Even the Cheapest Jet Should Breathe Like a Reynst!

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Postby Rossco » Thu Apr 15, 2004 9:33 pm

So, i have to go for constant gas pressure through the blast! Thats not going to be easy! CC shape! It is a closed end chamber in the blast phase, so shouldnt be too hard to accomplish. Now that i think about it that may have been where Bruno and Gary R were going with the coned CC in their half inside intake engine, constant pressure.
The down side of this if i get velocity up will it make up for it with a loss in mass flow? This would give me a louder engine, with no more or even less thrust. The energy would be absorbed maintaining such a gas velocity. Again all speculation! Have you seen any such thing done?

(jjjjjje...xG111111234 my daughters contribution to the conversation)

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Postby Bruno Ogorelec » Thu Apr 15, 2004 10:20 pm

Great stuff, Larry! I love it!
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Postby Mike Everman » Thu Apr 15, 2004 11:38 pm

Larry, I can't wait for the proverbial "IT RUNS!" post! Good luck!
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The Rest of the Construction Photos

Postby larry cottrill » Sat Apr 17, 2004 2:48 am

Guys, here's the rough start of a WIP page for the Elektra I project. This has all the construction photos taken so far, through last Saturday's work. Lots more than I was willing to post yesterday:

http://www.cottrillcyclodyne.com/ElektraI/ElektraI.html

Enjoy!

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No Fire Tonight

Postby larry cottrill » Sun Apr 18, 2004 3:28 am

Mike Everman wrote:Larry, I can't wait for the proverbial "IT RUNS!" post! Good luck!

Mike ... I'm afraid you'll just have to wait a couple more days.

I really wanted to get the Elektra fired by sundown today, but just couldn't quite do it. I finally felt hurried to get it finished, and in this sort of thing, danger is usually spelled H-U-R-R-Y. What I did get done is get the engine mounts welded onto the lower part of the combustion chamber, and last night I worked out the first 'crude but effective' [as I always say] version of the fuel pipe. It slips in and is held by gravity alone, but seems stable enough to not be vibrating around.

Tonight's work did completely finish the prorotype version of Elektra I. Total weight is about 2.5 pounds, which I consider clinically obese, especially with a tailpipe ID of only 1 inch. A good T/W ratio will be impossible to come by. But then, I will probably be very fortunate indeed if I can even get it running.

What's left now is just making up a plank with four bolt holes and probably a thin aluminum reflective shield. I have the valve & regulator assembly and a 5-foot hose, my old trusty Model T ignition system, and one cylinder each of Propane and MAPP gas. I even came up with a nifty stand for the fuel cylinder being used, sort of a 'third hand' to prevent knocking it over. And, of course, I have the Cottrill Cyclodyne Corporation labarotory standard cinder block and C-clamp to hold it down.

Looks like the first firing will probably be Monday evening, unless somehow prevented by weather.

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Postby Anthony » Sun Apr 18, 2004 4:08 am

I hope it's gonna turn out ok! Good luck!
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Postby larry cottrill » Sun Apr 18, 2004 4:45 am

Avenger wrote:I hope it's gonna turn out ok! Good luck!

Avenger -

Thanks much. We shall see what the Lord wills for me and Elektra.

One important thing I need to do to that Web page is get a big warning box on there about welding galvanized / coated steel. That stuff is very nasty! I really had to be careful tonight, as there was no breeze at all while I was working. But, that part is finished -- the test stand will be a snap compared to what went into the engine.

Hope you enjoyed the welding shots at that new link.

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Postby mk » Sun Apr 18, 2004 6:19 pm

Larry wrote:Hope you enjoyed the welding shots at that new link.

Really nice pictures and work, too, of course! I really hope this pj will run self-sustained.

Good Luck!
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Postby Anthony » Mon Apr 19, 2004 2:18 am

Larry Cottrill wrote:
Avenger wrote:I hope it's gonna turn out ok! Good luck!

Avenger -

Thanks much. We shall see what the Lord wills for me and Elektra.

One important thing I need to do to that Web page is get a big warning box on there about welding galvanized / coated steel. That stuff is very nasty! I really had to be careful tonight, as there was no breeze at all while I was working. But, that part is finished -- the test stand will be a snap compared to what went into the engine.

