Helio H-550A Stallion

djohn, e-mail, 19.06.2011 20:55 Helio HST-550A /AU-24A Helio Stallion HST-550 /A (18-constructed, c /n 001 -018) s /n 72-1319 t0 72-1333, One factory prototype, One demonstrator HST-550 c /n's HST-1 & 2, HST-550 #2 later converted to HST-550A (c /n HST-001). (c /n 005 was never manufactured). Fourteen were sent to Cambodia ,Khmer AF, (c /n 009) remained at Davis-Montham USAFB. Three were shot down in combat operations they were recovered and apparently used for parts. One (c /n 017) crashed in Cambodia. One ran out of fuel over the Tonkin Gulf. Three (c /n 004,006,007) escaped to Thailand and returned to the US in 1976. b 6 were captured by Kmer Rouge. One was placed on display later broken up, an Five were reportadly sent or sold to China. N550AA 1968 HST-550 HST-1 now c /n001 NC prototype N9551A, goes to Columbia HK-??? later returns as second 001, owner Tim Greene N10038 1968 HST-550 HST-2 Factory demonstrator N9550A, becomes c /n001 upgraded to HST-550A N550HE 1968 HST-550A _001 Flagstaff , AZ N9550A, N10038, N550HE, briefly N55OAA, RP-C1550, owner David Maytag ? , Xprd Reg the one shown in picture N70850 1969 HST-550A _002 damaged beyond repair LA Saltwater immersion katrina sold ? "3" 69 HST-550A /AU24-HE _003 (72-1319) Khmer AF N9552A fate unknown N9991F 69 HST-550A /AU24-HE _004 (72-1320) damaged beyond repair N9553A Khmer AF, fatal crash Perry, CA N5779N 69 HST-550A /AU24-HE _006 (72-1321) Airborne Leasing, WA Khmer AF, N9992F, CP-1396, Steve Hill owner ,Tri? N550HZ 69 HST-550A /AU24-HE _007 (72-1322) damaged beyond repair Khmer AF, N1384X N9991F,N994PF,David Maytag owner Tri? '8" 69 HST-550A /AU24-HE _008 (72-1323) Khmer AF fate unknown "21324" 69 HST-550A /AU24-HE _009 (72-1324) scrapped at Davis-Montham USAFB, didn't go to Khmer AF "10" 69 HST-550A /AU24-HE _010 (72-1325) Khmer AF fate unknown "11" 69 HST-550A /AU24-HE _011 (72-1326) Khmer AF fate unknown "12" 69 HST-550A /AU24-HE _012 (72-1327) Khmer AF fate unknown "13" 69 HST-550A /AU24-HE _013 (72-1328) Khmer AF fate unknown "14" 69 HST-550A /AU24-HE _014 (72-1329) Khmer AF fate unknown "15" 69 HST-550A /AU24-HE _015 (72-1330) Khmer AF fate unknown "16" 69 HST-550A /AU24-HE _016 (72-1331) Khmer AF fate unknown "17" 69 HST-550A /AU24-HE _017 (72-1332) Khmer AF crashed Cambodia "18" 69 HST-550A /AU24-HE _018 (72-1333) Khmer AF fate unknown reply

Bud Schroeder, e-mail, 08.06.2011 04:51 I was the Project Officer for FAA certification of the H-550A. The airplane was aquired by the USAF as an "Off The Shelf" purchase which meant that the airplane was required to meet the design requirements of Part 23 of the FAA Certification Regulations for small airplanes plus any FAA Special Conditions issued applicable to the airplane. As I recall one unsual operating feature of the airplane was for it to fly downward at a very steep, if not vertical, angle and be able to maintain a maximum airspeed of 120 knots or less. I think this requirement had to do with dive bombing. One problem that surfaced during the certificatin program was an un-damped, if not gradually diverging, porposing mode in level flight that was related to the flying horizontal tail. Airforce test pilots were sent out to Pittsburgh, KS from Edwards Airforce Base to help with correction of the problem. I am still in contact with one of those pilots who later ended up as a flight test pilot in the FAA Transport Airplane Directorate in Seattle, WA. The flight tests involved many flight cycles of climbing to 8000 to 10000 feet and decending near vertically at 120 knots while ground ambient temperaturs were near 100 degrees F and humidity levels around 90% in Pittsburgh, KS. To maintain 120 knots in the near vertical dives nearly full "Beta" power on the PT-6 engine was required and engine exhaust fumes entered the cockpit at times during these maneuvers. The landing strip at the Pittsburgh facility was a short dirt strip. I remember the Stallions taking off when the end of the field was a mud bog and the wheels of the gear were shearing thru mud above the top of the tires during the initial take-0ff run. There was a house at the south end of the field and big chunks of mud would sometimes fall off the gear and land near the house. Another problem that surfaced was that the gattling gun mussle blast damaged the left wing flap which required structural reinforcement of the left flap for certification. reply

Walt Hoy, e-mail, 08.01.2011 17:25 I was the test directer on the AU-24 for Credible Chase. I'm scheduled to give a talk about the Stsllion on 7 Feb. 2011 at Wright Patterson AFB. I could use some good pictures of the bird. Can anyone help? reply

Bob Donaldson, e-mail, 18.12.2010 03:39 I checked out in the Helio Stallion in Oct, 1971 at the Pittsburg,Kan. factory as part of the USAF Credible Chase program. I flew it until May of 1973. Upon completion of the Credible Chase program which was a 9 month fly-off competition with the Pilatus Porter. The Stallion won the competition but the promised "buy" of 2400 aircraft never materialized because the VietNam war was winding down. I was then chosen to take all 22 Stallions and a 25 man team of USAF and Air America pilots and maintenance members to Cambodia for the purpose of training a Cambodian Air Force squadron to fly and fight with the Stallion. That program lasted from March 1973 to May of that year. These Stallions were armed with a 20MM gatling gun that fired out the left cargo door and two hard-point armament stations under the wings for rockets,CBU and various bombs up to 500 lbs. This squadron flew combat from May,1973 until April 1975 when it was overrun by the Kymer Rouge. All but 3 0r 4 of the aircraft were flown out of Cambodia. All squadron personnel,except 2 0r 3 were murdered by the Kymer Rouge. reply

Eric Barnhill, e-mail, 08.10.2010 06:37 I helped restore Stalion #1, it was recovered from Bogata Columbia. Beautiful aircraft, will hold anything, built like a truck. It sits in the maintenance hanger at CEU. reply

Bud Blankinchip, e-mail, 14.06.2010 14:12 I was poking around Pittsburg Kansas while on leave from Viet Nam in 1970 or 71. During my travels I discovered Helo Aircraft Company. I knocked on the plant door and was greeted by an engineer that I think was named Charles Casbeer. (probably not spelled correctly) The gentleman gave me a tour of the plant and showed me the prototype of the Stallion. That has to be the most beautiful airplane I've ever seen. The plant was not producing anything and it appeared they were prepareing to close it. reply

Alan Tyler, e-mail, 13.12.2009 05:25 Great aircraft, my father was the designer of the rear stab. & elevator assembly as well as the half slider half swing door on the starboard side. I have the original 1 /2 scale blueprint of the tail section as well as some black & white photos during the assembly. I also have pictures of the twin engine helio proto-type as well as the helio with the machine gun turret on the bottom & gun pylons on the wings. reply