www.pulse-jets.com

To me that seems like a lot of extra work to avoid 1 bad welding area.

Also from my experience "spouts" or the intake protruding into the engine really kills the performance. I think if you just had a straight shot into the engine you would get at least 50% more thrust.

Super !

Looks like you are in serious production.

Ed

Eric wrote:To me that seems like a lot of extra work to avoid 1 bad welding area.

Remember, that's not the main reason. For me, that area under the bend isn't that bad - just a nice challenge in the middle of the build. The main point is to get both the tailpipe and intake FULLY hidden behind the "shadow" of the front dome, to make as compact a cross-section as possible.

Also from my experience "spouts" or the intake protruding into the engine really kills the performance. I think if you just had a straight shot into the engine you would get at least 50% more thrust.

Eric, how can we quantify that? To me, it seems that if the disturbance is in the slow part of the chamber (i.e. the front end where the area is large), that the effect should be minimal. There's plenty of room behind for the gases to flow together (re-laminate? sounds dippy) before they get into the high-velocity stream into the tailpipe. Of course, maybe I'm just ... wrong, again.

What exactly do you mean by "straight shot"? A Thermojet configuration, with a simple squared-off cut at the spouting end of the intake? Obviously that would work, but please explain if this isn't your meaning.

Ed -

What would you think of this?

You go ahead and build yours following the plan as closely as possible. I'll build mine with a pipe that stays external to the chamber until the point where it turns down in. It will not penetrate the chamber, just open inside the cone. We will both use 3/4-inch EMT for the intake, and 1.25-inch OD antenna mast tubing for the exhaust pipe, and all lengths and longitudinal landmarks will be the same. Likewise, fuel tubing should be identical size and positioning.

Once built and tested, I'll ship mine to you. You can set up a head-to-head test (whatever method you want to use) and get a machine-to-machine comparison under the same conditions, at the same location. That way, we'll settle this issue once and for all.

L Cottrill

Yes, just cutting off that folded down portion so that the pipe is protruding into the intake with the end so it is perpeindicular to the midline of the tailpipe. It wouldnt be a thermojet setup because the cone section is way to shallow, but just cutting off that spout would allow much more exhaust to exit the intake and will be capable of delivering a much greater intake charge.

Any attempt I have made to try to direct or guide the incoming air to any specific portion of the engine either by spouting or necking down the intake really takes a big hit on thrust. From what I have seen it really doesnt matter where you shoot air into the combustion chamber so long as you just get a lot of it in there with as little restriction as possible.

I am in the process of drafting up my advanced FWE plans and writing a little thing up about the various phenomona I have done battle with. I should have the plans in PDF in a day or two.

I think the original-ish FWE is just a much better way about going about it.

Eric

ed knesl wrote:OK, Larry,

From now on, no more paper engines - everything must me METAL.
That will teach you !!! :-)

Ed

Next time try air nibbler or 4in grinder with cut off wheel, in both cases
distortion will not be a problem.

If I cut in small triangular sections, I can cut some very tight curves nice & smooth with my bandsaw. I have also used the petal valve electrolosis method for cutting intricate shapes in steel up to 16 gauge. You have to scribe your lines slightly to the waste side and do a little filing to get a perfect smooth edge, but sometimes it is a great compromise.

I agree that straight pipe charging the CC is the best way, also
expansion back to intake is more efficient.

From the construction point of view, Larry's idea is pretty sound.
Perhaps make that spout as flat as possible. Your objective is
minimazing drag and it is not clear if it is good trade off for some loss
of thrust. The truth is that turbulent air would negatively effect the
intake charge and thrust. It's kind of catch 22.

Larry, so far I built CC and tale pipe and the the dome is in.
Still waiting and see approach regarding intake. I may try to run it
directly thru to CC, than we could test them side by side.

( Simultaneously I am building something totaly new based on my
Concept 4x engine ).