Hope you enjoyed the welding shots at that new link.

L Cottrill


The Lord created the laws of the physics; success in controlling them for a certain goal is yours ;) .
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Postby larry cottrill » Mon Apr 19, 2004 3:08 am

Avenger wrote:The Lord created the laws of the physics; success in controlling them for a certain goal is yours ;) .


You're right on!

The problem is not in the laws, but in my limited comprehension.

It's not really a matter of controlling them -- it's how well I can align my thinking with them that counts. Perhaps tomorrow, I'll get to 'check my alignment' ;-)

All the best,
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First Fire -- but, nothing that would impress anyone here

Postby larry cottrill » Tue Apr 20, 2004 2:42 am

Well, I got the last 'bright and clean' photos and got Elektra I mounted on a board and clamped down, and hooked everything up. Conditions, basically cool and dry, maybe 60 degF. As briefly as possible:

Without starting air, all I got were variations on soft pops [some of which showed flame out the intake] and the 'silent blowtorch' effect. Pretty impressive visually, since it was about dusk, but no discernible power except as heat and light. Little heating of the chamber or tube.

I decided to try some air, by simply using the starting hose designed for the Dynajet. By letting the gas flow constantly and pushing the air closer and closer in toward the intake, I was able to get very definite weak pulsing. Nothing like strong explosions, however -- just a nice audible buzz that sounded like the Dynajet running far, far away.

Nothing I did came close to making me want to put on the ear muffs. When I was getting the pulsing, there was a little straight blue flame observable, and the chamber and pipe heated noticeably. There was absolutely no flame visible at the intake, but of course, I was dumping air into it like crazy to keep it going. At best, it was moderate sound volume, something like a radio playing normally in a home setting. At that point, the sound was good, though -- sharp and definite, not at all dull or mushy sounding. It really sounded like it could go, but as soon as the air was removed it died into blowtorch mode, instantly.

I think this may be the most important observation: I do not get more propane flow as I advance the regulator setting -- it plateaus out at a low flow volume, no matter how much I turn in the screw. That tells me that there is too much restriction upstream from the reg, even though I drilled out the check valve [this outfit was made from a torch head]. I thought that this would be plenty of delivery, but obviously, I was wrong -- I need to go with a full-size cylinder with a large valve and stem, for plenty of supply. The trickle of propane I'm getting just isn't adequate, in my opinion.

I do also have a cylinder of MAPP gas with the same connection, and I could try that before changing everything on the supply end. MAPP gas is supposed to be much more powerful by volume -- it costs over three times as much as propane for the same cylinder size. Most propane torch heads can't take it, although there are some more expensive ones now that are designed for both fuel types.

Any other suggestions, observations or questions?

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Postby Rossco » Tue Apr 20, 2004 11:31 am

Larry, nice work, soo methodical and carefull in comparison to myself!

When firing a new engine up i like to get a loose fitting pipe over the tail that can be slid in and out, and some different lengths that can go over the intake for a bit of crude tuning. Theres many a time that i have found issues or even interesting observations by doing this.
I know that you like to plan everything, but i have had a lot of unexpected progress by just doing some things out of the ordinary that came to me at the spur of the moment.
When you get this one going, or when you have any running can you do a quick test for me please? (or anyone try it if interested).

I have posted before about being able to get my engines going much harder by "pumping them up".
What i mean by this is get it going as hard as it will, self sustaining. While running, and hot, give the intake a sudden blast of air (as high pressure and volume as you can). At the same time crank the gas up a bit, then let it sustain at this new level. I can do it about 5 times with mine, and at a guess, i get about twice the thrust and heat level than at the highest throttle position that it would self sustain at originaly.
My theory on this is that all of my current engines have undersized intakes. By doing this to them it induces a lower intake phase pressure, and therefor suck more air, and will hence tollerate more fuel!

I would love another theory on this, or to see someone else try it!
Post it in the New PJ Designs thread as not to take over this one.

