Helio AU-24 Stallion

The Helio AU-24 Stallion was an American armed gunship, counter-insurgency, and utility transport developed for the United States Air Force. A total of 20 were built during the Vietnam War. Most aircraft were later sold to the Khmer Air Force.

Design and development
The Helio HST-550 Stallion was an STOL utility aircraft developed in the United States in 1963. The prototype flew in July 1964. Initially conceived by the Helio Aircraft Company as a turboprop-powered variant of the Helio Courier, it eventually emerged as a completely new design of the same general configuration and much of its design was initiated from components used in the Helio H-500 Twin. It was a much larger aircraft than the Courier, and Helio soon discovered that it was too expensive for the market.

The United States Air Force however, emerged as a buyer for the design, purchasing the aircraft for the Credible Chase programme as the AU-24A. This was the gunship version of the Stallion, with a PT6A-27 680 shp turboprop, equipped with a General Electric M197 three-barrel 20x102mm rotary cannon mounted in the left cargo door. It also had five underwing and fuselage hardpoints.

Of the 18 aircraft purchased, fourteen or fifteen were eventually sold to the Khmer Air Force.

Variants

 * H-550 – prototypes (2 built)
 * AU-24A Stallion (H-550A) – production version (18 built)
 * H-634 Twin Stallion – version with twin Allison 250 turboprops mounted on a beam across the nose of the aircraft (not built)
 * H-1201T Twin Stallion – version with twin engines in underwing nacelles, retractable undercarriage, tiptanks, and underwing cargo pods (not built)

Operators

 * Khmer Republic
 * Khmer Air Force
 * United States Air Force
 * United States Air Force