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Aviation History
1964
1964 - 1867.PDF
FLIGHT International, 18 June 1964 1036 S PORT AND BUSINESS Designing the Cessna 411 HAVING established numerical dominance in the single-engined field, Cessna are turning their minds seriously todeveloping their multi-engined line of aircraft in order to capture a greater share of the business in this field. Their older factory next to McConnell AFB, on the south-eastern edge of Wichita, now churns out some 16 single-engined aircraft every working day, plus a sprinkling of-the tandem-twin Skymaster, but their multi-engined work proper is concentrated in the newer factory of the so-called military division on the southern edge of Wichita municipal airport. Besides a few T-37 twin-jet trainers per month, Cessna here turn out their latest 310 and 320 Skyknight twins and are preparing for certification during the summer of their brand- new 411. Flight International was privileged to be first to see the notable new interior of this aircraft, the single prototype of which has now flown some 230hr. The design objective of the 411, as stated by the chief engineer of Cessna's military division, Max Bleck, is to provide the 310 owner with a suitable step-up, and mainly with an altogether new degree of comfort and "livability." Noting that the travelling executive is not really interested in moving around during flight, they have concentrated on cabin width rather than height. Indeed, the 411 offers the widest cabin in any aircraft up to the Gulfstream, with the maximum width at shoulder level, extra-comfortable seats one inch wider than any hitherto produced by Cessna, some 8 to lOin walkable aisle width and specially styled fixed, cantilevered arm rests with Royalite moulded styling, which really gives an air of solid arm-chair comfort. Oval windows have been introduced "to accustom occupants to the pressurized look"—of this more below. The partition between cabin and flight deck is raked rearwards to give knee room to an eventual forward-facing passenger and its upper section is trans- parent to give passengers a forward view and a feeling of additional spaciousness. Standard seating will be for four passengers, plus two crew, but another design aim has been the option of a high-density eight-seat cabin of a reasonable standard of comfort. The emphasis on width rather than height is a potent competitive sales factor in view of the narrowness of the average existing light twin-engined business aircraft. Personal experience of the sales mock-up fully bears out Cessna's claim to have produced a new standard of livability. The other main Cessna objective has been to keep the price within a $120,000 limit, in a market where the 310 costs about $62,000 and the Queen Air $140,000. Within this package, Cessna have aimed at, and are confident of achieving performance equal to or better than that of the Skyknight, using Continental TSIO-520 engines flat-rated at 340 h.p. These engines have performed extremely well in the prototype, and Cessna feel that the relatively high r.p.m. of well beyond 3,000 are now well within the capability of the manufacturers. The first strip-down showed the valves and top part of the engine to be in excellent condition. Cessna feel, incidentally, that the real purpose of turbo-super- charging in the Skyknight is being misunderstood. People tend to decry the high cruising heights of which the aircraft is capable on the basis that no one wants to spend hours with an oxygen mask over their face. But Cessna say that the supercharger has the principal function of giving the pilot the altitude capability to clear frontal systems or local bad weather in VFR flight, that it gives him real twin-engined safety where the conventionally-aspirated twin is operating well above its single-engined ceiling and that rate of climb at altitude is increased and sea-level performance restored at high airfield elevations—this last of relatively minor importance, because fields at high elevations tend to have longer runways. The great question, of course, is whether to provide pressurization. Cessna have no immediate intention of doing so in the 411 for the main reason that it adds some $40,000 to $50,000 to the cost of the aircraft—this is the price increase involved in pressurizing the Aero Commander 680FP. Heating and air-conditioning are regarded as quite separate from pressurization, and Cessna feel that the regions in which air-conditioning, that is refrigeration cooling, is really required are sufficiently limited to make its provision as standard quite unnecessary. Neither are the structural strengthening and testing considered to be major problems since their cost can be amortized over the production run. The real cost is the pressuriz- ation equipment itself—hydraulic drive, compressor, silencer, dehumidifier, flow controller and outlet valves—which have to be added to the cost of every aircraft. Cessna accordingly are holding their hands until some basically cheaper equipment can be developed and produced. There are two main prospects here. AiResearch are working on a "dual scroll" exhaust-driven turbo-supercharger, in which the second compressor circuit would feed the cabin. Alternatively, a Roots blower could be mounted directly on the engine as a normal accessory. When some suitably inexpensive solution is found, Cessna are evidently greatly interested in providing pressurization, which does after all make the full altitude potential of the supercharged engine available for continuous cruising. In this connection, the aircraft manufac- turers are distinctly annoyed at the proposed FAA lowering of the floor of positive control airspace, within which aircraft must be IFR equipped, flight-planned and flown by rated pilots, from 25,000ft to 18,000ft. Another $64 question is the precise degree of pressurization required. It might, for example, be possible by means of a ram intake, at some drag penalty, to lower cabin altitude from 15,000ft to 10,000ft, but this in itself may well not be sufficient to allow for all potential passengers. It only takes one aged or infirm passenger who cannot stand 10,000ft, to make the altitude capability useless: and such people do represent a moderate proportion of executive passengers. By the time a cabin has been tested, over-stressed and cycled, to prove a quite small differential, it must withstand quite a high differential, and it might as well be designed from the outset to operate at a relatively high pressure. It seems to be generally accepted that propeller-driven business aircraft should offer a cabin altitude of 8,000ft at 18,000ft. Yet another design aim in the 411 has been to produce an aircraft of an appearance fairly similar to that of the 310 and 320. The characteristic Stabila-tip tanks, nacelles incorporating baggage compartments, the Cessna swept fin shape and the racily pointed 310-type nose are all to be found on the 411. The aircraft sits at much the same height off the ground as the 310, but has a softer undercarriage "to make the same landings feel better" and has been designed specifially to offer simple, pleasant handling charac- teristics. In this connection, the wing of the prototype was moved lft rearwards and the tailplane 6in aft. A notable feature is that the extra-wide cabin benefits the pilots too. Switches and circuit-breakers have deliberately been moved away from the main panel on to a sloped outboard console andJ
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