Worlds simplest valveless?

Mike Kirney · Post by **Mike Kirney** » Fri Dec 05, 2003 12:08 am

I think you are having us on, Viv. I think you just typed "*" and then made a big fucking fuss over it, pretending it was blocking your filthy language, as a practical joke. If some of the other forum members publically express an interest, I am willing to conduct a web-test where I post ultra-profane messages to see which words get banned and which words don't. I was a bicycle messenger for seven years so I can think of all sorts of colourful language to use.

Viv · Post by **Viv** » Fri Dec 05, 2003 12:51 am

Mike Kirney wrote:I think you are having us on, Viv. I think you just typed "*" and then made a big fucking fuss over it, pretending it was blocking your filthy language, as a practical joke. If some of the other forum members publically express an interest, I am willing to conduct a web-test where I post ultra-profane messages to see which words get banned and which words don't. I was a bicycle messenger for seven years so I can think of all sorts of colourful language to use.

Maybe its just verbs then:-)

Viv"*"

George · Post by **George** » Fri Dec 05, 2003 10:37 am

Hello,

To answer to mike and pieter and as i said, i hav'nt more informations about the flying Ã©crevisse type C.

But, with the first photo i've published the first of december and if you know that the lengh is 2450mm and exhaust pipe diameter 185mm, it would be easy to deduce the others dimensions.

More, Milisavljevic says:

SNECMA Ecrevisse from one of the photographs is a part of my pulsejet database; if anyone is seriously interested in the dimensions and performance data for this engine, I will post it here. If anyone has a mind to build this engine, keep in mind that when "unfolded", this engine was over 4.5m long!
Hoping he can help you.

A question, did Bruce Simpson have a look on theses engines ? what did he think about them in comparison with the lockwood ?

I noticed that some people here seems to think that the SNECMA PJ don't use thrust augmentors, it's wrong, the H.S.1 had one behind the intake and SNECMA have some patents on that subject dated from 1952.

One other thing, Bruno is right (one more time) when he explain that 0.85 is a mach number, but these speed is not (as i know) the ecrevisse performance.
SNECMA tested an other valveless PJ not folded with a special intake (patented) without reflector, it's a part of the documents i'm gone send to Bruno.

Don't try to open your presents before christmas Bruno...

BBQ on the forest with a GS1:

milisavljevic · Post by **milisavljevic** » Fri Dec 05, 2003 11:02 am

DELETED.

Bruno Ogorelec · Post by **Bruno Ogorelec** » Sat Dec 06, 2003 12:10 am

George wrote:One other thing, Bruno is right (one more time) when he explain that 0.85 is a mach number, but these speed is not (as i know) the ecrevisse performance. SNECMA tested an other valveless PJ not folded with a special intake (patented) without reflector, it's a part of the documents i'm gone send to Bruno.

George, yes, the speed of Mach 0.85 was not achieved with Ecrevisse, but with another wonderful SNECMA pulsejet, Escopette.

This last picture of the helicopter in exhaust flames is fantastic! Thank you.

hinote · Post by **hinote** » Sat Dec 06, 2003 1:13 am

brunoogorelec wrote:
George wrote:One other thing, Bruno is right (one more time) when he explain that 0.85 is a mach number, but these speed is not (as i know) the ecrevisse performance. SNECMA tested an other valveless PJ not folded with a special intake (patented) without reflector, it's a part of the documents i'm gone send to Bruno.
George, yes, the speed of Mach 0.85 was not achieved with Ecrevisse, but with another wonderful SNECMA pulsejet, Escopette.

This last picture of the helicopter in exhaust flames is fantastic! Thank you.

The following is a quote from AIAA tech paper #98-3879. by Kentfield:

<Figure 11 shows the performance, predicted by
SNECMA 9 , of carefully installed pulsejet of the
SNECMA Ecrevisse type operating up to a flight Mach
number of 0.8. An engine of this type was subsequently
used as the sole propulsion unit of a UAV that achieved
a flight Mach number of 0.85.>

I thought the Escopette was optimized primarily for low-speed propulsion, as illustrated by its application for self-launching a glider. The substantial backflow up the tailpipe is responsible for more than 90% of its thrust (a built-in augmentor)--but limits its efficiency at higher speeds.

I have seen several mentions of the Escopette used at high-subsonic speeds, on this forum. Are we just confusing the Escopette and the Ecrevisse, or was this really done?

Bill H.
Acoustic Propulsion Concepts, Inc.

