Aircraft Production in Thailand
The intended replacements to the Hawk III and Corsair were the North American NA-68 and NA-69 respectively. These designs were fighter and light attack developments of the famous BC-1A/AT-6 Texan series. Their all-metal construction would have been a challenge to the Bang Sue factory, especially when one considers the problems experienced in producing the Hawk IIIs. Performance, speed, range and arnament was sacrificed. The emphasis was on standardization and ease of maintenance. By 1940, the front-line strength of the RTAF was made up of Hawk II and IIIs and Corsairs. These were easily out-performed by contemporary Japanese, American and British aircraft.
As such, the similarities between the NA-68 and NA-69 were considered to be of great advantage, as regards to airframe commonality and ease of maintenance. The RTAF was also offered the NA-16 basic trainer. If the RTAF ordered 12 aircraft of each type, the NA-16 basic trainer, the NA-68 fighter and the NA-69 light attack aircraft, North American would assist in reorganizing the Bang Sue facility. This offer was not taken up, because of the pressing needs for combat aircraft. However, ten NA-69s were ordered on November 29, 1939. Just over a month later, on December 30, six NA-68s were ordered. North American Aviation had previously delivered some N.A.-50 single seat fighters to Peru. The Siamese N.A.-68s differed in a number of respects from the N.A.-50s, having a redesigned rudder and main undercarriage. The N.A.-68 was also more heavily armed, having two 7.62 mm machineguns in the nose, and two 20 mm cannons mounted in underwing gondolas. The N.A.-68 could also carry one 250 kg bomb on an externally mounted ventral rack, or two 50 kg bombs mounted on underwing racks.
It was intended that both the N.A.-68 fighter and N.A.-69 light ground attack aircraft would be produced under license at Bang Sue. However, due to an export embargo in October 1940, no NA-68s nor NA-69s were delivered to Thailand. The six NA-68s were aboard a ship in Hawaii, awaiting shipment to Thailand. They were returned to the USA, allotted the serials 41-19082 to -19087, and used as advanced trainers under the USAAF designation P-64. One of the P-64s still survives as a museum piece, albeit not in Thailand. 41-19085 is preserved by the Experimental Aircraft Association at Oshkosh, Wisconsin, having spent some time in Mexico as a crop-duster. A converted SNJ-4 Texan (US registered as NX30CE), is currently preserved in flyable condition by the RTAF Tango Squadron at Chiang Mai, having been modified as an N.A.-68 in full RTAF markings and insignia.
The N.A.-69 light attack aircraft was outwardly similar to the BC-1/AT-6 series. However, it was equipped with a 785 hp Wright Cyclone R-1820-75, and was armed with five 7.62 mm machineguns (two in the nose, one mounted in each wing and one dorsal mounted). The N.A.-69 could carry four 50 kg bombs, mounted on underwing racks. The N.A.-69s were also embargoed and handed over to the USAF. They were designated as A-27s, and allotted the serials 41-18890 to -18899. They were sent to the Philippines, where they served with the 17th Pursuit Squadron at Nichols Field. All of the A-27s were destroyed during the Japanese invasion in December 1941.
During World War II, the Bang Sue factory was pre-occupied with repair and overhaul work on the existing fleet of RTAF aircraft. The marshalling yards at Bang Sue suffered two raids during the war, the first on November 4, 1944, by seven RAF Liberators. The second raid occured later the same month, on the 27th, when 55 B-29 Superfortresses attacked Bang Sue. It is not known if the aircraft factory received any damage during these raids. It is not known if any Japanese aircraft were overhauled and/or repaired at the Bang Sue facility. The 19th Yasen Koku Shurisho (19th Field Air Repair Depot) of the Imperial Japanese Army Air Force had its main base at Don Muang, as well as three branches, at Heho, Saigon and Rangoon. The Depot was responsible for major repair and overhaul of aircraft for onward delivery to front line units. New aircraft were also prepared (including painting) for front line service at the Depot. The 13th Yasen Koku Shurisho (13th Field Air Supply Depot) was based at Singapore, but had a branch at Bangkok. This Depot handled the supply of expendable materials. According to one source, some Japanese aircraft were apparently overhauled at a facility at Lampang, 100 kilometres south west of Chiang Mai. Lampang was the main base of the RTAFs Northern Air Wing, which operated Mitsubishi Ki-21s, Nakajima Ki-27bs, Hawk 75Ns and Vought V.93 Corsairs against Chinese Nationalist forces in the Shan State, Burma.
