www.pulse-jets.com

Here's a new version of the Kazoo calculator. For those of you new to this, it is also a geometry converter for Kentfield's Lockwood/Snecma and his own shorter, multi intake type successfully built and run by Bill Hinote. Mainly it's useful for creating dimensions when you have an odd-ball piece of pipe to start with.

New feature of note is the addition of an effective thickness of boundary layer you can specify, and it's effects on the dimensions when scaling down. By effective, it should be understood that the boundary layer is not as simple as a layer of fixed thickness, but the correction here at least considers the difference in surface area between original and Kazoo involved, and attempts a first order area correction. Set it to zero for no effect; at a guess I'd throw in .5mm (.020") in sub 75mm (3") engines.

I'm not sure whether boundary layers mean anything in highly turbulent oscillating flows along red hot surfaces, but the function is there in case. It may mean more at intake or exhaust; unknown at this time. I'll be squeezing several Kazoos soon to check and hone the calculator.

I'm wanting to start putting in some acoustic length logic to it, which would require we have a good idea of the temperatures along the length during intake and exhaust phases, and gas velocities. I'd also like it to predict operating frequency and generate timing charts.
How far do I want to go? Hmmmm. I guess I want it to track my understanding of the subject, which still is only at the level of "morphing known geometry".

Operations manager Jim Spink thought me humming, uh, doing a sine-sweep, orally, OK, yodelling into Locky Kazoo was the funniest thing he'd seen in a while. He insisted I post this. ;-P
I could feel what tones resonated with my hands. Kinda cool.

What's the gray box mounted on the tail section midway doing? Will there be an alpine version too?
Mark

I'd sure like several people to be trying different fueling methods on Kazoos to see what works best. They're so easy to make, guys! I can supply you with a steel one with sparkplug, without fueling pretty cheap if you don't want to mess with the crushing.

I'm wanting to try (mixing type) mist nozzles driving white gas with a small propane bottle. I like this approach because I may want just propane for starting, and the hand torch cylinder can be pretty light, and alternately made of a much lighter aluminum vessel. I need to work out if one bottle can aerosol deliver say, one gallon of gasoline.

Let's see, on the 2", I need nozzles for about 7 lb of thrust, assume 3 lb fuel/ lb thrust/hr, 6 lb per gallon, two misting nozzles need .25 GPH each on the high side. On the 3", I'll need 3.5 GPH out of each of two, for an estimated thrust of 14 lb. There's shoulders on the intake transition for mounting nozzles that seem fortuituosly placed.

What's the gray box mounted on the tail section midway doing? Will there be an alpine version too?
Mark

that's just an aluminum block band clamped to the exhaust so I can hold it in a vise for running.

It might be interesting to just use a sheet or two of thin .010ths of stainless for ~$15.00 from Enco and use the seam which could either be two flanged or one flange and a single sheet of steel to afix/hold the jet to the little flying object via the flange or even use the steel as part of the wing structure as well.
You could form a Schmidt shape or conical single section duct with a typical valved intake, which of course would have to be constructed from a disk of aluminum and reed valves. The jet could be very light and mounted to a balsa wood toy plane. For after all, a very small pulsejet needn't be very complex or weighty. It just has to be thought out.
One might practice with a sheet of paper or two sheets of paper and see how the form might come about. Too, if you anticipated/incorporated some sort of flexing, the thin spring steel would be an ideal material to work with.
I have some British literature on single section cone shaped pulsejets with typical thrust levels. Either you could fold the seam and lock it air tight with a long bar(s) and/or screws or adapt it to flange mount in some way where the heat is dissipated enough not to attack the wood of the air frame.
Mark

mark wrote:I have some British literature on single section cone shaped pulsejets with typical thrust levels.

do tell, or post. sounds interesting. for those of you lost by the previous post, Mark and I were talking recently about 2" Kazoos for model airplane use. some interesting problems arise when you consider mounting valveless types in a small vehicle, to be sure.

It was mentioned earlier in this thread that one might crimp the pipe all around the circumference like those paper things they put cupcakes in. If you hammered a bunch of grooves along the length you can just use a bunch of different sized hose clamps to squeeze it around a wooden form that you turned on a lathe. Then just set fire to the wood inside to remove it! Ta-da!

A corrugated surface is also good at absorbing sound so it might even run quieter than normal. It can also compensate for thermal distortion which is a trick they used on the wings of the SR-71 Blackbird.

Ah, Locky Kazoo, my first motor. Takes me back, looks like 10 years. Where has the time gone?
I too was obsessed with concentric and otherwise morphable designs. Unfortunately, one design goal is minimizing surface area. Round sections is the thing, I'm afraid, unless fire and noise is all you want!

Dang, I was so pleased with my cleverness I forgot to take that into account. Ah well.

What about a hybrid engine? If the pulsejet as the heat core of a ramjet? Crimped large-surface tube would make sense then, as it would increase the heat transfer to the passing air. You'd have a ramjet that would operate from zero speed.

Or it might melt down faster. Only one way to know...

tufty wrote:Or it might melt down faster. Only one way to know...

Sure enough. One would want to choose the core material wisely.

Ah, the boys are back in town! Back to the what was it called? P51 hot air ramjet thruster thingy? though nothing beats the heat transfer of burning fuel in the air that is the working fluid...

Mike Everman wrote:Ah, the boys are back in town! Back to the what was it called? P51 hot air ramjet thruster thingy? though nothing beats the heat transfer of burning fuel in the air that is the working fluid...

Sure enough. But...

In combustion efficiency stakes, nothing beats fluid pressure, yet, pulsejets make do with pitiful fluid pressures. You work with what you have.

In the pulsejet you have a great amount of heat going nowhere. Making it go somewhere useful might not be a bad idea. Especially if it makes the outside of the engine less hot in the process, suppresses a bit of noise etc. etc.

So, maybe you trade a bit of efficiency on the left and gain a bit on the right. What if you gain more than you lose? Everything depends on the bottom line.