FWE engine for valveless testing and valveless pulsejet calc

[Eric]

Its been a while since I have any free time to do anything lately. I have been working on PJC 1.5 and decided I might try to add a few valveless designs that can be "scaled" to larger sizes.

I ran a bunch of numbers and it seems that I should be able to put together a decent valveless engine calculator, as well as adding the valve head dimension generator for the valved engines.

I am going to build a bunch of engines tomorrow, I have all the cone patterns cut out rolled and ready to be welded. I plan on making the chinese valvless engine in 3 different sizes, and maybe a linear lockwood if I have time. Hopefully everything will work with my calculator based dimensions.

Larry,
I havent been on the forums to much extent in a long time and just want to congratulate you on your FWE design.... and I was wondering if I could try to build it :) I would love to see if the basic principle can be "scaled" up with much sucess according to my formulas. I was thinking around 3.5" tailpipe diameter? I havent had time to read all the posts yet but I was just wondering what kind of thrust you were getting out of it?

Thanks,
Eric

[steve]

my last thrust measurement from it was in the 500 to 600 gram (a little over one pound) range with a 1.25 inch tailpipe

[larry cottrill]

my last thrust measurement from it was in the 500 to 600 gram (a little over one pound) range with a 1.25 inch tailpipe

Eric -

There you have it, from the man who built the original prototype and got it to fire up the first time down the chute. I'm sure that mine is not as strong as Steve's, since I undersized the intake. If I were building it today, I would use the 3/4-inch EMT intake, but I would pinch the end inside the chamber to about 1/4-inch clear width. Steve pinched his a bit, but not nearly so much.

Go for it - you should have no trouble building it, especially if you take the tailpipe 'cheat' I used [1.25 in. OD antenna mast tubing] instead of rolling your own out of sheet. Be sure you go through all the FWE and 'Short Lady' threads. And, check out the main site page: www.bz9.com/fokus

I actually don't think this engine will scale badly at all (he said with supreme confidence ;-) simply because the whole design theory was wave-based from start to finish. I think what you're talking about would be a fine size for the engine. Of course, you'll want to use UFLOW1D or something to verify the operation of the larger size [just ignore the intake to set up your run]. I would NEVER advise a beginner to scale it, but an experienced hand who accepts that it may need a bit of tweaking should be able to handle it easily.

Just the lightest touch of air is needed to get it going - it's easy to "overblow" it and mistakenly conclude that it will never sustain! Note carefully how Steve ended up fueling his - that seems to work the best, though it's obviously something you could easily experiment with. My last experiments were trying to get it to carburete liquid fuel, but I had nothing positive to report, except that a smooth pinch in a round pipe WILL pull fuel nicely as a venturi, with very little air input.

Thanks, Eric!

L Cottrill

[Bruno Ogorelec]

Larry,

I forget -- do you still have some of those rolled cones that Steve made, or have you used them all up?

I think your Fokus is simply made for experiments with intake placement. I'd really like one with the intake positioned up front, Unicone-style (or, if you prefer, the way Rossco did it). It might work really well and it might also be simpler to build than the sidewinder.

Here's a picture of some old Unicone prototypes. 2001 vintage, I think. As you can see, we were going for a really short length. The exhaust and the intake should probably both have been about twice as long as they were. But, it did work! None too well, with a feeble amount of thrust, but it self-sustained.

It pushed no flame out of the intake. You could only feel pressure pulses if you put your hand there. Without equipment, it was impossible to see whether it sucked air back at the exhaust end. Back then, I thought it wouldn’t but it almost certainly did.

[Eric]

Larry,
I have most of the construction done on the large FWE and it is going to be one hell of an engine. Need to get more propane and some steel tubing for the intake, if it will run it should run tomorrow. I figure it will have around 10 - 11 pounds thrust. With the normal size FWE's i will try different levels of constriction for the intake - tailpipe junction.

Eric

[larry cottrill]

Eric -

Man, that's heavy-duty. I assume you've seen Steve's photos showing how the heat development is all contained in the chamber - or appears to be. It will be amusing to see whether a big one behaves in the same manner!

And, of course, what kind of thrust is actually measured.

I can hardly wait ...

L Cottrill

[steve]

make sure to take lots of photos! not just of it running, but of the construction of it as well.

[Eric]

Construction was going so fast and smooth that I didnt bother taking pictures. I suppose I can next time I work on it. It is really such a simple construction that it barely takes any time to make considerable progress. The only thing that even slowed me down was custom shaping the tubing to fit together for the intake. I flattened the intake-tailpipe section to a eliptical shape, not quite as distinct as in your pictures on the jetzilla site, but with the tubing I am using it will be difficult to go further without collapse.

