Focused wave engine runs!

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Bruno Ogorelec
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Re: Focused wave engine runs!

Post by Bruno Ogorelec » Fri Sep 24, 2004 5:31 pm

I think we desperately need someone who knows what he is talking about to analyze the sound recording of the Short Lady. It will throw additional light on the little sucker.

This is great fun! That's the beauty of this forum. Every once in a while something happens that throws the entire forum into a tiff, a frenzy of analysis and speculation -- and pure enjoyment. Increasingly, it is the participants' engines that do that. Wonderful!

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Re: Focused wave engine runs!

Post by tufty » Fri Sep 24, 2004 5:47 pm

Larry Cottrill wrote:At this point, I don't want to be guilty of sending everyone down a rosey path to ultimate disillusionment
Yeah, I guess we're all feeling real disillusioned right now - after all, all you've done so far is come up with a design for a completely new motor that ran on its first attempt, and seems to show the signs of running very well. Sure, we don't fully understand all its nuances, but I daresay I'm not alone in being over the moon (and not a little jealous).

As for whether UFlow is buggy WRT the tailpipe flare, there's only one way to know for sure, which is to make an otherwise identical one without flare and see how it compares, or better, make one without flare, run it and get readings, then add the flare, run it again, and get readings, then compare. Given the general sensitivity of pulsejets to changes in critical areas, and bearing in mind the 'butterfly effect', I'm actually not so sure it's an artifact of uflow. I'd really like it not to be - that would certainly vindicate the use of uflow to model these beasts, at least within certain parameters.

Whatever happens, I am gripped by this thread to the point that it's likely to give me RSI from clicking the 'reload' button so often ;-)

Simon

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Re: Focused wave engine runs!

Post by larry cottrill » Fri Sep 24, 2004 6:03 pm

tufty wrote:Yeah, I guess we're all feeling real disillusioned right now - after all, all you've done so far is come up with a design for a completely new motor that ran on its first attempt, and seems to show the signs of running very well. Sure, we don't fully understand all its nuances, but I daresay I'm not alone in being over the moon (and not a little jealous).
Simon -

Yes, things always look good up front, but remember - the disillusionment usually comes farther down the road. Otherwise, it wouldn't be disillusionment, would it? ;-)
As for whether UFlow is buggy WRT the tailpipe flare, there's only one way to know for sure, which is to make an otherwise identical one without flare and see how it compares, or better, make one without flare, run it and get readings, then add the flare, run it again, and get readings, then compare.
That is an excellent suggestion, and I could do that once I get a cone and front plate in my hands. Then, all I'd need to complete the picture is a truly simple and reasonably accurate thrust measurement system.

Hmmm ... let me think about that ...

L Cottrill

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Re: Focused wave engine runs!

Post by tufty » Fri Sep 24, 2004 6:39 pm

Larry Cottrill wrote:Then, all I'd need to complete the picture is a truly simple and reasonably accurate thrust measurement system.
IIRC, the postulated differences were radical enough that your measurement system probably doesn't need to be terribly accurate. Howsabout a 'roller skate & fish scales' setup, do 10 or 20 runs on the same settings and average the readings? I'd happily donate a roller skate ;-)

In fact, if what uflow says is true, you may well notice the difference well before getting thrust readings , when you're starting the engine...

No?

Although, for further development, an accurate thrust stand would be a godsend. Maybe Viv & Luc could oblige?

Simon

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Re: Focused wave engine runs!

Post by larry cottrill » Fri Sep 24, 2004 6:55 pm

Larry Cottrill wrote:
tufty wrote:As for whether UFlow is buggy WRT the tailpipe flare, there's only one way to know for sure, which is to make an otherwise identical one without flare and see how it compares, or better, make one without flare, run it and get readings, then add the flare, run it again, and get readings, then compare.
That is an excellent suggestion, and I could do that once I get a cone and front plate in my hands. Then, all I'd need to complete the picture is a truly simple and reasonably accurate thrust measurement system.
It occurs to me that I can do something like a heavy horizontal plank that would hang from the inner face of my garage door when it is open. How it would work is that it would be suspended at four points top & bottom [i.e. four hanger rods] so it would swing as a parallelogram, assuring that the mount plank would stay level throughout the swing, and the engine thrust would always be perfectly horizontal. The hanger rods would be sized so the mounting plank would be at a convenient working height at rest.

