Moderator: Mike Everman
Larry Cottrill wrote:The Elektra I engine, as presently configured, does NOT obtain its frequency of operation in any way from the length of the tailpipe or from the overall length of the engine. (snip) I believe that this engine, as presently configured, is able to control the frequency entirely from front-end resonance, and I am almost sure that the basic controlling factor is the "cold air column" of the intake, which is able to maintain a fairly stable temperature regardless of power being developed. True, the engine is pumped by the tailpipe "piston mass", but it is entirely controlled by the front end geometry and gas condition in that column [I think ...]
brunoogorelec wrote:Larry, in other words, you are saying that the intake determines the frequency while the tailpipe determines the amplitude. A curious idea. I cannot see a reason for that. It would imply that the frequency was set by the original layout and that your extension was ignored as an element in the acoustical chain. Yet, its existence somehow helped pump the engine up.
Could it be that your engine fails to utilize the fundamental oscillation in the combustion process and depends on some relatively high harmonics? I think that might account for a difficulty in detecting a change of frequency â€“ which must be taking place. It would also account for the obviously low energy output.
BTW. Is it possible that you have gone too far towards the lean mixture? Have you tried making it very rich?
Sorry; I was so taken by the dropping of your other shoe that I completely forgot to congratulate you on the wonderful result! Good stuff, Larry. Finally a reward after much frustration. You should really be commended for bravely sticking with designs that you knew were not very promising from the start. You are a pride of this forum. My hat's off.
Mike Everman wrote:congratulations Larry. Alright! Lots of action! Great story! I can't wait for you to drop the other shoe.
Just so you know, my latest wouldn't get close to running with a 1/8" stinger type fuel feed down the intake, but a simple tube aimed across the inlet to the CC made for easy starting. I think these two engines are similar volumes; you might try a CC mounted fuel feed. Here I am making suggestions in the afterglow of your success! Ignore me!
Thanks much, mate! Sorry I missed your post until late last night, when I was just too tired to answer.Rossco wrote:Larry, Good on ya!
Hey, i will refrain from saying to much on the length issue, tho i will say that i agree with you totaly on the driving from the front! I have been giving some very deep thought on the subject and will post in the "intake" thread very soon.
That's the way to do it. I figure I wasn't put here to solve equations ... I was put here to solve engines ...The "leaky" tail extension, from my experience, does not lessen the output at all im sorry! If anything it acts as an augmenter and increaces the output!
I do it all the time with my engines to iron out problems, and it doesnt matter how "leaky" they are. If you recall my smoke ring rambling in the New PJ design and Feedback thread, i had an 18" D pipe stuck on the end of my 3" D engine as an "extension"! I was just in one of those moods to try anything that is sitting around at the time.
Not much thought process as to the volumes. If I were to do it now, I'd have stuck with my original grab at .5 inch pipe for the intake. But if I'd done that, I might have missed all the fun of having something that behaves weirdly!I have to go over the Electra and have a look at the volumes again. I am very interested in your intake to CC volume ratio, and the thought prosses that dilivered it.
Though my experience is brief with this, I feel sort of argumentative on this one. I found such a profound difference made by the flare, that detail seemingly making the critical difference between sustaining and balking. What is usually missed in discussions of the flare is that, once the air starts to flow in, it acts as a nozzle, increasing velocity and reducing air density.Thinking of my engines, you have done remarkably well with the Electra, and in good time, considering. I could not get mine going, with any tail length, without just the right intake length! and i have previously said that i think that your intake is too long! and with that length intake the tail should be about 2 or three times longer!
May i ask that you do one thing with Electra, just for me. As my engines are similar in motion and i have had a lot of problem solving hours put into them, i am not just talking out of my ar.. without experience.
Before i put this to you, i would like to say that i dont think that the intake flare is as critical as you and many others are emphisising! ( i know that is a bold statement in here!) (it does cirtenly improve things tho) When i tuned my small engine, probably about the same volumes as Electra, i had great trouble getting the intake right. Just to add a bit of interest to the problem, it was (at first) square section steel. I got it running on this (eventualy) and it ran great! best it ever went. Well, the hardest. but anything and sometimes nothing would throw it. After that i cut the sqare section off, and welded a round intake on. This, a different volume to the square would again not run. I got it going again and had it getting a little better throttle range. Not until this time did i decide to put a flare on the intake, which didnt make it noticely different in sound, or running, but it did make it heaps easier to start and throttle. So, i think that the fact that your Electra will not start with out the intake flare, is not that it is critical, just that it is masking some tuning issues. Myself, i would try to get it running to optimise tuning without it and then put it on as a performance modification. Which brings me to the suggestion.
There is one basic problem here: The pipe is no longer a uniform cylinder, but now has a significant venturi squeeze in the middle of it. What this means is that all slices taken off from the top down would not be created equal. I really need to hack together another chamber and intake to do what you are asking. Or. cut this one off at the root and replace it with a clean cylinder. Neither is too much work, if it turns out we'd learn something important from it. It's a lot more work sawing off than welding on, at least for me.Anyway, what i want you to try for me, and every one else in the forum!
Cut that intake back, small section at a time. Dont go too far, as it gets to a point that it wont run, i cant tell you where that is sorry, but in mine with very similar volumes it was about 1 1/2" so you should have heaps to play with. Somewhere in between where you are now, and that short point is the optimum length that will give you the best starting and running. When you are doing this, cut-run-cut... the tail can be left out long. Then when your happy with the length and running, shorten the tail back to acomidate this new intake, it will shorten up quite a bit from where your at now.
I think you doing this to your engine will cause the best recorded sample that we can use in the intake and CC diameter and length threads that we are just tuching on now, because everyone here knows her so well, and you document everything so beautifuly! Thanx!
I still think the next thing to do is play with the length a bit more. It's already cut back 'too short to run' so I have to use the extensions anyway to get the sustaining mode I already found. So, I can cut back as much as I want now, as long as I leave enough of a stub to support a full-length extension. I don't mind going pack to a cylindrical intake for testing purposes, though. I could make a 'slip-on' flare out of brass or J-B Weld or something, that would just slip over the cut end, so the pipe could be shortened as much as desired. I'm betting the length of that little pipe will profoundly affect the running frequency!Just a last note on this supposedly short post, When altering the tail it does vary the frequency, but only VERY slightly, not even as much as going from minimum to maximum throttle! The front end drives it, and i tend to prove it in the other threads, so please join in. One thing that im playing with now is sticking larger diameter very long intakes in mine, trying to see if i can drop into a lower frequncy (then that would mean that were in a harmonic now) But, i doubt it, as i can "digeridoo" (trumpet) into my intake out of the test rig (Rosscog) and it sounds remarkebly similar to the engine running, and the first harmonic, is quite a step up. BUT If the engine is in 1/2 wave, and the intake in 1/4, then this may be so! (the sound from the running engine being a 1/4 of the intake frequency which is 4 times the frequency of what i am blowing?)
Ive just jumped in to way too deep water again! HELP
Mike, may i borow something! None of this is fact!
Bruno wrote:Larry, in other words, you are saying that the intake determines the frequency while the tailpipe determines the amplitude.
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