What's Wrong With M1E??

[larry cottrill]

Bill -

OK, since you promised not to knock any ideas ...

I wish there was some simple way you could experiment with the spacing between the exit face and the intake flare. I think they are a significant fraction of a wavelength apart (in cold air terms) and there could be some out-of-phase interference felt at the intake. Consider how carefully the longitudinal spacing is set up in the classic Ecrivesse. If you practically eliminate the longitudinal spacing, the lateral spacing between the axes of the duct ends might be pretty critical.

Hi Larry:

I'm sorry, but I'm not totally sure about what you're trying to convey here; could you expand on the concept (or maybe simplify it, for us old guys)?

Sure. From one doddering old coot to another, here's what I mean:

The phasing of the pressure waves between the exhaust and intake is surely capable of affecting the breathing of the engine if the phasing happens to be suboptimal - at least, the designers of the Ecrivesse thought so, and scientifically spaced the intake and exhaust at what they thought was a good separation, pretty far apart. Lockwood's original design, however, had the intake and exhaust in almost the same plane, though well separated axis-to-axis. I think basically what you want to avoid is phasing such that the emergent pressure wave from the exhaust goes down through the intake just in time to "fill in" the low pressure reflection wave as it gets back up the tailpipe to the chamber. That it can do this is not intuitively obvious where the external distance between the ports is small, but that's because we don't intuitively "see" the speed difference between the wave inside and outside the engine.

You introduced me to the idea of the "acoustic point" out somewhere beyond the open port face of both the exhaust and intake. But consider: one implication of the "acoustic point" is that it is the point in space from which the pressure wave radiates omnidirectionally after it exits either port! What this means is that to show the proper wave path distance between the exhaust and intake ports of your engine, we have to visualize it as a diagonal line between the acoustic points of the ports, NOT just a longitudinal measurement between the port faces!

The phasing will depend on this acoustic wave path length AND the realitive sonic speed in the tailpipe gas and the cool outer air. Wave travel will be MUCH faster inside the engine (high temp, low density) than in the air between the ports. In an engine like yours, there will always be a fresh supply of cool air in the region between the ports, because of the flows in and out of the ports - there will NOT be any hot gas hanging around out there! What this means is that the diagonal wave path between the acoustic points seems like a tiny fraction of a wavelength, but is really much more significant, because it's in a region of low wave speed, i.e. the basic engine frequency AND its harmonics have a far SHORTER wavelength in air than they do in the engine interior. Thus, it may be possible to get bad phasing between intake and tailpipe even though the distance is small. Also, if the path length is small, a lot more of the pressure wave energy gets into the intake than if the distance were longer, since the radiation of the wave essentially obeys the inverse square law (twice the distance would have 1/4 the impact).

I would conclude that it is not wise to have the intake and exhaust ports close together unless you are able to plan the phase relationship very carefully, at least for the case of the fundamental frequency.

L Cottrill

[hinote]

The phasing of the pressure waves between the exhaust and intake is surely capable of affecting the breathing of the engine if the phasing happens to be suboptimal

Larry:

OK--now I get it.

I thought about this--but the QD engines ran with their intakes in about the same location relative to the exhaust--and they were very good engines.

The current project could be different of course.

I'll try putting a flat piece of something between the intake and exhaust, to see if there's any change.

I'm also tempted to try straightening the engine overall, and putting the bend in the intake. With the intake and exhaust throat being the same diameter, this would be an easy change.

Bill H.
Acoustic Propulsion Concepts

".......some day soon we'll be flying airplanes powered by pulsejets."

[hinote]

I think that the most effective action would be to increase the CC diameter along with decreasing the intake length.

Eric:

I respect your opinion (after all, you're building some very good engines!), but I'm going to stick with tradition here, as follows:

The commonly held assumption with these engines is, the onset of combustion occurs along the wall of the combustion chamber and burns radially inward. Thus, the diameter of the chamber becomes the limiting factor--because the flame front has to reach the center of the combustion chamber in the time frame allotted.

Increasing the diameter of the chamber would also increase the necessary time for combustion, according to the assumption--and that implies slowing down the engine/lowering the frequency/making it longer.

I certainly consider my "fix" to be an experiment; it will be interesting to see if it's correct!

