Boeing’s continued use of QinetiQ’s 5m diameter wind tunnel to test its commercial aircraft confirms the facility’s place as a national asset, below; being wireless, the TorqSense sensor is easily transferred between testing rigs, bottom right; high-speed aeronautical bearings will be put to full-scale test at SKF’s new facility in Valenciennes in France, bottom left
are used for recognisance, surveillance and surveying, by both civilian andmilitary organisations . Because of the duration of their flights, their controlsmust be reliable and accurate otherwise the risk of losing the craft would be unacceptably high. Resembling a conventional fixed wing
aircraft, the principles ofMALE drone flight control are well established. Ian Maher of Deva Technologies inWrexham says: “High-performance servomotors are used to position the flight control surfaces. Our test rig’s role is to put themotors through long duration tests tomake sure they stay within specification, even after prolonged exposure to the arduous operating conditions they are likely to encounter.” In essence, the TorqSense transducer
constantlymeasures the power output at themotor shaft and this is compared to the instantaneous current draw. By taking a large number of individual readings over the duration of the test period, an accurate torque-load curve can be plotted for each motor and compared with the expected values.
TorqSense is highly innovative in that it
does not need to physically contact the shaft it ismonitoring. Instead, sensing is achieved through a radio frequency link. Two tiny piezoelectric combs are attached to the shaft of themotor under test, perpendicular to one another and at 45° to the axis of the shaft. These formhalf of a Wheatstone bridge circuit, which is in radio contact with the other half in the main body of the TorqSense. “When the shaft rotates, a phenomenon
known as Surface AffectWaves causes one comb to expand and the other to contract, changing their electrical resistance in proportion to the speed of rotation,” explainsMaher. “This unbalances the bridge and
generates a signal indicating the torque value. It imparts no extra load onto the shaft, someasurements are true and calculations are simple. The rig produces data in real time and records the torque curve for analysis and traceability.” Significantly, because TorqSense is
essentially wireless, it is easy to set up – no cablesmeans there is no need for delicate and fiddly slip rings. Thismeans test rigs can be both set up and operated easily. “It alsomeans we can just as easily take
the TorqSense off one test rig and fit it to another. Thus we expect to use each one onmultiple projects. Not only do we save money by not having to buy a new one every time, but we save again because we have become familiar with the technology and are now highly skilled at installing, calibrating and using it,”Maher concludes. EE
December 2017 /// Environmental Engineering /// 35
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