Roaring Becomes Elektra

Moderator: Mike Everman

Postby larry cottrill » Tue Jun 22, 2004 4:56 pm

brunoogorelec wrote:Heartfelt congratulations! I am really glad to see a totally new configuration work, rather than just iterations of the familiar ones. This is what this forum has done best, I think -- encouraged a number of people to try something completely new.

You are one of the people in the forum who deserved success the most, so I am doubly glad, for I have also seen justice done.

Thanks very much, Bruno! As you well know, most of what I do around here is speculation ... the one thing I take some secret pride in is the thought that somewhere along the line, I might have gotten someone to think about the problem in a little different way. That's a wonderfully exciting thought!

Of course, the debt I owe to you and Graham, and later on to just about everyone here, is staggering! That fact is not lost on me, I assure you!

Larry
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Postby larry cottrill » Tue Jun 22, 2004 5:06 pm

Avenger wrote:Congratulations, superb work Larry!

I'm wondering, if you change the rectangular combustion chamber for a spherical one, would you get better performances?

I agree with Bruno on this one [except at the transition, of course!] -- I think in the case of Elektra, the bottom of the chamber being a sort of narrow channel should be good, getting the air/fuel charge well forward so the explosion starts toward the nose end of the chamber.

Keep in mind that in pulsejets, the important action of the chamber is mostly at fairly low velocities -- its main function really is to contain the blast just long enough to get the pressure up so things will get kicked into motion in the 'long' part[s] of the engine.

Also, in this case, the primary concern was something that could be hacked together out of the cheapest, most common materials possible, without resorting to visiting the city dump. I certainly think that was proven as a viable premise. Even in tuning this thing up, I'm going to strictly stay away from anything exotic or hard to make by hand.

Thanks!

L Cottrill
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Postby Mike Everman » Tue Jun 22, 2004 7:04 pm

I love that "good run" video! What's the throttleability like on it?
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Postby larry cottrill » Tue Jun 22, 2004 7:37 pm

Mike Everman wrote:I love that "good run" video! What's the throttleability like on it?

Mike, I have no idea, except it seems to be more complex than just tweaking the gas flow -- all that seems to do is vary the richness of the run, which would alter the power output, of course, but it looks to me like one like this really needs air throttling. Sounds like a complication to me. Of course, it is something that should be tested at some point.

What I really need to do is set up some simple, reasonably sensitive way to measure thrust, so I can find out what happens with changing the intake impedance! Also, that would make possible a rough measurement of thrust specific fuel consumption.

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Postby Bruno Ogorelec » Tue Jun 22, 2004 7:44 pm

Larry Cottrill wrote:
Mike Everman wrote:What I really need to do is set up some simple, reasonably sensitive way to measure thrust


Run the Elektra vertical, on the bathroom scales. That's (rougly) what the German rocket pioneers did, well before WW II. What's wrong with that?
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Postby larry cottrill » Tue Jun 22, 2004 8:41 pm

brunoogorelec wrote:
Larry Cottrill wrote:What I really need to do is set up some simple, reasonably sensitive way to measure thrust


Run the Elektra vertical, on the bathroom scales. That's (rougly) what the German rocket pioneers did, well before WW II. What's wrong with that?

Well, I was going to set that to one side, to keep track of the weight of the propane used. Besides, it doesn't exactly seem like a "sensitive" instrument to me.

Actually, now that I think about it, when I step on it, it does usually seem somewhat more sensitive than it used to be ...

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Postby Bruno Ogorelec » Tue Jun 22, 2004 9:00 pm

Larry Cottrill wrote:it doesn't exactly seem like a "sensitive" instrument to me.


Ok, so borrow a more sensitive set of scales.

Don't go too far, though. We have a set here in Zagreb that is among four or five most sensitive in the world -- some kind of electrostatic device -- but it takes about three months for the technicians to set it up for measurement and each session costs a great number of thousands of dollars. One run of a pulsejet in the vicinity would probably ruin the million-dollar thing right away.

(I think they are using the thing for gravity measurements but I'm not certain.)
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The Measure of the Beast

Postby larry cottrill » Thu Jul 01, 2004 4:29 am

I just posted the dimensions of the Elektra I prototype for Steve on the Elektra I Builders Web Log, so I might as well plug them in here, too. The blog is at http://www.elektra1.blogspot.com

L Cottrill
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Elektra_I_prototype_dims.gif
Elektra I prototype dimensions - Drawing Copyright 2004 Larry Cottrill
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Postby steve » Thu Jul 01, 2004 6:25 pm

thanks larry!
now I just need to get the electrical box thingy. would they have it at a local hardwhare store of do I need to go to home depot or someplace similar?
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Postby larry cottrill » Thu Jul 01, 2004 7:21 pm

steve wrote:thanks larry!
now I just need to get the electrical box thingy. would they have it at a local hardwhare store or do I need to go to home depot or someplace similar?