Mark · Post by **Mark** » Sat Dec 06, 2003 1:29 am

hinote wrote:
brunoogorelec wrote:
George wrote:One other thing, Bruno is right (one more time) when he explain that 0.85 is a mach number, but these speed is not (as i know) the ecrevisse performance. SNECMA tested an other valveless PJ not folded with a special intake (patented) without reflector, it's a part of the documents i'm gone send to Bruno.
George, yes, the speed of Mach 0.85 was not achieved with Ecrevisse, but with another wonderful SNECMA pulsejet, Escopette.

This last picture of the helicopter in exhaust flames is fantastic! Thank you.
The following is a quote from AIAA tech paper #98-3879. by Kentfield:

<Figure 11 shows the performance, predicted by
SNECMA 9 , of carefully installed pulsejet of the
SNECMA Ecrevisse type operating up to a flight Mach
number of 0.8. An engine of this type was subsequently
used as the sole propulsion unit of a UAV that achieved
a flight Mach number of 0.85.>

I thought the Escopette was optimized primarily for low-speed propulsion, as illustrated by its application for self-launching a glider. The substantial backflow up the tailpipe is responsible for more than 90% of its thrust (a built-in augmentor)--but limits its efficiency at higher speeds.

I have seen several mentions of the Escopette used at high-subsonic speeds, on this forum. Are we just confusing the Escopette and the Ecrevisse, or was this really done?

Bill H.
Acoustic Propulsion Concepts, Inc.

Pardon my French, but it seems to me the Ecrevisse translates as crawfish and the Escopette something akin to machine gun? Perhaps Ecrevisse denotes the flippy curved tail of a crawfish. The US had Project Squid and the French Project Flippy Tail.
Mark

Post by **Mike Everman** » Sat Dec 06, 2003 7:35 am

Bastard bastard bastard,,, bastard!

Viv

Don't gush, it's embarassing!
Pip pip old boy. Bugger if I'm not going off all higgledy piggledy, but a pasty and a warm pint and your pecker'll be right up!

I really must go to visit team albion sometime...

milisavljevic · Post by **milisavljevic** » Sat Dec 06, 2003 8:51 am

DELETED.

hinote · Post by **hinote** » Sat Dec 06, 2003 6:01 pm

milisavljevic wrote:Hello Bill,

I believe your concern is with the apparent drag generated from aspiration at the exhaust of the Escopette. This is in fact something of a non-issue, and in any event, the differences between the Escopettes, Ecrevisses, and the Lockwood-Hillers with respect to exhaust aspiration would have been a matter of degree only. All three design families utilised internal augmentation; the Escopettes obtained the greatest leverage from this effect, and the Lockwood-Hillers obtained the least.

In any case, it's probable that an effective high-speed application would be housed in an efficient shroud, utilizing pressure-recovery and control, and taking advantage of heat recovery. This would largely eliminate the arguments made as to "suitability" of an engine for low or high speeds--and even opens up the possibility of using a PJ for supersonic applications.

Bill H.
Acoustic Propulsion Concepts, Inc.

Bruno Ogorelec · Post by **Bruno Ogorelec** » Sat Dec 06, 2003 6:10 pm

Milisavljevic,

Thanks for the treatise. Well reasoned. Answers some of my questions. I've always wondered at the amount of energy spent on the reverse flow. Now the picture is more clear.

If you could answer one question that has bothered me a lot over the past year or so, I'd be tickled pink.

Namely, a number of people here in the forum (especially those among the better educated in the field) have exerted some effort to debunk the idea that pulsation in the pulsejet is sinusoidal in character.

Graphs of pressure readings etc. were marshalled to prove the case.

Yet, you say (and so do a number of experts in their papers on the pulsating combustion topic) -- and I heartily agree -- that a pulsejet is a resonationg combustion device.

The point that bothers me here is -- how can they resonate if the pulsation is not sinusoidal? Is there such a thing as a non-acoustical resonance? I have never heard of it, but what do I know. Maybe I'm missing something.

This is doubly perplexing for me as Kentfield has run interconnected pulsejets in out-of phase mode, which again suggests sinusoidal pulsation of both combustors.

Do you have a good explanation?

Post by **Mike Everman** » Sat Dec 06, 2003 7:56 pm

It does resonate, and true any one frequency component of the aggregate wave form is sinusoidal, but that does not make the output waveform sinusoidal. The addition of several frequencies make it anything but. Looks like it leans more toward a "sawtooth", which for any significant audible acoustic band cancellation is not good enough, but pressure waves will see the desired amplification/cancellation effect, just not 0x or 2x amplitude.

