Focused wave engine runs!

Moderator: Mike Everman

Re: Focused wave engine runs!

Postby hinote » Sat Sep 25, 2004 4:51 pm

Bruno Ogorelec wrote:Interesting! (The fuel injector placement, I mean.)


It appears that one of the necessities of the rear-facing-intake type of pulsejet is that fueling HAS to take place within the intake tube. The Chinese, the Thermojet--and now Larry's engine--all have their fueling point there.

Does anybody know of a successful (running) engine of this type that has the fuel supply feeding in a different location? For example, at the base of the intake.

Bill H.
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Re: Focused wave engine runs!

Postby steve » Sat Sep 25, 2004 5:38 pm

Bruno Ogorelec wrote:Interesting! (The fuel injector placement, I mean.) I have gone hoarse telling people that the best way to fuel a pulsejet is to shoot propane into the mouth of the intake tract from the outside, as the Bunsen burner does. That way, the first thing you get is some ram effect from the ejector intake. Propane powers the mixture into the engine, so to say. The initial pressure before ignition is higher. The second thing you get is perfect mixing -- better than the wild injector configurations spitting into the combustion chamber will ever achieve. Finally, you increase the resistance to reverse flow of the intake tract and halp the engien exhaust through teh exhaust, rather than through the intake.


OK Bruno, I'm sold! Where exactly do you think I should put it- Just inside, just outside, or even with the intake flare?

give me a few days to make the modifacation :-)

Does anybody know of a successful (running) engine of this type that has the fuel supply feeding in a different location? For example, at the base of the intake.


would the Tharrat count?
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Re: Focused wave engine runs!

Postby hinote » Sat Sep 25, 2004 6:02 pm

steve wrote:
Does anybody know of a successful (running) engine of this type that has the fuel supply feeding in a different location? For example, at the base of the intake.


would the Tharrat count?


Steve--that engine doesn't work.

I know--I built one and spent several weeks trying to get it to sustain.

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Re: Focused wave engine runs!

Postby steve » Sat Sep 25, 2004 6:09 pm

Mike Everman wrote:Steve, I don't have a pic of a running Chinese, got one? The heating pattern on Lady doesn't surprise me, I'm sure the closed end becomes the main acoustic antinode, where all the action wants to happen.


check this out: http://www.jetzilla.com/Vol01Num01/jetZilla.html

Steve--that engine doesn't work.

I know--I built one and spent several weeks trying to get it to sustain.


you don't sound too happy about those weeks ;-)
Oh-well, it's still a neat concept nonetheless.
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Re: Focused wave engine runs!

Postby Bruno Ogorelec » Sat Sep 25, 2004 7:40 pm

Viv wrote:I still cant find the original papers for the engine though only papers from other projects that have used it, seems it was developed by one research group and then all the others borrowed it


Viv, I have the A.S.M.E. paper on development of the pressure-gain combustior for a turbine, based on teh NRL, if you're interested.

The NRL (as it name says) was developed by the Naval Research Laboratory (NRL) at Chesapeake Beach, MD, in 1957 and ’58, by team led by Carroll D. Porter. The railway heater and de-icer was developed rather closer to your present abode -- by the Low Temperature Laboratory at the National Research Council of Canada.
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Re: Focused wave engine runs!

Postby Viv » Sat Sep 25, 2004 8:00 pm

Bruno Ogorelec wrote:
Viv wrote:I still cant find the original papers for the engine though only papers from other projects that have used it, seems it was developed by one research group and then all the others borrowed it


Viv, I have the A.S.M.E. paper on development of the pressure-gain combustior for a turbine, based on teh NRL, if you're interested.

The NRL (as it name says) was developed by the Naval Research Laboratory (NRL) at Chesapeake Beach, MD, in 1957 and ’58, by team led by Carroll D. Porter. The railway heater and de-icer was developed rather closer to your present abode -- by the Low Temperature Laboratory at the National Research Council of Canada.


Yes thats the same paper I read Bruno, very interesting i thought, thanks for the other referance I will see if I can get any information directly.

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Re: Focused wave engine runs!

Postby larry cottrill » Sat Sep 25, 2004 11:13 pm

steve wrote:I may be getting some thrust measurements soon- My physics teacher is willing to let me borrow some precision spring scales.