Bill H.
Acoustic Propulsion Concepts

".......some day soon we'll be flying airplanes powered by pulsejets."

[Mark]

I think for fun a pudding test would be in order. That is, make a linear track straight up into the sky. Have the pulsejet in question see how much it can lift. In this way you could be certain of what you have.
The scale would consist of a weight. I guess this would be considered one moving part, but little to troubleshoot.
Mark

[hinote]

I think for fun a pudding test would be in order. That is, make a linear track straight up into the sky. Have the pulsejet in question see how much it can lift. In this way you could be certain of what you have.
The scale would consist of a weight. I guess this would be considered one moving part, but little to troubleshoot.
Mark

Mark--that's basically what my thrust stand is doing. The fact that the engine travels horizontally can be totally discounted, because of the linkages which rotate the motion.

Also--you would want to include the weight of the engine itself as part of the total, wouldn't you??

Bill H.
Acoustic Propulsion Concepts

".......some day soon we'll be flying airplanes powered by pulsejets."

[Mark]

Yes, I'd count the weight of the engine, everything that went up. I remember in Schmidt's long expose', about a test stand that was acting up and not measure thrust correctly, hammering or building up some kind of resonance, playing off the scale. You wouldn't have to worry about conflicting results with the verticle lift acid test.
Mark

[Mark]

I wonder if you could throw off results with a spring that sprung out of phase with the pull? I'd stay away from springs and opt for a steel cord or solid mount.
Mark

[Eric]

Posted: Fri Sep 30, 2005 2:12 pm Post subject: re: What's Wrong With M1E??

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Hi Bill,

Yes, it has been a ruff day for everyone I beleive ... Lets put this behind.

The best exemple I can give you is this one :

If you stand infront of me and I put my hand on your chest and apply a CONSTANT 100 pounds pressure on your chest for one second. I will displace you for a X amount of inches ... Let say 10 inches for exemple.

Now, instead of pushing constantely, let say I give you 10 punch of 100 pound each in your chest, you will still move but you won't move as much as you did when the pressure was constant, because now, there is a time delais between each punch and at each punch, I need to crank my harm and re-accelerate my fist.

Now, add some weight (mechanical arm) bearing friction and other resistance to my fist, and the time and force to accelerate this get increased ... And when I hit your chest again, I don't have that 100 pound anymore. BUT, my arm mussles ALONE, are still capable and deliver that same 100 pound to the fist.

I am not saying your stand is not good. I am just saying that your stand look at all what is infront of the fist, where ours looks at the mussles.

Let me show you one more thing. You guys all know Dave Raibeck. Well, when he did his first 20 lbs. engine, he came back to us a bit disapointed saying "My engine only delivers 15 pound of thrust" which was measured by a mechanical fish scale. I told him that is engine was probably above that 20 lbs. mark and he was quite surprised.

We explained to Dave that when we did our first 20 Lbs. demo, our thrust stand was not ready yet. So, we used a digital 50 lbs. fish scale and measuring the thrust, we got 16 lbs of thrust.

So, like you Bill ... Viv and I went saying "Ok ... we have to tune the engine". Then, a few days later, we got all our parts and our dynamic loadcell (Calibrated and certified) and finished our thrust stand.

Then, we decided to try our UNTUNED engine on this new stand. NOW GUESS WHAT .... 33 lbs. of thrust, right there and untuned.

And like you Bill ... We were about to start waisting alot of Hours in tuning this engine, and maybe even modifiy it, trying to go where the engine already was. We just had the wrong measuring device.

So, every time our engine delivers a blow, as miniute this peak can be in time, each blows are 33 lbs.

Now, you guys can spend the entire morning arguing about this, writing your wildest theories and mile long calculations ... This is real life experience, fact, reality and it was endorced by engineers, fighter pilotes helicopter technicians and many others.

Heyyy ... Ask our buddy Dave Long .... He saw the stand, the results and he was in the first seat when peoples commented.

Your engine is probably good Bill ... Just wrongly measured. Look, your are retired. Why don't you take a few days of traveling vacations, jump in your car and bring that engine. We will go hunting, relaxing and benchmark that engine of your ..... For free.

Regards,

Luc

Luc

Every time that guy gets punched in the chest with 100 pounds force, there is also a person behind him hitting him in the back with 50 pounds force! You are totally excluding the suction phase!

