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  • #46
    Which is effectively the torsional stiffness, you just haven't bother to give it it's name.

    Your point seems to be that if you don't call a black sheep "a black sheep" then its not a black sheep.

    Phil

    Originally posted by Evan
    X load produces Y twist. Period.

    Comment


    • #47
      I think what Evan is after is a poor way of measuring the twist in the shaft, based on Bubbas calibrated ear...When Bubba says "If it grunts anymore it'll f^&%in fly to bits"(Add your favorite regional hill billy accent ). Then measure the twist. This being the "Maximum Twist". That is probably ok for a backwoods arrangement. But the reality is you DO NOT know anything about the HP or the shaft. The addition of a Dyno, will give you a maximum Bubba applied torque, which still tells you NOTHING ABOUT the shaft other than: this much Bubba=this much twist. What is needed is the diameter, the wall thickness (If any), the length, and material type. Will all allow you to calculate the maximum allowable stress for a given torque.

      Evan's method will not tell you if you are operating in a safe range. As Bubbas calibrated ear, may well be (And usually is) pushing things to the MAX. So you may be right on the verge , but repeatedly pushing to Bubbas max, will cyclically weaken the shaft and one day operating within the Bubba calibrated system will fly to pieces anyway. Bubbas calibration does not take into account other factors, such as shock loads, a whole new problem.

      Plus the point of the original post was/is to do something which doesn't so much worry about the shaft as it is already a reliable shaft, but to give the driver some feedback information. This is easily accomplished with a load cell under an engine mount and knowing the distance from the Crank center line to the load cell. A small electronics package can condition the signal and display the information.

      Comment


      • #48
        Originally posted by Evan
        No you don't. You only need to calibrate whatever phase difference occurs with a certain applied load. You don't even need to know what material the shaft is made from. It could be metal or wood or fiberglass or day old french bread. Why is this so difficult to understand?

        X load produces Y twist. Period.
        Evan is correct - if the shaft already exists. However, everybody else insists on knowing the properties of the shaft as if they had to engineer it into existence for the application. I would perfer to know the material properties and do the calculations - instead of empirically starting with day old french bread and working my way up to 4140, heat treated.

        Given a mix of superior intellegence, knowledge, experience, intuition and luck, the TLAR method (That Looks About Right) sometimes works for new applications. I've used the method myself, but I perfer to do the calculations - not real easy as I tend to be math challenged.

        Now, if I had an existing application, apply a known load, measure the deflection and call it good. In such case it would be good to know the material characteristics to know what the limits are.
        Weston Bye - Author, The Mechatronist column, Digital Machinist magazine
        ~Practitioner of the Electromechanical Arts~

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        • #49
          Torque Shaft

          Contact a company by the name of "Himmelstein" as they offer a wide range of torque measuring equipment. (bring money) A big diesel engine would be a problem mounting torque measuring load cells directly on the engine mounts. Many years ago I installed a big Mack diesel engine on a test stand it rough on the drive line and couplings.

          JRW

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          • #50
            What is needed is the diameter, the wall thickness (If any), the length, and material type. Will all allow you to calculate the maximum allowable stress for a given torque.
            The poster didn't ask for that information, only a way to quantify the torque in an existing system.
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            • #51
              Originally posted by Evan
              You sure are going to great lengths to try and cover up your mistake. Reminds me of a cat trying to scratch dirt over some *hit on a rug.

              The torque is whatever the drive system is rated to produce. I am sure somebody knows that. The propellor is the load. Duh.

              Sorry, no mistakes here......Unfortunately for your cute efforts to transfer the cat crap to me, you do NOT KNOW the torque the system is "rated" to produce IS ACTUALLY BEING PRODUCED..... That would be part of the reason for the testing.....to prove that the contract has been fulfilled.

              For a ship, the owners contractually specified a penalty if the custom designed propulsion system did not produce the specified power output AS MOUNTED IN THE SHIP. They may or may not have allowed a bonus for overage.

              Therefore, the legal system is involved, and "Mr Bow Tie" may have calculated a certain power from the turbine and boiler system (a few years ago of course), but that cuts no ice.... the owners want to know that it works in the final "product"....*

              So, you may use the propellor as a load, which is rather obvious if you take measurements while under way, as is normal, but you haven't got it calibrated.... So either the shaft has been calibrated in the shop, or the shaft has been calculated, whichever the owners accept...

              But you MUST know something about the shaft in order to get a numeric, quantified, traceable measure of the output by measuring what happens to the shaft.....