BTW the completed weight (with sparkplug) is 27.4oz

Larry, I am making good progress on the cones and they should be done in a few days so shoot me an e-mail.

Steve -

Yes, EVERYONE wants to know what you get for thrust. Again, I would emphasize, though, that it means more if measured in lean running than in cranking it up to the max. The weight seems pretty good to me - it's over a pound and a half, but 3 ounces of it has got to be the spark plug!

The cones look absolutely great! I have sent you an email with my shipping address, etc. I wish you would explain to us how you do that superb rolling on these tiny pieces. They look so absolutely round, with no 'flat zone' at the edges where they come together! What kind of rig does that? How long does it take to run them through, and is it accomplished in a single pass or many passes gradually working up to where it almost closes? How were the pieces initially cut? Did you happen to try rolling one with the oval hole already cut through, as I suggested earlier?

In any case, it looks like beautiful work.

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Re: Focused wave engine runs!

Postby larry cottrill » Sat Sep 25, 2004 11:40 pm

Bruno Ogorelec wrote:
Bruno Ogorelec wrote:with different implications for the Short Lady.


Oops. I just noticed I've been referring to the Short Lady, which is a different design entirely, rather than the Focused Wave Engine. Sorry. My tired brain is not concentrating as well as it once was....

No, Bruno - shake your head till it clears. Focused Wave Engine is just the technical name for the Short Lady, which was the 'mystery' name that I threw out there before revealing what she really looked like.

More importantly, Larry, have you rethought the intake stack behavior?

When I suggested bent rather than 'broken' intake, you said you expected the stack to be useful mostly as a resonator and that exhaust flow would probably not be of importance.

Now that it is demonstrably not just a wave vessel, but also pushes out quite some gas flow, would you be motivated to redesign it? If so, what would you do?

I don't know. The present design doesn't seem to be suffering much from the crude 'elbow'. However, since blast mass is obviously moving there, a straighter path would theoretically be better. Do we care how much thrust is from the tail and how much is from the intake? I hardly think so. So, you could have just a slightly curved pipe that stops abruptly at just the right station inside the cone, with the cutoff facing forward, a la Thermojet. That also might be better in terms of less disruption of the flow of gas along the upper cone wall toward the tailpipe.

Also, you mentioned a very small flare at the tailpipe end. The very similar NRL engine has a larger but still very small flare. Do you think there is something about those engines that makes a small flare better than a large one? Mind you, the NRL was meant only to generate a great amount of hot air, not thrust.

The only reason I wanted the small flare was because of the weirdness of the curve UFLOW renders when it's included. It would be really odd to find out that there really is a physical singularity because of that tiny detail being just so! I doubt that's really the case, and see no reason why a big flare wouldn't be advantageous, in terms of a little more cold mass in the pipe.

You obviously like straight pipes. I don't think i remember a Cottrill engine with a bustle tailpipe. Is it just an affectation or some theory about pipe shape?

You might as well call it an affectation, since I do like the way that looks, but there's a practical aspect, too: Many scale jet models will need a pretty tight tail end to be truly scale, and you still have to have plenty of cross-section back there to get the cooling air flow moved out. It's a shame to ruin the sideview profile of a nice airplane by broadening the tail end. Some planes, like my unfinished F-104 Starfighter design, have plenty of rear-end cross-section, of course. And, there's another practical reason: ease and cost of construction. Most engine designs are, in my view, almost absurdly complicated. Look how much discussion recently went into describing precisely how to build the intake skirt properly for the Chinese! I want something that goes from the drawing board to the test stand simply and cheaply. In this case, I was willing to draw up a design with a front end that I'm not tooled up to build, and now I'm glad I did. But, darn it, I don't want it much more complicated than that, if it turns out to already work well. I want a machine that's easy for you if you want to build it, and cheap if you want me to build it and sell it to you. Not sophisticated, but the kid flipping burgers for a living will thank me for it, by gladly buying it off the shelf instead of the pretty Zannin sitting next to it.

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Re: Focused wave engine runs!

Postby Mike Everman » Sat Sep 25, 2004 11:54 pm

Mike Everman wrote:I analyzed the video, you're sitting at 260 Hz. Fabulous! One of the main reasons I've been so interested in the Chinese style layout. A Locky this long, 26", would be 370 Hz, give or take. SNIP


Yikes, quoting myself...;-)

I just thought I should mention that this 260 Hz is just about right if you consider this engine being a "folded Locky"; that is, add up the acoustically corrected length from intake to closed end, and from closed end to tail exit, which comes to 36" or so.

