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Aviation History
1950
1950 - 0246.PDF
The superiority of the diffuse beam of the Harley lamp (upper views) over the hard beam of the R.A.E. " K " type unit can be clearly seen in these photographs, which were obtained during the comparative trials conducted by British Overseas Airways Corporation. FOR "LIGHTER" LANDINGS •' Recent Developments in Landing-lamp Design : The Harley Range THAT some pilots, particularly those of the olderschool, consider the aircraft landing-light to be moreof a nuisance than an asset almost certainly arises from the fact that they have never had the opportunity of landing with a really efficient lamp. The question then arises, " What are the essential qualities of a really efficient landing-light?" A consensus of pilots' views would show that the ground ahead should be brightly illuminated for as great a distance as possible in all directions ; and that at the same time the beam itself should not be* so ' 'harsh*' as to distract the eyes and prohibit retention of a wide field of vision. In fact, it might be said that the essence of a good landing lamp is that a pilot should be able to see by its illumination in spite of its beam. To this end the firm of Harley Aircraft Landing Lamps has devoted considerable research over recent years and has evolved a principle which appears to be giving very satisfactory results. In the Harley lamp the user has an extraordinarily powerful light for a relatively small current consumption, distance-intensity being combined with good local illumina- tion of wide spread and depth. These lamps differ notice- ably from other types in the addition of a fluted lens fitted behind the upper half of the glass. The object is to project and diffuse the beam from the upper half of the reflector down through the beam from the bottom half, thus giving a graduated area of light while retaining distance-intensity and eliminating the effect (normally experienced with high- power conical-beam lamps) of a hard, glaring beam with a sharply defined cut-off at its edge. A recent comparative demonstration of lamps of varying size and power, all using the Harley principle, showed con- vincingly its distinct superiority over a unit (in this case a standard R.A.E. "K" type lamp) employing the hard- beam principle. Even with the lamp elevated to give its extreme range—dependent, of course, on the power of the unit in question—a wide span of diffused light, in which objects could be clearly distinguished, extended to either side of the almost invisible beam. The ' 'K'' type of lamp, however, gave its intense illumination over a more restricted area surrounded by an impression of complete blackness in which it was impossible to recognise even comparatively large objects. Incidentally, it may be remarked that cer- tain American lamps, mostly developed on the "sealed- beam" principle, go some way towards eliminating the more undesirable qualities of a hard beam. A double-filament arrangement can be supplied at option on most of the Harley lamps. In this case independent switching enables the secondary filament—normally rated at a lower wattage than the primary—to be used for taxy- ing purposes. The life of the main filament is thus lengthened and the load on the battery reduced at a time when the generator is not giving its full output. Comparative tests have been carried out by the B.O.A.C. development flight at Hum, using a Lancaster aircraft, and results of these tests were based on a series of twelve night landings and take-offs. The lamps in question were a Harley model 19KS-500 with a single-filament 500-watt bulb and, for comparison, a standard R.A.E. modified "K" type, fitted adjacent to the Harley lamp. Extracts from the reports indicate the pilots' definite preference for the Harley system : " With the Harley lamp in its fully extended position, on the descent it was quite easy to look down through the beam and see the approach The Harley model 9K as fitted to the Viscount and Comet, «f"
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