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Postby larry cottrill » Tue Apr 20, 2004 4:36 pm

Rossco wrote:I have posted before about being able to get my engines going much harder by "pumping them up".
What i mean by this is get it going as hard as it will, self sustaining. While running, and hot, give the intake a sudden blast of air (as high pressure and volume as you can). At the same time crank the gas up a bit, then let it sustain at this new level. I can do it about 5 times with mine, and at a guess, i get about twice the thrust and heat level than at the highest throttle position that it would self sustain at originaly.
My theory on this is that all of my current engines have undersized intakes. By doing this to them it induces a lower intake phase pressure, and therefor suck more air, and will hence tollerate more fuel!

Rossco

Rossco -

I doubt that you can hang this on "undersizing" of the intake [OK, maybe you can in its final condition, where you can't 'pump it up' further, but the intake must be doing OK up to that point!]. I do agree that there must be a lowering of average pressure in the suction phase of the cycle. What I mean by this is that it could be that the deepest pressure isn't lowerered further, but rather that the low part of the pressure graph is made broader in time value under 'pumped' conditions.

What I'm saying is, the pressure curve of an engine running hard may not be a vertically magnified version of the pressure curve of the very same engine running easy. There!

Whatever the exact situation is, it has to mean that you're getting a better energy conversion per cycle than at the last plateau [more work in the same period of time]. It all boils down to the momentum you actually achieve in the tailpipe 'piston' - more momentum means more thrust, but also means a more powerful draw at the front end [all other things being equal].

What this observation proves is that it is not necessary to alter system geometry to achieve stable operation at various power levels. I have usually assumed that an engine runs up [in the first few cycles] until it reaches a limiting condition where negative feedback catches up and we have a stable condition beyond which we can't go. Obviously, this is not true [in the case of your engine, at least] and that is important. It means that we should not necessarily give up on a design that sustains in a 'weak' thrust condition - it may simply be operating in the lowest stable state that we can find [or, some low stable state we happened upon]!

Remember that if your engine were in motion, the action you're describing would not involve coordination between an artificial air source and the fuel valve, but merely a careful synchronization of air- and fuel-throttling. ['merely' - ha!]

The next time you get this to work, you should see if temporarily restricting the air causes a step downward to a lower-powered stable state, and try the same with fuel restriction, i.e. is the transition air-led or fuel-led, or must it be a coordinated adjustment? Even if the theory isn't quite immediately grasped, a set of practical guidelines for how it works could be invaluable.

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Elektra I Photos: Finishing Up

Postby larry cottrill » Tue Apr 20, 2004 8:27 pm

Here are a few of the shots I just got back from the lab. I will add these and seven more to the Elektra I page a few hours from now. The BZ9 'short link' is: http://bz9.com/elektra1

L Cottrill

-----------------------------------
All right, I didn't get that page updated, after all -- I had auto troubles last night on the minivan that gets me back and forth to work. It may be the weekend before I get the Elektra I page updated. Also, as far as more testing goes, it looks like we're in for cool and stormy weather for the rest of the week, so I don't know if I'll get anything done on that front either.

You can tell you're getting old when the weather becomes an excuse for holding off on potentially world-shaking research ;-)

L Cottrill
Attachments
ElI_chamber_welding_crop1.jpg
Running weld around the cover plate to finish the chamber - the filler rod is only needed at the corners. Photo Copyright 2004 Larry Cottrill
ElI_chamber_welding_crop1.jpg (43.61 KiB) Viewed 5383 times
ElI_engine_mount_weld_prep_crop1.jpg
Jigging engine mounts for tack welding: scrap wood base, brick to level the engine body, and scrap metal flame shields. Photo Copyright 2004 Larry Cottrill
ElI_engine_mount_weld_prep_crop1.jpg (48.01 KiB) Viewed 5383 times
ElI_engine_finished_vise_crop1.jpg
All finished, with fuel pipe and spark plug in place. Engine mount weld is just visible in black zone along bottom. Photo Copyright 2004 Larry Cottrill
ElI_engine_finished_vise_crop1.jpg (54.56 KiB) Viewed 5383 times
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All New WIP Photos Now On Site

Postby larry cottrill » Wed Apr 21, 2004 11:47 pm

OK, I managed to get the minivan working again in record time, for a mere $703.50, and just now I got the Elektra I page updated with all the remaining 'under construction' photos:

http://www.cottrillcyclodyne.com/ElektraI/ElektraI.html

The next time I post pictures of Elektra I here, there will be some kind of blue flame erupting from it somewhere!

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