You are saying your engines produce twice as much thrust, when they just plain and simply are not! While it has a peak instantaneous thrust of 33 pounds, it does not produce 33 pounds of thrust over the average of one cycle!

It doesnt take a rocket scientist to figure out that when you have forces in oposed directions that you must combine the forces to get a net force with a single direction. That works for constant forces, and it works as an average over 1 cycle for pulsed forces. The net force in the pulsejet is what does the propulsion!

If an engine can push down 50 pounds on a mechanical scale that means that it can hover with 50 pounds in the air (the margin for error with 50 pounds thrust would be very small). THAT MEANS IT HAS 50 POUNDS THRUST.

I can not stress this enough! If your pressure jet only pushes 16 pounds on a scale it is only producing 16 pounds net thrust +/- small error!!! It will not accelerate a vehicle as if it has 33 pounds of thrust, and it will not lift 33 pounds into the air!!!!

To say that you have doubled the pressure jets thrust is totally misleading any potential customer/investor, and if you actually believe it yourself it is even worse!

I am totally baffled at how you two could possibly believe that! What the hell good is having all that expensive equipment when you cant seem to understand the basic concepts of propulsion! You talk about practical real world experience as if we all have none, any decent highschool physics student could see that it does not work like that.

When you are using electronics to measure thrust of a pulseating combustion engine you MUST have it set up in order to read forward and backward forces! If you only have it set up so that the engine pushes on the mechanism, any negative thrust will only be displayed as ZERO. If you average the thrust from 0 to maximum instead of negative to maximum of course you are going to get a hell of a lot more, because you are totally ignoring the other component!

Your punching analogy is exactly what you are doing! The engine is punching with a peak of 33 pounds thrust in pulses, not exerting a constant 33 pounds of force like a push. The suction force and the thrust force averaged over one firing cycle will equate to a 16 pound constant push! For propulsion it doesnt matter how much peak thrust you have, the net force is what does the propelling.

So it comes down to that you are either extremely naive or that you are trying to pull one over on everyone, and I don’t know which one is worse.



______________________________________________________

To all who want to be on the mechanical rig side of the challenge

I can make two or three poles covered in neodymium magnets, and two sleves that fit over the poles with a connecting rod in between, allowing the engine to move up and down vertically with zero friction, and keeping it from flying off into oblivion.

We can put a cup on top of the engine rig, weigh the entire thing, and then slowly fill the cup with sand or oil or water or whatever until the engine starts to sink down, when that happens we will have found the maximum thrust of the engine, as it can not produce more thrust than the weight of the aparatus plus the weighing medium. It will not tell us the exact thrust to the 1/100th of a gram, but we can be 100% certian that the engine is not producing more thrust than the entire weight of the engine/stabalizing aparatus/cup/ medium.

Eric

[Viv]

The test rig measures both positive and negative thrust, -500 to +500Lbs

The test rig measures all thrust pulses weather positive or negative.

The test rig gives average thrust as defined as a steady applied force the same as a wight on a scale.

The test rig gives instantainous values for individuel pulses positive or negative or the average of all including or excluding negative pulses.

The test rig gives values for forward thrust and reverse thrust from suck back and also the sum of both.

Basically the rig reads the forces in both directions accuratly and with out distortion, these are then processed to give dynamic or static readings on simple bar meters or as XY charts against time or frequency.

The rig does give the correct static thrust equivelant of a pulse jet and also its dynamic peek values, its calibrated both dynamically and statically.

The measurments are seperate and not confused in any way what so ever between static, dynamic, peek or average.

Your assumptions are incorrect, your accusations are baseless.

A pressure jet delivering 33 Lbs is giving 33 Lbs of thrust static equivelent not peek, not some of the time but all of the time!

Is there any part you still don't understand? ask and I will answer preferably before you start making any more incorrect and misleading accusations.

Viv

[Eric]

Here is a concept render of the magnetic test stand, which guides the engine straight up and straight down but without friction of rolling components.

Even with a rolling mechanism the frictional losses would be negligible in every respect. There is no way in hell you will lose 16 pounds of thrust from the stand rolling.