              Since you want to be cute, Evan, I will point out that others made this same point, and your reply was that "no you don't need to know anything about the shaft......" Which would only be true if you don't care about the numbers.

              You seem to have , as John S says, "backpedaled fast" on that statement.

              I don't get any particular pleasure from pointing out your mistakes and re-directions of discussions, but I do very much resent someone turning everything upside down and trying to spin their own mistakes and mis-statements in a discussion so as to attempt to fasten your own mistakes onto others.

              Frankly, Evan, I have NEVER ONCE seen you admit to being "wrong". The rest of us do so whenever it is appropriate.....

              Now, your MODIFIED statements that you don't NEED to know anything about teh shaft IF you calibrate it, are almost correct..... EXCEPT THAT KNOWING WHAT YOU SUGGESTED

              Originally posted by Evan
              No you don't. You only need to calibrate whatever phase difference occurs with a certain applied load.
              STILL CONSTITUTES KNOWING AT LEAST ONE PROPERTY OF THE SHAFT....... I am not sure why this is so difficult to understand......

              You are using the shaft as a comparison meter, and the one essential thing about a meter is that you want the scale factor...... otherwise the only information you know for sure is that the conditions are now 'different" than before... possibly "more different" possibly "less different".... But how MUCH different, that you know nothing usefully numeric about unless you find the scale factor, i.e. calibrate.

              Personally, given the obvious issues dealing with the shaft, I think it could be a lot more useful and direct to use a reaction of the shaft driving device against its mounts to get the torque..... That can often be easily calibrated by measuring physical distances.

              And, for devices such as the prony brake, is exactly how it is done... measure reaction force on a lever pivoted at the shaft, and you have the torque. All weights and measures stuff, quite easy to calibrate. You might need to compensate for bearing friction, depending on how fussy you want to be.

              For hundreds of thousands of HP in a ship, it is not practical, and the prop as a load, with the shaft as a meter makes sense... it is worth the efforts of calibration etc, to get that measurement via the shaft, as it is the easiest point to attack.

              *These days, with diesel engines instead of turbines and boilers, it is credible to get a test-bed power number........ and the requirement for in-place testing is less, but still that measurement would, I am reasonably sure, be part of the test conditions, as a power check. If you look through the "Doxford" thread over at PM, you will see some rather large water brakes coupled to big marine diesels on the test bed...
              Last edited by J Tiers; 04-14-2010, 10:05 PM.
              1601

              Keep eye on ball.
              Hashim Khan

              Comment


              • #52
                Frankly, Evan, I have NEVER ONCE seen you admit to being "wrong". The rest of us do so whenever it is appropriate.....
                That is because you either don't bother to read all the posts in a thread (which you have admitted) or you have poor reading comprehension or both. I have on various occasions admitted to being mistaken.


                I don't give a shi* about your ship Jerry. You, as usual are flailing madly about trying to distract the audience and wandering further and further from the question. The simple fact is that in this instance I am correct and you are not. Weston understands my point, you do not.

                STILL CONSTITUTES KNOWING AT LEAST ONE PROPERTY OF THE SHAFT
                Oh? What property? Keep in mind we don't know the actual amount of twist.
                Last edited by Evan; 04-14-2010, 10:29 PM.
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                • #53
                  And still, as I said before Bubbas calibrated ear isn't a "Quantity". Knowing nothing about the shaft, and using this sort of test would only show you how much the shaft deflects (Twists) under Bubbas "Umm, this is enough throttle" calibration system. You cannot derive any torque from that, you cannot derive HP from that, you cannot derive a factor of safety, or safe limits from that information, unless you know something about the shaft. The twist of the shaft is useless, except in the instance that the engineering department specifies a certain deflection between two points at a given distance. Then this is ok for operators with little or no understanding of what they are measuring, and could care less. It still does not tell the operator anything about HP or torque, without a table to explain it or the proper information to calculate it.

                  Comment


                  • #54
                    The twist of the shaft is useless, except in the instance that the engineering department specifies a certain deflection between two points at a given distance. Then this is ok for operators with little or no understanding of what they are measuring, and could care less. It still does not tell the operator anything about HP or torque, without a table to explain it or the proper information to calculate it.
                    This is one of the most important instruments on a helicopter. Notice anything special about it?

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                    • #55
                      Gee, waddaya know? Looks like somebody else likes my idea too.