Unfortunately I have hit a snag. My arc welders infinate amperage control has gone crazy, well i guess crazy is not a strong enough word to describe it. Now it sporattically decides to change to high and vaporize whatever I'm working on, and I cant seem to get it set to low no matter what. I have decided that I am just going to buy a MIG, maybe tonight if the snow lets up. Unfortunately I think the waranty was only for 4 years, and I dont really think its worth getting fixed professionally.

The intake is totally finished with the propane injector and is tack welded to the tailpipe, and the tailpipe end cap needs to be welded on.

As far as the other engines go I am about 50% done with the chinese style engines, and the small FWE is about 25% welded up. I really wish I was somewhere warm like california and had more than 3 hours a day above freezing :(

What is the angle that the intake slopes at on the inside of the engine? It was a little hard to tell in the Paint plans so I tried to make it as close to the diagram as I could. If you want I can autocad everything and print it to a pdf so anyone can print it out in high res.

Eric

[larry cottrill]

What is the angle that the intake slopes at on the inside of the engine? It was a little hard to tell in the Paint plans so I tried to make it as close to the diagram as I could. If you want I can autocad everything and print it to a pdf so anyone can print it out in high res.

Eric

Note that, as far as the original FWE goes, Viv and Luc will be doing a complete set of drawings. If you want to do your big one, well, go for it.

I showed the angled part of the intake going into the chamber at 45 degrees to the centerline, so the angled cut-back should be just a bit more, like maybe 5 to 7 degrees 'relief'. The idea is just to rake it back enough that the [presumably rearward] mass flow at the center of the chamber will slip around it without getting snagged into it, i.e. it is not acting as a 'scoop' for rearward flowing combustion gas. There is really nothing critical about this motor, theoretically, except the length ratios and the location of the point where the intake CL crosses the chamber CL.

The idea of flattening the inside end of the intake pipe is nothing more than providing a nozzle for incoming air/fuel mixture and a diffuser to put the brakes on any outbound blast gas. I really want the air coming in fast and getting to the front 'dome' to break up in turbulence and form the explosion right there against the dome face. That should give you a 'cold spot' at the bottom of the chamber where the mixture hits hard and washes forward before it diffuses enough to ignite.

Very sorry to hear about your welding glitches, and I hope you can resolve that quickly, to your satisfaction. I was starting to wonder what happened, imagining all sorts of evil outcomes to the initial test - hospitalization, house burned down, neighbor's house collapsed from vibration, etc., so I'm happy it was none of those!

L Cottrill

[jmhdx]

Excellent work on the closed end approach, I think it's about nailed the chinese priciple, It's down to where you put the gap in the tube. For a closed end length of pipe there is a mean harmonic when running at L/? the Logan point. I thank Larry for his explanation of this some time ago.
I would reccomend the next step of developement using the same cones would be an annular gap. Cut the cone short, use same exhaust pipe, but calculate the gap outside the exhaust and inside of the now larger cone end to match the surface area of the original intake pipe, blank old hole.
Sorry just need to fire one off now and then.

Mike.

[Eric]

Here is a picture of the "tall lady" standing above the tiny little dynajet. The pipes are slightly longer than what I calculated, but are proportional to eachother. As far as the intake flare goes, I am going to see if the engine will run without it, and either way i will put them on afterwards and see how that changes thrust. The propane is gonig to be injected perpendicular to the intake axis, and I will also try mounting one parrallel like Steve did. There is a little mounting nut on the back side of the intake, and I have these fancy little stainless steel propane injector tubes used in some mannor in a friends wind tunnel. As for more up close pictures, I will take more when its done but I am very self concious about the holes my arc welder vaporized that have yet to be patched :(.

Eric

dont know if the picture uploaded properly, might take another try after this

[larry cottrill]

Here is a picture of the "tall lady" standing above the tiny little dynajet. The pipes are slightly longer than what I calculated, but are proportional to eachother. As far as the intake flare goes, I am going to see if the engine will run without it, and either way i will put them on afterwards and see how that changes thrust. The propane is gonig to be injected perpendicular to the intake axis, and I will also try mounting one parrallel like Steve did. There is a little mounting nut on the back side of the intake, and I have these fancy little stainless steel propane injector tubes used in some mannor in a friends wind tunnel. As for more up close pictures, I will take more when its done but I am very self concious about the holes my arc welder vaporized that have yet to be patched :(.

