FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1955
1955 - 0247.PDF
25 February 1955 247 of the visibility along the runway from the point of touch-down;and should this be too low for safety he will not, of course, start his approach at all. It is a particular feature of the cross-barlighting system that it provides the pilot with the visual guidance he needs to correct his lateral position, assisting him in separatingthe effect of bank, and lateral displacement from the centre line, which, when viewing a single line of lights, produce a similarvisual impression, but a very different sequence of movement. The factors which have had a radical impact on the all-weatherlanding problem in recent years have been the increased precision possible in the radio beam, and ground radar, and the introductionof the cross-bar lighting system. These advances have allowed the development of safe landing techniques for weather down to"runway-visual-range" visibilities of about 500 yards. Abortive approaches, however, are not rare in conditions near the lowerranges of visibility, and the reason for this is not far to seek. It is that the "runway visual range," though the best criterionreadily available ... is nonetheless misleading in some cases as a guide to the slant range at which the pilot will be able toacquire a full visual grip on the approach lighting system. Recent advances in radio and instrument technology will pro-vide further improvements in the accuracy of definition of the approach path, and will supply the pilot with simplified indica-tions to assist him to fly the path accurately. They will also provide the means of so coupling the signals received in theaircraft from the approach beam radio transmitters to the auto- matic pilot that the aircraft can fly automatically with precisionand reliability down the approach path. I will not consider these advances in further detail save to remark that they will enablecivil operators to work safely and reliably down to the minimum visibility needed to permit a safe visual landing to be made; Iwill, however, discuss how we may hope to take the matter further. There are two approaches to the problem, the first to providesuch assistance to the final phase of "flare-out and touch down" —the phase below the critical height—that it is made withoutreliance on visibility. The second is to increase the visibility for touch down by dispersing fog. It may well be that a combinationof both will provide the eventual solution. As a complement to a solution, means will be needed to enable the aircraft to taxisafely on the airport in bad visibility—there is no point in achieving a landing only to become lost in the fog on the openarea of the airport. In Fig. 17 is illustrated an airfield equipped with a numberof devices with which we have experimented recently. I must say immediately that this airfield does not exist, for the experi-ments of separate components have been made in separate places, but the results are nonetheless valid. I will divide the equipmentinto these categories, to be dealt with separately: The automatic landing element, the fog-dispersal element, and the taxyingelement. The Automatic Landing Element.—In an experimental equip-ment with which we have made automatic landings the airfield is equipped with the I.L.S. radio beam system to define theapproach path, and with a leader system, carrying an alternating electric current, as indicated in Fig. 17. The aircraft is equippedwith an automatic pilot, into which the I.L.S. signals are fed, and_ which guides the aircraft down the approach. On reaching thecritical height, control of the automatic pilot is transferred from the I.L.S. radio beam to elements in the aircraft which, derivingtheir information from the magnetic field of the leader cable system, land the aircraft automatically. The system lands theexperimental aircraft with a vertical velocity at touch down and with an error in positioning relative to the centre of the runwaywhich compares favourably with the performance of skilled human pilots working in good visibility. There is no doubt that, for civil aviation, the step from usingI.L.S. or G.C.A. approach, followed by visual landing, to the use of an automatic system such as this would be a major one, involvingthe most careful consideration of reliability and safety. I do not think that the "state of the art" is such that it is ripe for such achange yet—though considerable progress has been made in ensuring the reliability of the equipment and in making sure that,if it fails, it "fails safe." The Fog-dispersal phase.—During the late war the remark-able fog clearing device known as Fido was developed, and it proved itself capable of greatly facilitating landings in quite thickfogs. It was a fine achievement of the Petroleum Warfare Depart- ment, and it is no criticism of that achievement to say that thesystem was so costly to operate for short runs that when viewed against a background other than that of war it was unable to servea civil need. . . . We have been trying to produce a system which uses a cheapfuel, which can be started and stopped very quickly, and which is controllable in intensity of burning so that the fuel consumptionis no more than the particular fog condition demands. These aims have been largely achieved in a system which operates on gas-oil.Atomising burners have been developed which can be opened-up without a preliminary warm-up and which cut-off immediately on