Prettiest FWE (?) - the 'Lady Anne Boleyn'

[larry cottrill]

Here is a proposed design that is (perhaps) the most aesthetically pleasing FWE ever. This is closely based on Graham & Nick's "Type 07" tailpipe design, which Graham gave me to use in future developments. What I've done here is squeezed the Type 07 mid-engine cylinder into a long cone, which smooths and stretches the pressure wave slightly while preserving the significant reflection from the (approx.) 2L/3 point. It also has the effect of slightly trading off massflow for higher exhaust velocity, but that's probably about a wash in terms of thrust contribution by the tailpipe.

Anyway, this is a lot of cones to put into an FWE planform, but I hope the performance will be worth it. You can probably expect more exacting startup technique than with any of the straight pipe versions. And, it uses a form of the 'Advanced FWE' intake that Eric has so ably demonstrated. The intake shown is a chunk of 3/4-inch EMT pre-formed bend (or "sweep" as it's sometimes known), available anywhere. The intake is moved to the bottom side, where its outflow runs between the mounting lugs (located at the approximate engine CG, of course).

This is a very small-scale drawing; I may follow up with some full-size drawings if I can find the time. I have included a simplified form of my air starting tube, for compressed-air starting. Using this method is entirely optional, of course.

I think a liquid-fueled version of this would be the best design I have in terms of an engine to put into production, and I would do so if I could.

L Cottrill

[Eric]

Well youve managed to add an extra 17" of welding, and numerous hours cursing and forming cone sections to one of the most simple engine designs in the world :P

I think it would make a very nice looking contraption if it could be machined from a solid piece of round stock or spun from tube, but in practice I think lining up all those conical sections, and then welding them, would probably make it look like the FWE's ugly cousin.

Beauty aside, it looks good.

[larry cottrill]

Well youve managed to add an extra 17" of welding, and numerous hours cursing and forming cone sections to one of the most simple engine designs in the world :P

Eric -

I was almost sure you'd be the first to comment; I knew you'd love it.

I think it would make a very nice looking contraption if it could be machined from a solid piece of round stock or spun from tube, but in practice I think lining up all those conical sections, and then welding them, would probably make it look like the FWE's ugly cousin.

Get a 32mm OD round rod or tube and turn a couple of conical collars; jig for tack welding as shown below.

Beauty aside, it looks good.

Thank you, sir!

L Cottrill

[vhautaka]

Anyone yet try hydroforming an entire FWE or a Chinese? You could add as many cones as ever needed, all welding would be boring and easy, and the engine would be both smooth and leak-free once in shape. And lighter weight than with the standard tubes.

Wonder how easy it'd be to make the intake from the same piece as the rest (the same two pieces). Maybe getting the angle to look right would require some trying.

[milisavljevic]

Anyway, this is a lot of cones to put into an FWE planform, but I hope the performance will be worth it.

Hello Larry --

A sweet-looking motor, to be sure! You know, if this were Mike's design, he would KAZOO this motor, not weld it!*

Cheers,
M.

*Of course, the intake and headplate (or cap) both require welding.

[Graham C. Williams]

Dear Larry
I've got a soft spot for this type of motor. Nice looking motor Larry. The Type 07 allows you to take complete control over the velocity profile during the pressure build period and late into combustion.
I'd like to hear Mikes (analytical) comments.

Regards
Graham

[larry cottrill]

Thanks, M and Graham!

I wondered right away after designing this if the main shell could be formed from two pieces of 32mm tubing, in the following way:

Make a heavy-duty center screw, something like 20mm OD all-thread rod. Lathe turn two long conical dies (perfectly matched to each cone angle) for each half that would thread onto the rod. Cut the appropriate length of tubing (might take a couple of tries) and thread the greased dies in, cranking down heavily until you have stretched out two venturi-like pieces, the chamber-to-mid-cone half and the tail-to-choke-cone half. Then, take it all apart and just weld the shells together at the single middle seam. I wonder if there's enough ductility in common stainless tubing (type 304, 308 or 316) to take this kind of action. I'll bet most mild steel tubing would split before it would stretch 2-to-1 !

The forces created within the tubing wall would be tremendous, without putting much effort into turning the dies in, because the slopes are so long (equivalent to great leverage). You would probably have to run it in a bit, ease it back, tighten a bit more, back off again, etc., so it would take a while. Still, you'd have a very elegant solution to the problem. Of course, the wall would be mighty thin at the maximum diameters at the two ends.

Would this scheme work? Only Al Belli knows for sure ...

L Cottrill

[milisavljevic]

Hello Larry --

This is just my evil idea, but why not ask Mike to kazoo the main body of your 'Lady Anne' and ship it out to you?
He can place it in the same box as your Dynajet. Think of this service as rent for keeping the Dynajet for so long!

Evil M.

[Jonny69]

Hi Larry, I've made a few bits and pieces in the past using a similar slightly cruder method. You're right, it can't go very far without work hardening and splitting. You have to apply heat while you work it, r at least work it a bit, anneal it and start again.

Forgot to mention if you cold form it, when you apply heat it has a habit of shrinking back slightly so your motor with shrink!

