www.pulse-jets.com

Bummer, Drew!

dadruid wrote:Wow Mike, that's awesome! Seeing that video almost made up for the fact that I drowned my truck tonight...
Great work, job very well done.

oops... in NZ there has been lots of flooding latley, there have been housed drowned!!!... thouthands of dead cows and sheep to!

Stephen

I've decided that I'm going to make a handful of 50mm Kazoo's and play with pairing, triples, ring arrays and such. First would be moving two running ones together with different lengthwise offsets and get some dB and thrust readings. Got to get a dB meter, eBay, here I come...

Mike,
is it possible to make the pjet with a straight tailpipe?

Alexander

alex wrote:is it possible to make the pjet with a straight tailpipe?

Yes it is, Alexander. Here's one, if you want to try. But, 'straight pipers' are usually less powerful than 'trumpets'. That's why most people use flared tailpipes.

Regarding that Kumar thing,

I've always wondered why valveless inlets never extend into the CC. Well, apparently some do. Great. Another "original" idea stolen probably before I was born... :)

Now... if this design has any ease of starting at all, I think those areas could be where to start with the annular thingy. :) Simple, straight, and intake already a bit inside the CC, I never thought I'd run into something this close to what I have in mind. Thanks!

One question though; is the Kumar (or whatever the engine is called) meant to be bent in the middle, i.e. does any significant part of the thrust come from the intake?


- ville

vhautaka wrote:One question though; is the Kumar (or whatever the engine is called) meant to be bent in the middle, i.e. does any significant part of the thrust come from the intake?

The 'Kumar' part comes from the name of the designer, Mr. Sudarshan Kumar. The thing is not bent because it was used to test various parameters like fuel consumption etc., not for propulsion. If you wanted to power anything with it, you would have to bend it, or add some kind of a deflector or 'recuperator' to the front.

brunoogorelec wrote: If you wanted to power anything with it, you would have to bend it, or add some kind of a deflector or 'recuperator' to the front.

Oh, no worries about that. I would turn the front inside out and just try to keep the areas somewhat right.

This would reduce the outer diameter/length ratio, the engine would be larger and heavier, but probably have some interesting characteristics.

First, there would be the possibility for the extra air suction effect I'm looking for, to get some static thrust. And for flame donut photography!
Also, this thing would not reject foreign objects, so I could probably throw / fire things through it while it's operating. Anything caught inside an augmentor should get thrown out pretty fast, huh?

Another drawing, variations of which I've scribbled before.


- ville

Ville, listen to Nike -- Just Do It!

I am intensely interested in annular layouts for my own reasons, as some people in the forum know. Can't wait to hear of your results and the verdict.

Hmm, would this be the same Kumar as in http://cgpl.iisc.ernet.in/high_int_low_ ... burner.pdf ?

Kinda familiar shapes there too!

Interesting, they seem to be doing good research in India. Not meaning propulsion, but distributed renewable energy production and such. I hope Europe wakes up someday...


- ville

I second that, do it Ville, go, go, go!

Okay! :)

Say, something like the design in my line drawing, I'll start with an outer pipe of 6" dia. or thereabouts.

In order to follow the specific relations of the Kumar design, CCdia of 165, intake 25, tailpipe 50:

The innermost pipe will be 3" dia, so the CC cross-section area in the front will be the area of a pipe with sqrt(6^2 - 3^2) diameter. Intake/CC transition cross-section area will have to correspond to about the area of a tube of diameter CCdia/6.6, and the area of the tailpipe (the area between the mid and outermost pipes) CCdia/3.3.

Lessee... the largest CC area will be the area of, what, a 5.19" pipe? And the tailpipe gap would be something like the area of a 1.57" pipe... hmm, this still seems a small gap, a 5.7" pipe inside a 6" one. :/ Could probably try with 5" pipe and also make the intake gap a bit larger. Hey, this would only require modifying / changing one of the pipes..

I'm not sure if my math holds, I'm almost asleep after a day of computer maintenance. I think I'll take another look with a real calculator and pen and paper once awake again. :)


- ville

vhautaka wrote:Hmm, would this be the same Kumar as in http://cgpl.iisc.ernet.in/high_int_low_ ... burner.pdf ?

Yes, Mr. Kumar is one of the recognized experts in combustion. He worked with J.A.C. Kentfield on at least one pulsejet project. BTW, Kentfiled's main field of interest is not pulsejets, either, but aerodynamics.

The intake and cc section reminds me of a glass wasp trap...without the upper plug it could give a good jam jar...we'll see...

75mm Kazoo update-

The first throttleable length, without any other iterations is about 9" longer than calculated, and several of the dimensions as built are quite off (see spreadsheet detail). The length extension may well be because of the greatly over-expanded tail. I want to be monitoring some things before I squeeze this down, and I may not ever do it to this particular unit. I really didn't attempt to follow the calculator too closely at the time, I was just playing with the method and figured that there were so many variables that any starting point was going to be good enough. It's funny but, I never really believed it would work! I plan to really follow it closely next time, but it's difficult to gage where a dimension applies, considering the wild geometry at the transitions.

It may be that my sloppy adherence to the dims fortuitously made for a nice runner. Sometimes the best paper airplanes are the sloppiest folds. I'm getting pretty enamored with the lines, I think the transitions (see photos earlier in the thread) make for a great deal of turbulence, in a smooth organic way, if you take my meaning... (God, I'm starting to sound like Mark!)

I plan to make some different injection pipes, single row, 90 and 120 degree double row, and rotate it while running for upstream and downstream injection, and at different angles. I placed the pipe in the CC at the nearest easily drillable location to the intake transition. I like the venturi effect of the slit-like intake running around the fuel tube. I'd like to try starting air thru a similar tube just aft of this one. Thrust is pretty good right now, subjectively, but I won't do serious work (changes, that is) until I can gage thrust and fuel mass rate.

The sliding sleeve has an unexpected beauty, born of pure necessity. It is truly slidable and sealable (while still being geometrically "conical"), which has been a problem for other conical constructions. The "cone" of the exhaust is always the same circumference. I'm very interested in this being a permanent feature, allowing you to adjust length on the fly for various conditions. Of course, there may be an optimum length that serves cruise and max power settings, for various environments, but I'm not so sure. See how the more "permanent" weldless extension is attached (and runs) with just a band clamp.

The more I think about this construction, the more it looks like the perfect platform for optimization of geometry. Everything can be changed, and changed while running! All throats, intake and exhaust areas can be adjusted by clamping or pulling for an endless matrix of relationships in a short period; virtually eliminating cut and try.

This is fun!