|
de Havilland Canada DHC-2 Beaver
The two-bladed Hamilton Standard constant speed propeller tends towards the noisy; often replaced in the US and Canada with a three-bladed Hartzell propeller with a smaller diameter.
The newly independent Kenya built a small air force, assisted by British advisors. The first planes to be acquired were DHC Beavers and Caribou. Kenyan pilots were trained by the RAF in Britain.
There followed a single Beaver II with the Alvis Leonides radial and, in 1964, a few 10-passenger Turbo-Beaver III powered by the 431kW United Aircraft of Canada Ltd (later Pratt & Whitney Aircraft of Canada) PT6A-6 or -20 turboprop. Most of the Turbo-Beavers were used by civil operators. In New Zealand one Beaver had an AiResearch TPE331 turboprop engine installed. Production ended in the mid-1960s.
Compared with the earlier Beaver, the DHC-2 Mk. III has several modifications apart from replacement of its P & W piston-engine by a Canadian P & W turboprop. A 30in front fuselage extension brings the cockpit well forward of the wings and allows the installation of another pair of seats, bringing total capacity to nine, including crew.
Despite the cruise thirst of the 0.68 lb/eshp/h PT6A, fuel capacity of the Turbo-Beaver has been increased by the addition of a third fuselage tank, plus wing-tip auxiliaries. Under the centre section floor there.are now tanks containing 43, 56 and 20 Imp. gal from front to rear, plus 18 in each tip, totalling 155 Imp/gal in all.
Apart from a taller fin and a ventral strake, for better directional stability, the Turbo-Beaver is otherwise generally unchanged. It is also beefed up for its increased gross weight of 5370 lb and the longer nose enables two large doors to be provided for access to the crew compartment.
The standard Beaver throttle quadrant at top centre of the panel is retained, but the pitch vernier is moved below it. The power lever on the left has an idle gate and moves aft for reverse thrust. An unusual feature for a single-engined aircraft is a feathering facility, which is a characteristic of the PT6. After light-up, the starter is disengaged at 45-47 per cent gas generator rpm, and the Turbo-Beaver is taxied just in the Beta range, with about +6 degrees indicated on the blade angle gauge.
When the closed-circuit hydraulic hand pump is used to lower 30degrees of flap for take-off, the ailerons droop too. The Turbo-Beaver floats off the ground at about 45mph IAS, and climbed away at 65 mph, before being cleaned up for a 90 mph en route ascent.
At 1000 ft low-altitude cruise, the Turbo-Beaver speed is about 140 mph IAS, at 26 lb/sq.in and 85 per cent propeller rpm. The Beaver will maintain its 135-140 mph cruising speed just below the yellow line of Vno, with only about two gallons per hour variation in fuel flow between sea level and about 12,000 ft on 290 hp from the 578 eshp PT6A, using about 32 Imp. gal/h.
Clean, continued aft pressure on the control wheel with power off simply results in a nose-high sink at a minimum flight speed of about 68 mph with full lateral control, and an accompanying rate of descent of about 1500 ft/min. Application of power simply cushions the descent, and the same effect accompanies extension of flap. Slight tail bullet can be felt with full flap but, with the wheel hard back again, the Beaver simply mushes down at about 45 mph IAS.
About 40 Turbo-Beavers had been sold by 1966, built as new aircraft, although DHC was also offering conversions of customers' piston-engined aircraft for around $60000. F.a.f. price of a new Turbo-Beaver was $108 575, and some used piston-engined versions are reported as much as $50 000, which is more than their original selling cost.
DHC-2 Beaver I
DHC-2 Mk. III
L-20
|
