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Aviation History
1989
1989 - 0552.PDF
FLIGHT TEST Harry Hopkins finds that the Let 410's very rugged qualities, which have served it well on Aeroflot's very-short-haul routes, make it a contender in the West for airline services from small airfields. Flight's Janice Lowe took the photographs. In a new drive for Western sales, Czecho-slovakian export agency Omnipol brought a Let 410UVP Commuter to the UK. Let test pilot Miroslav Srenec flew OY-CTE from the company's Kunovice factory, via Sweden, to Southampton, from where Flight made an evaluation. It was later demonstrated on the l,725ft-long runway on the Isles of Scilly. Swedish carrier Liz-Air, which helped to promote the visit, will be the first Western operator. UVP means STOL in Czech and Russian. The aircraft is competing for the niche occupied by several 20-seat, high-winged aircraft produced in the West, including the STOL DHC-6 Twin Otter, no longer in production. Let 410 airliner sales to date total 600, and about 800 units have been built for all uses since 1966. The first few 410s were fitted with Pratt & Whitney Canada PT6A-27 engines, like the Twin Otter. The present power unit is the Walter 601E. The slightly heavier Walter engine is similar to the reverse-flow PT6. It has a "separator vane" at the back of the intake to deflect solids, but has one less stage both in the compressor and the turbine. The 750 s.h.p. unit in the Let 410-E variant is optimised for economy. Its service life is 6,000hr, with intermediate overhauls every 2,000hr. The engine is of modular construction, designed for borescope inspections and fitted with chip detection. The airframe life is set at 20,000hr. With no APU, cabin pre-heating is said to be essential if outside temperatures are below -20°C. The aircraft can operate in temperatures ranging from +50°C to -50°C. The engine has a fuel/oil heat exchanger to avoid the need for a fuel additive in extremely cold weather. Water injection can be used above 23°C at sea-level, lifting the power over 800 s.h.p., and take-off rating is sustained to 35°C. The total water delivered over one minute can be adjusted to one of three settings before departure. Lift-dump spoilers were added on the "E" version, and the high aspect ratio (10-45) is increased by the new tip tanks. All fuelling is over-wing. The short and thick-set fuselage is emphasised by the relatively tall swept fin. Below the mid-set tailplane, the fin's lead ing edge carries six vortex generators. All flying-surface leading edges are pneu matically de-iced. The primary control surfaces are fabric covered. The five-bladed Avia 510 propellers (replacing the three-bladed units of earlier series) turn close to the fuselage, which is protected against shed ice by a rubber strip. The upward-opening entrance door is simpler (and cleaner) than a lowering airstair. The sill is 2ft 2in above the ground, and simple steps hook on to it. The 4ft 9in-high door splits vertically, allowing the 2ft 8in-wide entrance to become a 5ft 9in wide for freight. The unpressurised 6ft 5in-wide cabin benefits from a good height (5ft 5in) for an aircraft of this size. There is an adequate 13in aisle between the low backs of single left and paired right-hand seats. A simple toilet can be put alongside the rear baggage space. This space takes only 3301b; the nose space, now doubled to take 3101b, has a fire extinguish ing system. Capacity was increased by fitting new solid-state navcom equipment. Accessible seats The flightdeck seats are accessible, with some turning of the body, from each side. Centre-hinged doors unfold to lock into the sidewall and cover the entrances. When the cabin is full of freight, the pilots can leave through an exit door on the right. The simple seats are comfortable enough, even without armrests, for short flights. Each adjusts on a parallelogram frame, rising and then sinking slightly in forward travel. Adjustment, by a screw jack lying at 45° to the vertical under the seat, is achieved by handwheel—and an arm must be slid 30 FLIGHT INTERNATIONAL, 4 March 1989
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