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Aviation History
1956
1956 - 0224.PDF
222 JGHT, 'ebruary 1956 Fig. 1 :m (Right) Fig. CITY-CENTRE HELICOPTER OPERATIONS . . . beam rotated, the output of the receiver being of the form shown in Fig. 3. If the helicopter were further from the vertical axis, at point Y', the depth of modulation would be greater (Fig. 4) and, thus, a means of determining the helicopter's distance from the vertical axis of the cone was obtained. A means of determining the helicopter's bearing from the vertical axis, down which it wished to descend, could be seen from a study of Figs. 5 and 6. The dotted line in Fig. 5 repre- sented the path of the beam axis. The helicopter was assumed to be at a bearing of 300 deg relative to the scan axis. By suppressing the beam for a brief instant as it passed through north, a signal of the form shown in Fig. 6 would be received by the helicopter. This could be displayed to the pilot on a small cathode-ray tube on the face of which a spot would be caused to rotate continuously, synchronised with the rotation of the beam. The spot would pass through the point P (Fig. 7) each time the beam pointed due north. The instant when signal strength was at a maximum (t, in Fig. 6), as the beam axis passed through the helicopter, could be marked by increasing the brilliance of the spot on the cathode-ray tube. To complete the picture a radial line on the face of the tube repeated the indications of the heli- copter's compass and this provided the pilot with an indication of his machine's heading. In practice, the pilot homed on the station by means of his navigational aid and then switched on his landing aid. If pre- sented with the picture shown in Fig. 7, he increased his heading from 045 deg to 120 deg so that the radial line pointed away from the brilliant spot marking his own position. Distance from the vertical axis of the cone would be indicated by making the diameter of the circle described by the spot proportional to the depth of signal modulation. As he approached the centre, there- fore, the diameter of the circle would shrink and the brilliant spot would approach the centre of the tube face. When the spot was in the centre, the pilot reduced height, correcting for lateral dis- placement as required. F.xact altitude could be measured by using short range FM radar installed on the flight deck. THE DISCUSSION MR. R. H. WHITBY (British European Airways) opened the discussionby saying that Mr. Shapiro had introduced a highly controversial subject. What had been said by the supporting speakers followed logically if theoriginal premise of vertical operations was accepted, but he was concerned by the possibility of the helicopter entering the vortex-ring state duringthe descent and becoming uncontrollable. He thought that vertical approaches might make the operations more difficult for the pilots. Hehad had experience of landing on a high roof platform in New York and was somewhat doubtful whether the majority of passengers would favoursuch methods. MB. SHAPIRO, in reply, said that the availability of a fully automaticallystabilized helicopter had been assumed and he was hoping to hear from other contributors to the discussion that such equipment did exist. It waspreferable that the machine should be stabilized with reference to gravity axes and not with reference to the air. In fact, it might be desirable thatthe stabilization be effected with reference to ground features so that it AMPLITUDE !OA I OB AMPLITUDE TIME TIME Fig. 3 Fig. 4 could be used as an alternative landing procedure controlled from theground. With regard to the danger of entering the vortex-ring state, more knowledge was certainly required; but he thought that the danger-ous state would be at a rate of vertical descent of 1000 ft/min, whereas they were proposing a let-down speed of 500 ft/min.MR. G. HINCHLIFFE (Decca Navigator Co.) gave a brief description of the navigational aid manufactured by his company and stated that theaccuracy of the system was already sufficient to enable the type of opera- tions described to be earned out. If at certain points on the fringe ofthe Decca chain the accuracy was not sufficient to ensure that the heli- copter pilot could navigate to the let-down cone, a small auxiliary chaincould be set up at a cost of approximately £10,000 to provide an accuracy down to 15 yd. A large scale version of the Decca Flight log had nowreached an advanced stage of development. This would provide security against collision in the helicopter traffic pattern, since it could be readwith greater accuracy by the pilot. Helicopters could fly on parallel tracks 400 yd apart and the maximum margin of error in reading the logwould still allow a safety zone between them, 270 yd in breadth, where helicopters would never appear. He thought the speakers had paidinsufficient attention to air traffic control problems. MR. SHAPIRO, in reply, said they had not discussed air traffic controlbecause they thought that a reliable navigation aid would provide the solution to problems of this nature.MR. C. A. RICHARDSON (Sperry Gyroscope Co.) described the recently perfected helicopter control system which had been developed by Sperryin the U.S.A. The system provided all that was asked for by the originators of this proposed type of helicopter 'bus operation. The basicequipment weighed 60 lb and provided automatic stabilization about the pitch, roll, and yaw axes in all flight conditions including hovering. Inaddition, it incorporated a height control and rotor speed control. It could be switched in by the pilot and operated through the normal heli-copter controls or, alternatively, could accept control signals from a ground station. The system had successfully completed an extensiveflight and ground test programme and was now going into production in the U.S.A. It could be made available in Britain. MR. A. E. BRISTOW (Bristow Helicopters, Ltd) considered that theproposals for helicopter operations of this nature were far too ambitious and futuristic. As a practical operator of helicopters he wanted to workinto city centres but not, at the present time, on roof-top sites; these were generally far too small.DR. O. P. MEDIRATTA (Louis Newmark, Ltd.) said that his company also had produced an automatic pilot for helicopters which had been inoperation in Britain for sorfie time. It was not possible to give details at the present time but it would be available later for future use in thistype of operation. They were also in course of developing a lightweight automatic pilot for smaller helicopters, and this equipment would weighapproximately 30 lb. MR. P. HEARNE (British European Airways) thought that, until fullyautomatic landing was possible, the pilot must be able to see the ground during the final approach phase. Since he had to make the transitionfrom instrument flight to visual, the minimum operating conditions should be considered as cloud base 200 ft with visibility 500 ft approxi-mately. In vertical approaches, handling qualities were poor and they deteriorated as helicopters increased in size. He thought the sector-scantype of radar held promise as an approach aid or, alternatively, the centrimetric I.L.S., but his experience led him to believe that verticaloperations could not be considered. MR. SHAPIRO, in reply, said he felt there was no justification for sayingthat future helicopters would be more difficult to fly or that vertical operations were difficult. With fully automatic stabilization the heli-copter would be transformed. MR. T. MEFFEN (member of Coventry City Council) said that inCoventry they had allocated space for both roof-top stations and ground- level landing grounds; but he was not convinced that the helicopterwould prove to be an effective rival to the train over such a short distance. DR. G. S. HISLOP, the chairman, in winding up the meeting, said thatsuch a distance was indeed a border-line case for the helicopter when competing with mainline railways. However, over the same distance thehelicopter could justify itself easily away from the mainline railways or in providing direct connections to a main airport. Where an inter-vening stretch of water had to be crossed, the time-saving by helicopter was even more considerable. • AMPLITUDE Fig. 6 Fig. 7 2 7O :!2O°
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