12/31/2013. Remarks by Johan Visschedijk : "The light observation Helicopter (LOH) competition announced by the US Army in 1960 resulted in final proposals from Bell and Fairchild Hiller, with Hughes being included in the short list at the last moment.
The Hughes proposal was for a compact helicopter with what is best described as an egg-shaped fuselage with a tapered tailboom and four-blade semi-rigid rotor. Designed by Mal HarnÁd (who later conceived the Gates Twin-Jet Helicopter) the Model 369 (YOH-6A) was powered by an Allison 250 turboshaft, and five prototypes were built and evaluated at Fort Rucker in 1965.
The YOH-6A was smaller than its competitors but its performance, ease of maintenance and the ruggedness of its construction resulted in Hughes being awarded the production contract - much to the annoyance of Fairchild Hiller. Above all, it had a very competitive price and it was evident when the OH-6A went into production that Hughes would earn little or no pro fit on the contract.
The definitive OH-6A embodied a number of changes over the prototypes, notably the replacement of the tapered monocoque tailboom with a slimmer unit mounting a three-finned tail. The U.S. Army ordered 714 OH-6A 'Cayuses' (subsequently increased to 1420) which were delivered between 1966 and 1970. This was in time for the Cayuse to be deployed to Vietnam where it was used widely for armed support of the larger UH -1 transports, and for observation and artillery marking. The OH-6A was fitted with external weapons, most commonly including a 0.30 in (7.62 mm) XM-27E gun pod mounted under the left-hand cabin door.
While the Cayuse was progressing through its military evaluation, Hughes was also working on the civil Model 500, which was announced in the spring of 1965. Four prototypes were built and the Model 500 (or 369A to quote its official factory and certificated number) received its type certificate on August 24, 1966. The civil model sold well, even though it had a somewhat smaller cabin than the competing Bell Jet Ranger. Its strengths were in having a higher maximum speed and greater range than the Bell aircraft.
The Model 500 was progressively improved with increasingly powerful variants of the Allison 250 turboshaft engine. The 500D, introduced in 1976, had a modified T-tail, and the 500E was distinguished by a reshaped fuselage pod with a slightly pointed nose. The 500 was also built under license in Italy by BredaNardi who delivered a substantial number to the Italian para-military Guardia di Finanza and a couple to the Maltese Armed Forces.
Military versions of all the later models were offered - particularly the 500MD Defender which was an unarmed scout or general purpose machine for export sale. Its offensive version, the Scout Defender, had armor plating and multiple external weapons hardpoints. Defenders have been delivered to a number of countries including the Philippines, Colombia and Mexico.
Hughes 'civilized' an OH-6A into a civil Model 500 and registered N9000F it first flew on September 13, 1966. In nearly overall-white it was first publicly presented at the Helicopter Association of America convention at Palm Springs, Colorado, January 15 to 18, 1967.
Subsequently it was further modified and demonstrated by the company pilot Harold 'Hal' W. Hawkins at the 27th Paris Air Show May 26 to June 4, 1967. After receiving a new color scheme it was used as a demonstrator for the next two years."