Bell 207 Sioux Scout

The Bell 207 Sioux Scout was a modified Bell 47 helicopter, developed by Bell Helicopter under contract from the United States Army, as a proof-of-concept demonstrator for the Bell D-255 helicopter gunship design, featuring a tandem cockpit, stub wings, and a chin-mounted gun turret.

Design and development
After several years development Bell displayed the mockup of its "D-255 Iroquois Warrior" to Army officials in June 1962, hoping to solicit funding for further development. The D-255 was planned to be a purpose-built attack aircraft based on the UH-1B airframe and dynamic components with a new, slender airframe and a two-seat, tandem cockpit, featuring a grenade launcher in a ball turret on the nose, a 20 mm belly-mounted gun pod, and stub wings for mounting rockets or SS.10 anti-tank missiles.

A proof of concept contract was awarded to Bell in December 1962 for the Model 207 Sioux Scout, which was, in essence, a new forward fuselage and Bell 47G-3 dynamic parts fitted to a Bell 47J center and rear fuselage. The Sioux Scout included all the key features of a modern helicopter gunship – a tandem cockpit, stub wings for weapons, and a chin-mounted gun turret. The tandem cockpit placed the gunner in the lower front seat and pilot in the rear, with both crew positions featured flight controls. The gunners position featured a gun sight and turret controls located in the centre, so the flying controls were moved to the side of the front cockpit. The gunner controlled a chin-mounted gun turret with twin 7.62 mm (.308 in) M60 machine guns. The stub wings held external fuel tanks.

First flown in July 1963, the Bell 207 demonstrated improved manoeuvrability over the Bell 47/OH-13, derived from the stub wings. A variety of different wings, cowlings and tail surfaces were tested on the 207 before it was turned over to Army pilots at Fort Benning, Georgia for further testing at the end of 1963. After evaluating the Sioux Scout in early 1964, the Army was impressed, but also felt the Sioux Scout was undersized, underpowered, and generally not suited for practical use.

Later in 1964, the Army requested proposals for its Advanced Aerial Fire Support System (AAFSS). In response, Bell proposed the D-262 (Model 209), a smaller version of the D-255, making better use of the T53 engine from the UH-1. However, the Bell D-262 was not selected as a finalist in the competition, which was won by the abortive Lockheed AH-56 Cheyenne. Despite losing the AAFSS competition the Model 209 achieved great success as the Bell AH-1 Cobra.