FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1964
1964 - 2552.PDF
fUGHT International, 24 September 1964 555 TWIN OTTER de Havilland Canada Launches its New 15-seat STOL Transport A FIFTH new transport aeroplane is being developed by deHavilland Canada. Development and production havestarted at the Downsview, Ontario, plant on an initial quantity of five Twin Otters, powered by two Canadian Pratt & Whitney PT6A-20 free-turbine engines of 550 shaft horse power each. Flight trials will begin in June 1965, and certification is expected in time for deliveries in January 1966. Preliminary details appeared in Flight International for September 10. The Twin Otter is a simple and practical response to the world need for a small transport that can open up or maintain local air routes of low traffic density, whether airfields exist or not, and yet will have the modern appeal and advantages of turbine power, and multi-engine security. This is a requirement which de Havilland have had under study for a long time. Clearly there are both civil and military applications. The Twin Otter design is distinct from other available multi- engine aircraft, except for the Skyvan, in its unique combination of size, short-field ability and load handling facility. These features together appear to be necessary for a break-through in the impasse that has been troubling operators of small local services, and authorities facing public demands for such. Much technical development has been concentrated on larger aircraft for major routes, but the short-haul operator—whose routes could generate new traffic if he had an aircraft truly designed for his purpose—has been relatively neglected. In many instances second-hand and sometimes obsolete equipment have been used, and in some cases recently twin-turbine airliners have been replacing them. However, this took place only on routes where traffic growth produced satisfactory load factors on aircraft seating 30 to 40 passengers. No replacement aircraft was offered for those routes where the topography or local finances did not permit the construc- tion of airfields suitable to receive the new turbine-powered airliners. In some regions no airfields at all are available to link the many scattered communities whose economic and political survival calls '°r communication with major commercial or administrative centres. Even in the United States 72 per cent of all airfields are •ess than 2,200ft long, and therefore require operating character- ises not normally found together with reasonable seating capacity. Beavers, Otters and Other single-engined utility aircraft have Proved useful in some of the situations referred to, and the new Turbo-Beaver will continue its part of this work for a long period jwead. But de Havilland research indicated that the specification "est suited to satisfy these needs would be a twin-turbine aircraft °f approximately 15 seats capacity, having utilitarian characteristics and STOL capability. In the course of this research it became also 'wdent that the widespread military experience with the Beaver, «er and Caribou since 1948 pointed to the need for "a twin- ers'ned Otter" for military liaison and light transport. In the civil tha !t WaS found that if the number of seats is appreciably more ^n 15 the aircraft-mile cost may well be too high. Also operatorse a lert to the strong appeal of frequency: two 15-seat departures more of a traffic stimulant than is one 30-seat departure. Turbine power was chosen because the spreading adoption of turbines generally has brought fuelling, servicing and overhaul facilities into many of the more remote areas of the world, despite their modest facilities, enabling operators in such regions to benefit by the turbine's advantages of lessened maintenance and longer overhaul life. This allows them to offer travellers, even on such third-category services, the undoubted appeal of cabin quietness and turbine smoothness as experienced on inter-city airlines. Much was contributed towards the design of the aircraft by a research programme undertaken in co-operation with the Defence Research Board of Canada, quite independent of any need for a production aircraft. In this programme an Otter adapted to take two Pratt & Whitney PT6A-6 turbines has been used for two years for general research work towards still shorter take-off and landing capabilities. It is significant that the DHC-3 Otter airframe was selected for this advanced STOL research (performance, stability and control) because of its highly suitable configuration, particu- larly its powerful double-slotted flap feature which provides exceptional power-on lift coefficients. The clean twin-turbine adaptation, with its large proportion of slipstream-swept span, therefore affords attractively efficient aerodynamics, and no time was lost in recognizing that the research aircraft, producing such economical figures even before the application of sophisticated reverse-thrust experiments, offered an ideal basis for the market opportunity that was under study. Exploratory work had been proceeding concurrently in the de Havilland Future Projects Group. By the end of 1962 some 25 design studies had been made. These narrowed down the para- meters, and soon it was plain that the payload should exceed 3,OD0lb ("about 15 passengers") and the basic range should be in the region of 500 n.m. with provision for exceptional long-range flights. For such range a speed 30 per cent above Otter speed would be suitable. Otter field length was desirable. Turbines were necessary and soon would be essential, and the twin-engine form met the case best. These prime factors all confirmed the earlier feeling that the twin- turbine Otter offered the most saleable aircraft. Other consider- ations pointed the same way. For example, a proven and simple structure and system were extremely important in this class of fairly remote operation; the basic Otter airframe and systems would be ideal and could be adopted with minimum change. Their design refinement was based on long, world-wide experience. Another consideration was that first cost and spare-parts prices must be kept low; nothing could be better than a twin development of the Otter, retaining a high percentage of common parts. There are more than 400 Otters operating in some 30 countries, and maintenance experience has been gained over 12 years. The Pratt & Whitney PT6A engine, which has a light installed weight, was considered to be the best developed, and the most promising, of the small turbines, and was a Canadian domestic product with American co-opsration. It was in a category which is assured a vigorous development for several applications. The undercarriage and airframe generally must be tolerant of
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
