A new propane line, Larry you better sit down for this :D

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Re: A new propane line, Larry you better sit down for this :

Postby Eric » Mon Mar 07, 2005 5:18 pm

Larry,
You definately need to make an animated gif of that picture, and add in a bunch of colors to show intensity, that would be quite a sight, and maybe overlay a sound file for a full cinematic experience.

Oh yea, im shipping the latest ebay engine to canada, anyone know what should I put on the box for customs?

Its really nice out, maybe ill go cause some more chaos.

Eric
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Re: A new propane line, Larry you better sit down for this :

Postby larry cottrill » Tue Mar 08, 2005 1:36 pm

Eric wrote:Larry,
You definately need to make an animated gif of that picture, and add in a bunch of colors to show intensity, that would be quite a sight, and maybe overlay a sound file for a full cinematic experience.

You must think that I have a great deal of time on my hands! Remember, I'm not retired yet!

The circles are from a program done at my request by my son, Jonathan. You can specify the regular spacing [i.e. the wavelength], the spacing of the innermost circle [i.e. the fraction of one wavelength representing the phase difference], the overall size of the circle pattern you want [has to be MUCH larger than the piece you want to use!] and the circle thickness. Then, hit the button, and voila - a .png file you can save wherever you want.

Based on the scaled-down drawing of the FWE that I quickly hashed together, I decided on a 'wavelength' of 100 pixels. One circle was drawn with a starting radius of 100 pixels, then another with 25 pixels [i.e. a 25% 'lead' or 75% 'lag' in phase], and these were saved as separate files. A line thickness of three pixels seemed bold enough. These were then overlayed on the FWE plan drawing using MS Paint. Next, I stretched lines in to connect the crossing points of the 'wave crests' [circles]. Most of these lines should be slightly curved, though I only had to 'bend' one of them at this scale on this particular layout. Then I decided how close the crests would have to be to constitute 'very high' and 'high' intensity zones and drew those lines in by eyeball measurement. Finally, I used the 'paint bucket' to fill in the gray areas, and added the verbiage. All this took a couple of hours, not counting the time [roughly one hr] Jonathan spent on the circle creator [done at the drop of a hat at my request so I would quickly have something to post].

The fact that there is a low-intensity zone to the rear and a high-intensity zone to the front is accidental, and is purely the outcome of the phase relationship, the distance between the noise source points, and the wavelength chosen. It would be perfectly possible [and possibly, reasonable] to choose dimensions that would give the highest sound intensity at the rear. Results will vary wildly, depending on the numbers. Only an accurate calculation of wavelength in cold air and precise scaling would give a true representation of a real-life case.

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Re: A new propane line, Larry you better sit down for this :

Postby Bruno Ogorelec » Tue Mar 08, 2005 2:28 pm

Larry,

You might try your program on SNECMA Ecrevisse.

Namely, it appears that one of the reasons why the Ecrevisse was not bent into the U-shape, like the Lockwood, but rather in a kind of J (i.e. immediately after the combustion chamber), was precisely to get the waves emanating from the intake phase well with those coming out of the exhaust.

It would be interesting to see what they got.

Here's a picture.
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Re: A new propane line, Larry you better sit down for this :

Postby larry cottrill » Tue Mar 08, 2005 3:11 pm

Bruno Ogorelec wrote:Larry,

You might try your program on SNECMA Ecrevisse.

Namely, it appears that one of the reasons why the Ecrevisse was not bent into the U-shape, like the Lockwood, but rather in a kind of J (i.e. immediately after the combustion chamber), was precisely to get the waves emanating from the intake phase well with those coming out of the exhaust.

It would be interesting to see what they got.

Here's a picture.

Cool. However, I'd need to know the actual dimensions [well, just one - the distance from the intake to the tail] and the typical operating frequency. Then, I would assume a particular speed of sound under average sea-level conditions to get a reasonable shot at the primary wavelength.

The intake and exhaust diameters are so close to each other that I wouldn't need to bother with the end corrections for the acoustic points. It would be an interesting exercise, since they claim to have gone out of their way to achieve that kind of geometry! Such an engine would have a maximum intensity in a fairly broad swath directly behind it, sort of like the front end noise in my drawing.

If you're saying that their claim was that the intake and exhaust were precisely ONE wavelength apart, of course, I could go ahead and draw it up knowing nothing more, just assuming that they were able to get it right for sea-level air of "normal" temperature. [They would not achieve such grand acoustic performance under all possible conditions, of course - the dimensions of the engine are fixed, the wavelength of a given frequency in variable condition air is not.]

