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Aviation History
1947
1947 - 1669.PDF
SEPTJSMBER.25TH, 1947 FLIGHT 367 New Autopilot ..-adM*^ useful feature is the incorporation of a torque switch which automatically disconnects the autopilot when the voltage rises or falls beyond predetermined limits or in the event of fuse failure in any of the three-phase supply lines. All the separate units are expressly designed for rapid installation and removal in order to facilitate servicing. In this connection, it should be emphasised that the policy is for any defective unit to be unshipped from the aircraft and replaced on the spot by a service- able replica, the defective unit being returned to the makers for repair. As the designed maintenance-free life of the units is, at the moment, no less than 1,000 hours, whilst the intention is to make this 2,000 hours, such a servicing scheme has obvious advantages ; not the least is that it is far better that any fiddling with the unit viscera should be done by the makers alone. To facilitate unit change, the junction box and amplifier are made with quick-action lock- ing and anchor points giving three-point mount- ing. This is the static mounting of the enclos- ing case, the "works" being supported on a flexibly-mounted chassis inside the box. The gyro-unit base-plate is bolted at three points to a tubular sub-frame, which itself is carried on three anti-vibration mountings from a supporting frame. This latter .is mounted in the aircraft by two bolts and a single jacking point whereby the base-plate may be levelled. The "permanent" (torque shaft) halves of the servo-motors have three mounting feet for attachment to the airframe, the motor side of the unit having a three-bolt attachment to the torque shaft sub-unit. The switch unit has '' IN '' and '' OUT '' press button switches—supplemented by an " OUT '' instinctive switch on the control column—and separate circuit switches for each of the three servos so that individual operation can be periodically checked by the pilot for trim accuracy. A system master switch incorporating a solenoid "hold-on " is also carried on the unit, the purpose of the hold-on being that the master switch can be maintained in the "ON" position only whilst a power supply satisfactory junction box with enclosing cover removed to show torque switch (centre top), reversing links (bottom left) and sensitivity adjusters (bottom right). for correct operation of the autopilot is available. If anything goes wrong with the supply, the switch at once flies to "OFF" and will not hold at "ON" until the proper supply is restored. On the side of the unit are an amber and a green light, the amber light indicating that the autopilot is ready for use but not in operation, and the green light indicating that the autopilot is in use. Should one of the three servo-motor switches have been inadverently left at " OFF," both the amber and the green light will indicate the abnormal condition ; these lights embody dimming control for day or night relative bright- ness. An elevator trim indicator is also incorporated in the switch unit so that the pilot may see at any time the trim condition that obtains; he should, of course, make sure that the indication is in the zero region before disen- gaging the autopilot. Destructive Elegance Ths first picture of the new Boeing Xb-47 bomber prototype for the U.S. Army Air Forces. Six axial-flow turbo jets, the distribution of which is evident, are fitted, and the main wheels of the undercarriage retract into the fuselage. The most significant design feature, however, is the sweep-back on the wing and tail surfaces.
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