Roaring Becomes Elektra

[larry cottrill]

It runs.

It is the first Cottrill designed engine ever to self-sustain. It ran without spark or added air for something less than two minutes. I think the only reason it died was that I was leaning out the fuel flow little by little, and apparently cut it down a hair too much.

However, it is not quite as envisioned. For this engine to be anything more than a science fair project, it needs a LOT of work.

BASIC FINDINGS -

I managed to get sustained operation using a not-quite snug fitting sleeve set up for a tailpipe length of 35 inches, or a total engine length of 38.5 inches from front wall to exhaust port. Starting is relatively easy at this length, if you have the propane set anywhere near correctly. This was without the intake turbulator, and with an intake pinch of approximately 0.5 inch minor axis width, only slightly flattened from a true elliptical section. The polyethylene intake flare was in place, as in the last test series. Air supply was the leaf blower, but it worked fine with its nozzle several inches away from the intake flare. There is no question in my mind that a thin stream of compressed air would have worked just as well, but I didn't have time to try it. Fuel feed is still just a crude 1/8-inch OD copper line spilling propane at a point about halfway down the intake pipe.

TEST METHOD -

I stopped at Menards on my way home today, looking to buy a short piece of larger conduit to use as an extension sleeve. This was too heavy and expensive, and there were only ten foot lengths available. What I did find, though, was a wonderful piece of stuff: 1.25 inch OD TV antenna mast. This is painted mild steel tubing, perhaps 1/20 inch in thickness. A hacksaw cuts it almost like paper. I cut two extension sleeves, one 15 inches long and the other 22 inches long [the original tailpipe length]. This slips over the 1-inch ID conduit tailpipe with just enough gap to prevent binding up when things get hot. In my first tests, it kept creeping longer as I tried to run the engine, but was easily tightened by deforming it to a slight ellipse with ordinary pliers. That having been done, I could position the sleeve with ease and get it to stay put.

Various lengths were tried with not much variation, at increments of a couple of inches. When I finally got out to 28 inches, it became apparent that good roaring could be obtained with the leaf blower a lot farther back from the intake flare. Obviously, a good sign. By the time I got out to 32 inches, I ran out of video tape, just as I thought things were starting to get good. Also, I only had a few minutes left to mess with it. So, I decided to keep going for a couple more small increments before folding it up for the day, even though I couldn't tape any more.

When I increased the tailpipe length to 34 inches, I knew it was going to run, because suddenly, the exact aim of the leaf blower was no longer critical! About anything you could do with it about 6 inches out from the intake would get roaring operation, as long as enough propane was going in. I increased it just one more inch and tried again, and knew for sure that I had it. You could just tell. I just moved the blast of air off of the intake and shut it off, and there it was. Next, I lifted the brick off the doorbell button that runs the Model T coil [crude but effective] and unhooked the spark leads. I was able to gradually lean the mixture out little by little, getting smoother and quiter running until it finally quit.

DEFICIENCIES NOTED -

TOO LONG - How can an engine with such relatively small explosion volume need this kind of length? It's ridiculous -- there is just no way this engine should have to be this long. Of course, there is some chance that a solid tailpipe [vs a slightly leaky sleeve] would behave properly at a significantly shorter length.

EJECTION FROM INTAKE - There is a LOT of ejection from the intake pipe. It is not uncomfortably hot a few inches out, and was not hot enough to cause even the slightest dulling of the plating that is still on the intake tube. It did, however, start to melt the polyethylene 'flare kit'. This does NOT bode well for validation of my design theory re the extended intake with carefully angled cutoff in front of the tailpipe.

WEAK EJECTION FROM TAILPIPE - Although the noise from this engine is unbelievably good [so much like the Dynajet I swear I can't tell the difference] the output from the extended tailpipe is INCREDIBLY weak. When I put my hand back there about a foot behind the extension, I was totally disappointed. The leaf blower does better than this! Of course, again, this may have something to do with the slight leakage of air around the extension sleeve.

PROBABLE MODE OF OPERATION - I believe that the engine in this configuration is operating as an abysmally tuned Lockwood; or perhaps, this is the normal mode of operation of a Chinese. NO WONDER they have that intake pointing rearward! At any rate, that seems to be the mode right now -- alternating exhaust gas and air through the intake pipe, with the alternating blasts from the tailpipe running a poor second.

FUEL FEED - Unless someone thinks there is a serious flaw in mixing leading to the poor operating characteristics just mentioned, there is nothing obviously wrong with this crude type of fuel arrangement -- vapor injection in the midst of the intake air stream. Of course, I should try operation again with everything the same but with my turbulator back in place, just to make sure. And of course, more complex fuel arrangements could be tested, as well. It should be reiterated that the reason I use this method is so that a standard regulator and needle valve can be used to finely adjust and maintain the fuel flow.

INTAKE FLARE - Since the flare was distorted and actually ended up with a hole melted in one side, I removed it for the final test. Now, though the engine could be made to roar with boosted air, the aim of the blower was very critical, and it was absolutely impossible to get sustaining operation back again. So, thanks, Mike! Yes, folks, that flare IS important!

