Piper PA-23

The Piper PA-23, named Apache and later Aztec, is a United States twin-engined monoplane originally designed in the 1950s.

Design and development

The PA-23 was the first twin-engine design from Piper and was developed from a proposed "Twin Stinson" design inherited when Piper bought the Stinson Division of the Consolidated Vultee Aircraft Corporation.^[1] The prototype PA-23 was a four-seater low-wing all-metal monoplane with a twin tail, powered by a two 125 hp Lycoming O-290-D piston engines^[1] the prototype first flew on 2 March 1952. The aircraft performed badly and it was redesigned with a single vertical stabilizer and an all-metal rear fuselage and more powerful 150 hp Lycoming O-320-A engines.^[1] Two new prototypes of the re-designed aircraft, now named Apache, were built in 1953^[1] and entered production in 1954; 1,231 were built. In 1958 the Apache 160 was produced by upgrading the engines to 160 hp (119 kW); 816 were built before being superseded by the Apache 235, which went to 235 hp (175 kW) engines and swept tail surfaces (119 built).

In 1958 an upgraded version with 250 hp (186 kW) Lycoming O-540 engines and a swept vertical tail was produced as the PA-23-250 and was named Aztec.^[1] These first models came in a five-seat configuration which became available in 1959. In 1961 a longer nosed variant, the Aztec B, entered production.^[1] The later models of the Aztec were equipped with IO-540 fuel-injected engines and six-seat capacity, and continued in production until 1982. There were also turbocharged versions of the later models, which were able to fly at higher altitudes.

The United States Navy acquired 20 Aztecs, designating them UO-1, which changed to U-11A when unified designations were adopted in 1962.

In 1974, Piper produced a single experimental PA-41P Pressurized Aztec concept. This concept was short-lived, however, as the aspects of the Aztec that made it so popular for its spacious interior and ability to haul large loads did not lend themselves well to supporting the sealed pressure vessel required for a pressurized aircraft. The project was scrapped, and the one pressurized Aztec produced, N9941P, was donated to Mississippi State University, where it was used for testing purposes. In 2000, N9941P was donated to the Piper Aviation Museum in Lock Haven, Pennsylvania, on the condition that it never be flown again. It now sits there on display.

Variants

PA-23 Twin-Stinson

Original designation of the Piper PA-23 Apache.

PA-23 Apache

Initial production version, 2047 built (including the Apache E, G and H).

PA-23-150 Apache B

1955 variant with minor changes.^[1]

PA-23-150 Apache C

1956 variant with minor changes.^[1]

PA-23-150 Apache D

1957 variant with minor changes.^[1]

PA-23-160 Apache E

PA-23 powered by two 160 hp O-320-B engines.

PA-23-160 Apache G

PA-23 with longer internal cabin and extra window.

PA-23-160 Apache H

Apache G with 0-320-B2B engines and minor changes.

PA-23-235 Apache 235

Apache with 5 seats and 235 hp O-540 engines, 118 built.

PA-23-250 Aztec

Apache G with modified rear fuselage, new fin and rudder and 250hp Lycoming O-540-A1D engines, 4811 built (including sub-variants)

PA-23-250 Aztec B

Aztec with longer nose for a baggage compartment, six-seats, new instrument panel and changes to systems.

PA-23-250 Aztec C

Aztec B with either IO-540-C4B5 engines or turbocharged TIO-540-C4B5 as an option, also modified engine nacelles and modified landing gear.

PA-23-250 Aztec D

Aztec B with revised instrument panel and controls.

PA-23-250 Aztec E

Aztec D with longer pointed nose and a single piece windshield.

PA-23-250 Aztec F

Aztec E with improved systems and cambered wingtips and tailplane tip extensions.

PA-23T-250 Turbo-Aztec

Generally similar to the Aztec F, powered by two TIO-540 piston engines, fitted with a Garret turbocharging system.

U-11A

United States Navy designation formerly UO-1.

UO-1

United States Navy designation for PA-23-250 Aztec with additional equipment, 20 delivered later re-designated U-11A.