                      News Release Number: EJK201004091 09-Apr-10

                      FRCSE DET Mayport upgrades engine test cell
                      FRCSE DET Mayport upgrades test cell
                      “improves helicopter engine efficiency”

                      By FRCSE Public Affairs

                      Fleet Readiness Center Southeast (FRCSE) Detachment (DET) Mayport upgraded the Engine Test Cell propulsion support equipment in February to improve GE T700-401C helicopter engine efficiency and accuracy for the squadrons the detachment supports.

                      The equipment was upgraded from a reaction-based torque system to a phased-shift torque system that measures the twist of a shaft mounted between the engine and a dynamometer, an instrument used for measuring mechanical power.
                      Mechanical Engineer Brian Zarko from Naval Air Systems Command, Lakehurst, N.J., assisted with the upgrades. He said the engine produces the torque (turning force) and the torque meter measures the torque transmitted by a rotating shaft.

                      “Mayport FRCSE is the only activity currently using the new torque measurement system,” said Zarko. “The new torque meter uses two pick-ups to measure the twist of a toothed shaft for improved accuracy.”

                      Zarko said the system reduces the need for expensive periodic testing, which requires an engine with known performance to verify the correction factors are still accurate on the engine being tested. It requires an oil supply and return, which prompted the modification. The upgrades also replace dated equipment that can prove problematic when finding replacement parts.

                      Test cell operator Aviation Electrician’s Mate Terry Lamb said the new system makes calculating the torque values easier and faster for the technician at the beginning of the performance run.

                      “You no longer have to allow for a correction factor for the torque to each engine,” he said. “You still have to compute the torque value, but there is one less step.”

                      The technicians ensure the engine is outputting the correct horsepower using a dynamometer to simulate the load from a turning rotor head. They conduct a performance calibration on all required instruments and make sure all gauges are reading correctly.
                      http://www.navair.navy.mil/press_rel...4301&site_id=7
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                      • #56
                        Originally posted by Evan
                        T

                        Oh? What property? Keep in mind we don't know the actual amount of twist.
                        You said it yourself......... did you forget?

                        You want to know the reaction of the shaft in some measureable property, to a given load...... In this case you suggest the twist, as expressed by your phase difference.

                        Squeal and squirm and kick as much as you like...... that is "knowing something" about the shaft..... how is this difficult to understand?

                        You are calibrating the shaft in twist, or measured phase shift, or whatever. Nitpicky points about the method of measurement make no difference, you come out with "SHAFT UNITS" of some sort which calibration translates to internationally accepted "units". And equally nitpicky points about not calculating the shaft etc are invalid, because that is merely arguing about the MEANS of calibration, and not the FACT of it.

                        ANY measuring element gives you a varying output..... but you need to scale that output relative to known units in order to use it to get "real", relateable-to-real-world numbers..... Otherwise it is, as Mr Bye said, simply "Bubba units".....

                        When people said previously that you needed to calibrate the shaft in some way, you flat denied it, and then you turned right around and agreed both then and now that it needs to be calibrated.....as if it was your own new and novel idea.

                        In the case of a known system, where you already know everything, can know maximum power, and have a way to calibrate the shaft, I can easily see that a twist-based (call it phase if you want) measurement could be lighter than other types, and so more desirable for a device (helicopter) with a slow-moving shaft.

                        In that case, you don't need to calibrate the same way as when everything is unknown, you set the system to known max, and label your output 100%, zero is obviously at rest, or with some minimum condition if at rest isn't appropriate.

                        Assuming the shaft is linear in response, which it should be, you now can mark the dial between those points, and a reasonable amount past 100%.

                        In the specific case in your quote, an engine test cell, the shaft is part of the equipment, calibrated once, and any engine connected to it can be measured by it, because they "KNOW" the shaft response to torque, and can use that to determine the engine input. That would be an "absolute" calibration, not a relative one like the instrument panel dial.

                        They didn't make up numbers..... I'd wager that 100% or 120% on that dial has a real meaning in terms of output to the rotor.... which means they did calibrate the system at least as I describe, and probably more thoroughly.

                        That PRESUMES the ability to provide known inputs to the system..... But you are STILL "knowing something" about the shaft...... see above.

                        You may WISH I didn't understand the point as well as Weston bye, but in fact I do quite well understand it.

                        of course if it suits you to deny it..... so be it, we know what's up.
                        Last edited by J Tiers; 04-15-2010, 12:23 AM.
                        1601

                        Keep eye on ball.
                        Hashim Khan

                        Comment


                        • #57
                          Squeal and squirm and kick as much as you like...... that is "knowing something" about the shaft..... how is this difficult to understand?
                          A phase difference isn't a property of anything. It isn't even an entity. It is no more than a concept. I thought you claim to be an engineer.

