nosepicker Posted February 10, 2012 Share Posted February 10, 2012 Greetings all, I am currently employed as an instructor for the US Navy. I teach the T56-A-14's (same thing, except your guys' motor is upside down...haha), just kidding... One of my students asked a question today in class that I didn't have an answer for: "Why does the torquemeter have 40 exciter teeth, and does it have anything to do with the 0.040" gap between the pole pieces of the torquemeter pickup?" I referenced my Rolls Royce manual and all my literature from years past but to no avail. Anyone know? Quote Link to comment Share on other sites More sharing options...
HercMX Posted February 10, 2012 Share Posted February 10, 2012 40 teeth have nothing to do with the .040" gap... The large number of teeth allow closer alignment during assembly... Jack... Quote Link to comment Share on other sites More sharing options...
Lkuest Posted February 10, 2012 Share Posted February 10, 2012 As a fellow instructor, my answer would be "Who Cares". What's important is how the torquemeter measures torque, not how many teeth it uses to do it. If he wants an answer, you could probably get away with making something up that sounds good. Something that sounds like this: "The power source for the torque indicator operates at 400 hertz. At 13820 RPM, the signal at the pickup pulses at a frequency of 9213 Hertz, over 50 times that of the indicator. At that rate, the signal to the analog indicator would appear fluid, making torque indication smooth instead of jumpy. If the frequencies were matched (a single tooth), misalignment oscillations would cause an indicated fluctuation, much like how the props cause varying beating noises at the same RPM without the synchrophaser(assuming you are on an aircraft where your T56 wasn't upside down.)" The gap is standard for any electromagnetic pulse. Your pulse generator has one (assuming your prop has one on a P3), but there is a gap because if the tooth (magnet) touched the electro magnet, friction would wear them out. If they are a few feet apart, the signal strength would not be enough to generate a pulse. There is a specific gap so that the magnet and electro magnets do not touch, but they are still close enough together to send a meaningful signal. If they don't like those answers, just tell them it's magic and to quit sniffing paint after work. Quote Link to comment Share on other sites More sharing options...
NATOPS1 Posted February 10, 2012 Share Posted February 10, 2012 It has nothing to do with the gap ... 9 degrees was chosen because it is the radial distance between the centers of the teeth on the exciter wheels. 40 teeth is based on the "twist rate" the number is the torque (in inch-pounds) required to twist the shaft 9 degrees. 9x40= 360 degrees If there were more teeth they would "overlap"... From the Lockheed maintenance training manuals... Assume that the calibration number is 29,850. The electrical difference between CAL A and CAL B is equivalent to 29,850 inch-pounds of torque on the torque shaft. This figure, representing the amount of torque which causes a 9-degree twist in the torque shaft, was chosen because it is the radial distance between the centers of the teeth on the exciter wheels. Quote Link to comment Share on other sites More sharing options...
Lkuest Posted February 10, 2012 Share Posted February 10, 2012 So theoretically, if the engine were to magically put out a torque of 29850, the exiter teeth would line up with the next set of teeth, and the torque indicator would read 0. I'm not adding anything to the arguement, just thinking aloud. With my keyboard. Quote Link to comment Share on other sites More sharing options...
jrkaegi Posted February 10, 2012 Share Posted February 10, 2012 And if you work on 501D-13, And that would show 13,820 on RPM Ind. Same calibration Cal a Cal B. Quote Link to comment Share on other sites More sharing options...
nosepicker Posted February 10, 2012 Author Share Posted February 10, 2012 Thanks for the replies guys. I know about the 40 teeth and the amount of torque that will turn them one tooth is the calibration number of that torquemeter and all, it was just the pickup question that threw me off. I don't think i was clear before. I didn't mean the clearance between the pickup and the TM, I meant the accuall pole pieces on the pickup and how they are offset 0.040" ( _____--------). It's to measure the difference between positive and negitive torque but why .040", and is it just a couinsidence that there are also 40 exciter teeth. Thanks again my T56 brothers (and sisters). Quote Link to comment Share on other sites More sharing options...
NATOPS1 Posted February 10, 2012 Share Posted February 10, 2012 The reference pickup is located slightly ahead (.040) of the torque pickup to allow the torquemeter system to measure negative torque. The time difference is already know (the .040) so if the time between pulses is "less" you get a indication of negitive torque without the pulses haveing to be "equal" then negitive. Engine not running reference tooth is aheard of torque tooth. (true "zero" torque) Engine running there is torque so the reference tooth is still "first" then the torque tooth. The time between the pulses is positive and sets your torque indicator needles. As we move towards "negitive" torque, the reference tooth is still first... Then the torque tooth, BUT the time between the pulses is less than the original .040 so a early indication of negitive torque can be determined. If the (pickups) were not "gapped" we would have to "wait" until the pulse "timing" was more negitive to see the indication. Quote Link to comment Share on other sites More sharing options...
nosepicker Posted February 11, 2012 Author Share Posted February 11, 2012 Thanks for the reply NATOPS! Good info. Quote Link to comment Share on other sites More sharing options...
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