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Aviation History
1938
1938 - 0511.PDF
FEBRUARY 24, i938- FLIGHT. 181 Commercial Aviation AUTOMATIC HOMING Two Navigational AMs—D/F and the Automatic Pilot—Combined for Air Survey : A Development With Great Possibilities. Two views of the interior of the survey Dragon. The first of them shows the cabin arrangements with the drift sight, linking unitar.d D/F receiver on the left ; the two axis control unit and short-wave receiver in the centre ; and the transmitter anJ the camera cradle stabiliser on the right. Through the door beyond the transmitter may be seen the automatic pilot control panel.The picture on the right shows the installation in the pilot's cockpit, with the loop control, direction-finding receiver and charging switchboard. The lateral automatic unit is-below the pilot's seat. ALTHOUGH the idea of linking an automatic pilotwith radio D/F equipment is not altogether new—^ some experiments have already been carried out in America and elsewhere—this country can reasonably take the credit for producing the first combination of this equipment to be used in practical operations. It was, perhaps, somewhat natural that a survey company—Air Travel and Survey Pty., Ltd., of Sydney—should first take a serious interest in the commercial possibilities of sucha development, since survey work involves very accurate fly- ing for long periods if the results are to be really useful.Nevertheless, the idea has far greater possibilities. In the transport world, for instance, the pilot has already been re-lieved by the automatic pilot of the need for constant course- keeping and bump correction during a long flight, so that hemay be free to attend to his navigational problems and so that, incidentally, his nervous energy may be properly con-served for the more difficult business of making the final ap- proach and landing in weather conditions which are oftenvery trying. ' There is no reason why this useful relief should not be, tosome extent, now extended to the approach itself, the machine being held on its course down an ultra-short wave beam, orother radio guide, with far greater accuracy than would be possible by human endeavour, while the pilot concentrates al-together on his stop-watch, his sensitive altimeter and his air- speed indicator. The two firms which have recently been working on thisinteresting combination are Marconi's Wireless Telegraph Co., Ltd., who, of course, carried out the radio work, and P. B.l>eviator, Ltd., who supplied and installed the automatic pilot. The initial experimental flying was done by Capt. Philip"ailey, of the P. B. Company, in his Puss Moth, but the equipment is now installed in a D.H. Dragon, which, afternnal tests, will be flown out by Mr. Macarthur Onslow in easy stages to Australia, where it will be put to work. Ihe principle behind the operation of the equipment is really quite a simple one, though, as is usually the case, there is aur| y Iarge gap between principle and practice. Briefly, the directional and fore-and-aft unit of the automatic pilot layoutis constantly readjusted through electro-magnets by meaiis of the microammeter, used in the ordinary course of events forindication of course changes, while homing on a fixed route. In fact,' the equipment will work equally well while flyingwith the loop in the fore-and-aft plane and the receiver tuned in to a broadcasting or other transmitting station lying to theright or left of the track, though in this case the course which is automatically flown will be in the form of a curve, theradius depending on the distance of the station from the machine. The idea was particularly applicable to the type of automaticpilot developed by the P.B. Company, since an electro-mag- netic form of gyro-precessing control had already been in usefor some time. In the case of any machine fitted with this form of automatic pilot a control panel can be arranged so that bythe depression of different press-buttons, electro-magnets radially disposed._around a soft-iron armatvye, on the extensionof the gyro spindle may be suitably energised. By this means the gyro axis is tilted to provide, through the servo-operatingmechanism, the necessary change of course or attitude. The Linking Method It was only necessary, therefore, to connect this electrical control in some way with the direction-finding indicator. This indicator is so designed that lag prevents the pointer from fol- lowing individual pulse changes in the signals, and it simply records an overall change in signal strength. With the loop adjusted at right-angles to the line of flight while the machine is flying toward a transmitting station, deviations to the right or left, with a consequent increase in signal strength, cause the needle to deflect one way or the other. A sensitive moving-coil relay is arranged so "that its tongue follows the movements of the needle. On either side of this tongue is a contact connected to two subsidiary relays, either one of which is energised when an off-course reading is registered. These subsidiary relays are also provided with contacts which com- plete the circuit and suitably energise the gyro's electro-mag- nets. As the gyro is precessed, valves operate the appropriate servo motor to correct the deviation.
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