What's Wrong With M1E??

[hinote]

The so-called "Forum M1E" project is a success, in that it resonates, and accepts a range of fueling rates/thrust producing levels.

So,--What's wrong with the poor beast??

The main thing is, she's not producing the power she's capable of, when optimized (that would be at least 50 lbf, and probably more like 60 lbf); currently, she's producing a max value of something like 35 lbf. Also, it's obvious that the combustion efficiency isn't right, because she shows us a slightly rich flame (observed from in front of the intake tube), in the form of a slightly orange tinge instead of the beautiful sky-blue we would like to see.

I have intended for this project to be a learning experience, for those who would like to gain more knowledge about this type of pulsejet.

So, the original question stands--what's wrong with the Forum M1E, as currently presented??

I think I have the answer, but I would like some participants to propose their solutions to the problem.

I respect all opinions, and will honor all replies. We all need to learn from our experiences, and I would like to share this one with those who may be interested enough to learn something here.

Bill H.
Acoustic Propulsion Concepts

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

[Eric]

I always have the urge to throw out my 2 cents as soon as I see these kind of things. I guess I will wait until a few posts to see if anyone can come up with a theory.

Eric

[hinote]

I always have the urge to throw out my 2 cents as soon as I see these kind of things. I guess I will wait until a few posts to see if anyone can come up with a theory.

Eric--thanks for your reply.

I've noted a lack of overall interest, in participating in this discussion.

I'll allow another 24 hours, and hope somebody else replies.

I'm in the process of modifying the engine, and I'll be reporting the results some time next week.

Bill H.
Acoustic Propulsion Concepts

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

[El-Kablooey]

I'm interested, and eagerly awaiting an answer! I'm just not experienced enough to make a good guess. That's why I'm here, to learn from you guys. If I was absolutely forced to make a guess, I would say that possibly the intake was either slightly too long, or too small in diameter.

[Mark]

I'm interested too, but I couldn't hazard a guess. What's it suppose to do, have more transitions to mix the fuel better? The tail end is not as gradual as some I have seen, maybe the air breaks up the feedback from the rapid expansion on the outflow cycle.
Mark

[luc]

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[hinote]

What's a M1E?

Look at:

http://www.pulse-jets.com/phpbb2/viewtopic.php?t=2339

and

http://www.pulse-jets.com/phpbb2/viewtopic.php?t=2282

This is an effort to bring the development of a valveless pulsejet to the appropriate Forum, to provide educational information about the design and operational character of the type.

I'm using a discarded, unsuccessful engine from last year to provided the material for the basic engine, and modifying it in such a way as to produce an operating version. I've already run it at 35 lbf--and I'm in the process of modifying it for further expected performance increases.

Bill H.
Acoustic Propulsion Concepts

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

[luc]

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[hinote]

Hoooo ... Okey ... An odd shape lockwood. Okey, I get the picture now.

Before you start tampering with this engine, tell me more about your thrust measuring device.

I hope you are not doing the most common mistake of using a "Strain" type loadcell ... Or I will have to go there and kick your but Buddy.

There is only one good thrust measuring device setup that will tell you your real thrust figures.

If your setup is not correct, only this can take out 50% of your real thrust figures. Especially when running a lockwood type engine.

Remember, this type of engine is well known to have a massive air suck back cycle ... Up to the point it can even collapse its own tail pipe. Now this is called "Negative thrust" and if your loadcell setup is not correct, that what you get ... Poor reading.

This engine owes most of heritage to the Escopeta, developed by SNECMA and IAME in the 1950's. Documentation (from the so-called "SNECMA papers") shows this engine produced a TSFC of 1.6--a number I demonstrated with the "mini"-Escopeta at the Burning Grape meet.

You're right--this engine produces a lot of its rated thrust by the reingestion of cold air up the tailpipe--it's actually equivalent to a built-in augmentor.

My thrust stand is all mechanical; it uses a rising-rate weight arm, with a pointer connected to the deflection. I calibrate it using a Dillon X force gauge. The weight arm provdes good inertial absorption and redistribution--and I think it's a pretty usable system overall.

I'd be interested in your comments about the use of a load cell (which I'm considering). I had thought that a buffer circuit would remove the sampling error in the load cell. Inertial (mass) damping would seem to be another possible solution. Please comment.

Bill H.
Acoustic Propulsion Concepts

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

[luc]

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[hinote]

You can buff, compensate, callibrate all you want ... There is only one accurate way to measure dynamic jet engine thrust and it is shure not oil bellow, strain gauge loadcell or any other mechanical device.

THE only way is with dynamic loadcell with a minimum sampling rate of 10 times the frequency of the engine.

I beleive this is why your readings are wrong and we beleive you should invest a bit in your thrust measuring device, before you tamper with this engine anymore.

Sorry, guys--retirement money is too hard to come by, these days.

I'm appealing to Mike E. at this point, to verify the workability of the design of my current thrust stand.

There's no engineering reason why this method can't be accurate, IMHO.

Just because it's not what you guys are using, doesn't mean it isn't any good.

Bill H.
Acoustic Propulsion Concepts

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

[hinote]

Let me just add a note Bill, all the methods I have seen and a few I came up with are only good for "static" measurments! and also are only accurate when calibrated with a static load.

But fundamentally we are trying to measure a dynamic event, the pulse jet produces thrust in pulses, so we have to read the pulse amplitude and pulse rise time accuratly.

This discussion is out of my league, engineering-wise--but I feel the need to defend my method.

First, I'm trying to measure thrust the way it will be used--as an overall force created by the engine--NOT the peak value. I pull or push on the thrust stand when calibrating it, the same way the engine would push an aircraft through the air. I'm not concerned with instantaneous values--just the force available to do the work I desire.

Although instantaneous values have an engineering interest for me--they're not what I'm really after.

Also, Viv-- The existence of any motion in your system (however small) implies to me the existence of inertial damping created by the acceleration/deceleration of the masses involved. Do you account for this mathematically, electronically--or do you just disregard it?

Bill H.
Acoustic Propulsion Concepts

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

[luc]

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[hinote]

Let me just add a note Bill, all the methods I have seen and a few I came up with are only good for "static" measurments! and also are only accurate when calibrated with a static load.

I think this statement provides the dividing line, between you and me.

Although the pulsejet is dynamic within a single cycle of its operation, I'm concerned with steady-state output.

Even if you include extravagant summing equations, with corrections for phase angles, rise-times, etc., you're still going to get a net result that represents the thrust stand as I'm currently using it. I believe that the rest of the PJ enthusiasts are interested in net thrust, as I am.

I'm not going to pursue this any further. I appreciate your input.

Bill H.
Acoustic Propulsion Concepts

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

[luc]

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