Argentinian Short Lady Has Nice Build

[larry cottrill]

Received this email and pics:

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Estimado Larry, estas son algunas de las fotografías de mi último trabajo: el "Short Lady", un excelente pulsorreactor que pude construír gracias a los dibujos disponibles en su sitio de internet.

Es extraordinario poder escuchar el sonido de una máquina que es tan simple y tan complicada a la vez, que puede ser fabricada por cualquier persona que sólo tenga algunas herramientas simples, materiales fácilmente disponibles y sobre todo mucho interés y "amor" por los pulsorreactores.

Muchas gracias por difundir este valioso conocimiento de manera desinteresada y siga adelante con su genial trabajo!!!

Martín ..., Argentina
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My translation, based on an attempt by Babelfish:

Dear Larry, these are some of the photographs of my latest project: the "Short Lady", an excellent pulsejet that I was able to construct thanks to the drawings available on its Internet site.

It is extraordinary to be able to listen to the sound of a machine that is so simple and so complex at the same time, and that it can be made by anyone who only has some simple readily available tools, but mainly just much interest in and "love" of pulsejets.

Thank you very much for sharing this valuable knowledge at no cost as you go forward with this good work !!!

Martín ..., Argentina

Some of the photos he sent appear below. Looks like a really nice build of the Short Lady. Unfortunately, he didn't mention anything about materials, welding techniques, starting method or fuel used.

L Cottrill

[Ray(GB)]

Larry,
To scale up your S.L. ought I just to increase the lengths and widths,and ignore the volumes?.
I think if one doubles the lengths and widths then volumes are tripled.
Thnaks,Ray.

[larry cottrill]

Ray -

The "simplified" method I recommend is this:

1. Decide what tailpipe diameter you want; then, calculate the ratio of the new diameter to the original 1.25 in (32 mm) FWE pipe. Let's say you want one three times the original - your diameter would be 96 mm and the ratio would be 3.0
2. Take the square root of that ratio - the square root of 3.0 is 1.73, approximately.
3. Multiply the original FWE tailpipe length by that new ratio: 1.73 x 461 mm = 798 mm for the scaled-up tailpipe length.
4. Make the combustion chamber cone length 3/7 of the tailpipe length. 3/7 x 798 = 342 mm for the length of the chamber cone. Total cone + pipe length of our engine is now 798 + 342 = 1140 mm.
5. Divide the cone length by 5.9 to get the INCREASE in diameter from the nozzle end to the large end (this keeps the cone ANGLE identical to the original!), then add the tailpipe diameter to get the front end diameter: 342 / 5.9 = 58 mm, approximately. Front end diameter = 96 + 58 = 154 mm ID. Note that this makes a much stubbier looking cone than the original FWE chamber, BUT it keeps the VOLUME ratio of chamber to tailpipe in a reasonable range!!!
6. Design (or procure) your front-end dome - use anything you want. Its volume will have little effect on the total chamber volume, BUT you MUST keep track of its height, from front to rear! At this point, you can use Eric's Pulsejet Calculator to get the cone layout(s). Draw a full-size plan of the chamber, including your dome, using inside dimensions. Let's say our dome is a cone 30 mm high.
7. Calculate the acoustic length of the pipe. Add the dome height, chamber cone length, tailpipe length and 0.6 x tailpipe ID: 30 + 342 + 798 + ( 0.6 x 96) = 1228 mm, approximately. This is the design length L for our engine.
8. Calculate L/5 and L/8 (246 mm and 154 mm, respectively). I would recommend Eric's "Advanced" style intake, rather than the original plan that penetrates into the chamber. On your full-size chamber plan, measure from the dome apex along the centerline and mark the L/8 position. From that point, strike a line perpendicular to the CL out to intersect the upper cone wall - this intersection will be the point where the intake port is centered. Also use this point as the beginning point for the L/5 path length of your intake. Design your intake to cover this L/5 length, THEN pull the intake rear edge forward from that end point by 0.6 times the ID you use (use the pipe ID, NOT your planned flare ID, for the calculation!). The intake ID can be fairly large, 70 or 80 percent of the tailpipe ID, perhaps even larger. Design the flare by what looks about right for the size of your intake - Eric suggests that the intake flare should be pretty large, though I think that proportionately less should be needed as you scale farther up from the original.

That should do it. What you will have is an engine that is about 30 percent chamber and 70 percent tailpipe, with the chamber cone slope exactly the same as on the original FWE with a ratio of chamber to tailpipe volume that should be about right and approximately the right intake flare location. Any adjustments needed should be minor.

L Cottrill

[larry cottrill]

Larry,
To scale up your S.L. ought I just to increase the lengths and widths,and ignore the volumes?.
I think if one doubles the lengths and widths then volumes are tripled.

Ray -

Doubling both lengths and diameters multiplies the volumes by EIGHT!

Though it would work OK, it is unnecessary to increase the volumes that much to drive the increased tailpipe area. A large engine can be made proportionately MUCH shorter than a small one and still develop full power potential for the tailpipe size chosen. The engine example described above is only about double the length of the original Short Lady, but should theoretically develop nine times the thrust - and actually, it would probably do much better than that, since drag-related effects would be proportionately far less important than in the original.

