Moderator: Mike Everman
The short answer is that no kind of rig does that- it is almost entirely done by hand with a hammer and anvil. To start with I use a slip roll to begin to curl the metal but after that there is no machine to help me. I will squash part of it with the vice grip, then then hammer it smooth on the anvil and repeat this many times. I gradually work the two edges together untill they are close enough for me to tack weld.
Graham C. Williams wrote:Dear Bill.
I agree with you. The motor is a quarter wave resonator. The induction pipe can be sized to allow 2 or 3 reflections between the highest and lowest pressures.
hinote wrote:I'm currently looking at it as a 1/4-wave (closed-end) resonator, with a half-wave intake riding along in synch.
Bruno Ogorelec wrote:
Graham (and I think Hank) have said that the intake should be longer. Changes to its length would certainmly be very instructive. The first impulse is to make the outer part longer, but I would also like to see it extended inwards, towards the concave chamber bottom.
hinote wrote:Placement of the inside end of the intake HAS to be critical, because it must coincide with the nodes of the primary acoustic system. It's possible (probable?) that the inside end must be relocated when the intake length is changed. More research required.
Bruno Ogorelec wrote:
That is exactly my point. If the intake is a quarter wave resonator riding on a harmonic of the entire tube, the extension inwards should not matter in terms of resonance. It might change the pattern of gas flow to some extent, but not the resonance. Why? Because for the intake, the entire bottom area of the chamber is the pressure antinode. The resonant length is the distance between the geometric center of that volume and the outer end of the intake, or possibly between the bottom of the chamber and the end of the intake. In either case, the exact placement of the inner end should not matter.
However, if the intake is a half-wave (open tube) resonator, which I doubt, extending its length inwards will have a similar effect to extending it outwards, because it will change the acoustic length.
I think (or, better to say, I hope) that we have a clearcut alternative here, ideal for the testing of our assumptions. A rare opportunity. However, as frequently happens in pulsejets, other factors may be at work here, clouding the theoretically simple and clear case.
hinote wrote:Interesting discussion, don't you think? Somebody needs to take an operating engine and modify it to confirm some of the theories, and bury others as incorrrect.
Hank wrote: This engines pushing the reversion wave out the intake and the fact that all of the exaust duct appears to be cool to the combustion chamber suggests something amiss with tune. I wish to retract my original suggestion of increasing the length of the intake tract and suggest that some one-third of the length of the exaust be cut off. Perusal of the photos suggests that this engine is, in fact, running backwards. Too great a flow inwards from the exaust is creating a back-pressure that is not allowing thrust to flow the course it should. I'd start lopping off incremental bits of the exaust and start watching for heat coloration to start moving down the pipe while leaving the intake the length it is now.
Hank wrote:This engines pushing the reversion wave out the intake and the fact that all of the exaust duct appears to be cool to the combustion chamber suggests something amiss with tune. I wish to retract my original suggestion of increasing the length of the intake tract and suggest that some one-third of the length of the exaust be cut off. Perusal of the photos suggests that this engine is, in fact, running backwards. Too great a flow inwards from the exaust is creating a back-pressure that is not allowing thrust to flow the course it should.
Mark wrote:There are so many factors I think, when you start to toy with one, some other variable/dimension might need tweaking. I think with my tiny Logan for example, if I shorten the tail pipe, it doens't like that, even though it is spewing most of its exhaust and thrust out the side port. I think a larger and/or longer side port would be the way to go. Sorting it all out is like a can of worms in uncharted territory. To say something is one thing and not contingent on the other several segments is where the confusion begins. To me, it's as if every feature is a subset of some other greater whole, and the whole keeps moving around.
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