HEATING - During the self-sustaining run, absolutely no red hot zones were observed. This was afternoon daylight, not dusk [as when the last photos were taken], so maybe that just wasn't a long enough run for it to be visible. It seems to me that as hard as this mill was running, there should have been some observable heating, as in the Dynajet. Of course, the Djet is stainless and the shell is probably a sixth or eighth as thick as the parts of Elektra I.

TRYING TO RUN SHORT - As predicted by Rossco and many others, running with a short tailpipe was futile. What I was able to get, interestingly enough, was a kind of loud low growl -- a sort of "sub-roar" that didn't come close to being able to sustain. That was a tailpipe cut down to 15 inches, with the total engine length equal to the full length of the Dynajet tailpipe section. The sleeve used for the more successful tests was slipped onto this very abbreviated tailpipe.

I have to leave now, for church music practice. When I return in a couple of hours, I'll reveal The Weirdest Observation Of All.

Stay tuned.

L Cottrill

[milisavljevic]

DELETED.

[Anthony]

Congrats Larry! Just keep working on it, you did a lot these last weeks! I'm sure you will achieve your first goals pretty soon.

This weirdest observations sounds good to me hehe.

[Mike Everman]

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!

[larry cottrill]

Thank you, M and Anthony! Now, fasten your seat belts for what I'm going to say next -- you're going to swear I'm making this up, but I think it could be a very important bit of knowledge, somehow:

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.

There. I've said it. Now, of course, it does care about the length in terms of how hard it will pulse, how much air you have to push in, and whether it will self-sustain -- but it doesn't care about the length in terms of operating frequency, once true pulse combustion is achieved. Though I have seen this engine pulse only a few times, and only once self-sustaining, I have seen strong pulsing operation throughout a wide range of engine lengths; easily enough variation to cover more than half an octave of frequency variation -- but it doesn't happen. It also does not seem to increase in frequency as it heats up [although this may be deceptive, since I'm used to hearing the Dynajet, which changes temperature very quickly after startup].

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 ...]

Obviously, altering the engine enough to run as my theory predicts it should might completely change this characteristic. I have no idea whether any builder of a "Chinese" type engine might bear witness to anything like this from similar experience.

What it amounts to is, right now, the acoustics of the chamber-tailpipe combination don't matter. The only function of the tailpipe is to set up a workable mass to achieve proper compression to support the cycle. I have never read of anyone coming to this conclusion concerning any other pulsejet geometry. It makes me wonder if a VERY long tailpipe could even set up a condition where the engine would self-start without forced air, say by just starting the spark and goosing it with a rapid opening of the fuel valve. Who knows?

For an engine to run as I envisioned, some changes to the chamber/intake geometry would need to be made. I already have some ideas in mind. I won't do those in this model, however. In the next week or two I'll try to create some video to demonstrate the claim being made here, so everyone can evaluate it.

As far as the Elektra I prototype goes, I think the only immediate change will be to provide a permanent intake flare before further testing.

Again, thanks, gentlemen!

L Cottrill

[Bruno Ogorelec]

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 ...]

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 – 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?

[Bruno Ogorelec]

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.

[larry cottrill]

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 – 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.

Bruno -

Thank you for the kind words. Thank you also for a couple of years of correction, comfort, rebuke and encouragement. I don't get around to thanking people enough for what they do and say here.

I woke up this morning with several answers, and with THE answer. You won't like it. M won't buy it. Rossco won't believe it. Others will think the old guy's finally gone over the edge. But here it is:

Almost the entire reason this engine is behaving as it is, is because I have gotten the main body in resonance with the front end by reaching the 3/4 wavelength node. This engine was not intended to run at a length of approximately 39 inches -- it is made to run at a total machine length of THIRTEEN INCHES.

Why is the tail end so weak, and the intake blast so strong? The tailpipe impedence is about three times what it should be. Why is there such apparently good, high noise oscillation, but little output power? Most of the energy is being consumed by excessive harmonics that fail to contribute power in phase.

Yes, there are several things that are less than optimum. I'm pretty sure that the intake pipe could/should have been smaller, for higher impedance in relation to the body. That could be corrected just by pinching more of a venturi into it. This also means that the cold mass in the intake is relatively large, which would help explain its power to control the cycle, rather than deferring to the influence of the tailpipe. The tailpipe is acting more like an auxiliary wave source, once it reaches resonance. I would not be surprized if I could build a steel 'forced jam jar' comprising the chamber and intake pipe alone that would oscillate at exactly this same frequency with sufficient air input.

I obviously need a permanent inlet flare. The failure of the front end to operate according to the design theory is almost certainly due to the bad impedance match -- if the tailpipe were opened up, the rearward flow would dominate, and the blast would slip past the intake, just like it did when I was blowing lots of air in. But the absolutely dominant number one fact of the case is that I'm half a wavelength too long. The frequency is almost exactly the starting frequency of the Dynajet, which is less than half the length I've arrived at.