                          You are calibrating the shaft in twist, or measured phase shift, or whatever. Nitpicky points about the method of measurement make no difference, you come out with "SHAFT UNITS" of some sort which calibration translates to internationally accepted "units". And equally nitpicky points about not calculating the shaft etc are invalid, because that is merely arguing about the MEANS of calibration, and not the FACT of it.
                          Nope. Notice the helicopter torque gauge? What is it telling you about the shaft? Nothing at all but that is where the value is derived. You can measure a phase difference because of torque reaction without even knowing how the torque is transmitted. There might be a shaft inside the black box, or a torque convertor, or a pair electric motors acting as a servo pair, or a magnetic drive or an eddy current drive. Measuring the phase difference tells you about the LOAD since that is the only reference you have when you calibrate it. It is also the only thing that you need to know in a helicopter and in the truck that the OP asked about.
                          Last edited by Evan; 04-15-2010, 01:23 AM.
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                          • #58
                            What a ridiculous statement, a phase difference is a property of a shaft under load. You are using this very property of phase difference to produce your torque gauge. You are spouting nonsense in order to justify an insult, clearly you are not an engineer.

                            The fact that the user of a torque gauge doesn't know anything about the shaft doesn't mean the torque gauge doesn't. When you measure (calibrate) the shaft twist for a given load you are measuring its torsion rigidity, this can equally be calculated. This value, measured or calculated, has to be input to the torque gauge by the designer or builder at some point. Clearly you understand this but equally clearly you seem unable to concede the point.

                            My last word on the matter.
                            Phil


                            Originally posted by Evan
                            A phase difference isn't a property of anything. It isn't even an entity. It is no more than a concept. I thought you claim to be an engineer.

                            Comment


                            • #59
                              What a ridiculous statement, a phase difference is a property of a shaft under load. You are using this very property of phase difference to produce your torque gauge. You are spouting nonsense in order to justify an insult, clearly you are not an engineer.

                              Wow! Another victim of hoof in mouth disease. It boggles the mind. The difference (a derivative) in position in time of something is not a property of anything. It is a purely mathematical concept. It has no realizable existence.

                              Even the values required to determine a phase difference are not properties of anything. Location is not a physical or mechanical property. Location can only be described as relative to something else as there is no such thing as absolute location in time and space.

                              Tell me, from what property is a phase difference derived, in your mind? RPM, Torque? You will need to show that both of those are also mechanical or physical properties. That will prove very problematic since a property of something cannot be defined by when it happens. That is called an "Event".

                              You would do well to avoid pursuing this line of argument further as it can only reflect badly on your knowledge and judgement.
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                              • #60
                                Hi,
                                As an observer from afar, Sydney Australia, I find the somewhat heated discussion on this subject interesting.

                                About 27 years ago (1983) I was responsible for fitting torque measurement equipment on the drive shafts to 2 x 1200 kW drives to the upper and lower rollers on an aluminium (spelling is correct for us) rolling mill.

                                The instrument used drive-shaft cemented strain gauges connected to a battery operated FM (frequency modulated) transmitter with a receiver and display to the mill operator, and to recording instruments.

                                Calibration was done at standstill with known performance current/torque values for the DC motors, followed by (as best we could with 20T blocks of aluminium at speed) steady-state runs with records of DC motor power ( volts and amps) and speed.

                                The calibration procedure removed the need to know anything about the shafts and we did not know what the actual torsional twist (phase shift) in the shaft was.

                                Torque applied to the shaft provides a torsional stress that results in a twist, or phase shift. The amount of twist is dependent on the elastic properties of the shaft, Young's Modulus of the material and the physical size.

                                All we knew was that a certain amount of kNm (1000s of ftlb) torque produced a predictable and repeatable display on the meter.

                                The important thing is that we went through a "calibration procedure" to get there.

                                The measurement equipment was installed on the mill to improve the knowledge data base on the statistics of block impact dynamic torque peaks to provide some predictions on the expected fatigue life of the shafts, gears and couplings.
                                We had just had our first major failure after 25 years of mill use ( mill commissioned in 1958 ), a shaft coupling, and the block size and mill throughput rate were increasing each year by management decree.

                                Hope this description of an actual installation helps,
                                Happy machining,
                                John.

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