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Aviation History
1931
1931 - 0445.PDF
FLKJHT, MAY 8, 1931 THE DEVELOPMENT OF THE LONG-RANGE FLYING BOAT By MAJOR J. D. RENNIE, A.R.T.C, A.M.Inst.C.E., F.R.Ae.S. [Major Rennie, who is Chief Seaplane Designer to the Blackburn Aeroplane & Motor Co., Ltd. read this paper before the Home Aircraft Depot, R.A.F., Henlow, some time ago. It is of such extraordinary general interest that we have felt that it deserves to be known as widely as possible, and we are, therefore, publishing the paper in full.—ED.] IntroductionI T will be appreciated in a paper of this length it is only possible to treat briefly the fundamental aspects of the subject, as the detail problems involved, such as fuelling, mooring, etc., although of great importance, are too numerous to be discussed, and are beyond the scope of this paper. Also, it should be stated at the outset that the treatment of the subject refers in particular to military aircraft, although in many respects there is no strict line of demarcation between purely military and mer- chant flying boats. It may be advisable also to state, so far as this paper is concerned, what is meant by " long range," as the term is purely a relative one. In the future the flying boat is likely to be used extensively of a size greatly exceeding the practical and economical limit of the aeroplane, and hence it will of necessity be compelled to transport itself to its base of operations. From the geographical position of Great Britain, an all-red route to the East would be indicated, which would mean initially a two-stage flight to Malta, refuelling at Gibraltar. Fig. 1 shows the track chart of this route, with the sea miles marked on. It will be seen that a fuel capacity for 1,500 miles' range is likely to cover this requirement, and a study of a map will show this should suffice for all further exten- sions from Malta as may be dictated by military strategical operations, unless a further easterly route were chosen via the Red Sea in preference to the Persian Gulf. Provision for longer range would, from the military load point of view, be uneconomical, as obviously the fuel load as part of the military load should be a minimum. In other words, Dead track distances in Nauhcat Miles, albwing SXcrrorFor bad visibility . in navigahon. G/8. - PL YMOUTH - 1IO2 there is no justification for specifying flying boats with a range exceeding the requirements which may be visualised tor military operations in the future, unless warranted by exceptional circumstances. In the same way, in the case of the merchant flying boat operating on long-distance Routes, for the paying load to be an economic proposition there is a limit to the range beyond which it would pay to refuel at convenient stages on the route. Design in Relation to Policy. It is imperative that military operations should suffer "he least possible interruption from either aircraft or power :llant failure or adverse atmospheric and sea conditions, as any advantage to be gained in this respect is of immense value and may in many cases be a deciding factor in military superiority. It is well known from experience that a normal or over- loaded flying boat, which, once air-borne, would be a per- fectly normal controllable aircraft capable of carrying out its military duties, would, under certain sea conditions, fail to take off, or, if the attempt were made, be severely damaged and probably be put out of action. In other words, the difficulties to be met are mainly concerned with the sea and not the air. These difficulties have been the subject of much thought, and have led to several sugges- tions as to possible design characteristics or to policy in order to overcome, or at least mitigate, this unfortunate state of affairs. Further, the design difficulties are in- creased, as a high aerodynamic performance, especially as regards high cruising speed and long range, generally is specified, and although not explicitly stated, the criterion, up to the present, for the " take-off " times under no wind conditions has been accepted as, and based upon, a maxi- mum of 30 sees, and 60 sees, under normal and overload conditions respectively. Now, broadly, there are three sea conditions in which a flying boat has either to take off or alight. Firstly, in comparatively sheltered waters with light winds ; secondly, in seas moderate to rough, winds variable, light to strong ; and, lastly, in a long heavy swell with slight winds. Obviously, the second and third conditions are the worst, especially the latter, which, although uncommon in this country, is fairly prevalent in various parts abroad, espe- cially at Malta, in the early part of the year. Bearing in mind the above, the various suggestions put forward from time to time as regards design and policy may be conveniently stated in the form of three design specifications, each of which would define uniquely the general layout to meet the same requirements. They are as follow : — Specification A The aircraft is to be designed to operate in inland waters or between sheltered bases. To ensure a quick and safe take-off the horse-power loading should not exceed 12 lbs./ h.p., and the take-off speed 50 knots. It should be fitted with not less than three engines, and the design should be such that, with one engine out of action, straight level flight may be obtained at an altitude of not less than 2,000 ft., with the remaining engines working at 10 per cent, lower than the normal revolutions, and the rate of climb at this altitude to be no less than 100 ft./min. Specification B The aircraft is to be designed to operate within reason- ably sheltered waters ; an exceptional degree of seaworthi- ness, therefore, is not expected or required. Under these conditions it should be capable of taking off with the maxi- mum possible load, subject to the following condition: — At any stage of a flight, in the event of an engine cutting- out, it should be possible to jettison sufficient fuel to enable- the aircraft to continue flight to the nearest base, without losing height, and the engine revolutions not exceeding the normal. Specification C The aircraft is to be designed with seaworthy qualities, comparable with a surface ship of at least the same dis- placement, to enable it to operate under similar sea condi- tions, subject to the following condition: — At any stage of a flight, in the event of engine failure, it should be possible to jettison sufficient fuel to enable the aircraft to continue flight, if required, to the nearest base, without losing height, and the engine revolutions not exceeding the normal. Let us now examine briefly these specifications in the light of the military requirements outlined above. With regard to the conditions in the event of engine failure. 413
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