It's the classic case of amateur valveless design: Lengthen the pipe until it roars! Then sit back and wonder why the power is such a trickle of what it should be; a 'hamster breathing through a straw'.

Cutting Elektra back to 1/4 wave resonance will give me a 3.5 inch combustion chamber with a 9.5 inch tailpipe. IMPOSSIBLE proportions.

But I'll bet it runs.

L Cottrill

[Rossco]

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.
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.

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.
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.
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!

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!

Rossco

[larry cottrill]

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!

Mike -

Thank you, sir! Thanks also for all your great input on the forums. There really is a wealth of knowledge here, and it's always a privilege to be able to turn on the tap to draw some. Sorry I missed your post on my first pass through the thread this AM.

Note my response to Bruno -- you'll probably want to take back everything you've just said ;-) Except, maybe about the fuel feed.

With the present fuel feed I have, the starting is so easy [once the length of the pipe is sufficient] that I really don't feel like there's much improvement needed. I think the only reason the intake pipe isn't being skipped over by the blast is because of the awkward impedance match between the intake and tailpipe. If that were corrected, I'm sure it would work just like when I'm driving air in.

Incidentally, there certainly seems to be a strong validation of what you observed in terms of ram air overcoming the forward blast through the intake tube while the cycle is maintained. I could run this thing all day that way, if desired, with practically no observable change in how it operates. In my case, it would be interesting though to see how that affects what gets out the tailpipe! It would be hilarious [and important] to find out that with a little ram air going in, the tailpipe output becomes a mighty blast that could actually be used for propulsion. One can always dream.

L Cottrill

[Mike Everman]

HERESY! Just kidding. I can't wait to see how short you can get it. All this frequency and wave talk has my head hurting. I think you need to consider that with intake and exhaust pointing in predominately the same direction puts an acoustic pressure antinode on the far wall of the CC. I think this has the effect of making the CC seem twice as long vs. when they are in-line.

[larry cottrill]

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.

Thanks much, mate! Sorry I missed your post until late last night, when I was just too tired to answer.

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.

That's the way to do it. I figure I wasn't put here to solve equations ... I was put here to solve engines ...

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.

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!

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.

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.

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!

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.

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!

Rossco

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!

Thanks again for your kind words and suggestions!

L Cottrill

[larry cottrill]

Last night I attempted to duplicate the success of a few days ago, in order to get some video of it running. To my chagrin, I was not able to get sustaining operation, no matter what length I tried.

There were a couple of basic differences between this and the other day. That day was moderate and dry. Yesterday was in the 80s [degF] and unbelievably humid, all day [fog in the morning, etc.]. But I think the most basic difference, actually, was that the other day I was starting out with the intake flare in perfect condition, and ended up with it somewhat deformed and VERY leaky [a couple of fair-sized holes melted through]. I have a feeling that, at least on my engine, having a smooth flare going in may be extremely critical. I will not try again until I have that problem solved in some permanent way. The degrading of the flare may, in fact, be what ended up killing that good run.

I also tried the engine in its severly cut back form, settling on a total length of 15 inches, tip to tail. While not promising, the testing of such a shortened version is fascinating. The best I could get is by running very rich, and comes off as a deep roar [maybe 10 hz or something] with an occasional high whine [who knows - maybe 500 or 600 hz]. Of course, this was with plenty of forced air driving it, and yes, the highly defective intake flare.

Altogether I messed with it for about an hour and a half. This time, it was more of an overcast dusk kind of lighting, so the flame action could be clearly seen. When good pulsing was happening, the ejection from the intake was a blue conical feather, not filling the pipe [as in the Lockwood photos we've all seen] but rather, coming up through the center. At those times, the tailpipe gets very hot but there doesn't seem to be flame emerging from the end of the pipe. Again, I think the impedance is far too low at the intake, so that's where all the action is. This is not what I observe in trying to run the engine short, however -- it all comes out the tail there, but of course that's under extremely forced conditions.

All in all, not much accomplished, and very poor grade video due to the very limited light conditions. I should be able to post a minute or two of video from the other day, when she was first starting to roar, maybe this weekend or Monday.

L Cottrill

[mk]

CONGRATULATIONS to you, Larry!

Larry, in other words, you are saying that the intake determines the frequency while the tailpipe determines the amplitude.

In my way of thinking it should be opposed.
In a minimum of words:
The tailpipe/ exhaust has the main (but NOT the only) influence onto the operating/ resonance frequency and the intake determines the amplitude, by having the main influence onto the engines breathing cycle.

[Bruno Ogorelec]

I must say I have often toyed with the idea that the intake tries to determine the frequency. It is up to the designer to adjust the tailpipe to suit. The more the exhaust fits the intake, the better the engine. Just look at the comparative sizes of intake and exhaust opening on a Lockwood. The exhaust looks like an afterthought. In the Reynst, there is no exhaust. It has withered away, leaving only a big intake that does both jobs. But, this is mostly a semantic issue. The engine does not care what name a particular orifice will have.