Roaring Becomes Elektra

Moderator: Mike Everman

Postby larry cottrill » Fri Jul 16, 2004 12:28 pm

steve wrote: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).

Steve -

This is a good question, and I'd like you to go to the web log and post it as a comment on the Intake Pipe Detail Drawing article there:
http://www.elektra1.blogspot.com

The short answer is, I don't see why another arrangement won't work just as well as mine. The important thing, I think, is the fairly large flare. That could be made in some other way, of course, like flaring the tube end itself. As long as you get it flared out to about twice the ID of the tube, it should work fine.

One reason I made mine the way I did was that I thought there might be the possibility that a strong burst of propane directed down into the chamber would make it self-starting without supplemental air. That doesn't seem to be the case, however.

L Cottrill
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Attempted Thrust Measurement

Postby larry cottrill » Tue Jul 20, 2004 1:10 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, last night I tried this. It turned out to be one of the most frustrating and difficult times I've had so far in getting a pulsejet to run.

I learned one thing that is nice to know: It is possible to start Elektra I with air from my shop vacuum. I was able to get it running by using the nozzle of the vac practically right up against the intake flare, and then just backing it away fairly slowly after good firing started up. However, rightly or wrongly, I convinced myself that it wasn't running up to full power, so I went back to the leaf blower and never saw it self sustain again for the next couple of hours.

Of course, I had grand plans of getting a five minute run with measured thrust and measured fuel consumption. It was close to 90 degF in late afternoon with very high humidity. I set up the bathroom scale in the driveway, locating it carefully so it showed level with a spirit level. I weighed the propane tank and recorded the weight, then set the concrete block on and clamped the engine stand to it with the C-clamp. After attaching the fuel hose, I recorded the total dead weight as 31.0 lb [it's not a whole block, maybe 2/3 of the whole]. I managed to remember to get a photo of the setup at this point.

I figure I can read the bathroom scale, with care, to the nearest quarter lb, though values need to be taken with a grain of salt, since the scale hasn't gone back to the US Bureau of Standards for calibration for a few years now ;-)

I decided right away to give the shop vac a decent try, and after much trial and error got it to work when I held it in close enough. This resulted in a fine smooth run, with no perceptible variation in operating frequency, as previously reported. However, the scale showed only about a pound of increased loading, no matter how much I fiddled with the needle valve setting! Very disappointing, needless to say. Though the run seemed nice and loud, I jumped to the conclusion that either the engine was 'running light' [i.e. not at all 'pumped up' as our friend Rossco might put it] OR that an astonishing fraction of this engine's energy is devoted to driving gas out the intake [at a highly ineffective 60 deg angle to the intended thrust line]. At any rate, it didn't amount to much.

Note that the present configuration is still a 1-inch [25mm] ID tailpipe about a foot long with a 35-inch long 1.25 inch OD thin-walled sleeve slid all the way over it, for a total length of 38.5 inches [1 metre for all practical purposes]. Note also that output from the intake is significant. When you get your first explosions during starting, the impact into your air supply feels to your hand almost like the recoil of a small calibre pistol. This is especially observable with the shop vac nozzle, but can be felt even with the vastly more massive leaf blower in hand. Also, when the engine is running, you can feel quite a push a few inches away from the intake, as well as observable flame up through the center [of course, my fuel arrangement may be feeding this flame, especially at the low fuel pressures I use]. The output is not dangerously hot, however, so there must be a fair amount of fresh air content being kicked back out.

At any rate, I made the decision to use the leaf blower from this point forward. Try as I might, I never did get more than a few seconds of good pulsing combustion at any time, and it never would carry over into sustaining operation. I recognized at one point that the Model T coil was sounding pretty weak, and re-charged the battery, but while I now got easier bangs and roars, I still couldn't hit that 'just right' condition where it would take off and keep going. I had to stop when I got low on propane and vapor pressure, with ice all around the base of the tank.

When I finally gave up on it and disassembled everything, I found to my amazement that the scale was still reading 30 lb, with nothing on it! I tried stepping on it a couple of times and found that it would only swing up slightly and hang, then drop back to 30 when I stepped off. After shaking it a bit, it fell back to 0. When I then stepped on it, it zoomed up to about 50 and stopped. Now friends, I knew I had lost a lot of sweat out there, but surely not two thirds of my former weight! I tried shaking the thing fairly briskly in various positions, and managed to sift out a fair amount of dust and sand-like crushed rock particles of various grades. This restored the scale to normal operation. So, that was it -- my use of the blowers had caused infiltration of dirt into the scale mechanism, effectively blocking it! So, was this already happening by the time I got those first smooth runs? I'll never know.

