Focused wave engine runs!

[Bruno Ogorelec]

Quicker yet -- Steve, go to the FAQ section in this forum (it's on the top of the page) and see my single-page advice on augmenter proportions.

Your augmenter opening is too small and too close to the end of the intake/exhaust pipe.

The front (inlet) diameter of the augmenter should be two to three times the diameter of the exhaust pipe. So, cut the small end of your cone down. Make a new flare on the edge then -- the flare is very important.

The front end of the augmenter should be further back. It should be mounted at about twice the distance from the end of the exhaust pipe that you have used.

The augmenter cone should have a milder taper. It does not even have to be a cone, really, though it is slightly better than a straight tube. The important part is the front flare (which you have done, as I can see).

[larry cottrill]

Steve -

Yes, I think Bruno is spot on with this one. From what he's said before, you're still close enough in that your augmentor is forcing a slight de-tuning of the intake, i.e. it's no longer acting as the right acoustic length. And, as you increase the gap, you have to increase the diameter. I would even guess that the outer diameter of your flare should be significantly larger than the throat diameter.

The flare you have looks like a nice hammered flare, though. Nice workmanship. For a bigger one, after you cut back the front of the cone, you may have to use a rolled one to get the larger outer size needed. Great length is not nearly as meaningful as good throat and flare dimensions and proper spacing, I believe.

Of course, I've never tried any of this ... all I know is what I read in the papers ...

Steve, it was a good try, though. I like the way you go ahead and turn ideas into action! I always like to see a 'hands on' approach to problems [within reason, of course!]. This is an area where we have the advantage over guys building The Big Guns: we can play with this stuff without going broke, either on materials or tools! Not to mention that someday ... someday ... we might actually get to fly what we build - imagine that, my friend!

Haven't seen the parts yet, but I'm staying home from work tomorrow, and maybe that will be the day!

L Cottrill

[larry cottrill]

Yes, Steve, I got the parts today and I've started to build! I would recommend your work to anyone who wants to build a prototype model of this engine.

Thank you, Steve!

I worked about four hours, not counting setup & cleanup. I got the seams welded on both long cones, the seams welded on the "dome" cones, and I got the spark plug mount nuts fully welded onto the domes. I got both tailpipes cut from antenna mast tubing, and one cone fully welded to one tailpipe. I will leave the tailpipe ends un-flared to begin with, as mentioned some time ago. There was one extra step that Steve didn't have to do: the tubing I use is 1.25 inch OD, not ID -- therefore, I needed to slightly flare the front end of the tailpipe, for a perfect fit with the tail end of the combustion chamber cone. Once this was done, the pieces were easily brought together, though is was impossible to achieve perfect alignment without proper jigging. I got it pretty good, though.

I will not weld on the domes until I put the intake pipe in place, so I can easily manage the alignment and exact position of the intake interior end. Since it appears that the original 3/4-inch EMT pipe is too low in impedance [as witnessed by the now notorious front-end heating of Steve's build], I might make the first pipe out of 1/2-inch EMT [actually about .675 inch ID]. I still want to see Steve start to gradually apply a pinch to his intake, at about the location shown on my original drawing, and report on what happens. If this significantly improves performance, I might even forego propane testing and try carbureted liquid fueling from the very start. Note that a smaller ID would mean slightly increasing the physical length of the intake tube to get the same acoustic length, since the end correction will be smaller at each end.

The next step in the one I've got half-built will be to cut the oval hole in the cone and fabricate the intake pipe, then get it welded in. Then, if I decide to go ahead with carburetion, a spray bar / needle valve assembly will need to be chosen. I'll probably weld my usual Elektra-style engine mounts on, so I can mount it on my standard test plank and heat shield.

The weight of the cone and tailpipe I have welded up is 19 ounces; a tad heavy for my taste, but OK for a prototype. It will undoubtedly end up at about the final weight Steve managed to get. We would have to work this thing up to an unbelievable thrust level to have a flight engine. But, in stainless fabrication, we could probably reduce the material thickness to half of what it is. So, we eventually might end up with something flyable yet!

L Cottrill

[larry cottrill]

Graham -

In another thread, you have said:

Viv commented on the Q of the system. I'm absolutely with him on this point and was about to start a thread on this.
Over a small number of samples 'Easy starting' motors have all had a Q less than about 1. Larry’s motor is a fine example of such a soft motor.
Higher Q (Q>1) motors offer better potential performance; the wave structure being more focussed on the combustion area.

