Helio AU-24 Stallion

The Helio HST-550 Stallion was an STOL utility aircraft developed in the United States in 1963, with the first prototype flying 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 (USAF) 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 {{convert|680|shp|abbr=on}} turboprop, equipped with an M197 three-barrel 20x102mm rotary cannon mounted in the left cargo door. It also had five underwing and fuselage hardpoints.Davis and Greer, Gunships, A Pictorial History of Spooky (1982), pp. 63-64.

Of the 18 aircraft purchased by the USAF, fourteen or fifteen were eventually delivered to the Khmer Air Force (KAF) between January and November 1972 under the Foreign Military Sales program for use in border surveillance and counter-infiltration roles, where the threat of encountering anti-aircraft fire (other than small arms) was minimal.{{Cite web|url=https://www.globalsecurity.org/military/systems/aircraft/au-24.htm|title=AU-24A Helio Stallion}}Davis and Greer, Gunships, A Pictorial History of Spooky (1982), pp. 63-64.Conboy and Bowra, The War in Cambodia 1970-75 (1989), pp. 20-21.Conboy, FANK: A History of the Cambodian Armed Forces, 1970-1975 (2011), p. 219.

An important addition to the KAF, the AU-24A mini-gunships were assigned to a newly raised Mini-gunship Squadron (French: Escadron AU-24) stationed at Pochentong Air Base near Phnom Penh, which broadened supply convoy escort operations on the lower Mekong-Bassac Rivers corridors. Such operations had been carried out in conjunction with the Khmer National Navy (MNK) since mid-1971, when the KAF began to provide air cover to MNK convoys with their Douglas AC-47D Spooky gunships.Davis and Greer, Gunships, A Pictorial History of Spooky (1982), pp. 63-64.Conboy and Bowra, The War in Cambodia 1970-75 (1989), pp. 20-21.Conboy, FANK: A History of the Cambodian Armed Forces, 1970-1975 (2011), p. 219.

Under Project Flycatcher, an improvement programme for the KAF, the Americans delivered among other aircraft types a single AU-24A mini-gunship before the programme was officially terminated on June 30, 1973.Jan Forsgren, Cambodia: Khmer Air Force History 1970-1975 (Part 2) - http://www.aeroflight.co.uk/waf/aa-eastasia/cambodia/cam-af-history2.htm Although the AU-24A mini-gunships delivered to Cambodia acquainted themselves well in the river convoy escort role, they were found to be beset with a long list of technical faults, which became painfully clear on August 10, 1973, after a Stallion crashed on a rocket pass, killing its crew and forced the KAF Air Command to temporarily ground the entire mini-gunship fleet.Conboy, FANK: A History of the Cambodian Armed Forces, 1970-1975 (2011), pp. 220-221.

In the final months of the Cambodian Civil War, the KAF employed their AU-24A mini-gunships in night bombing operations against entrenched Khmer Rouge 107mm rocket positions north of Phnom Penh,Conboy and Bowra, The War in Cambodia 1970-75 (1989), p. 22. but after virtually expended their entire ordnance reserves, three Stallions escaped on April 16–17, 1975 from Pochentong Air Base flown by their respective crews to safe haven in neighbouring Thailand.Conboy, FANK: A History of the Cambodian Armed Forces, 1970-1975 (2011), p. 223. The Khmer Rouge did manage though to salvage intact nine AU-24A mini-gunships for the Air Force of the Kampuchea Revolutionary Army (AFKRA) of the new Democratic Kampuchea Regime, although poor maintenance and a chronic shortage of spare parts ensured that only one of these machines was still airworthy when the AFKRA was neutralized by the People's Army of Vietnam (PAVN) in February 1979 during the Cambodian–Vietnamese War.Conboy, FANK: A History of the Cambodian Armed Forces, 1970-1975 (2011), p. 223.{{cite web|url=http://www.flightglobal.com/pdfarchive/view/1983/1983%20-%201422.html|title= World Air Forces 1983 |page=358 |publisher= flightglobal.com |accessdate=30 March 2013}} This remaining Stallion was subsequently taken after 1979 into service of the air force component of the Kampuchean People's Revolutionary Armed Forces (KPRAF; later, CPAF), remaining operational until 1993, when was finally decommissioned.

• 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)

;{{flag|Colombia}}

• Colombian Air Force. A single aircraft seized for drugs and used as liaison.

