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Aviation History
1946
1946 - 2160.PDF
t/ FLIGHT OCTOBER 31ST, 194ft VfcN TOWARDS COMPLETE AUTOMATICITY one "turn" knob, an aileron trim control, and three indi-cators. Outside the control box are the mechanical engage- ment controls which clutch-in the servos, and two emer-gency release buttons, normally mounted on the control columns, which electrically cut out the automatics. Inthis case the servos are still engaged, but the friction intro- duced is comparatively small. When using the A. 12, a master switch is moved to the"on" position and, when the aircraft has been trimmed more or less level laterally, the servo controls can be en-gaged. The aircraft will then continue to fly in the same attitude. It the engagement has been made slightly winglow, the lateral trim is afterwards adjusted on the aileron trim knob, which has no other purpose. The pilot switchcannot be moved to the "on" position (or, alternatively, will be automatically moved to "off") if there is noelectrical supply, or if this has not been on for at least two minutes, if the master servo controls are engaged, orif the turn control knob is not in its neutral position. The turn control feeds in bank—according to the rateof turn desired—and an amount of co-ordinated rudder movement to make a correct turn. Co-ordination is main-tained during turns regardless of changes in air-speed, but they will not necessarily be level unless the altitude con- V The flight amplifier assembly, showing the "tuning" adjustments which are made and set after installation. trol is used. This is brought into action by moving thesecond switch already mentioned. Altitude is then main- tained within certain limits (plus or minus 20ft), whileattitude corrections are still fed to the elevator servo. Means are incorporated in the control to ensure that initialcorrections are made gradually, so that any malalignment of the aneroid signal system will cause no sudden changeof attitude. Whenever the master switch is "on," the gyro correc-tion signals are continuously fed to the servos, so that these follow the changing attitude of the aircraft ; thus, whenthe servos are hist engaged, there should be a smooth transition from manual to automatic control The relationship between the gyro signals and the air-craft's attitude is shown on the three indicators on the control pedestal. Whereas the separate elevator trim-tabservo would keep the fore-and-aft trim correct, and its indicator needle would consequently fluctuate around theneutral position, a continuous indication one way or other - of the rudder or aileron meters would show quite clearlythat the automatic pilot was fighting an out-of-trim condi- tion, and would thus suggest the need for re-adjustment ofthe manual trimmers. As an example, if the starboard outer engine faded through fuel starvation, the constant-speed airscrew would be likely to maintain cruising revolu- tions and the boost figure^ would, therefore, be unaltered.With the automatic pilot in action the captain might not The gyro controls for the three servos. On the left isthe Gyrosyn compass control and on the right that for pitch and roll control even be aware of the loss of this power. But the fact would be made obvious by the way in which the rudder and aileron meters would be continuously offset in relation to their normal datum. Before disengaging the auto- matic pilot, these three indicators will therefore show whether or not the aircraft is in trim to suit the par- ticular attitude. . The Gyrosyn Compass As already explained, directional corrections are provided by a Gyrosyp compass, which might be described as a combination of the distant-reading magnetic compass and a directional gyro. When an aircraft is fitted with the A.12, the compass control is part of the automatic pilot equipment, and the visual readings for maintenance of course are given on a series of repeater dials. The principle of the compass control is, however, entirely similar to that of the basic Gyiosyn compass which can be installed independently with, as many as six separate repeaters. The stabilizing gyro of this compass is basically similar to that of the standard directional gyro, but the dead-beat movements of the indicator are moni- tored thiough a selsyn by the flux valve, which is very small and can be mounted wherever the mag- netic deviations are slight. This flux valve, which has no rotating parts, senses the magnetic heading, which is recorded electrically and used to " slave " the gyro indi- cations. The result is that the Gyrosyn compass has the: is iha One of the three control servos installed in a Liberator. Itslength is about a foot. The cables are taken round the drum seen on the left.
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