Do you believe the low Q of this engine de-bunks my claim that we really have achieved good acoustic proportions? It seemed to me that we couldn't have achieved a start right off the bat without getting that about right. Do you feel that the Q of the Lady is so low [what I would call 'broad tuning'] that there is no reason to believe that the proportions are in fact very close to what they need to be? Do you believe that reasonable performance may actually be unattainable with anything like the prototype geometry?

Please comment. Again, I think it is important for me not to make claims for this design that can't really be supported.

Thanks!

L Cottrill

[larry cottrill]

Since I have already raved about the quality of the parts Steve made for me, I thought it would be good to critique them in detail, for anyone out there who, like myself, feels unable / unwilling to fabricate them.

As Steve described, they are hand-made pieces, so, if you're expecting something that looks lathe-turned, your expectation is unrealistic and you'll be disappointed. The pieces I received can best be described as "excellent hand wrought" work.

The long cones were slightly out-of-round: probably 1/16 inch or a bit more out at the large end of the long cones, probably half that at the small-diameter end. If you don't think that's excellent, just try it! As is apparent in the photos Steve published, they are curved right up to the seam where they come together - no flat zone at all. Welding the seams actually threw them more out-of-round, so I had to tweak them in the bench vise after they cooled. I thought the finished pieces ended up quite nice, well worth getting them from someone whose craftsmanship is this good. "The workman is worthy of his hire."

The short cone "end domes" had a different effect of out-of-roundness: the rim does not lie in a perfectly flat plane. However, again, the effect is small, probably less than 1/16 inch. What I did was first weld up the seam, then file the center hole out a bit and weld the spark plug nut into the center [using a short bolt to hold alignment], and then [after cooling] gently use the vise to 'straighten' the rim by chucking the whole piece - imagine the plug nut up against one vise jaw and two points of the cone rim up against the other. Doing this at a few points around the rim brought them in so they would lie flat on the concrete garage floor, and they also fit the large end of the combustion chamber cones fairly closely. The edge of the dome overhangs the large end of the cone slightly, so I can probably weld them in with practically no filler rod reinforcement. Again, perfectly fine quality for the intended purpose.

Steve, I know you can take an honest criticism, and I do have one. The tack welds were a lot bulkier than I expected, and took some time to blend down into the surrounding surface. I know practically nothing about electric welding, and perhaps getting them finer is just a matter of continued practice. What I did on the long cones is add a couple of intermediate tack welds of my own, then blend yours in until they had a kind of mountain shape, then run the continuous weld between them all. After cooling, I filed the 'mountains' down with a big flat file. No real problem, of course; just a detail that you might want to work on in your copious free time ;-)

Altogether, the parts were excellent, and I would heartily recommend negotiating with Steve to make these for you if you are interested in this engine and don't have the skills or tools to do the cones yourself. I would definitely recommend using tubing for the tailpipe, rather than "rolling your own" as Steve did, but "to each his own" I always say.

Steve, you [and others] might be interested in what the pricing of cutting these parts would be from eMachineShop, which was mentioned earlier in another thread. The price for single quantities is so absurd it won't be mentioned; instead, I decided that I could reasonably handle maybe 20 at a time. I designed the parts using Eric Beck's cone calculator, then printed them out full size and cut and pasted them as 'paper dolls' to make sure they were really right, and then priced them both in .8mm mild steel and .4mm 316 stainless sheet. Amazingly, the stainless comes out a little cheaper than the mild steel, since it's only half as much material by volume! Total in 316 stainless for 20 domes [+/- 2] would be $98.40, or $4.92 each, including shipping to me. Total for 20 chamber cones [+/- 2] is $184.20, or $9.21 /unit. Remember, these are just flat pieces; I'd still need to have them rolled somewhere. Also, on a stainless unit, I wouldn't try my own welding and would need to hire it done. This gives you some idea of how economically such devices could be produced - not very, when you consider the remaining material [mostly tubing] and fabrication required. Of course, no one in serious production would make such small lots, but without capitalization I felt this was about all I could estimate.

Steve, thanks again! I should be able to post some construction photos in a week or so.

L Cottrill

[Graham C. Williams]

Do you believe the low Q of this engine de-bunks my claim that we really have achieved good acoustic proportions?
L Cottrill

Dear Larry.

I do not have any strong ideas only trends and possibilities regarding this business of the Q of the motor. Viv mentioned it to me some time ago, I didn't understand (fully) what he meant then but its one of those things that sticks in your mind. Slowly, I'm seeing an accumulation of evidence that’s made me reconsider. I'm sure you can have such thing as a Low Q motor that will not run because the induction pipe is hopelessly out of tune or the fuel delivery is wrong, for instance.
If by 'Good Acoustic Proportions' you mean that all the elements are working harmoniously I'd have to say YES because the motor works. I'm also sure you will improve it.