PA-41P Pressurized Aztec

Pressurized Aztec concept, one built.

Operators

Military operators

 Argentina

 Bolivia

 Cameroon

 Colombia

 Costa Rica

 El Salvador

 Honduras

 Madagascar

 Mexico

 Spain

• Spanish Air Force
  • Escaudrón 912
  • Escuadrilla de Enlace 905

 Paraguay

• Paraguayan Air Force
  • Grupo Aéreo de Transporte Especial/GATE

 United States

• United States Navy

 Venezuela

Specifications (PA-23-250F, normally aspirated)

Data from Jane's All The World's Aircraft 1976–77^[2]

General characteristics

• Crew: one
• Capacity: 5 passengers
• Payload: 1,600 lb (725 kg) cargo
• Length: 31 ft 2¾ in (9.52 m)
• Wingspan: 37 ft 2½ in (11.34 m)
• Height: 10 ft 4 in (3.15 m)
• Wing area: 207.6 ft² (19.28 m²)
• Airfoil: USA 35-B (modified)
• Aspect ratio: 6.8:1
• Empty weight: 3,180 lb (1,442 kg)
• Max takeoff weight: 5,200 lb (2,360 kg)
• Powerplant: 2 × Lycoming IO-540-C4B5 normally aspirated air-cooled flat-six piston engines, 250 hp (187 kW) each
• Propellers: two bladed Hartzell HC-E2YK-2RB constant speed propeller

Performance

• Never exceed speed: 277 mph (240 knots, 446 km/h)
• Maximum speed: 215 mph (187 knots, 346 km/h)
• Cruise speed: 172 mph (150 knots, 278 km/h) at 10,200 ft (3,110 m) (long-range cruise)
• Stall speed: 68 mph (59 knots, 109 km/h) (flaps down)
• Range: 1,519 miles (1,320 nmi, 2,445 km) at long-range cruise
• Service ceiling: 18,950 ft (5,775 m) (absolute ceiling)
• Rate of climb: 1,400 ft/min (7.1 m/s)

Accidents and incidents

• On 18 April 1974, Aztec G-AYDE was involved in a ground collision with BAC One-Eleven G-AXMJ at London Luton Airport after the pilot of the Aztec entered the active runway without clearance. He was killed and his passenger was injured. All 91 people on board the One-Eleven successfully evacuated after take-off was aborted.

• On 29 November 1975, Formula One racing driver Graham Hill was piloting Piper PA-23-350 Aztec N6645Y from France to London, United Kingdom.^[3] His passengers were team manager Ray Brimble, driver Tony Brise, designer Andy Smallman and mechanics Terry Richards and Tony Alcock. They were returning from Circuit Paul Ricard, Var, where they had been testing the Hill GH2 car being prepared for 1976. They were due to land at Elstree Airfield, Hertfordshire, before onward travel to London to attend a party. Shortly before 10pm, the aircraft hit trees beside a golf course at Arkley, Hertfordshire in thick fog. In the ensuing crash and explosion everyone on board was killed.^[4][5]

• On 15 April 1978, Hollywood stunt flyer Frank Tallman was ferrying a Piper Aztec from Santa Monica Airport, California, to Phoenix, Arizona under visual flight rules when he continued the flight into deteriorating weather, a lowering ceiling and rain. He struck the side of Santiago Peak in the Santa Ana Mountains near Trabuco Canyon at cruise altitude, dying in the ensuing crash.

See also

Aircraft of comparable role, configuration and era

• Beagle B.206
• Beechcraft Baron
• Cessna 310
• Helio Twin Courier
• Let L-200 Morava
• Partenavia P.68
• Piper PA-34 Seneca
  

References

Notes

Bibliography

• Peperell, Roger W; Smith, Colin M (1987). Piper Aircraft and their Forerunners. Tonbridge, Kent, England: Air-Britain. ISBN 0 85130 149 5. 
• Taylor, John W. R. (1976). Jane's All The World's Aircraft 1976–77. London: Jane's Yearbooks. ISBN 0 354 00538 3.