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Aviation History
1931
1931 - 1266.PDF
FLIGHT, DECEMBER 4. 1931 Westland Rudder Bias Gear A Device which Relieves Pilot of Fatigue of Counteracting Turning Moment IN multi-engined aircraft it is necessary, when one of the outboardengines stops, or when its power falls off for any reason, forthe pilot to apply a not inconsiderable force to his rudder barin order to keep the machine from turning. Even in some single-engined types under certain conditions of loading and speed,it is necessary to apply rudder in one direction to keep the machine on its course. Obviously this quickly causes fatigue. When asimple spring-loading device is used for setting the rudder, the pilot can, of course, trim the machine to fly straight, but his ruddercontrol become? unsymmetrical because he is working with the spring in one direction and against it in the other. To avoid this trouble the Westland Aircraft Works of Yeovil haveproduced a device called a Rudder Bias Gear, which enables the rudder to be set either to port or starboard without causing un-symmetrical loads on the rudder bar or pedak. The gear consists essentially of two springs in a telescopic tube arrangement, onespring being the primary and the other the secondary or relief spring. The gear is shown in the illustrations.The primary spring is a helical spring adapted to operate either in tension or in compression. It is this spring which, through themedium of the. telescopic tube, applies the load to the rudder bar. CASE I. 64 tf< B'l 775 "A FIXED REACTION POINT MAY BE PLACED ANY- WHERE BETWEEN A1 & B1 WESTLAND RUDDER BIAS GEAR: Three positions, corresponding to normal, or all engines working, starboard engine off, and port engine off. For explanation see text. SUGGESTIONS FOR ATTACHMENT: At the top the gear applied to a rudder bar and cable system, and below, an arrangement for rudder pedal and push-and-pull tube system. By means of a crank on the end of a threaded shaft thespring can be compressed or tensioned to the desired extent. The relief spring allows the restoring force toremain substantially constant irrespective of the amount of displacement, and is adjustable by a knurled knob togive " light " or " heavy " rudder according to the wishes of the pilot. The complete unit is 2 ft. 6 in.(76 cm.) long and weighs 9 lb. The rudder bias gear has been used on the Westland " Wessex " for a considerabletime with good results, and is suitable without modifica- tions to rudder systems in which the load at the end ofa rudder bar lever 8| in. long does not exceed 50 lb. One of our illustrations shows the rudder bias gear asapplied to a three-engined aircraft. The illustration at the top shows the position under normal conditions, i.e.,with all three engines working. No load is applied to the bias spring A, and the effort required to compress ortension this spring is balanced by the initially compressed relief spring B. The centre diagram corresponds to case 2 (starboardengine off). In this position spring A has been tensioned by rotating the handle anti-clockwise, which screws the nutback and thereby automatically putting on port rudder. The lower diagram represents case 3 (port engine off),and shows spring A compressed by clockwise rotation of the handle, which screws the nut forward and thereby putson starboard rudder. In addition to its original use as a rudder bias gear, theWestland device can also be applied to a tail trimming gear, lor either movable tailplane or for the elevator. TWO VIEWS OF THE GEAR: On left in position corresponding to port engine off, and on right in that assumed for trimming when starboard engine is off. -.--;•. ::.,•:.'->,.• : : :. .. :. •'. /• .. : -.- -. 1188
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