Obviously, the crushed rock driveway is not the ideal place to try this kind of measurement, with the tools available -- just another of the many technical shortcomings of the Cottrill Cyclodyne Corporation's Propulsion Laboratory. I may try it again with the scale clothed in clear plastic to keep it clean, unless I manage to get some better equipment put together in the meantime.

What was the starting problem, really? I found it oddly awkward to work with the engine set up in a vertical position, possibly because this setup forced me to use the blower left-handed. I wonder, too, if there is a tendency for the engine to flood with vapor in this vertical orientation; I seemed to get the best bangs after shutting off the fuel for a while, allowing the blower to purge the machine. Or, could the extreme humidity be contributing to the problem? Or, all of the above? Hard to say, especially since I did manage to get a good start [though possibly not a full-power run] with the shop vac with relatively little experimental effort.

L Cottrill
Attachments
ElI_thrust_test_setup_crop1.jpg
The attempted thrust test setup -- the black platform at the bottom is the scale. Note genuine Iowa corn beyond. Photo Copyright 2004 Larry Cottrill
ElI_thrust_test_setup_crop1.jpg (73.23 KiB) Viewed 5448 times
Last edited by larry cottrill on Tue Aug 03, 2004 6:28 pm, edited 2 times in total.
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Postby Bruno Ogorelec » Tue Jul 20, 2004 1:34 pm

Larry,

This is one of the funniest pulsejet stories of late. My commiserations. But you seem to be progressing no matter what, which is the main thing.

Keep on! The world is watching.
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Postby Mike Everman » Tue Jul 20, 2004 2:45 pm

I think it's a little bit of everything, but mostly humidity keeping you from sustaining. As to thrust, I don't trust the scale approach for values of 1lb resolution, though 1 lb sounds right for this engine. As a sanity check, test the thrust of your leaf blower with the same setup. You'll get a couple of pounds. Then try blowing off your driveway with Elektra.

I don't know what you were expecting my friend, but a pound sounds pretty good for a bit of straight pipe and an electrical box.

You need a system with much less friction in any case, like the one you posted a while back. I'm building one like you designed with a blade pivot instead of bearings.
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Postby larry cottrill » Tue Jul 20, 2004 3:38 pm

Mike Everman wrote:I think it's a little bit of everything, but mostly humidity keeping you from sustaining. As to thrust, I don't trust the scale approach for values of 1lb resolution, though 1 lb sounds right for this engine. As a sanity check, test the thrust of your leaf blower with the same setup. You'll get a couple of pounds. Then try blowing off your driveway with Elektra.

I don't know what you were expecting my friend, but a pound sounds pretty good for a bit of straight pipe and an electrical box.

You need a system with much less friction in any case, like the one you posted a while back. I'm building one like you designed with a blade pivot instead of bearings.

Mike -

I dunno ... 1 lb seems pretty weak to me for a pipe with a full inch ID [better than .75 in^2], especially when the noise seems really strong. Of course, noise is both largely subjective and highly non-linear in terms of personal observation, especially through earplugs and sound muffs.

Yes, I originally thought of showing a blade bearing, but I wasn't confident of how it would do after some wear. They make a really good low-friction bearing, though the total swing has to be limited to make them workable. No problem in this case, obviously.

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Re: Attempted Thrust Measurement

Postby jmhdx » Fri Jul 23, 2004 6:57 pm

Larry Cottrill wrote:What was the starting problem, really? I found it oddly awkward to work with the engine set up in a vertical position, possibly because this setup forced me to use the blower left-handed. I wonder, too, if there is a tendency for the engine to flood with vapor in this vertical orientation.

L Cottrill

I have a poor but promising start to a pulse jet that only runs when in a vertical position, can't think which law of physics does this. Humidity is a killer with a poorly running pulse jet but when fine tuned it should't be too much of a problem. Don't be dissapointed with 1lb of thrust, it's probablly as much as I have ever achieved, you need a more accurate scale and hopefully you can squeeze every available ounce out of the Elektra by tweaking here and there. The lessons learnt in overcoming these problems will result in a much advanced engine in time.
Mike.
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Postby steve » Mon Jul 26, 2004 6:50 pm

Roaring became electra again:

I completed my electra and fired it up yesterday and disrupted a neighbor's family reunion in the process. He didn't care though and in his words: "I'm so used to it that I don't even hear it anymore"

anyway, the engine started up after about 30 sec. of poping and caughing. As larry discovered before, it will only run when it is hot.

