PIPER PA-25 PAWNEE · The Encyclopedia of Aircraft David C. Eyre (2024)

Country of origin:

United States of America

Description:

Single-seat agricultural monoplane

Power Plant:

One 175 kw (235 hp) Lycoming O-540-B2B5 four-cylinder horizontally- opposed air-cooled engine

Specifications:

History:

The Piper PA-25 Pawnee was flown for the first time in 1958, and was known initially as the Ag 3. During its production life it was produced in seven different variants. It has been operated all over the world as a crop-sprayer. In its PA-25-235 form it had a useful load of 654 kg (1,443 lb) and was an extremely versatile aircraft with a flexible work potential. When first offered on the market it was well received by operators around the world, and over 1,000 aircraft were sold in the first three years. Production was suspended in 1985 in favour of the PA-36 Pawnee Brave. It has been very popular in this region and, although getting quite old for its original intended role, it is still seen in the glider towing role as well as on agricultural duties. Quite a few examples are still registered in New Zealand and Australia.

A total of 5,167 PA-25 Pawnees was produced by the time production ceased in late 1981. First model was the PA-25-150 fitted with a Lycoming O-320 engine and having a payload of 362 kg (800 lb). In 1964 production moved to the PA-25-235 B series with a larger hopper, having a payload of 544 kg (1,200 lb) or 680 litres (150 Imp gals) and a 175 kw (235 hp) Lycoming O-540-B2B5 six cylinder engine as standard. This model later received the 194 kw (260 hp) O-540-E as an option. Next model was the Pawnee C, a model advance from the B in having a modified variant of the O-540 engine. This was followed by the Pawnee D in 1968, this having the 194 kw (260 hp) engine as standard with the 175 kw (235 hp) engine as an option. This model had the flaps and ailerons surfaces covered with metal and the fuel tanks were relocated to the outer wings.

The Pawnee was designed at the Piper development centre at Vero Beach in Florida by a team under the leadership of Fred Weick. Maximum pilot safety was the primary consideration. The pilot was seated high, with good visibility all-round in a strengthened, enclosed co*ckpit, with a steel-tube turnover structure built in, and a wire cutter mounted on the centre section of the windshield. The fuselage was built of rectangular-section welded steel tube with fabric covering, and Duraclad plastic finish. To reduce production costs, the design was largely based on the PA-18A Super Cub which, up until then, had been used extensively in the USA in the agricultural role. The fuselage longerons were bowed slightly so that they would buckle outwards in the event of a crash. The forward part, which was designed to collapse progressively, contained the engine, fuel tank and hopper. The wings were similar to those of the Super Cub, being braced to the fuselage by a V-strut. The structure was fabricated from riveted aluminium ribs mounted on extruded aluminium spars with tubular drag and compression struts, and stainless steel drag wires.

As production continued, the 112 kw (150 hp) Lycoming O-320-A2B model became the basic Pawnee, and the 175 kw (235 hp) model became the Pawnee B. Production continued through to the Pawnee C and D, each of which had only slight changes from previous models. Late models were only fitted with the 175 kw (235 hp) or 194 kw (260 hp) engines and the 112 kw (150 hp) model was dropped from the range. In 1975 the Pawnee Brave was released, being a larger aircraft with more power and greater capacity, and this model was marketed alongside the basic Pawnee.

The Pawnee could be used as a duster, sprayer, or seeder, and was flown extensively in this role in Australia for many years following its introduction in the early 1960s. Hazair of Orange, NSW modified a number of Pawnees to two-seat configuration, the conversion basically being the widening of the fuselage so the co*ckpit could accommodate a bench seat for side-by-side agricultural flying training, and fitted them with a more streamline rear fuselage top. The first so produced was a Pawnee 235 VH-PIJ (c/n 25-2218) but it crashed near Oberon, NSW in 1965 soon after conversion and was rebuilt as VH-WOF. Others include VH-PIT (c/n 25-2543) for Stawell Airways, VIC which became known as a Pawnee 235 S.2; VH-PAD (c/n 25-2007) which was for Benders Spreading Services of Tasmania, later becoming VH-BSB; VH-GWS for Alpine Aviation of Victoria; and VH-SMS (c/n 25-2958), the latter being rebuilt from a damaged aircraft.

Eventually Gippsland Aeronautics of Morwell, VIC commenced converting Pawnees to Fat Man configuration, this conversion involving the shortening of the fuel tank bay and widening of the two hopper bays, increasing hopper capacity from 568 litres (125 Imp gals) to 833 litres (183 Imp gals) and installing an O-540-B2B5 engine. Later new production aircraft were produced known as the G.200 series, being basically new-build Pawnees but with modifications to bring them up to modern regulation and manufacturing standards. In New Zealand the Auckland Gliding Club fitted its Pawnee ZK-CEB (c/n 25-2421) with a four-blade propeller.

In Sweden a Pawnee of the Eskilsltuna Gliding Club was fitted with a 3-litre Volvo motor car engine, the operators stating it was almost noiseless in flight, having very little vibration, and its climb rate was similar to the O-540-260 engine. An example at Benalla, VIC has been fitted with a converted 5-litre Chevrolet V-8 engine; and in 1989 the Gliding Federation of Australia was involved in a project to install a 3.8-litre Javelin Ford V-6 engine in a Pawnee for glider towing.