Eric

dont know if the picture uploaded properly, might take another try after this

Eric -

Looks good to me! The cone is a little short in relation to the pipes, but should work, I think. Why does the cone appear to be such dark metal, compared to the pipes?

I think you'll find that a good intake flare is important. My standard size Short Lady has no tailpipe flare, and runs OK, but might be stronger with it - it's one of those things I was going to experiment with and never got around to it.

Did you get the new welding rig? I certainly hope that helps you patch things up and get running.

L Cottrill

[Eric]

Well the cone is stuck in the grass a bit, and the pipes are over lenght a bit, so it does look slightly different, but will most likely be cut to propper size upon testing (intake is made as long as one with intake flare even though it has none, and the tailpipe was made from 2 sections of tubing and I just didnt cut it to exact lenght yet to allow for some experimentation). As for the different coloring, I just ground off all the crud on the tailpipe so its all shiny, and in order to form the cone I heated the metal until red and then slowly let the temp fall in order to take the temper out of the steel since it seemed very reluctant to roll.

With the intake, the ratio of areas is aproximatley the same as Steve used. I figure without having a nice aerofoil / cone intake it will effectively pull air into the engine as an intake with the ratio that you used. I like trying every possible permutation within reason.

The 3.5" ID tubing I used for the tailpipes were actually a bunch of old bar stool bases. Each has a very nice perfect aerofoil base leading up to the 3.5" tubing. They are about 10" at the base, and constrict to 3.5, if anyone is interested I have a bunch. I might use a small setion of a base to flare the tailpipe out to maybe 4.5" or so. I also plan on making a few augmentors.

The welder is supposed to be delivered tomorrow. Wether I will have time to assemble it and do much welding will be seen. I CANT WAIT to do some aluminum welding without borrowing peoples tig's.

Eric

[larry cottrill]

I think your Fokus is simply made for experiments with intake placement. I'd really like one with the intake positioned up front, Unicone-style (or, if you prefer, the way Rossco did it). It might work really well and it might also be simpler to build than the sidewinder.

Bruno -

I've thought of doing a Rosscodyne, but then, there are other things I'd like to try, too [yes, I still have one cone and dome left!]. Unfortunately, this is where things get complicated:

Whatever I do with it, I still want it to act in the 'Focused Wave' pattern, if possible. Sure, I could make a little Unicone, for example, but I don't want the explosion happening back in the apex of the cone like that. I want to keep the start of the action up against a wide dome at the front end. Even if I tried a Rossco layout, I would modify the inside end of the intake to try to move the f/a mixture up front before it goes off. With the 'sidewinder' layout you guarantee you can at least approach that theoretical ideal. Remember that the whole megillah to the Focused Wave design is to get all the wave energy of the blast to funnel rearward in a single smooth wave crest from front to rear, without additional front-end reflections or high-frequency ringing.

I plan to post some speculative plans for more things to try, when I have a chance to get them drawn up.

L Cottrill

[Bruno Ogorelec]

Whatever I do with it, I still want it to act in the 'Focused Wave' pattern, if possible. Sure, I could make a little Unicone, for example, but I don't want the explosion happening back in the apex of the cone like that. I want to keep the start of the action up against a wide dome at the front end. Even if I tried a Rossco layout, I would modify the inside end of the intake to try to move the f/a mixture up front before it goes off. With the 'sidewinder' layout you guarantee you can at least approach that theoretical ideal. Remember that the whole megillah to the Focused Wave design is to get all the wave energy of the blast to funnel rearward in a single smooth wave crest from front to rear, without additional front-end reflections or high-frequency ringing.

I could be wrong, but in my book, the action should happen in the front part regardless of the orientation of the intake. Most of the volume is concentrated near the front plate, after all, and this will be the imaginary center of the suction force, so to say. The important point, really, is to have the inner end of the intake in teh right position, acoustically speaking -- your L/4 position, if I am not mistaken. Or was it L/3? Have to look it up. I keep confusing the two.

That said, I appreciate very well yout thoughts about there always being something else to do.

As always, your FWE strikes a chord with me. I always have this strong feeling when I look at it that it mist be a good shape for a pulsejet. It must have something to do with a similarity to the Unicone. As Nick can tell you, one of the interim designs for the BCVP also featured similar-looking parts.

Nick, whatever happened to that nice-looking double-cone engine you built by hydroforming? The one with short intake/exhaust stacks? It looked very sexy.