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Aviation History
1939
1939 - 1238.PDF
APRIL 27, 1939 FLIGHT. r them to the heading of the aircraft the machine should be taxied round through at least 360 degrees, the compass allowed ample time to settle, and the readings again compared. Except with a very stable aeroplane on a large, smooth aerodrome with which the pilot is very familiar, the use of a fogline is essential, if only to give positive directional guidance up to the point of leaving the ground. Many air craft have to be " flown off," and, as actual sight of the ground is then needed, fogline guidance cannot be dis pensed with. If a fogline is not used the point and direc tion of departure must be known and verified beyond all possible doubt, but it is felt that because of the disastrous results likely from an error in this matter it is not really desirable to take off thus on any scheduled service. There is hardly ever any wind in dense fog, and the take-off is normally best made in the reverse blind- approach direction, this being the most obstruction-free. Needless to say the maximum run available is taken—it is often not easy even to find the fogline, let alone the usable end of it—and this is one of the points calling for familiarity with the aerodrome. If an approach beacon is available it can be of assistance as a check on the main tenance of the desired track after the take-off, and in this case the appropriate fogline, should there be more than one, is used. In using an approach beacon thus the re ceiver A.V.C. should be in circuit, so that the signal strength is kept constant within the limits of the receiver, for at the outset the aircraft will be very close to the beacon transmitter. The compass verge ring is best set to the take-off heading, and, for convenience, the directional gyros at "O" on that heading. The take-off is effected by sight up to the point of becoming air-borne and then continued on the instruments. Should sight of the fog line be lost before leaving the ground it is highly advisable to stop and return to the beginning again, for a swinging take-off may be difficult to correct on instruments, and can easily become dangerous. Self'Contained Navigation Undercarriage retraction is effected as soon as the machine is air-borne, and as usual every effort made to attain minimum '' one engine '' flying speed as soon as is possible, but the minimum safe heights at various dis tances out on the departure track must be borne in mind, and here the approach markers are of service in accurately indicating points on this track. It is obvious that great trust has to be placed in the sensitive altimeter, and the desirability of the provision of two of these, as mentioned above, is again stressed. After reaching the minimum speed referred to, the aircraft can be put into its normal climb and the usual adjustments to airscrews, flaps, throttles, etc., made. Given adequate equipment, and provided the pilot has the necessary skill and quickness on the up-take, the above procedure appears to make use of all avail able safeguards, to take care of all even tualities, and to be possible in regular scheduled operation. It is applicable to all cases when visibility is not as short as the minimum quoted, and greater visibility will naturally make things much easier. During foggy weather the actual journey will probably be made at least partly out of sight of the ground, and because of the radio congestion, which (whilst always existent in clear weather, by reason, amongst other things, of the shortage of frequencies for two-way communication) is greatly increased in bad weather, it is much more necessary for the aircraft's crew to be able to do their own radio navigation. This ability is, of course, a great advantage at all times with the logical '' above the overcast" flying on long-distance services. An example of duplicated instrument-flying panels—interesting because it is the control cabin of the Dornier D0.24 four-engined transatlantic flying boat. Notice the two distant-reading compass dials at the top of the panels. The radio equipment described will enable this to be done as far as is possible, and two-way communication can be reduced to the very minimum. As the loop is a very simple type of D/F aerial, it must be borne in mind that extreme accuracy cannot be expected, and in good con ditions errors of plus or minus 3 degrees are usual, whilst when night effect is present errors of large, unknown amount may occur. Selection of transmitters on which to take bearings must therefore be made with this in mind, and stations over 80 or 100 miles away should not be used unless no others are available. It is also found that trans missions of frequencies higher than about 800 kc/s or so will not generally give reliable bearings. Arrivals in foggy weather, and at other times when fog regulations are in force, are almost always effected by some sort of "zone procedure." When traffic is heavy it assists smooth working if, as soon as an aircraft arrives in the radio area of its destination, the fullest information is given in one comprehensive signal to the Ground Control as to height, speed, E.T.A., and intentions, and if Control can then allot a turn for landing and specify a time (as soon as possible after the given E.T.A.) at which the aircraft should arrive, the pilot can usually take steps to avoid having to wait his actual turn to land close to his destina tion in proximity to other waiting aircraft with earlier turns. Some form of " flight plan " system would be a great benefit, but, whilst such a thing is comparatively easy to arrange on a national basis, as, for example, in the U.S.A., its application internationally is by no means simple. One of the great difficulties found by pilots, particularly with fast aircraft, is that of keeping just outside an approach zone at a known position whilst awaiting their turn to land. It would perhaps be possible to make use of track beacons and markers, either medium or high-frequency, to mark zone boundaries and definite positions for waiting aircraft. Certainly the available ground D/F organisation, in this country at any rate, cannot cope satisfactorily with several fast machines at the same time. With the radio equipment as suggested on the aircraft, however, the best use of existing facilities can be made. For instance, at Croydon, by using the D/F set on London Regional transmitter (Brookmans Park) and the high-frequency beacon receiver simultaneously on the Lorenz beacon, station can be kept at a convenient position on the approach beacon axis. It is, of course, advisable to sit on an approach beacon axis only if Control has given a free height at which to do so, or if one is flying clear. Speed and ease of operation being so important, the great advantage of this use of track beacons and markers is that the information • they- give can be instantly available direct to the pilot with the minimum of effort on his part. However, if sufficient thought be given to the use of such equipment as can be installed, it is possible in many cases to cope fairly well with this aspect of the problem. The weak link in the chain is the one machine flving in fog with
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