Faaaaascinating. In light of this, I'm eating my words about it functioning as a 1/4 wave tube; it's nothing of the sort, but it does have the happy circumstance of overlapping acoustic paths which make for amplification of the pressure highs and lows near the closed end, and therefore it's more forgiving of the straight pipe exhaust. I suspect it is also why it's so easy to start.

Comments? Was this all discussed in the volumes that preceded this thread? If so, apologies, I wasn't able to pay as much attention to the development as I would have liked...
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Re: Focused wave engine runs!

Postby steve » Sun Sep 26, 2004 12:05 am

Larry Cottrill wrote:Yes, EVERYONE wants to know what you get for thrust. Again, I would emphasize, though, that it means more if measured in lean running than in cranking it up to the max. The weight seems pretty good to me - it's over a pound and a half, but 3 ounces of it has got to be the spark plug!

The cones look absolutely great! I have sent you an email with my shipping address, etc. I wish you would explain to us how you do that superb rolling on these tiny pieces. They look so absolutely round, with no 'flat zone' at the edges where they come together! What kind of rig does that? How long does it take to run them through, and is it accomplished in a single pass or many passes gradually working up to where it almost closes? How were the pieces initially cut? Did you happen to try rolling one with the oval hole already cut through, as I suggested earlier?

In any case, it looks like beautiful work.

L Cottrill



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. once they are welded I hammer it a whole bunch more untill it is as round as I can make it. It took me about 20 minutes to cut out each shape from the flat sheet metal, and another 25 minutes or so of hammering to make it into a cone. The cutting was done with a large shear and with smaller handheld shears for the curves- think dull scissors cutting through steel. I havn't tried rolling with the hole already cut but I definately could- it wouldn't interfere with the shaping process whatsoever.

BTW the spark plug weighs 1.4oz and it is not really as big as you keep hinting- its just that the engine is so small!
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Re: Focused wave engine runs!

Postby Mark » Sun Sep 26, 2004 12:40 am

It might be fun and funny to use a really large spark plug and dwarf the engine for comic effect. I've posted this before, but imagine a 3/4 inch NPT spark plug on a Craft Jet. The one the right is a 1/4 inch 32 thread spark plug.
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Re: Focused wave engine runs!

Postby mk » Sun Sep 26, 2004 9:14 am

CONGRATULATIONS to you two Larry and Steve!!

Really impressive work...from a thesis to working engine...

I'll follow your work with a lot of interrest, but I don't have a lot of time, so don't espect me to hang into every discussion.

I wish you two the very best!
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Re: Focused wave engine runs!

Postby hinote » Sun Sep 26, 2004 3:34 pm

Mike Everman wrote:I analyzed the video, you're sitting at 260 Hz.

I just thought I should mention that this 260 Hz is just about right if you consider this engine being a "folded Locky"; that is, add up the acoustically corrected length from intake to closed end, and from closed end to tail exit, which comes to 36" or so.

Faaaaascinating. In light of this, I'm eating my words about it functioning as a 1/4 wave tube;


I'm not sure I agree with your statement, Mike.

In a previous post I used a value of 263 Hz, derived by assuming a 1/4-wave (closed-end) resonance and assuming an acoustic temp of 300 C.

I don't have enough analytical skill to make a judgement on this, so I'll have to trust somebody else's observation.

Bill H.
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Re: Focused wave engine runs!

Postby Mike Everman » Sun Sep 26, 2004 5:50 pm

Yay, I got someone to talk about the frequency! I was about to say: "tap tap, is this thing on??"

Bill, I've changed my opinion on this a few times. Possibly both ways of looking at it are correct?
Mike
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Re: Focused wave engine runs!

Postby hinote » Sun Sep 26, 2004 5:54 pm

Mike Everman wrote:Yay, I got someone to talk about the frequency! I was about to say: "tap tap, is this thing on??"

Bill, I've changed my opinion on this a few times. Possibly both ways of looking at it are correct?


I'm currently looking at it as a 1/4-wave (closed-end) resonator, with a half-wave intake riding along in synch.

We won't know until we can get something fancier than Uflow to analyze things. (??)

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