During the lean post-war years, no aircraft production took place in Thailand until the mid-1950s. Surplus US and British aircraft were cheap and available in quantity. The RTAF received large quantities of Bearcats and Texans from the USA, while Spitfires and Fireflies were delivered from Great Britain. Post-war, an office of Aeronautical Engineering was created by the Royal Thai Air Force. It was named the Science and Weapon Systems Development Centre, SWDC. The aircraft that were designed and tested by the SWDC received the designation RTAF, followed by a consecutive number. The RTAF-1 was not a new design, being assigned to the 1927 vintage Boripatra bomber. The RTAF-2 was a four-seat liaison and utility aircraft, based on the Japanese Fuji LM-1, which in turn was a development of the Beech T-34 Mentor. One was tested during 1957-1958. It is preserved at the RTAF museum. Nothing is known about the RTAF-3 project, except that a model underwent wind tunnel tests in Japan.
Thailand had been an early customer for the DHC-1 Chipmunk. Both British and Canadian-built Chipmunks were delivered for a grand total of 66 aircraft. During 1974, one prototype and 12 more Chipmunks were re-engined with a Continental IO-360 engine. Apart from the new engine, the conversion also involved a new canopy and a redesigned fin and rudder. The conversion was called the RTAF-4 Chantra (Student). In 1974, two Pazmany PL-2 primary trainers were assembled. It is possible that they were evaluated for possible production, but no further aircraft were built. Instead, converted Chipmunks and AESL Airtourers were purchased. The PL-2 had its origins in a US homebuilt aircraft, the Pazmany PL-1B. Over fifty of these were built in Taiwan for use as primary trainers. The PL-2 was also used or evaluated by Indonesia, South Korea and South Vietnam.
It has been rumoured that Helio Couriers were assembled or built at Chiang Mai during the Vietnam War. Air America, the USAF as well as the RTAF were all large users of the STOL Helio Courier, but the assembly or production of Helio Couriers at Chiang Mai appears to be without foundation.
The RTAF-5 project was a trainer/Forward Air Control aircraft with the same configuration as the US North American OV-10 Bronco. It was powered by a 420 hp Allison 250-B17C turbo-prop engine. The first flight took place on October 5, 1984. Two aircraft were produced, the second of which was used for static testing. The RTAF-5 programme was terminated after the RTAF's chief test pilot, Wing Commander Soonthorn Wongnamsan was killed in a crash.
In August 1982, a contact was signed with the German manufacturer Rhein-Flugzeugbau GmbH, RFB, regarding the delivery of 31 RFB Fantrainer 400 and 16 Fantrainer 600 primary trainers. The RFB Fantrainer was unusual in that it powered by a centre-mounted ducted fan. The RFB Fantrainer was supposed to have similar flight characteristics of a jet powered trainer, albeit at a much lower cost. The two types had a 92 % commonality, the main difference being the type of engine (the 400 had an 420 hp Allison 250-C20B turboprop, while the 600 had an 650 hp Allison 250-C30). The first two were built in Germany and delivered in October 1984. The remaining 45 aircraft were assembled in Thailand from kits supplied by RFB. Initially, they were equipped with wings constructed from glassfibre, which were later replaced by all-metal wings built in Thailand.
During the late 1970s, a company called Thai-Am converted old piston-engined Sikorsky S-58s to turbine power. It is not known if this company was connected with the US company California Helicopter, who, during the mid 'eighties is said to have converted 18 S-58s to S-58T twinpac standard for the Royal Thai Air Force, as well as two additional S-58Ts for the Ministry of Agriculture, Kaset. Other helicopters have also been converted or built in Thailand. Several Hiller UH-12s have been converted to side-by-side seating for use by the Civil Aviation Training Centre, CATC, and the Thai Police. In 1988, two Rotorway Exec 90 helicopters were assembled at Kasetsart University, on behalf of a private individual. These were evaluated for agricultural as well as other uses. At least five more Rotorway Exec 90s were assembled in the early 'nineties by the University's Department of Aerospace Engineering. Some ultralight and microlight aircraft have also been built in Thailand.
One of the latest aircraft built in Thailand is not of the most modern design. In fact, the design dates from the late 'twenties. The aircraft in question is a replica of the first civil aircraft in Siam, a Travelair 2000 named "Miss Siam." The flyable replica, appropriately registered as HS-IAM, has been built by the Tango squadron at Chiang Mai. Two types of aircraft, old and new, can provide a spectrum regarding the production of aircraft in Thailand. Two static "look-a-like" replicas of Breguet 14s were recently built for use in the film "First Flight." The replicas "flew" against a back-projection screen. In 2002, a Zenith CH 701 homebuilt ultralight kit was delivered to the RTAF for use in an engineering exercise.
The author wishes to thank Walika Chomsongneru, Royal Thai Air Force Museum, Steve Darke, who maintains the excellent website www.thai-aviation.net, Nick Millman, Larry deZeng, Vidya Tapasanan and Edward Young, whose book "Aerial Nationalism" remains the best title on aviation in Thailand.