2004-02-14 - Pulsejet History Well and Truly Made

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milisavljevic
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2004-02-14 - Pulsejet History Well and Truly Made

Post by milisavljevic » Mon Feb 16, 2004 11:09 am

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Mike Everman
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Post by Mike Everman » Mon Feb 16, 2004 2:29 pm

Beautiful work, Bill and M. !!!!!
I know you've done this phenominal thing just to impress me, but the world will surely benefit, too! <GRN!!!>
Bill, impressive construction coming from your secret underground laboratory, I'd love to see the thrust measurement setup. M.: you truly have a sense of the dramatic, and you are clearly the stud of predictive math. It's a pleasure to see the fruits of your labors, congratulations!!

This is a great time to be a jet enthusiast! This is huge! I told my kids what a breakthru I just witnessed and they said: "can we have pancakes for breakfast?" Oh, well I've got three boys, three chances for a propulsion expert in the family...

Fantastic, and Faaaaaascinating!
Mike
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Bruno Ogorelec
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Post by Bruno Ogorelec » Mon Feb 16, 2004 7:34 pm

Milisavljevic, Bill,

Congratulations! A great job, a superb result. I'm glad to be active in the field at the time this is happening. It is a great privilege. I am really gratified to see the pulsejet field turn such a hotbed of activity all of a sudden. Very, very exciting. God knows where it will lead us.

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Post by hinote » Mon Feb 16, 2004 10:06 pm

Just to add my 2-cents worth:

This engine is ultimately easy to start. I'm still sorting out the electronic igniton thingy, so a piezoelectric barbecue "clicker" is substituting--and quite effectively. No belching of flames--just a clean start, every time.

Throttling range is amazing; I can turn it down so far you can't see any glowing metal, it's running so cool. Response to throttling is (of course) instant.

Although I'm using a leaf blower to start at the present time, I'm planning on developing a start-air system that is less cumbersome, and more consistent than waving an air source around near the intake.

I don't think M. made a big enough deal about the accuracy of his projections for thrust--before the engine was running. I find it fascinating that his predictions were accurate to the pound.

The hydraulic thrust stand is a success--simple to build and calibrate. It also is a large version of an automatic shock absorber, and damps out engine pulsations well.

This project went together quite rapidly, and the early success in its operating life is a testament to the excellence of the design. I would say that confirming maximum thrust on the second test session is a pretty amazing feat.

My thanks go to M. for allowing me to participate with him in this project.

Bill H.
Acoustic Propulsion Concepts, Inc.

Raymond G
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Post by Raymond G » Tue Feb 17, 2004 2:10 am

Hinote and Milisavljevic,

Beautiful work. I've been hanging out in the pressurejet forums, and just thought I would take a peek. Seems I picked the right day to do it!

Bill,
I notice you're in Centrall California. I'm in Chico, up north. Where are you located.

Regards,
Raymond

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Post by resosys » Tue Feb 17, 2004 2:25 am

Beautiful work gentlemen. The numbers finally start to speak.

I'm curious about the reasoning behind the higher resonant frequency being better. Any clues for us backyard engineers? I've been working on numbers for fuel burn time and the relation to the cycle time of a pulsejet resonating at about 190Hz. Interesting stuff.

Any thoughts on the ideal resonant frequency?

Thanks,

Chris

hinote
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Post by hinote » Tue Feb 17, 2004 2:29 am

Raymond G wrote:Hinote and Milisavljevic,


Bill,
I notice you're in Centrall California. I'm in Chico, up north. Where are you located.

Regards,
Raymond
I'm in (earth)quakey Paso Robles.

Bill

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Post by Mike Everman » Tue Feb 17, 2004 2:55 am

I like the disk on the exit. Does it serve to intensify the return wave?
Mike
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Mark
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Post by Mark » Tue Feb 17, 2004 3:20 am

Another superior black and white photo. What will you use this engine for, testing sound proof booths? God, I bet the noise is unbelievable. It's a study in energy to be sure.
Mark

hinote
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Post by hinote » Tue Feb 17, 2004 3:20 am

Mike Everman wrote:I like the disk on the exit. Does it serve to intensify the return wave?
Actually, it's VERY technical........................NOT!

The final (straight) section of the exhaust was formed from flat stock (because of its off-nominal diameter); I wasn't happy wilth the consistency of the circularity, so we cobbled-up a quick-and-dirty ring to hold the forward part while it was welded to the next section; then, we used it to fine-tune (that means, whack it with a hammer over a piece of pipe) the consistency of the section along its length.

And finally, I wasn't comfortable exposing the end of the tailpipe to the real-world of transporting, etc.--where it could be bent out of round very easily. So, we just tack-welded it into place about 3 inches or so back from the end, to maintain the shape.

Ain't THAT scientific?!

Bill H.
Acoustic Propulsion Concepts, Inc.

P.S.: Look at the Lockwood website, and observe how they welded a number of rings to the engine to maintain circularity. I'm betting the gauge of the engine's sheet metal is REALLY thin--and wouldn't stay where it was supposed to, given the level of heat achieved (look at the color).

hinote
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Post by hinote » Tue Feb 17, 2004 3:27 am

Mark wrote:Another superior black and white photo. What will you use this engine for, testing sound proof booths? God, I bet the noise is unbelievable. It's a study in energy to be sure.
Mark
Actually, I'm not sure why, but this engine is noticeably "quieter" than the 4-tube Kentfield--and I don't know why.

The 4-tube would bounce the headphone protection right off your head at full-chat, and I had to hold my (big!) nostrils pinched closed with my fingers to keep the sound-pressure from beating the hell out of my sinuses.

This engine doesn't do that. Makes me wish I had a Db meter.

Maybe M. will chime in on this (but I can't speak for him--he's really busy on other fascinating projects)

Bill H.
Acoustic Propulsion Concepts, Inc.

Mark
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Post by Mark » Tue Feb 17, 2004 4:19 am

I wonder if one like this is good enough for measuring pulsejets, also how does sound behave, might it follow the inverse square law and what distance from the sound source do you use to set the standard?

http://cgi.aol.ebay.com/ws/eBayISAPI.dl ... gory=52479

Mark

hinote
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Post by hinote » Tue Feb 17, 2004 4:23 am

resosys wrote:Beautiful work gentlemen. The numbers finally start to speak.

I'm curious about the reasoning behind the higher resonant frequency being better. Any clues for us backyard engineers?
Read SAE paper #840422; it says something like, "the primary driver for the operating frequency of the engine is the length".

There's ways to increase the frequency, but they're beyond us poor experimenters.

Bill H.
Acoustic Propulsion Concepts, Inc.

Bruno Ogorelec
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Post by Bruno Ogorelec » Tue Feb 17, 2004 6:25 am

resosys wrote:I'm curious about the reasoning behind the higher resonant frequency being better. Any clues for us backyard engineers?
hinote wrote:Read SAE paper #840422; it says something like, "the primary driver for the operating frequency of the engine is the length".
OK, it has long been established that the length sets the operating frequency, more or less, but it still leaves the question of why a higher frequency should be better. Empirical evidence suggests the opposite. Within a reasonable range of L/D ratios, the greater the ratio, the lower the frequency and the greater the thrust. That's been the received wisdom.

What has worked to invert this empirical rule of thumb?

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Post by milisavljevic » Tue Feb 17, 2004 9:56 am

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