Now, here's the beauty of this: That geometry means that the horizontal force necessary to move the engine and mount would be proportional to the tangent of the angle displaced; therefore, a horizontal scale, carefully leveled, would have markings of uniform spacing for the units of force, if one hanger rod is used as the pointer! The sensitivity and calibration would be controlled by the vertical height of this scale. So, what you would do to calibrate is get your engine set up on the mount, make sure it's at rest and calibrate the horizontal scale to zero; then apply a significant force [say 20 lb], being careful to apply the force horizontally while the scale is adjusted up or down to give a reading of that value, and locked into place. Because of the 'tangent rule' of this geometry, all intermediate readings will be accurate!

Although this would move engine testing inside my garage, the tailpipe noise and exhaust blast would be directed outside. And, since it could only be used with the garage door fully open, there will always be adequate ventilation. My garage also has roof vents and three openable windows at various points on two sides. The only permanent mods to the garage door would be four mounts attached on the inside of the door, for easy hanging of the test rig when needed.

What do you think? Any obvious flaws in this plan?

L Cottrill
Last edited by larry cottrill on Fri Sep 24, 2004 7:08 pm, edited 2 times in total.

Bruno Ogorelec
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Re: Focused wave engine runs!

Post by Bruno Ogorelec » Fri Sep 24, 2004 7:01 pm

tufty wrote:Maybe Viv & Luc could oblige?
No, no; now that they are going industrial, they should purchase the rights from Larry for a lot of money, develop the thing into a marketable product and make a killing. Larry would be rich and famous, they would be rich and famous, and this forum -- financed by a 1-percent royalty fee -- would become a big propulsion engineering portal with all kinds of utilities for the world's enthusiasts to use in the development of their engine concepts. You know, online sound analysis, CFD modeling... :o)

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Re: Focused wave engine runs!

Post by tufty » Fri Sep 24, 2004 8:18 pm

Larry Cottrill wrote:Now, here's the beauty of this: That geometry means that the horizontal force necessary to move the engine and mount would be proportional to the tangent of the angle displaced
A bit of schoolboy algebra backs this up. T = W tan theta where w is the weight and theta is the angle displaced.
therefore, a horizontal scale, carefully leveled, would have markings of uniform spacing for the units of force, if one hanger rod is used as the pointer
You're a bloody genius, man! Simple, and liable to be accurate. If you need more adjustment, you can add or remove weights on your plank, too.

The hangers need to be relatively friction-free, preferably bearings, and the whole needs to be at right angles when at rest, but it's a delightfully simple idea.

Simon

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Re: Focused wave engine runs!

Post by hinote » Fri Sep 24, 2004 8:36 pm

tufty wrote:

You're a bloody genius, man! Simple, and liable to be accurate. If you need more adjustment, you can add or remove weights on your plank, too.

The hangers need to be relatively friction-free, preferably bearings, and the whole needs to be at right angles when at rest, but it's a delightfully simple idea.
A couple of notes here, based on my own experience with thrust stand development:

Larry, why don't you build a simple wood frame to suspend your proposed project from--instead of the garage door? You could make it with bolts and wing nuts, so it could be easily taken apart. Cheap steel tie plates would strengthen the joints if necessary. I bet you could build the whole thing for less than a 20 out your pocket.

Making the parallelogram legs as long as possible reduces the error from friction at the hinge points. I'd say 2 feet minimum, 3 feet better.

Another way to measure the force is to record the event with a video camera, and then duplicate the deflection, pulling the assembly horizontally with a simple tension scale. A calibrated background would make this a very accurate alternative.

Food for thought.

Bill H.
Acoustic Propulsion Concepts

".......some day soon we'll be flying airplanes powered by pulsejets."

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Re: Focused wave engine runs!

Post by Mike Everman » Fri Sep 24, 2004 8:49 pm

Larry, that's very much schematically an adaptation of your previous thrust rig, while a bit simpler, which is amazing. Nice work.
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Re: Focused wave engine runs!

Post by Bruno Ogorelec » Fri Sep 24, 2004 10:02 pm

Bruno Ogorelec wrote:with different implications for the Short Lady.
Oops. I just noticed I've been referring to the Short Lady, which is a different design entirely, rather than the Focused Wave Engine. Sorry. My tired brain is not concentrating as well as it once was....

More importantly, Larry, have you rethought the intake stack behavior?

When I suggested bent rather than 'broken' intake, you said you expected the stack to be useful mostly as a resonator and that exhaust flow would probably not be of importance.