I also found that having the injector (brake line) at a 90 degree angle to the airflow in the intake works slightly better then when it is at a shallow angle. throttleability was decent but I haven't tested it in the lower throttle settings yet.
Attachments
DSC01358.JPG
I used the "reccomended" cut on the intake and fabricated a sheet metal flare rather then a cement one.
DSC01358.JPG (151.41 KiB) Viewed 5619 times
DSC01360.JPG
Nice sturdy stand.
DSC01360.JPG (143.94 KiB) Viewed 5620 times
Last edited by steve on Tue Jul 27, 2004 7:21 pm, edited 1 time in total.
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Postby mk » Mon Jul 26, 2004 7:01 pm

Congratulations (again), Steve!!

Steve wrote:I completed my electra and fired it up yesterday and disrupted a neighbor's family reunion in the process. He didn't care though and in his words: "I'm so used to it that I don't ever hear it anymore"



Lucky you!!

One neighbour of mine doesn't like my propulsion work, so I cannot test as much as I'd like to sometimes. The other ones are very tolerant, as long as I don't test early in the mornings, late at evenings or at nights and at the weekends, at least on sundays.
Could be worse, I think.
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Postby Mike Everman » Mon Jul 26, 2004 7:05 pm

Ohmigod, there's an Elektra club forming! LOL ;-P
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Postby Bruno Ogorelec » Mon Jul 26, 2004 8:22 pm

Mike Everman wrote:Ohmigod, there's an Elektra club forming! LOL ;-P


Don't you dare use any Carmen Electra pictures for the club! I hereby stake the claim on the use of her pictures in connection with pulsating jet engines. Whoever breaches this claim, his spine will turn weak, hair will grow on his palms and he may actuall go blind after a while.
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Postby Mike Everman » Mon Jul 26, 2004 8:46 pm

"Whoever breaches this claim, his spine will turn weak, hair will grow on his palms and he may actuall go blind after a while. "

Is that what happened to me??? I knew I should have stayed away from her...
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Steve - Send Info!

Postby larry cottrill » Tue Jul 27, 2004 12:58 pm

Steve -

Did you use the 1-inch conduit for your tailpipe, or the 1.25-inch tubing? You'd think I could tell from the photo, and I thought it looked like the galvanized conduit, but I decided I wasn't sure. It appears that you got your intake positioned a little farther forward than I did [I mean, same angle but slid forward slightly] -- if so, this is important in two ways: [1] It would prove that my claim that dimensions aren't critical is correct; [2] If it ended up this way by your carefully following my dimensioned drawing, I should re-measure what I really have and correct the dimension! [Of course, I may be imagining this, from what I see in your photo]. An important "selling point" of this design is that there are not supposed to be any critical dimensions.

I want some comments on the Web Log as to how you finished up your Elektra I and got it to run. HOWEVER: I want to set you up as a member who can post, rather than just inserting this as a comment to one of my posts! I would have done this way before now, if I had known how. Send me your name, a login name [you might as well just use 'steve' since that's what you've used on your earlier comments] and an email address.

Then, I'll set you up as a member [now that I actually know how!] and when I've done that, I'll let you know, and you can create a new post with a title and everything. Please go into as much detail as you like -- the more you share, the more it might help somebody else.

I'll do the same thing for anyone who wants to try to build an Elektra I -- again, all I ask is that we all stay on the 'Elektra I construction and operation' topic [yes, I'll allow discussion of mods, too]. If there's going to be a club, I want the Web Log to be the place where we meet.

Steve, congratulations on getting her built and running! Thanks for going ahead with this and giving me some independent verification of the workability of the design!

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Postby steve » Wed Jul 28, 2004 3:30 am

the tailpipe is 1" galvanized conduit and the reason that the intake position looks diferent is because it probably is. To be honest, I only made two measurements during the time I worked on it (tailpipe length and intake length) and everything else was just TLAR. I basically looked at your pictures and tried to match what I saw.
Last edited by steve on Thu Jul 29, 2004 10:32 pm, edited 1 time in total.
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Postby steve » Thu Jul 29, 2004 4:51 am

for your enjoyment and/or ridicule, here is what I posted on the blog:

