www.pulse-jets.com

Bruno,
Without an actual physical aparatus that forces the engine to be perfectly out of tune each cycle, I am afraid that I will end up with two engines operating at a slightly different frequency and their cancelation would form a 180 dB 7.5 htz sound wave frying my internal organs in the proccess. For now I am sticking with my valved design to do this. :P

Larry what do you think of the jumbo FWE?

Eric

Those French gliders use groups/clusters of three escopettes under the wings. I wonder how they interacted. I wonder how ten or twenty little pulsejets would interact? Tharratt drew up a huge cluster of tiny pulsejets that were theorized to amplify each neighbor and gain a great deal more power.
Mark
http://www.pulse-jets.com/valveless/

Point taken Bruno, and I may sit corrected, that the lowest energy state of a pair being out of phase. You may have noticed that I must prove to myself even some of the most "obvious conclusions"! ;-)

Of course I would like to see those references involving pairs; I hope you can find some time...

I liked that bit from the Tharratt page you posted of the cluster also, Mark.

Here's a proposal to elliminate noise and that cluster design of Tharratt's.
Mark

The last page.
Mark

Eric, that is one heck of an interesting bar stool adaption.
Mark

Mark wrote:Those French gliders use groups/clusters of three escopettes under the wings. I wonder how they interacted.

My information -- and I hope to be proven right by the impending translations of the French papers -- is that they always used an odd number of pulsejets together in order to prevent them from synchronizing into pairs. An odd bunch will forever hunt a little here and there around more or less evenly spaced intervals.

They wanted to avoid the synchronization because of the observed decrease in thrust of synchronized pairs.

Now, this decrease is something that has mystified me for a long time. I hope the answer lies where i think it lies. If it does, it offers hope for great things. But, we'll see.

Mike,

Haven't found the reference to automatic operation out of phase, but here's what Kentfield says about his experiments at coupling two pulsejets:

I have also found a reference in Reynst where he says that two quarter-wave resonators, if connected so that a pressure antinode is between their intakes, or exhausts, or both, will automatically operate 180 degrees apart from each other. Will that do?

Here's a crude illustration of how the noise might lay out around a running FWE engine. In this drawing, the wavelength in air is assumed to be a small fraction of the effective wavelength inside the engine. At this particular moment in time, a whole wavelength has been propagated from the corrected acoustic point behind the intake flare, and the wave crest from the tailpipe acoustic point is assumed to be lagging by 75%, which is why the last crest to emerge is such a small circle around that point.

This is an illustration only; the actual layout of intense and rarified zones will depend on the actual wavelength of the sound in cold air and the phase difference between the two points. If we were to show a higher frequency [harmonic], the pattern would be MUCH more complex, though the principle would be the same.

In the drawing, the most heavily reinforced sound is shown in dark gray, heavily reinforced is in light gray, and less reinforced sound is the white zone. The borders are arbitrarily selected by me.

It just happens that my illustration shows one heavily reinforced zone that roughly corresponds to Eric's observed 45-degree "line". That was purely accidental. An accurate layout could only be drawn if the frequency and air temps were accurately known.

L Cottrill

Mark wrote:Eric, that is one heck of an interesting bar stool adaption.

Yes - it's nice to see someone really taking the ever-crucial tailpipe flare seriously.

L Cottrill

Eric wrote:Larry what do you think of the jumbo FWE?

Yes, that is truly impressive. In the video, the frequency varies somewhat depending on exactly what you're doing, but seems to hover around 110 Hz or a little higher once it takes off on its own. Seems about right for a machine almost three times the size of the original, when you consider that it probably runs somewhat hotter internally.

Amazing stuff! Sometime you should do a simple drawing with a full set of the actual final dimensions.

L Cottrill

Yes - it's nice to see someone really taking the ever-crucial tailpipe flare seriously.

I thought it was quite funny. I was going to hammer the tailpipe out a bit but figured what the heck and decided to go a little overkill. It starts up super fast now, not sure how it affects thrust. I would love to trombone it out to a foot or two and see what happens.

I had the plans around here somewhere...... Well anyway I will measure it again. The frequency was definately changing depending on how lean I would have it. Its still not getting a lot of fuel, it might be quitting because im still only getting barely enough fuel into it. Maybe I can flip the tank quick while its running and get it to sustain. Summer time will bring about the liquid fuel systems I have been working on, but its still too cold out to toy with them to work out the kinks.

Eric

Great illustration, Larry. Hmmm. Ahhhh. Hmmmm, etc. Very nice.

Eric, if this keeps up, we are going to have to dedicate an entire wing of our Pulsejet Land Museum to you. Too, just imagine all the wacky shapes everyone has presented here on the forum, it's starting to really add up.
Mark