Ed

El-Kablooey wrote:

ed knesl wrote:OK, Larry,

From now on, no more paper engines - everything must me METAL.
That will teach you !!! :-)

Ed

Next time try air nibbler or 4in grinder with cut off wheel, in both cases
distortion will not be a problem.

If I cut in small triangular sections, I can cut some very tight curves nice & smooth with my bandsaw. I have also used the petal valve electrolosis method for cutting intricate shapes in steel up to 16 gauge. You have to scribe your lines slightly to the waste side and do a little filing to get a perfect smooth edge, but sometimes it is a great compromise.

Right !

Bandsaw is perhaps the best tool - unfortunately not too many people have it.

Electrolytic etching could be a problem on stainless steel and it is
quite slow - still good viable option.

Ed

jm & Ed -

All right, I have made my decision: I am going to build this one as a true prototype based on the drawing. I realized that if I changed it now, my construction photos would be meaningless to use on the web log, where I've gone to great care to illustrate how to build this. So, I decided that I just need to stay on track for this build. I could always try another variation later - the 28 ga steel is certainly easy enough to work with.

Obviously, anyone else is free to do whatever they wish - go for it! Just get good photos of your mods, so everybody can see what you did. I am always especially interested in mods that increase ease of building.

L Cottrill

My first hand-formed cone.

L Cottrill

Some photos of making the front end dome. This project is going really slowly, since I have almost no spare time to give to it.

The first photo shows how I chucked a 3/8-inch twist drill in my little vise and used the smooth shank as a crude mandrel to bend the conical curvature of the dome. I was even able to use this crude device with light hammering to finish the two straight edges where they come together. The second photo shows the dome welded up with the spark plug mount nut "jigged" for welding with an M10x1 bolt and a couple of extra nuts. The last photo shows the finished dome, ready to weld onto the chamber.

L Cottrill

Photos below show getting the dome put on the front end of the chamber cone.

L Cottrill

Building the tailpipe / intake assembly

I was wondering if you are left or right-handed Larry. I was trying to figure out which way I would hold the torch and rod. I'm right handed but as a child my parents said they didn't know which I was going to be. My Dad was left-handed. Looks like the engine is coming along nicely.
Mark

Mark wrote:I was wondering if you are left or right-handed Larry. I was trying to figure out which way I would hold the torch and rod. I'm right handed but as a child my parents said they didn't know which I was going to be. My Dad was left-handed. Looks like the engine is coming along nicely.
Mark

I'm right handed; Sharon and my two sons, left-handed. I always put the delicate work in my left hand, the fatiguing part in my right - like playing guitar.

The engine is actually finished - I stayed home yesterday and wrapped it up in time for a photo shoot last night for Wired magazine (what could be next - Newsweek? ;-) It refused to start for me, though it seemed really close - the length may need slight adjustment, or maybe my technique was just poor; I was in kind of a hurry.

The Wired article is basically about development of the Short Lady, and is supposed to appear in the November issue. Just a one page thing. They shot about 50 pictures but will supposedly use just one. The photographer and his assistant were highly impressed with the "original" Short Lady running. I gave them about half an hour in one run - the longest I've ever had any pulsejet engine running, ever! Easy with a propane tank fuel supply.

L Cottrill

Here's how the two main assemblies - the chamber and the intake / tailpipe assembly - are jigged up and tacked.

To jig this up for tack welding, I just set up firebrick on the garage floor and held the tailpipe in place with two more slabs of firebrick. The corners of these slabs aligned the rear of the chamber cone with the tailpipe. Side-to-side alignment of the chamber is automatic, due to the good fit of the intake pipe to the front end of the oval slot in the top of the chamber. Near the rear, I had to push the cone edges down in a bit to lessen the gap.

Note the large gaps between the chamber cone and the edges of the 'spade' - I really should have cut it closer to a full inch wide to achieve a better fit. For me, such gaps are no problem, but they are tough for beginners. Excellent for practice, though ;-)

L Cottrill