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Aviation History
1946
1946 - 2137.PDF
OCTOBER 24TH, 1946. FLIGHT Rotol Development Two New Contributions to Comfort and Safety A LTHOUGH the modern airscrew per se may be accepted /-\ as having become as efficient a device for its purpose A. JL as it is possible to make it, there still exist methods and practices concerned with its functioning which are dis- tinctly capable of impiovemeut In two of these, namely those of engine speed synchronization and of airscrew de- icing, it was felt by Rotol Limited that there were considerable grounds for revision and, accordingly, they turned themselves to the development of means whereby the existing position could be changed. It does seem essentially wrong that, with all the development which has taken place in power plants and instrumentation, flight engineers should still be trying to effect synchronization of engine speed by visual and aural methods, nc matter how proficient the individual may, with practice, become. To rectify this anomalous position, which has so important a bearing on passenger and fiight-crew comfort, Rotol have developed a simple and entirely automatic synchronizer. It has been extensively test-flown on both twin- and four-engined aircraft, and a pointer to its efficiency is, given by the fact that on recent flight trials on a Lancaster, the r.p.m. varia- tion over a given test period was shown by a synchroscope to be nil. The system is based on the selection of one of the engines as a "master," the remaining power units being subject to continuous automatic correc- tion to the governing r.p.m. of the master. This is accom- plished by fitting an alternator and a differential corrector motor to each engine. The rotors ot the corrector motors are joined by worm gears and crank pins to the normal engine/airscrew constant-speed units, one winding of each cor- rector motor being electrically connected to its own engine's alternator and the other wind- ing connected to the alternator of the master engine. Thus the rotor of each cor- rector motor will always turn at a speed proportional to the difference in speed between the master engine alternator and, 453 The method of de-icing fluid supply from pump to slinger ring, and thence to blade root cups can be followed in this sketch. DE-ICIN6 PUMP that of its own engine. Fur- thermore, the direction of rota- tion will be dependent on whether its own alternator The governing corrector motor with toggle action differential linkage for connection between pilot's speed control lever and c.s.u. ^MMIICVERWOR ^^^ iltJIT ENGINE DRIVEN VUJEHNATOR TO srtib OUTER MOTOR AND ALTERNATOR Diagrammatic layout of synchronizer installation showing effective link-up of the various components. speed is greater or less than that of the mas>ter. Through its mechanical linkage with the constant-speed unit control, the rotor will then make the necessary correc- tion to the c.s.u. to balance or harmonize the engine r.p.m. Operation ol the synchronizer system is very simple. All that is necessary is for the pilot (or engineer) to select the desired engine r.p m. in tne normal way with the airscrew constant-speed controls, and then to select a " master " engine on the control panel. The synchronizer is then switched on and the action will continue indefinitely, provided no •-onstant-speed lever is moved relative to its iellows further than a posi- tion equivalent to a difference of 250 r.p.m., it being considered that this gives a suffi- cient range to cover a reasonable displace- ment of controls through wing flexure, climatic change, etc. Adaptability is such that any engine can be selected a? the master, and so in the event of faiiure of the master engine, the lemaining engines can continue to operate synchfonously by the selection of a new master When the synchronizer is not in operation all the corrector motors are auto- matically returned to a datum setting which permits the constant-speed controls to be operated normally. A great advantage of this type of synchronizer is its inde- pendence of any external power supply, and although at present the corrector motor is designed as an independent unit, on production versions, where weight will obviously be of cardinal importance, this component will be produced as an integral part of the constant-speed units for multi-engined aircraft. Blade De-icing The second Rotol innovation is actually an extension of the normal de-icing system revised to ensure a better distribution of the protective fluid over the blade. In the past, it is doubtful if more than 15 per cent of the leading edge has received sufficient fluid to deter ice accretion, and it was thus obvious that a system based on sounder principles was needed if the very real danger of airscrew icing was seriously to be resisted. Conventionally the de-icing system for airscrews incor- porates a pump for delivering the alcohol-glycerine mixture
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