[Mike Everman]

Sorry, Graham, I forgot about this until too late! I really want to check Larry's motor as soon as I get some sleep...zzzzz

[larry cottrill]

Hello Larry --

This is just my evil idea, but why not ask Mike to kazoo the main body of your 'Lady Anne' and ship it out to you?
He can place it in the same box as your Dynajet. Think of this service as rent for keeping the Dynajet for so long!

Well, that would be an easy build for the proof-of-concept motor, but the esthetics would be, well ... just too different. (Remember, I am an artist, not an engineer ;-)

Beauty aside (as Eric might say), I prefer to prototype as close to my original drawing as I can make it, since this is what others would most likely try to build from. That way, I have a handle on potential glitches with the published design, which can be passed on in the form of tips, fixes, etc. to other builders.

Not a bad idea for a super-quick shot at it, though. If Mike wants to try it, I wouldn't hold it against him. (Besides, I'd enjoy seeing my old Dynajet one more time before I'm gone ;-)

L Cottrill

[Mike Everman]

Graham,
Are you running your combustion model on this motor? I expect Larry is doing UFLOW on it. I'd like to suggest a move of the second pinch to a new place for comparison to what you've got. To whit:
the 42mm diameter moving left to 45% of the acoustic length, and the 32mm pinch after it to 55%. Otherwise, I think yous guys nailed the throat location.

I'd have put the center of the intake ellipse at 15%, but I'd like to try that on a test duct to be sure...

The attached pic traces out the peaks and troughs that arise from harmonic sums in a closed end duct. The intake location can be input, and I'm not considering that at the moment, other than setting it to Larry's favorite spot!

[larry cottrill]

I expect Larry is doing UFLOW on it.

That's correct, though the model I'm using is unfolded, based on Graham and Nick's "linear" Type 07 that they got to run.

I'd like to suggest a move of the second pinch to a new place for comparison to what you've got. To whit:
the 42mm diameter moving left to 45% of the acoustic length, and the 32mm pinch after it to 55%. Otherwise, I think you guys nailed the throat location.

Well, that's a pretty big move. Is this based on the pressure curve you're showing? My opinion is, you have to look at what this nozzle does over time, not the effect at a particular instant. Looking at this with UFLOW in the linear model, what the present location gives us is the following:
1. The pressure at the throat is perfectly in sync with pressure in the front of the chamber, i.e. exactly ZERO phase difference!
2. Both velocity and mass flow in the throat are virtually perfect mirror images of velocity at the intake, i.e. exactly 180 deg phase difference! See the UFLOW graphic, attached below.

Why is this good? I'm not really sure, but it is a truly unique situation. It's sort of amazing the first time you see it graphed out. It has something to do with the Type 07's pumping ability - both UFLOW and Graham's NUDIS example show the engine's astonishing ability to re-pressurize almost the whole pipe at once. It also shows a really long and strong draw through the intake as this very broadly distributed internal pressure is building. The impression is that the central 'reservoir' in the pipe has an impact far beyond what such a visually 'small' feature might suggest.

I'd have put the center of the intake ellipse at 15%, but I'd like to try that on a test duct to be sure...

Well, yes, it's a little aft of what I would consider the ideal location. Close enough, though, since the nose of the ellipse at least gets into that fairly sharp pressure trough. Part of the location was my desire to use a very simple, off-the-shelf part (a 3/4-inch EMT sweep) for the intake. This would mean nothing to a stainless steel builder (or anyone who decides to make up the intake as a weldment), since he could extend the front end a little farther forward. At least, I get the inflow stream "aimed at" the desired point, which is surely worth something ;-)

The attached pic traces out the peaks and troughs that arise from harmonic sums in a closed end duct. The intake location can be input, and I'm not considering that at the moment, other than setting it to Larry's favorite spot!

Thanks! That's really pretty impressive - fun to see it broken down in that way. Also, it's amusing to see how far the rear acoustic point lies outside the physical edge - must be 20 mm or so, almost an inch out. The effect of the large exit diameter, of course.

L Cottrill

[Mike Everman]

Well, then let's talk about how you unfolded the motor. How about a screen shot of your unfolded geometry and I'll apply the open-open model to it. As it is now, there is little acoustic reason for that pinch to be where it is, but if UFLOW is telling you it's an optimum spot...
M. I think is saying this has open properties, vs. closed, so there's probably something to that. If closed properties were to dominate, then my recommendation would be a good one.
I would have considered the duct without intake and run in NUDiS as closed, rather than unfolding it, and make sure the intake hits at an acoustic minima, but that of course has similarity drawbacks, as unfolding does.

[Mike Everman]

Oh, the plot I posted is not a snapshot of one point in time, nor is it a temporal plot. It indicates the points along the length where the richest harmonic content can be excited as a pressure pulse travels the length.
Maxima, for lack of a better description, are places where you'd want (excitation moving from left to right) pressure changes due to changes in cross-sectional area to occur, and pinches should occur at minima, where gas velocity is highest and therefore pressure is lowest.

For instance, a small diameter would be positioned at a minima, and the area should increase, pressure increasing, until a maxima, where the area must stop rising, and either must move in to a cylindrical section or begin a new pinch. Crudely, the passing pulse has "sucked on the acoustic minimum", amplifying it, and "punched the maximum", amplifying IT.

Sounds like for 1D analysis, the unfolding methodology has got to be dead on for any of this analysis to be meaningful.