www.pulse-jets.com

I just got this one built, but so far have not been able to get it to sustain at any length I've tried. The 750mm length shown in the drawing is definitely not right.

This engine is slim in cross-section, but very blunt-nosed, as the chamber is an ordinary 2 x 4 inch electric switch box. One problem with this engine [and a possible cause of tricky starting] is that the chamber confinement value is very low. It's possible that I should have used 1-inch EMT conduit or maybe even 3/4-inch EMT for this design, to get the confinement up to a more reasonable level. I DO get good roaring out of it, though; it just refuses to sustain. Of course, this has been the story with all of the Elektra series, so there may be some tailpipe length that will get it working once I get the starting air just right.

Note that one other oddment is the fact that the tailpipe protrudes slightly into the chamber, rather than being smoothly nozzled. This possibly could also have profound effects on starting and running, I suppose. It is certainly different from my normal practice of trying to get the smoothest transition I can from the chamber into the pipe.

The reason I built it this way is so I could re-use the intake / tailpipe assembly scavenged from the deconstruction of the original Fo Mi Chin engine, which refused to sustain until it was lengthened to the absurd value of about FOUR FEET overall. You will recall I tore it apart to used the chamber for the vastly superior Fo Mi Chin II, beloved of Bruno. The present engine was very easy to build, since all I had to do was file a big "keyhole" in the rear end of the chamber, weld the pipe assembly in, weld in a spark plug mount and finally weld the solid cover on the top. Then, add my trademark starting air / fuel pipe, of course. Nothing to it, really, all easy smithing and welding done basically in one afternoon.

Anyway, here it is, as originally built. It has been both shortened and extended from the length shown. I am presently working on a larger variety of extensions for the 1.25-inch OD tubing, so that all practical tailpipe lengths can be achieved with some combination of the engine and one or two extensions.

L Cottrill

it looks as though you may need to pinch the intake and exaust a little to get it to run, but then again it may run fine as is. I really like how the sparkplug is positioned!

steve wrote:it looks as though you may need to pinch the intake and exaust a little to get it to run, but then again it may run fine as is. I really like how the sparkplug is positioned!

The intake is actually pinched out in the straight part, due to later experiments with the early FMC engine, so it's no longer the smooth cylinder that this early photo shows.

Yes, I was surprised to find that modern switch boxes [at least the ones from Menards] have a big 'dimple' with a threaded hole stamped near one end - not at all what I remembered! So, I just filed out the hole with the needle file until I could assemble a bolt and nut into it and welded in the nut as the plug mount. I really liked that orientation. But, the plug could be put in the end of the box and would work fine of course, and it would give the engine a more 'streamlined' look, perhaps. You can just barely see the plug mount out of focus at the far end of the upper surface in the 'keyhole' shot.

L Cottrill

Larry, have you made any more progress on this engine? I know you are getting sidetracked with the new FWE derrivative but you can't leave us hanging with this design! I look foward to hearing more!

Steve, I'm sort of stalled on it - limited time, the other FWE project, and maybe the Paralysis of Analysis. Another thing I've done is build a range of 'snap-on' extensions of the 1.25 OD tubing, so just about any practical length can be built up.

One problem is, I don't want to pinch the pipe quite yet. I had a lot of good buzzing at a lot of different lengths. It occurs to me that this is similar to the situation I was in early on with the Elektras, and then it turned out I needed to back way off on the starting air to be able to tell what I was doing with the length adjustment. I'll say it again: I think the number one problem with people not getting their valveless engines to start is trying to force TOO MUCH air! On this engine, I use the same kind of air/fuel pipe setup I used on the bigger-chambered engines, and I was trying to use the same level of air flow - but, maybe that's just wrong! I need to go back to the beginning and use much lower air pressures, just to see if that narrows the range of what lengths will buzz. That could be the whole problem, all along. But, there's no way to know without a lot of trying.

I'll get back to it, someday soon! I really like the concept and style of this little engine. And of course, it may in fact be that the confinement really is just too low with the full 1.25-inch pipe - that's a pretty big leak for such a small volume chamber! Same story with the Henri engine, another design that I'd really like to prove will run.

L Cottrill

Larry Cottrill wrote:And of course, it may in fact be that the confinement really is just too low with the full 1.25-inch pipe - that's a pretty big leak for such a small volume chamber! L Cottrill

NO. No. Larry.
We have working examples with just a straight pipe. Can I suggest you try for a similar length relationship as Ed's straight pipe motor? The solution can then only be diameter relationships. Try reducing the induction pipe diameter and try a Rossco injector. Use the sparkplug for ignition and no starting air.
Regards
Graham.

It would be funny to post a no-weld plan for a straight duct don't you think? ha
Mark

Finally got my roll of film processed, so we have a few shots of what she really looks like.

L Cottrill