shut-down. Each burner head has three atomizing nozzles ofthe swirl-chamber type, operating from a fuel line at 1,000 lb/sq in pressure. The burner heads are set in slotted plates mountedin concrete pots so that they can be used at runway intersections without causing interference to aircraft using the intersectionwhen the system is not operating. In the part of the installation ahead of the threshold of the runway the burner can readily bemounted on riser pipes at heights to suit local conditions. Control is obtained by grouping the burner heads in lines of three, fed bytwo main feed-lines, one connected to a single burner in each group and the other to the remaining pair. Output can thus bereduced by one-third, or two-thirds, by simple valving. Rapid- action spring-loaded cut-off valves are fitted between each burnerand its supply line, to ensure that there is no spillage of fuel when starting or stopping. Ignition is by means of heater-coil igniters.This system gives a very clean flame which provides about 30 therms per yard per hour on about 18 gallons of gas-oil per yardper hour. The stage has now been reached at which the economics andeffectiveness of this system can be assessed by practical test; a complete installation is to be made at an airfield, for trial. Shouldsuch a system prove reasonably economical for use in civil aviation, the visibility at which routine visual landings could be made offI.L.S. or G.C.A. would be very substantially lowered. Were this done, a system permitting taxying on the ground subsequent tolanding would be desirable, and one such system is described1 in the next section. The Taxying Phase.—We have made some experiments inthe use of a leader cable installed in the taxi-track as shown in Fig. 17 to direct the movement of aircraft on the ground in con-ditions of bad visibility. The aircraft carries equipment for receiving magnetic signals from the cable, as in the automaticlanding equipment. These signals feed a pilot's indicator showing displacement from the centre line of the taxi-track, and deviationfrom "correct" heading, the "correct" heading being such that, when the aircraft is displaced from the centre line, and it is put on,and kept on, correct heading, it approaches the centre line ex- ponentially. In aircraft equipped with a steerable nose-wheel,there will be no difficulty in arranging for automatic steering. In a complete airfield installation, the leader cable could beswitched in sections in order to guide the aircraft along one of several alternative tracks. Used in conjunction with a micro-wavesurveillance radar, which would show the position of all aircraft and vehicles on the airfield, it could provide mobility in dense fogconditions. Where Will This Take Us?—The experiments I have describedat least show that progress can be hoped for in reducing the effect of bad visibility on regularity of operation. I have no doubt thatother methods may emerge. Indeed, the developments in ultra- high-frequency radio transmission are such that the replacementof several of the devices I have mentioned above by what might be described as "radar-television" is by no means impossible.Such a system might eventually be capable of providing a picture of the airfield ahead of the aircraft to a fineness of detail onlya few times poorer in resolution than the impression gained by eye. If this proves to be the case, the pilot might well be providedwith a synthetic picture of what is before him which is sufficiently little different in the essentials from what he normally sees by eyethat he could make a landing without other aid. There can be no doubt that, whatever system is used for badvisibility operation, the task of the system and of the pilot is rendered easier as the approach speed of the aircraft is lowered.The gain of ease and safety with drop of speed is, I think, a very rapid one. Most of the critical issues are matters greatly affectedby "time available" for decision and action or for automatic mechanisms to do their work. The wisdom of using some of thetechnical advances available in aircraft design to lower approach speed, rather than to take the "last ounce" on economies in thecruising phase, will be well repaid by greater regularity with safety. If we are to achieve what we should seek in bad weatheroperability, the task should not be left entirely to the instrument and electronic engineer; a contribution from the aeronauticalengineer, in terms of lower fully controlled approach speeds, is needed. Conclusion.—Many of the possibilities before us are exciting—aviation will continue to move fast. The engineer is sometimes accused—sometimes rightly, sometimes wrongly—of wanting thenew when the consolidation of the old would be wiser. The civil aviation scene needs some of both. In the long-range field at leastwe need new breeds of aircraft to provide the economy and service the passenger needs, and the possibilities are before us,but we must eliminate the not entirely incorrect idea that aviation still has some hazards. This is the major matter to be borne inmind when capitalising the newer possibilities. It is to this that attention must be continuously directed, and if we have an eyeon the distant possibilities—as it is right that we should—we should nevertheless see to it that the fullest use is made at theearliest opportunity of those things which make for a safe, reliable journey at a reasonable price.
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
