- May 26, 2006
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Extensive model tests were made as the Caribou's fuselage had to be angled sharply upwards to give adequate truck loading clearance, and included a large-scale model tested in flight mounted above the Otter RCAF 3667.
The prototype, CF-KTK-X, was first flown on 30 July, 1958, at Downsview by George Neal and David Charles Fairbanks, with flight engineer H. Brinkman. It was found that to obtain the required range of centre of gravity movement, a 45 in (1.14m) section had to be inserted in the forward fuselage. All subsequent DHC 4s had this built in and the prototype was later modified. Also it was found that an oscillating vortex was created off the rounded edges of the rear fuselage, causing a slight weaving of the aircraft. Initially a dorsal fin was fitted but was not effective. Then strakes were added along the lower edges of the fuselage and these created a stable vortex and the weaving disappeared. It was the solving of this stability problem that resulted in the sharp lower fuselage corners of the DHC 4 development, the DHC-5.
An improved DHC 4A version was planned, with two General Electric J-85-GE-7 jet engines with adjustable nozzles, mounted in the rear fuselage as tested in the experimental STOL Otter which would give enhanced STOL capabilities. This version was not built as priority was given to the Caribou II which became the DHC-5 Buffalo. It was then planned to make a version of the DHC-5 with these jet engines installed but this was never done owing to the restrictions placed on the US Army for operating fixed wing aircraft.
With a payload of some 9,000 lb the DHC-4 will have Pratt and Whitney
R-1830 or R-2000 engines at first, later changing to Dart, T55 or Gazelle
(Source: http://www.airvectors.net/avdhc4.html)“The US Army developed fuel bladders, in the form of rubber cylinders that looked like very fat tires, that could stow 1,326 liters (350 US gallons) each. Up to three could be hauled in the cargo bay, primarily to increase range for ferry flights, but also potentially for delivery of fuel to forward areas. There was also an experiment with using the Caribou as an inflight refueling tanker, but it appears this was never done operationally.”