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Re: A new propane line, Larry you better sit down for this :

Postby larry cottrill » Tue Mar 08, 2005 4:02 pm

Ben wrote:There's also the issue of timing. It seems that you are assuming that the pulse comes out of both the intake and exhaust at the exact same moment, which seems unlikely for some engine geometries.

Ah, you're right. In the discussion immediately above, I conveniently forgot about the phasing part! Note that I had this covered in my original discussion with my drawing.

So, Bruno, I guess what you're saying is just that their geometry is supposed to get the crest of the intake wave to cross the tailpipe exit just as its crest emerges; we still need some value for the wavelength in normal air [based on the operating frequency, and the physical dimension separating the two starting points. An alternate method would be if they actually state somewhere what the phase difference is supposed to be between the intake and exhaust ports.

Another clarification: Note that the emerging crests from the two points need not [necessarily] be from the same explosion event! The phase difference in outside air is NOT identical to the phase difference of the internal pressure wave in the engine [this is shown in my drawing, above, where the cold air whole wave is illustrated, rightly or wrongly, as MUCH shorter than 1/4 wave in the engine!].

Ben, thanks for the correction!

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Re: A new propane line, Larry you better sit down for this :

Postby Bruno Ogorelec » Tue Mar 08, 2005 10:01 pm

Larry, unfortunately, I do not have the necessary data on the Ecrevisse, but hope they will surface in the translations.

I will look up a Kentfield paper (maybe it was a patent application) in which he describes a somewhat different approach to the same thing.

He used a curious recuperator-cum-thrust-augmenter for a straight Lockwood-style engine. That contraption coiled around the main engine duct, so that it was a bit longer than the engine itself.

This was also done in order to have just the right length for the good timing of two pressure waves. (Kentfield explicitly says so.)

That particular effort looks to me like he was timing the exhaust wave to coincide with the intake-generated wave of the preceding cycle. It is far too long to be able to do anything within the same cycle, I think.
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Re: A new propane line, Larry you better sit down for this :

Postby Bruno Ogorelec » Tue Mar 08, 2005 10:05 pm

Meanwhile, I have found the sketches of Kentfield's successful efforts to couple two valveless pulsejets. (Much trickier than with valved engines.)

I think his approach was not the best, but then, I am convinced of so many other unusual things....
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Re: A new propane line, Larry you better sit down for this :

Postby Bruno Ogorelec » Tue Mar 08, 2005 10:16 pm

Ah, here's Kentfield's Snaking Synchro Recuperator. Enjoy.
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Re: A new propane line, Larry you better sit down for this :

Postby steve » Wed Mar 09, 2005 1:09 am

hehe, that reminds me of one of larry's MSpaint drawings. It definately looks like something he might have concieved!
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Re: A new propane line, Larry you better sit down for this :

Postby Eric » Wed Mar 09, 2005 2:48 am

Holy crap, I didnt know you could put pictures in the signature... or did I?

That coil thrust recouperator looks like soo much fun to build! Just makes me want to jump up and try radically bending thin walled pipe without any kinks.

Before I got snowed in today, I stuck a brass T shaped contraption from some old wind tunnel parts on the end of a running FWE, It changed frequency a bit but it still ran. I dont know how it would be to start but I might try a setup like Troy Legner used with his twin precision jet and see if it works.

Eric
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Re: A new propane line, Larry you better sit down for this :

Postby Mark » Wed Mar 09, 2005 8:26 am

Bruno, the coupled Kentfield looks very nice but it's no weekend project! And don't be trying to sneak any optical illusion designs in either that might cause seizures in the uninitiated. Might be funny though to have a drawing of something like the 3-prong illusion drawn up as a puslejet. Would make for a wonderful logo, and how fitting because pulsejets can be so illusory.
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Re: A new propane line, Larry you better sit down for this :

Postby Bruno Ogorelec » Wed Mar 09, 2005 9:30 am

Mark wrote:Bruno, the coupled Kentfield looks very nice but it's no weekend project! And don't be trying to sneak any optical illusion designs in either that might cause seizures in the uninitiated. Might be funny though to have a drawing of something like the 3-prong illusion drawn up as a puslejet. Would make for a wonderful logo, and how fitting because pulsejets can be so illusory.
Mark
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Interesting! You know, I did try something of a sort a long ago. I was looking at the Klein bottle as a possible interesting layout for a pulsejet and eventually came up with the Unicone.

Maybe it's a good thing I didn't stay with the Klein bottle. Here's what one explanation I have found says about it: "The Klein bottle is an example of a two-dimensional differentiable manifold." There's a further explanation, too: "A differentiable manifold is a second countable Hausdorff topological space that has been endowed with a differentiable structure."

Once you get that, it is very easy to apply the Hinote Criteria onto it and, voila! you have a single-surface pulsejet.
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