Bruno Ogorelec · Post by **Bruno Ogorelec** » Sat Dec 06, 2003 9:14 pm

Mike Everman wrote:It does resonate, and true any one frequency component of the aggregate wave form is sinusoidal, but that does not make the output waveform sinusoidal.

But, if the components are sinusoidal, wouldn't that mean that a resonance can be established with another, near-identical engine? The other engine would have the same mix of components in the aggregate, wouldn't it? What would prevent a series of standing waves from establishing, connecting both engines acoustically in common resonance?

The recent argument in the forum has been that this is impossible because the aggregate waveform is not sinusoidal. But, why should the aggregate be important, rather than components?

Post by **Mike Everman** » Sun Dec 07, 2003 12:07 am

I seem to want to go on about noise cancellation, but perhaps there's something here to answer your question:

If you look at pg. 3 of the Kentfeild paper and fig. 12 of the Schmidt, you see the pressure wave-form is strange, and will not cancel if summed with the same wave shifted to the right so troughs coincide with peaks.
The higher frequency acoustics (not showable on these graphs) have many components all of different frequencies and therefore different periods.

So, by shifting the exits a little, like you do like the Ecrevisse did for the constructive interference of the pressure waves, to get any particular acoustic frequency to distructively interfere, all the other frequencies (of different period, remember) will not be affected, or may cancel or amplify if they are a harmonics of the one you have aligned.

Acoustically, though, this is an impossible situation with two engines; they will be to entirely random in the signature of the noise coming out, and it will change every cycle. The only hope for acoustic noise cancellation is in ONE engine, splitting the noise path so that you have two absolutely identical noise spectra and a passive method of acoustically inverting one half (the fabulous "and then a miracle occurs...") , then re-integrating the two paths for distructive interference at all frequencies. You certainly do not want this treatment of the pressure wave, of course!

This is the single most fascinating part of the supreme engineering puzzle of PJ's, since I find that the engines in several configurations to be within striking distance of usability in a civil sense, but the noise, the noise! I get to go hear Bill's engine sometime after the holidays for my first up close experience, so I am going from heresay to date!!!!

Bruce · Post by **Bruce** » Sun Dec 07, 2003 1:22 am

The noise issue is a vexing one, and one which I'm presently looking very closely at.

However, what most people forget is that aircraft, no matter what form of propulsion they use, are very noisy devices.

You can hear a Huey coming from miles away because of the slap of its rotors.

Something as ancient as a Harvard trainer can produce enormous amounts of noise as its propellor tips flirt with the speed of sound and produce shockwaves that propogate long and far.

Your average large piston engine as used in an aircraft has no silencer attached and, at full throttle, produces an ungodly amount of noise.

Gas turbines are also hideously noisy at close quarters and can produce noise levels far in excess of pulsejets.

So why does the pulsejet come in for such a bashing over the noise it produces?

Well it has a lot to do with the distribution of energy within the audio spectrum -- ie: the sound it makes (as opposed to the noise).

The sound of a gas-turbine disipates very quickly at distance because it is largely white noise plus a very high frequency component. This means that, although standing close to a big jet engine will ruin your day, they don't actually sound very loud once they're in the air and any modest distance away from you.

Likewise, a large piston engine has the noise pulses from its exhaust rapidly disspiated, diluted, and diminished by the effect of the propwash and other factors.

The answer to making pulsejets less "noisy" is not simply to try and reduce the amplitide of the pressure waves it produces -- but to alter the spectral distribution of the energy contained in those pulses such that they are more rapidly attenuated by the environment around them, or such that they sound more harmonious to the human ear.

One very simple option would be to use a huge number of engines all synchronized but operating with a slight phase difference such that the combined frequency emitted by such a cluster would be beyond the range of human hearing. Such high frequencies would suffer greater attenuation as they travelled through the air -- further improving the effect.

Of course this approach is rather unwieldy -- but there are many others that can be used to reduce the "noise" without reducing the energy.

I have to say that this field is every bit as interesting, complex and exciting as the combustion/CFD aspect of the pulsejet.

www.pulse-jets.com

Worlds simplest valveless?

Nice Try, Asshole

Re: Nice Try, Asshole

Thanks for all the fish!

Team SNECMA and the need for speed

Re: Team SNECMA and the need for speed