Now that it is demonstrably not just a wave vessel, but also pushes out quite some gas flow, would you be motivated to redesign it? If so, what would you do?

Also, you mentioned a very small flare at the tailpipe end. The very similar NRL engine has a larger but still very small flare. Do you think there is something about those engines that makes a small flare better than a large one? Mind you, the NRL was meant only to generate a great amount of hot air, not thrust.

You obviously like straight pipes. I don't think i remember a Cottrill engine with a bustle tailpipe. Is it just an affectation or some theory about pipe shape?
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Re: Focused wave engine runs!

Post by steve » Sat Sep 25, 2004 3:57 am

Here is some video for you guys to analyze / drool over!

EDIT: Video now includes my stand catching on fire!!! Enjoy!
(notice the heat shield for the subsequent run)

If you look at that intake flame you realize that this thing is practically screaming for thrust augmentation!

I tested the fuel injector setup as was suggested and it turned out to be a disaster. I moved the injector back towards the CC about an inch to see if it would reduce the intake flame at all and what I got was an engine that was almost impossible to run. I guess there wasn't sufficient time for mixing. I will convert it back to the origonal setup soon.

I may be getting some thrust measurements soon- My physics teacher is willing to let me borrow some precision spring scales.

BTW the completed weight (with sparkplug) is 27.4oz

Larry, I am making good progress on the cones and they should be done in a few days so shoot me an e-mail: Sbuk@juno.com
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Re: Focused wave engine runs!

Post by Bruno Ogorelec » Sat Sep 25, 2004 12:00 pm

Interesting! (The fuel injector placement, I mean.) I have gone hoarse telling people that the best way to fuel a pulsejet is to shoot propane into the mouth of the intake tract from the outside, as the Bunsen burner does. That way, the first thing you get is some ram effect from the ejector intake. Propane powers the mixture into the engine, so to say. The initial pressure before ignition is higher. The second thing you get is perfect mixing -- better than the wild injector configurations spitting into the combustion chamber will ever achieve. Finally, you increase the resistance to reverse flow of the intake tract and halp the engien exhaust through teh exhaust, rather than through the intake.

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Re: Focused wave engine runs!

Post by Graham C. Williams » Sat Sep 25, 2004 12:41 pm

That Video makes me wonder what would happen if the intake was a bit longer. Have you tried this?

Perhaps better would be to pinch the intake pipe a little just behind the bell mounth, increasing the induction velocity a little. Have you tried this?

Graham.

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Re: Focused wave engine runs!

Post by Viv » Sat Sep 25, 2004 2:18 pm

Bruno Ogorelec wrote:
Bruno Ogorelec wrote:with different implications for the Short Lady.
Oops. I just noticed I've been referring to the Short Lady, which is a different design entirely, rather than the Focused Wave Engine. Sorry. My tired brain is not concentrating as well as it once was....

More importantly, Larry, have you rethought the intake stack behavior?

When I suggested bent rather than 'broken' intake, you said you expected the stack to be useful mostly as a resonator and that exhaust flow would probably not be of importance.

Now that it is demonstrably not just a wave vessel, but also pushes out quite some gas flow, would you be motivated to redesign it? If so, what would you do?

Also, you mentioned a very small flare at the tailpipe end. The very similar NRL engine has a larger but still very small flare. Do you think there is something about those engines that makes a small flare better than a large one? Mind you, the NRL was meant only to generate a great amount of hot air, not thrust.

You obviously like straight pipes. I don't think i remember a Cottrill engine with a bustle tailpipe. Is it just an affectation or some theory about pipe shape?
Hi Bruno

I have been looking in to the NRL motor, this one is the CN modified engine though, that cone is not from NRL it is just tack welded on to the tailpipe, the plan also shows the engine with out it but has had it crudly drawn in.

This was the points heater version that CN used, the other NRL info points to the engine being used in a pressure gain combustor test for turbines and it did not have the tailpipe cone but it was in an enclosing combustor shroud.

I still cant find the original papers for the engine though only papers from other projects that have used it, seems it was developed by one research group and then all the others borrowed it:-)

Viv
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Monsieur le commentaire

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Re: Focused wave engine runs!

Post by Mike Everman » Sat Sep 25, 2004 3:13 pm

I analyzed the video, you're sitting at 260 Hz. Fabulous! One of the main reasons I've been so interested in the Chinese style layout. A Locky this long, 26", would be 370 Hz, give or take. Thanks for the fuel location experiment, Steve. That was cool!
Mike
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