Any good hardware store should have them. It turns out that there are two styles -- one for conduit, and one for a mix of conduit and Romex style wiring. I think the Romex style [like the one shown here] is easier to work with, because there are fewer knockouts that have to be welded tight. On the other hand, it has a few little slots to fill in, as you can see, I think. The other type has five knockouts on the flat face of the box alone!

When you buy the box, be sure to get the matching cover plate as well. You'll find a single knockout to seal up, right in the center. This is shown lying behind the box in the photo.

L Cottrill
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ElI_knockout_welding_2_crop1.jpg
Note the little slots to be filled in -- but, very few knockouts to seal up. Photo Copyright 2004 Larry Cottrill
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My Propane Outfit

Postby larry cottrill » Sat Jul 10, 2004 11:17 pm

I finally got a picture of my working version of a small-engine propane vapor supply. As you can see, the regulator is fairly compact, yet it is a high-volume design, with very large internal port area, quite different from the design of welding regulators. The model number stamped on it seems to be L.1B; it's supposed to be the highest volume low pressure regulator Victor produced [maximum input pressure is only 500 PSIG]. I had to mount the propane stem and needle valve [from Menards] and the gauge, which is just an old one I had lying around. A lower range gauge would actually be better, for more accurate duplication of settings. The hose is from Menards, and was designed for water hookup to kitchen ice makers; the fittings have rubber O-rings, so it isn't necessary to wrench them tight to get a perfect seal.

The 26 PSI shown on the gauge is NOT what I ended up with to run Elektra - it shows the maximum pressure to which this unit can be set. I am able to run Elektra I with 10 or 15 PSIG, and it would probably run with even less, with this type of regulator.

The idea with a setup like this is to make sure the regulator isn't the flow-limiting element; rather, you want a duplicable pressure setting that allows a good range of needle valve settings for fine control. The propane is delivered early in the intake air stream of the engine, to provide adequate path length for mixing. This method works wonderfully in the case of Elektra I.

L Cottrill
Attachments
Good_propane_regulator_setup_crop1.jpg
The final version of my propane delivery setup to power Elektra I and other small vapor-fueled pulsejets. Photo Copyright 2004 Larry Cottrill
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Re: My Propane Outfit

Postby Bruno Ogorelec » Sun Jul 11, 2004 9:01 am

Larry Cottrill wrote:The propane is delivered early in the intake air stream of the engine, to provide adequate path length for mixing. This method works wonderfully in the case of Elektra I.


Well, thank God that someone is experimenting with this. I have not seen this done since the Thermojet days, yet it's the only type of gaseous fuel supply that makes sense to me.
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Re: My Propane Outfit

Postby larry cottrill » Mon Jul 12, 2004 1:25 am

brunoogorelec wrote:
Larry Cottrill wrote:The propane is delivered early in the intake air stream of the engine, to provide adequate path length for mixing. This method works wonderfully in the case of Elektra I.


Well, thank God that someone is experimenting with this. I have not seen this done since the Thermojet days, yet it's the only type of gaseous fuel supply that makes sense to me.

Bruno, I agree - I don't know how I'd make it work any better than it does. How I actually rigged it is that a 1/8-inch OD copper pipe runs straight down the chute, practically up against the wall of the intake; but then, I bent the last 1/4 inch inward at about a 10-degree angle, so it actually cuts across the airflow slightly, to try to start some mixing action right away. And of course, in the Elektra I design, there's plenty of path length after that to get the mix to the combustion zone up front.

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Re: My Propane Outfit

Postby larry cottrill » Tue Jul 13, 2004 6:05 pm

Larry Cottrill wrote:How I actually rigged it is that a 1/8-inch OD copper pipe runs straight down the chute, practically up against the wall of the intake; but then, I bent the last 1/4 inch inward at about a 10-degree angle, so it actually cuts across the airflow slightly, to try to start some mixing action right away.

Here's a drawing of how the fuel pipe is actually built. My hand-bending of the 1/8-inch pipe is not as smooth as the idealized picture here, but the principle of the design is clearly shown, and minor imprecision or even some variation from this design should not keep it from working well.

L Cottrill
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Elektra_I_intake_detail.gif
Detail drawing of the intake tube, showing how the built-up flare and fuel tube are set up. Drawing Copyright 2004 Larry Cottrill
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Postby steve » Thu Jul 15, 2004 10:02 pm

The whole intake setup seems a bit complicated to me. Wouldn't it be easier to simply drill a angled hole in the side of the intake and put the injector tube through it? if you drill the hole one size too small and then hammer the injector into place it is very sturdy. I have used this method on my mini pipejet (mike's logan) and on another intake for my valved engine and can attest to its strength and simplicity. Also this would greatly simplify the construction of the intake flare (if it is made from fireplace concrete).
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