Best Regards
Graham.

[steve]

Larry-
I'm glad to see that you like them! If you want to get rid of the slight out-of-roundness of the cone then clamp it in a vise until it assumes the desired shape and then weld the dome on while it is still in the vise. Works every time! I could make the tack welds smaller using the torch instead of the MIG but I probably would've gotten carried away and welded the entire seam :-) When you run these engines the cones / domes will become completely covered with black flakey oxidization. I have found that it is best to simply leave as much of it intact as possible because it will prevent more oxidization from forming on future runs.

good luck!

[larry cottrill]

Just so you'll know, I finished my 'Short Lady' FWE this morning, trimming off not quite 1/2 inch of tailpipe to get it to the exact length specified. Welded on engine mounts last night, and with spark plug in place, total weight was 24.5 ounces [fuel pipe not on board]. Note that I did use 1/2-inch EMT for the intake pipe [actually about .675 inch ID], so the intake area / exhaust tube area is approximately 25%. And, I'm still using the miniature V size plug from the Dynajet, which kind of made up for the weight of the engine mount lugs. I got a lot more weld around the intake pipe than I really wanted, but used almost no filler rod getting the front dome on, as anticipated. I will go ahead and try it with propane first, just to find out if I have something that really runs. No pictures until sometime next week, though.

If I get it running this afternoon or evening, I'll start another thread, since it's a different build from Steve's prototype.

L Cottrill

[steve]

I wish you had used a stand similar to mine! (no, not the clamp) The advantages include VERY light weight, and it is also compatable with both the elektras. Dissassembly requires only that you unscrew the sparkplug- thats it! nothing else!

I'm somewhat suprised that you built a modified engine first rather then the original design- Isn't there supposed to be a "constant" in scientific experiments and investigations? (Or is mine the constant?)

anyway we look foward to seeing the pictures! (I say "we" because my mother has recently started folowing these threads with some interest)

[larry cottrill]

I wish you had used a stand similar to mine! (no, not the clamp) The advantages include VERY light weight, and it is also compatable with both the elektras. Dissassembly requires only that you unscrew the sparkplug- thats it! nothing else!

Yes, Steve, I have to admit that is a flaming good stand ;-)

I'm somewhat surprised that you built a modified engine first rather then the original design- Isn't there supposed to be a "constant" in scientific experiments and investigations? (Or is mine the constant?)

Yes, that would be the ideal - but in this game it's just hard to do things that way. Look at what I'd need to do to build it like yours and then try the smaller pipe; I'd have had to cut out the big pipe and then bridge a pretty large gap around the smaller pipe while achieving near-perfect position and alignment! Since I thought there was good evidence that the impedance was far too high, I thought making the change was a good gamble. This didn't exactly pan out - see my new thread, 'The Short Lady Sings', which I just started up.

Anyway we look forward to seeing the pictures! (I say "we" because my mother has recently started following these threads with some interest)

Steve, that's great ... do you think you can get her started welding?

L Cottrill

[Bruno Ogorelec]

I wish you had used a stand similar to mine!

A great stand! Mount the uprights on lockable hinges, add a load cell and you might use it to measure thrust.

I say "we" because my mother has recently started folowing these threads with some interest)

I am not surprised. I come from a family of bold-thinking women. My grandmother and mother were fans of science fiction in times when SF was exclusively a boys' own thing, for instance. My Mom was always filching Dan Dare comics from me. Anyone here that remembers Dan Dare? You'd probably have to be British, I guess.

[larry cottrill]

OK, I finally have available a few WIP shots from while I was still building her up.

L Cottrill

[Viv]

I wish you had used a stand similar to mine!

A great stand! Mount the uprights on lockable hinges, add a load cell and you might use it to measure thrust.

I say "we" because my mother has recently started folowing these threads with some interest)

I am not surprised. I come from a family of bold-thinking women. My grandmother and mother were fans of science fiction in times when SF was exclusively a boys' own thing, for instance. My Mom was always filching Dan Dare comics from me. Anyone here that remembers Dan Dare? You'd probably have to be British, I guess.

Dan Dare! sorry Bruno way before my time! you must be really old to remember him.

Viv

[Bruno Ogorelec]

Dan Dare! sorry Bruno way before my time! you must be really old to remember him.

You missed a lot.

[Bruno Ogorelec]

Oops! I just remembered this is NOT the off-topic forum. Sorry, everyone.