Fishmouth tailpipe increases thrust?

[Irvine.J]

I feel like saying... "Don't come the raw prawn with me!"
Is this true, I found it here...

http://www.rqriley.com/gluharef.html

"The fishmouth cut at the rear of the tailpipe also has sonic effects. It reduces noise and increases thrust. "

Is this really true? Seems to defy a few critical tailpipe rules... but if someone can confirm it, I guess its interesting. I don't see how its going to reduce noise... maybe it will make you deaf within 2 seconds instead of 1?

[mk]

Search in the Pressure-Jet Forum. There, those days, Viv and Luc posted some interesting things.

To keep it brief: They said exactly the opposite (wrt. thrust) of what that advertisement says. And I would be with their opinion in this case as well.

[larry cottrill]

Basically, a fishmouth cut would "soften" the tuning of a pipe so it will hit resonance over a small range of frequencies rather than just sharply tuning to a single fundamental frequency. Essentially, you are lowering the system 'Q'.

L Cottrill

[_Rahul_]

Seen http://www.rqriley.com/glu-heli.htm long ago and thought that was just a myth! In the pic u can figure out that one end is the PJ( or something alike .. but looks a pj!)

Is it possible to fly a helicopter like this with a PJ?
I doubt that a PJ, that size, can create enough thrust to make that blade revolve at enough speed to lift that heavy machine with a rider on it! Pretty heavy for a PJ .. Isnt it?

Or is that a thermojet? .. never read much about 'em .. but a chopper powered by these motors is very interesting! Anyone who knows about this chopper..willing to share some information?

[thecheat]

if I remember correctly, that's a pressure jet (I think that's the type jet a "gluey" was...) Not a PJ, those are too heavy, and not a ramjet.

PS: I really don't know much about these... just that is the shape of a pressure jet and the name-glu-heli sounds like gluey (however that's spelled) which is a pressure jet...

[Irvine.J]

Mk wrote

To keep it brief: They said exactly the opposite (wrt. thrust) of what that advertisement says. And I would be with their opinion in this case as well.

I'd have to agree. After reading the PDF files on the forum I would be of the oppinion that, as larry said, lowering the accuracy of to which the tailpipe was tuned would disrupt the pressure difference in a negative way. If I was to quote from the pdf...
"If we make a pulsejet engine that looks like this the reflected shockwave will decrease even more, and the engine will have serious trouble to run properly. So if you would like to design a new type of pulsejet rear end you have to have this phenomenon in your head. Another thing thats matter is also the relation between wavelenght and resonance pipe diameter...."

and also...
Let’s go back to the pulsejet sequence. After the explosion, the static and thedynamic pressure will fall. This will finally open the valves and let new fuel/airmixture enter the pulsejet engine. Next thing that happens is that the resonance shockwave will raise the pressure and trigger the ignition, and a new sequence will begin.

So with this in mind, and as Larry said this would lower the resonant frequency quality of the tailpipe so its negatively attenuated. Then I belive that it would like most things be a trade off between thrust and noise level. (not that the "volume" would change, just the peak frequency amplitude would be alot less)
Also, the returning shockwave would be of lower amplitude, (as the pressure difference is less) henceforth making operation a little less reliable as a small change in fuel pressure might make the returning shockwave a little "soft" to recipricate the next explosion.

Wow I've surprised myself here, have I properly considered this?[/i]

[Najm]

It would, at least, be quieter.
Less powerful explosion.