like to say that its not expensive or difficult (or dangerous!, unless you are hydrophobic).

I made simple hand powered pump and some one way valves coupled to some braided brake hose. This cost me nothing at all as i had varoius stock materials, block of steel 1/2" reamed hole therein, 1/2" dia steel rod etc etc. this simple device provides more than sufficiant pressure to form 1mm steel from two dead flat plates into a nice tapered "U" Bend, you will soon find the pin holes in your welding once you start pumping!.
One more thought is, use water!, i know some have used oil or hydraulic fluid but given that you may need to mig up any little holes by way of repair whilst pumping the shape up i would rather weld a sealed tank that has just held water than a potentially explosive oil. Nuff said.

try it its surprisingly effective.

Nick

Ps Bruno, you can show that pic if you like, it s somewhat superseeded now.