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An AU-24A in storage at Davis-Monthan AFB in July 1972.
TL;DR: STOL plane armed with small bombs, rockets, gun pods, and door guns.
The Helio AU-24A Stallion was a gunship, COIN, and transport aircraft developed for the USAF in the 1960s and operated by the Khmer Air Force (and its various successors) from the 70s to the 90s. It was developed from the Helio Model H-550A, a lightweight turboprop STOL aircraft, by adding five hardpoints and an M197 rotary cannon in the left door. The USAF acquired and evaluated 17 or 18 aircraft with the intention to give them to the South Vietnamese Air Force but found their flight performance unsatisfactory, and subsequently sold 14 or 15 of them to the Khmer Air Force, where they served until the 1990s.
History
The Helio Aircraft Company began designing a turboprop-powered STOL aircraft in July 1963. The HST-550 prototype made its first flight on 5 June 1964 and was FAA-certified in August. The production model was designated the H-550A and was FAA-certified in August 1969. Meanwhile, the USAF was becoming interested in a light gunship that could operate from short runways. They hoped to arm the South Vietnamese Air Force with such aircraft, a program known as Credible Chase that began in May 1971. Therefore, Helio began constructing an armed version of the H-550A, which was designated the AU-24A. It received four underwing pylons and a fuselage centreline pylon, as well as a M197 rotary cannon. The second aircraft also experimentally carried four Sparrow missiles, but as the AU-24A didn’t have a radar, the pilots joked they could only be used by dropping them on someone’s head.
The AU-24A and its competitor, the Fairchild AU-23A, participated in the USAF combat evaluation known as Pave Coin, which lasted from June to July 1971. The USAF found the aircraft unsatisfactory, as its low speed and operating altitude made it vulnerable to enemy anti-air fire. After some further testing, the USAF finally gave up on the idea of supplying the AU-24A to the South Vietnamese Air Force, and eventually, 14 or 15 of them were sold to the Khmer Air Force instead. These aircraft served through the Cambodian Civil War and provided effective fire support despite technical issues and lack of spare parts, and were finally retired in the 1990s.
Specifications
General characteristics:
- Crew: 1 (2 or more if door gun is implemented)
- Length: 39 ft 7 in (12.07 m)
- Wingspan: 41 ft (12.50 m)
- Height: 9 ft 3 in (2.82 m)
- Wing area: 242 sq ft (22.5 m²)
- Empty weight: 2,860 lb (1,297 kg)
- Max takeoff weight: 5,100 lb (2,313 kg)
- Fuel capacity: 120 US gal (450 L)
- Powerplant: 1 × Pratt & Whitney Canada PT6A-27 turboprop, 680 hp
Performance:
- Max speed: 216 mph (348 km/h, 188 kt) at 10,000 ft (3,000 m)
- Cruise speed: 160 mph (260 km/h, 140 kt) at 10,000 ft (3,000 m)
- Never exceed speed: 218 mph (351 km/h, 189 kt)
- Range: 641 mi (1,032 km)
- Service ceiling: 25,000 ft (7,600 m)
- Rate of climb: 2,200 ft/min (11 m/s)
- Takeoff run to 50 ft (15 m): 660 ft (200 m)
- Landing run from 50 ft (15 m): 750 ft (230 m)
Armament:
- 1x 20 mm M197 autocannon as door gun
- 5x hardpoints, 350 lbs (158 kg) on outboard stations, 500 lbs (227 kg) on inboard stations, 600 lbs (272 kg) on fuselage station
- SUU-11A gun pods
- CBU-14A cluster bombs
- LAU-32/LAU-68 rocket pods
- various light bombs
More pictures
Another view of an AU-24A in storage at Davis-Monthan AFB in March 1973
(source: Jane’s All the World’s Aircraft 1974-75)
An AU-24A carrying Sparrows, though unable to launch them (source: Davis)
Sources
- Jane's all the world's aircraft : 1974/75 : Taylor, John William Ransom : Free Download, Borrow, and Streaming : Internet Archive
- Gunships, a pictorial history of Spooky : Davis, Larry, 1942- : Free Download, Borrow, and Streaming : Internet Archive
- Helio Aircraft : Our Planes - Helio Stallion
- AU-24A Helio Stallion