L Cottrill

[hinote]

Larry:

How's it going with Carl Lithgow, and the test engine?

Any news of it running yet?

[larry cottrill]

Bill -

Oh, you mean Carl Litzkow ;-)

Bill, I have reason to believe that the next time I hear from him, he'll have it! I'll know it's him right away because he'll send about 10 jpegs that will slow my email (here at home) to a crawl while I'm getting them. Every time I open my email here, I eagerly anticipate that crawling blue bar ;-)

L Cottrill

[hinote]

Oh, you mean Carl Litzkow ;-)

Oops! Watching too much TV (John Lithgow). Carl and I have exchanged e-mails; I hope he's not offended by my faux pas.

Carl's work looks first-class;I hope he can help you sort out some of your developmental issues.

[Ray(GB)]

Larry,
Many thanks for your detailed explaination,I appreciate the time and effort you pu it for it.
Best Wishes, Ray.

[francisco]

HOLA LARRY, LA VERDAD QUE LO QUE USTEDES HACEN, (PERSONAS DE TODO ESTE FORO) ES DE MUCHA AYUDA PARA NUESTRO PAIS, NUESTRO PAIS ESTA HUNDIDO EN PROBLEMAS, Y SIEMPRE CUANDO UNO ESTA TRISTE APARECE ALGO QUE IDENTIFICA A LA ARGENTINA. LA MUSICA, EL FUTBOL, O LOS AMANTE A LA MECANICA.

LARRY, LE MOLESTARIA DARME LA DIRECCION DE MAIL DE MARTIN?, ASI YO PODRIA CONTACTARLO Y MOSTRARLE MIS MOTORES, PUES EL FWE QUE CONSTRUI YO NO ME ANDUBO.

FRANCISCO COOREMAN

[larry cottrill]

Oh, you mean Carl Litzkow ;-)

Oops! Watching too much TV (John Lithgow). Carl and I have exchanged e-mails; I hope he's not offended by my faux pas.

Bill -

You must mean faut pas, since you only made one mistake - faux pas would be plural, if I remember rightly.

L Cottrill

[larry cottrill]

HOLA LARRY, LA VERDAD QUE LO QUE USTEDES HACEN, (PERSONAS DE TODO ESTE FORO) ES DE MUCHA AYUDA PARA NUESTRO PAIS, NUESTRO PAIS ESTA HUNDIDO EN PROBLEMAS, Y SIEMPRE CUANDO UNO ESTA TRISTE APARECE ALGO QUE IDENTIFICA A LA ARGENTINA. LA MUSICA, EL FUTBOL, O LOS AMANTE A LA MECANICA.

LARRY, LE MOLESTARIA DARME LA DIRECCION DE MAIL DE MARTIN?, ASI YO PODRIA CONTACTARLO Y MOSTRARLE MIS MOTORES, PUES EL FWE QUE CONSTRUI YO NO ME ANDUBO.

Ben, can you help me out here? Babelfish fails to produce anything comprehensible. About all I can get out of this is that he would like to email Martin and show him his engines.

L Cottrill

[larry cottrill]

Larry,
Many thanks for your detailed explaination,I appreciate the time and effort you put in for it.
Best Wishes, Ray.

Ray -

As you can see, it's a very simple idea. It's actually based on getting a consistent ratio of chamber VOLUME to tailpipe AREA, then providing a reasonable tailpipe volume to match. It just happens that above a certain size, the chamber length hovers around 30 percent or a little less, so that turns into a simplifying factor. When you scale the Lady DOWN, a more complex scheme has to be used, and the chamber takes up more and more of the total length, looking more disproportionately huge for the tailpipe chosen as you go smaller.

L Cottrill

[Carl Litzkow]

Oh, you mean Carl Litzkow ;-)

Oops! Watching too much TV (John Lithgow). Carl and I have exchanged e-mails; I hope he's not offended by my faux pas.

Bill -

You must mean faut pas, since you only made one mistake - faux pas would be plural, if I remember rightly.

L Cottrill

Hi Bill and Larry,

Thanx for thinking of me, I have not been very active on anything lately (health problems). Trust me- you guys are my inspiration. Seeing the young man in Argentina build his first bueatifully done pulse jet is a credit to you Larry. You always take time to give such a clear and detailed explanation. There is no way of knowing how many others you have "sparked" including me. I studied the forum a long time before I voluntered to be your extra pair of hands so I could learn to.

AS far as Bill's concerned about his possible "faux pas", I thought that was what you tried not to step in when feeding the cows. I'm the one who has to be carefull about my four letter words on the radio, The FCC is not noted for a sense of humor.

Both of you and all the PJ community " stay safe, but have fun"

BBQ with attitude --- Invite a PJ to Dinner.

Carl

[larry cottrill]

Ben -

Good job! Thanks very much.

L Cottrill

[francisco]

Larry, would it bother him if you gave me Martin's e-mail address?

francisco cooreman