Eric

[Viv]

In fact I just reread your post, first I answered your technical points but on second reading I notice that you are nothing but insulting in your post with accusations galore!

Exactly were do you get off with a limited understanding of the subject and any experiance throwing accusations like that around?

Very deffinatly I ask the moderators to look at your posting

Viv

[Eric]

Viv,

That definately clears up how your thrust system is setup. Before the whole peak thrust argument I stated to Bill that I believed you were saying that you use higher sampling frequency so you could average the thrust value accurately.

However that was before the peak thrust comments. I purely believe that averaging all the forces is the correct thing to do, and if you are doing that then I am more inclined to believe the thrust results.

If you read lucs various posts, talking about the peak thrust values being 33 pounds, and then saying the overall thrust is 33 pounds, it just gives the wrong impression.

Even someone of limited experience can tell that if the peak thrust is 33 pounds for a tiny fraction of a cycle, and the thrust drops and even goes to negative that the static thrust can not be 33 pounds.

So in reality the 33 pound static thrust engine is actually producing more than 33 lbs peak pulses. That clears a lot up right there.

The thing that I am not easily inclined to believe is that most mechanical methods take away 20%-50% of the thrust. The mechanacal aparatus by nature averages the pulses and delivers an average static thrust figure. The more mass you have in the system the less it will be swayed by any individual pulse, and delivers a more accuate measurement of the total thrust.

Larrys bathroom scale FWE measurements for example, he had a vice and other weight on the scale, and measured the thrust very accurately for the device and input range. A bathroom scale will not give a good reading with such a small thrust because its not a precision device. If you use a 50 pound or 100 pound thrust engine on the scale you will have a much much lower uncertianty. I just find it very hard that a large group of intelligent people could get such innacurate readings with all their various mechanical test stands.

I think we would all be interested in seing a single cycle graph of thrust output. It might also be wise to try adding large masses to the test engine in order to dampen the effect of any single pulse, while it wouldnt work well for analyzing geometry etc etc it would help smooth the measurements into a single more continuous push.

The peak thrust comments along with how innacurate the mechanacal thrust measurement figures are just made me very suspicious. It is my nature to question everything, sometimes a little too much. Im sorry to offend you but those points needed absolute clarification.

Eric

[Mark]

Let me show you one more thing. You guys all know Dave Raibeck. Well, when he did his first 20 lbs. engine, he came back to us a bit disapointed saying "My engine only delivers 15 pound of thrust" which was measured by a mechanical fish scale. I told him that is engine was probably above that 20 lbs. mark and he was quite surprised.
We explained to Dave that when we did our first 20 Lbs. demo, our thrust stand was not ready yet. So, we used a digital 50 lbs. fish scale and measuring the thrust, we got 16 lbs of thrust.
So, like you Bill ... Viv and I went saying "Ok ... we have to tune the engine". Then, a few days later, we got all our parts and our dynamic loadcell (Calibrated and certified) and finished our thrust stand.
Then, we decided to try our UNTUNED engine on this new stand. NOW GUESS WHAT .... 33 lbs. of thrust, right there and untuned.

So what might be the explanation for the fish scale measurement?
Mark

[Viv]

Let me show you one more thing. You guys all know Dave Raibeck. Well, when he did his first 20 lbs. engine, he came back to us a bit disapointed saying "My engine only delivers 15 pound of thrust" which was measured by a mechanical fish scale. I told him that is engine was probably above that 20 lbs. mark and he was quite surprised.
We explained to Dave that when we did our first 20 Lbs. demo, our thrust stand was not ready yet. So, we used a digital 50 lbs. fish scale and measuring the thrust, we got 16 lbs of thrust.
So, like you Bill ... Viv and I went saying "Ok ... we have to tune the engine". Then, a few days later, we got all our parts and our dynamic loadcell (Calibrated and certified) and finished our thrust stand.
Then, we decided to try our UNTUNED engine on this new stand. NOW GUESS WHAT .... 33 lbs. of thrust, right there and untuned.


So what might be the explanation for the fish scale measurement?
Mark

Do springs vibrate?

Viv

[Mark]

I wonder if you could throw off results with a spring that sprung out of phase with the pull? I'd stay away from springs and opt for a steel cord or solid mount.
Mark

Here's something I posted earlier today.
Mark