De Havilland Canada DHC-3 Otter


The de Havilland Canada DHC-3 Otter is a single-engined, high-wing, propeller-driven, short take-off and landing aircraft developed by de Havilland Canada. It was conceived to be capable of performing the same roles as the earlier and highly successful Beaver, including as a bush plane, but is overall a larger aircraft.

Design and development

The rugged single-engined, high-wing, propeller-driven DHC-3 Otter was conceived in January 1951 by de Havilland Canada as a larger, more powerful version of its highly successful DHC2 Beaver STOL utility transport. Dubbed the "King Beaver" during design, it would be the veritable "one-ton truck" to the Beaver's "half-ton" role.
The Otter received Canadian certification in November 1952 and entered production shortly thereafter. Using the same overall configuration as the Beaver, the new, much heavier design incorporated a longer fuselage, greater-span wing, and cruciform tail. Seating in the main cabin expanded from six to 10 or 11. Power was supplied by a 450-kW Pratt & Whitney R-1340 geared radial. The version used in the Otter was geared for lower propeller revolutions and consequently lower airspeed. The electrical system was 28 volts D.C.
Like the Beaver, the Otter can be fitted with skis or floats. The Otter served as the basis for the very successful Twin Otter, which features two wing-mounted Pratt & Whitney Canada PT6 turboprops. A total of 466 Otters were manufactured.

Operational use

The DHC-3/CC-123/CSR-123 Otter was used until 1980 by the Royal Canadian Air Force and its successor, the Air Command of the Canadian Forces. It was used in Search and Rescue, as the "CSR" denotes Canadian Search Rescue and as a light utility transport, "CC" denoting Canadian Cargo.
During the Suez Crisis, the Canadian government decided to provide assistance to the United Nations Emergency Force and the Royal Canadian Navy carrier carried 4 Otters from Halifax to Port Said in Egypt early in 1957, with all four flying off unassisted while the ship was at anchor. This was the only occasion when RCAF fixed wing aircraft operated from a Canadian warship.
It was also operated on EDO floats on water and skis for winter operations on snow. The EDO floats also had wheels for use on runways. It was used as army support dropping supplies by parachute, and also non-parachute low-speed, low-altitude air drops, to support the Canadian Army on manoeuvres. In the end it was operated by the Primary Air Reserve in Montreal, Toronto, Edmonton and Winnipeg, with approximately 10 aircraft at each base, as well as by the RSU at those bases. It was usually flown with a single pilot in the left seat and a Technical Air Crewman in the right seat. The Kiowa helicopter replaced it in Air Reserve squadrons.
Although the Otter found ready acceptance in bush airlines, as in a similar scenario to the DHC-2 Beaver, the United States Army soon became the largest operator of the aircraft. Other military users included Australia, Canada, and India, but the primary role of the aircraft as a rugged bush plane continues to this day.
An Otter crossed the South Pole in 1957. The Otter is also popular in the skydiving community and can be found in many dropzones throughout the world.
Otters were used by Qantas, from 1958 to 1960 in Papua New Guinea. The Qantas aircraft were then transferred to Trans Australian Airlines a major Australian domestic airline which operated the Otters in Papua New Guinea until 1966 when they were withdrawn from use. TAA was merged with Qantas in 1990.

Modifications

The most extensively modified Otter was RCAF Otter 3682. After initial service as a standard Search and Rescue aircraft it was used to explore the aerodynamic aspects of STOL. In 1958 it was fitted with flaps so outsized that, with their 45 degree droop, it became known as the Batwing Otter. In addition, its tail-wheel undercarriage was replaced with a high energy- absorption 4-wheel arrangement and a very high vertical tail. The next modification replaced the flaps with fully retractable flaps suitable for cruising flight and high drag was obtained with reverse thrust from a J85 turbojet installed in the fuselage behind the cockpit. The third configuration looked a lot like the future Twin Otter and was the first twin-PT6 fixed-wing installation to fly in May 1963. The piston engine in the nose was replaced with wing-mounted engines to blow over the flaps.
Stolairus Aviation of Kelowna, BC, has developed several modifications for the DHC-3 including a STOL Kit, which modifies the wing with a contoured leading edge and drooped wingtips for increased performance. Stolairus has also developed a 400 lb "upgross" kit which increases the gross weight of the DHC-3 to 8,367 lbs on floats.
Some aircraft were converted to turbine power using a PT6A, Walter 601, or Garrett/Honeywell TPE331-10, by Texas Turbine Conversions. The Walter M601E-11 Turbine Engine conversion is manufactured and installed by Stolairus Aviation.
A Polish Pezetel radial engine has also been fitted. Re-engined aircraft have been offered since the 1980s by Airtech Canada as the DHC-3/1000 using current-production 1,000 hp PZL ASz-62 IR radials.

Variants

;DHC-3 Otter: Single-engined STOL utility transport aircraft.
;CSR-123 Otter: STOL utility transport aircraft for the Royal Canadian Air Force.
;YU-1 Otter: Six test and evaluation aircraft for the U.S. Army.
;U-1A Otter: STOL utility transport aircraft for the US Army.
;UC-1 Otter: STOL utility transport aircraft for the United States Navy. Later redesignated U-1B Otter in 1962.
;: Otters fitted with either Pratt & Whitney Canada PT6A-27 or Pratt & Whitney Canada PT6A-34 turboprop engine.
;Airtech Canada DHC-3/1000 Otter:Conversions powered by PZL Kalisz ASz-62IR engines.
;Texas Turbines Super Otter:Turbine conversion powered by a Garret TPE331 turboprop engine

Military operators

As of June 2019, there have been 118 incidents and accidents involving the DHC-3 resulting in 242 deaths. Listed below are a select few of the most notable ones.