;{{flag|Khmer Republic|name=Cambodia}}

• Khmer Air Force

;{{USA}}

• United States Air Force

{{Aircraft specs

|ref=Jane's All The World's Aircraft 1976–77Taylor, Jane's All the World's Aircraft 1976–77 (1976), pp. 301–302.

|prime units?=imp

|genhide=

|crew=1

|capacity=9 passengers

|length m=

|length ft=39

|length in=7

|span m=

|span ft=41

|span in=0

|height m=

|height ft=9

|height in=3

|wing area sqm=

|wing area sqft=242

|aspect ratio=6.93:1

|airfoil=NACA 23012

|empty weight kg=

|empty weight lb=2860

|gross weight kg=

|max takeoff weight lb=5100

|fuel capacity={{convert|120|USgal|impgal L|abbr=on}}

|eng1 number=1

|eng1 name=Pratt & Whitney Canada PT6A-27

|eng1 type=turboprop

|eng1 kw=

|eng1 hp=

|eng1 shp=680

|eng1 note=(effective shp)

|prop blade number=

|prop name=

|prop dia m=

|prop dia ft=

|prop dia in=

|perfhide=

|max speed kmh=

|max speed mph=216

|max speed kts=

|max speed note=at {{convert|10000|ft|m|abbr=on}}

|cruise speed kmh=

|cruise speed mph=160

|cruise speed note=at {{convert|10000|ft|m|abbr=on}} (econ. cruise)

|never exceed speed mph=218

|never exceed speed note=(Calibrated airspeed)

|range km=

|range miles=641

|range nmi=

|ceiling m=

|ceiling ft=25000

|climb rate ms=

|climb rate ftmin=2200

|more performance=*Takeoff run to 50 ft (15 m): {{convert|660|ft|m|abbr=on}}

• Landing run from 50 ft (15 m): {{convert|750|ft|m|abbr=on}}

|avionics=

}}

{{aircontent|

|related=

|similar aircraft=

• Fairchild AU-23 Peacemaker

|lists=

|see also=

}}

{{Reflist}}

• {{cite book |last= Simpson |first= R. W. |title=Airlife's General Aviation |year=1995 |publisher=Airlife Publishing |location=Shrewsbury |pages=208–10 }}
• {{cite book |title= Jane's All the World's Aircraft 1965–66|last= Taylor |first= John W. R.|author-link=John W. R. Taylor |year=1965|publisher= Sampson Low, Marston|location= London}}
• {{cite book |title= Jane's All the World's Aircraft 1976–77|last= Taylor |first= John W. R.|author-link=John W. R. Taylor |year=1976|publisher= Jane's Yearbooks|location= London|isbn=0-354-00538-3 }}
• {{cite book |last= Taylor |first= Michael J. H. |title=Jane's Encyclopedia of Aviation |year=1989 |publisher=Studio Editions |location=London |pages=506}}
• {{cite book |title=World Aircraft Information Files |publisher=Bright Star Publishing|location=London |pages=File 896 Sheet 28 }}
• Kenneth Conboy, FANK: A History of the Cambodian Armed Forces, 1970-1975, Equinox Publishing (Asia) Pte Ltd, Djakarta 2011. {{ISBN|9789793780863}}
• Kenneth Conboy, Kenneth Bowra, and Mike Chappell, The War in Cambodia 1970-75, Men-at-arms series 209, Osprey Publishing Ltd, London 1989. {{ISBN|0-85045-851-X}}
• Larry Davis and Don Greer, Gunships, A Pictorial History of Spooky – Specials series (6032), Carrollton, TX: Squadron/Signal Publications, 1982. {{ISBN|0-89747-123-7}}
• Joe F. Leeker, Khmer Air Force AU-24As, University of Texas at Dallas 2006–2015. – [https://www.utdallas.edu/library/specialcollections/hac/cataam/Leeker/aircraft/kau24.pdf]

{{commons category-inline|Helio AU-24 Stallion}}

• [https://www.globalsecurity.org/military/systems/aircraft/au-24.htm Helio AU-24 Stallion at globalsecurity.org]
• [https://web.archive.org/web/20161104003304/http://www.helioaircraft.com/ourplanes_stallion.htm Helio AU-24 Stallion at helioaircraft.com]
• [http://www.khmerairforce.com/ Khmer Air Force official site]

{{Helio aircraft}}

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{{US utility aircraft}}

Category:1960s United States civil utility aircraft

Stallion

Category:1960s United States attack aircraft

Category:Counter-insurgency aircraft

Category:Single-engined turboprop aircraft

Category:Single-engined tractor aircraft

Category:Shoulder-wing aircraft

Category:Aircraft first flown in 1964

Category:Aircraft with fixed conventional landing gear