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Aviation History
1939
1939 - 0262.PDF
96 FLIGHT. FEBRUARY-2, 1939 PLANNING for the FUTURE The Air Ministry's Zoning and Layout Scheme for Standard Aerodromes The Need for Obstruction-Free Approaches SINCE the earlier days of air transport, ideas in the matter of safe and convenient aerodrome size and location have steadily changed. Not only have wing loadings and machine sizes increased, so that longer take-off and landing runs are necessary, but the ability to fly and to navigate in really bad weather has meant that the most careful attention has had to be paid to the ques tion of removing all surrounding obstructions. Actually, the present-day aeroplane, with a large flap area, can, if necessary, make an approach at a very steep angle if the comfort of the passengers is ignored, but such a technique of approach is particularly unsatisfactory at night or in bad visibility. Furthermore, and speaking .generally, take-off runs have increased out of all propor tion, and the post-take-off rate of climb has, in addition, been tending to decrease year by year. Municipalities, therefore, and others concerned with the layout of aero dromes are finding that it is necessary to buy, or at least to control, a considerable area of land in addition to the already comparatively large space taken up by the landing field itself. It might be thought that aerodrome layouts could be standardised by reason of the fact that every machine must have a Certificate of Airworthiness and that this certificate is only given when certain take-off, tlimb, and landing- run figures have been accepted. These figures are quite definite ones, but it must be remembered that they are often obtained by experienced pilots in chosen weather conditions and that they do not usually apply to operations with full load in normal service. For instance, many machines have a tendency to be somewhat lacking in lateral control near the stall, and it is normal for pilots to hold such machines down until more than ample flying speed has been obtained. For the same reason approach speeds and angles vary within big limits. During a bad-weather approach, too, the actual touch down is often made at a very much higher speed than that of the normal stall, and the landing run, consequently, is a good deal longer. Three years ago the May bury Committee, in their report, enunciated the principle that, in order to ensure air service regularity in all conditions, it was necessary to arrive at some minimum standard of aerodrome dimensions, and a recommended aerodrome size and general layout was illus trated in an appendix to the report. These recommendations involved not only minimum lengths of run—which were i,oooyd. in at least four direc tions, with a longer run for bad-visibility work—but also a system of obstruction '' zoning'' for the district around the aerodrome. By such means numerous approach lanes can be arranged and any unreasonable building can be pre vented in certain selected areas. Clearing the District Only by preserving the natural approaches from the out side is it possible to prevent what amounts to a reduction of the effective dimensions of the aerodrome itself. In the same way this zoning plan allows for the layout of essential administration offices and hangars in positions where no serious obstruction can be formed by them. The Air Ministry, consequently, has formulated a series of principles governing aerodrome planning. In these prin ciples it is considered that two different types of aerodrome are necessary. The first is known as a " standard " aero drome and is intended to be suitable for the operation of regular day and night services, while the other is considered as a " secondary " aerodrome, and this would be intended for other purposes, such as school and club flying. In the case of the first or standard aerodrome, it is sug gested that the landing area should consist of not less than four runways, each of which is supposed to be at an angle not greater than forty-five degrees to its neighbour. The minimum dimensions of these runways should be i,oooyd. by 200yd. wide, while one of them, designed for low-visi- Lijnite of Landing Area Comprising 3 Runways of 1,000 x 200 Yds. and 1 of 1,300 x 400 Ydi No Obstruction above a slope of 1 in 15 measured from the end of the Runway. No Obstruction above 35 feet in theae areas. Sites 50 x 50 feet for Inner and Outer • Radio Uarkerbeacona. 100 Indicates no Obstruction above 100 feet. 200/ ,, n H , 400 „ „ The Datum from which heights shall be measured is the Mean Level of the Landing Area. Wherever two different height restriction zones overlap the permissible height shall be the lower of the two. Small departures from the restrictions shown may occur with alternative runway arrangements. An idealistic representation of the aerodrome zoning scheme described in this article.
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