I had been folowing Larry's progress with the electra concept since its conception and was delighted when it was finally made to work. At the time I was working on other engines and had no intentions of building the electra. However when school let out for the summer and I was suddenly seperated from all my (their) metalworking supplies I became very bored very quick. After keeping myself occupied for a week with a small valveless engine made from short sections of pipe, I remembered the electra which could be built with no sheet metal fabrication and decided to give it a try. Luckily an industrial complex near the place where I work had some old sections of electrical conduit lying around so I was able to aquire them for free. (by the way, did you know that it can be cut with a standard tubing cutter?) I paid about $2.50 for the electrical box and another $1.50 for the cover plate at a local hardwhare store and started working. WARNING: This design requires A LOT of filing by hand so a dremmel tool with lots of bits would be nice to have. (I actually stabbed myself with the file a couple of times while working and don't reccomend it) I just learnde how to weld with the oxy torch and am not nearly as skilled as larry is so my tailpipe was attached diferently then his: I carefully filed the hole so that the 1" conduit would fit snugly into it rather then leaving a gap as was reccomended. I also filed the inside of the tailpipe so that it flared outward slightly to help channel the exaust gasses more effectively. I then began to work on the intake flare. I decided not to use the fireplace cement flare because I could just as easily make a flare from some sheet metal I had grabbed from school. the flare was small enough that I could work it by hand without too much dificulty. As long as you measured the intake length and exaust length accurately you should be alright even if all your other measurements are a little off. Just make the layout look pretty close to what you see in the pictures and the engine should run fine. After welding the intake in place I started looking for the cover plate but was unable to find it. Aparently my dad (who is an obsessive-compulsive neat freak and pulsejet hater) threw out my brand new cover plate (with the price tag still on it!). I made him get me a new one and then welded it on. (one note about welding: If you can remove the galvinization, DO SO. Grind it off or soak it in acid overnight, whatever! It is really nasty stuff when it gets hot and leaves ugly white blotches everywhere. The fumes are poisonous so only weld outside if possible.) For the sparkplug I drilled and tapped a hole in the front of the engine and simply screwed it in (this saved me some acetlyne). for the fuel injector I reccomend a smal section of 1/4" tubing that is nearly flush with the inside wall of the intake and at a 90 degree angle to it. mount it around 1.5" down fron the intake flare. I didn't make a stand for my engine but instead clamped it tightly in a vice (again this saved me some acetlyne) To start the engine turn the fuel supply (propane) on untill you can just start to hear the hiss through your hearing protaction. Apply starting air seccond and spark third. For air I used a small tank of compressed air. For spark I used the circut from Bruce Simpson's website (although model T sparking coils are also very popular among pulsejet enthusists). Do not expect the engine to burst into life imediately. Instead it should make frequent bangs and pops and sputter ocasionally. If it does this then continue to let it do so. After about 20 sec. of this it will begin to roar quietly then get louder and louder untill the engine is running completely on its own. At this point thak the starting air away and turn off the spark. If the engine dies imediately then increase or decrease fuel flow and try again. You will find the sweet spot eventually. Once the engine is running feel free to play with the throttle settings to see how high or low you can get them, but be careful as too much or too little fuel will kill the engine (although re-starting it when it is hot is much easier)

Overall I enjoyed building this engine and would reccomend it to anyone with some welding experience and some time to kill (or neighbors to anoy) While it is not the best engine for a beginer (due to its difficult starts when compared to some other designs) it could definately be done by one. (and the price is right so why not try it?)
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Postby larry cottrill » Thu Jul 29, 2004 1:18 pm

Steve -

Yes, that was a fine post, and I'll post a congratulatory response later on.

The thing I find fascinating when I read this is the incredible number of things you approached differently, but still ended up with essentially the same engine! I think that's wonderful, and is yet another part of validating the Elektra I as an easy-to build design: not only can you slop around some with the dimensions, but you can even vary the building and starting technique all over the place and still end up with a roaring pipe!

How in the world did you successfully thread a hole cut in a shell 1/16 inch thick? I about fell off my chair when I read that one -- I would never have thought of even trying it, though I have thought of doing that on pipe engines like Mark's littlest ones, with miniature plugs like the H-2/V-2 size [tap size 1/4-32 NXF, exactly like a standard US glow plug].

I'll have a lot more questions and comments after I think about your post for a while, and post my reply on the Web log. I also want to work with you on getting a picture included in your post. Do you have a Web host where your pictures can be parked? If not, just give me permission to host copies and we can edit your post so your picture of the engine in its 'Handy Mount' can appear at the top beneath the title of your post. I think a good picture at the top always provides a nice "hook" to get people to go on to read through the post.

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