Photograph:
Grumman G-73T Turbo Mallard VH-JAW (c/n J-26) of Air Whitsunday on Sydney Harbour, NSW in 1983 (David C Eyre)
Country of origin:
United States of America
Description:
Business and executive amphibious flying boat
Power Plant:
(G-73AT)
Two 559 kw (750 ehp) Pratt & Whitney PT6A-34 turboprops
Specifications:
- Wingspan: 20.36 m (66 ft 8 in)
- Length: 14.75 m (48 ft 4 in)
- Height: 5.76 m (18 ft 9 in)
- Wing area: 41.24 m² (444 sq ft)
- Max speed: 330 km/h (205 mph)
- Cruising speed: 296 km/h (184 mph)
- Rate of climb: 457 m/min (1,500 ft/min)
- Service ceiling: 3,658 m (12,000 ft)
- Range: 1,477 km (918 miles)
- Empty weight: 3,856 lb (8,500 lb)
- Loaded weight: 6,350 kg (14,000 lb)
History:
To increase the performance and load carrying capacity of what was becoming an old flying boat, a number of persons and organisations looked at replacing the engines and equipment in the Grumman Mallard. One of these was Mr R Peterson of Northern Consolidated Airlines in the United States, he having obtained an example (c/n J-36) in 1964, having one of the Pratt & Whitney R-1340 radial engines replaced by a PT-6 turoprop, and then operating it for a period with one radial and one turboprop for test purposes.
The tests were successful but the PT-6 produced less power than the radial and the aircraft was returned to Pratt & Whitney R-1340 power. In the meantime the PT6-27 was developed by Pratt & Whitney Canada to produce 507 kw (680 shp) and Frakes Aviation obtained c/n J-36 and fitted two of these engines. Eventually 12 were converted by Frakes for Chalk Airlines to G-73T standard in Texas, being re-engined with PT6A-34 engines which produced 559 kw (750 shp).
A few Mallards have remained on the Australian Civil Aircraft Register, three operated by Paspaley Pearling out of Darwin, NT and, although one operated up until the late 1990s with piston engines, all have since operated with turbines.
These aircraft were VH-JAW (c/n J-26 – ex N2419X, C-CHUM, N2966) which, after operating with Air Whitsunday in Queensland, later went to Jayrow Helicopters and operated in Western Australia. It was then exported to the United States where it became N73AH. It was again imported to Australia and became VH-PPT with Paspaley Pearling, being fitted with turbines in Darwin.
VH-OAW (c/n J-23) was initially registered to Air Whitsunday in May 1989. It was later sold to Paspaley Pearling, converted to turbine power, and became VH-PPI.
VH-PPE (c/n J-22) was initially imported for Air Whitsunday of Airlie Beach, later becoming VH-PPE with Paspaley Pearling and re-engined with turbines.
The Mallards operated by Paspaley have been improved in a number of areas over those previously converted to turbine power and have become known as the G-73AT (Australian Turbine). This company has been well known for successfully farming pearls in the warm waters west of Darwin and around Broome, WA. They have operated regular services to the farms from Darwin conveying staff, mail and perishables, and occasionally have been used for medevac flights when required.
These aircraft initially operated with piston engines but in 1995 the company decided they needed to be refurbished and rebuilt. This was carried out by SkyWest Engineering of Perth, WA, this work including a re-designed hydraulic system, complete re-wiring, relocation of the battery, a new cabin heating and ventilation system, and the cabin main door eing modified to open upwards, the bow door opening forward, helping to facilitate loading and unloading. Other changes included wing-tip drooping, vortex generators, aerodynamic balanced horns on the elevators and re-design of the engine cowlings to improve ram-air recovery. The engines drive 2.39 m (7 ft 10 in) Hartzell four-blade propellers and aluminium auxiliary fuel tanks were installed.