|The Bell D-245 Warrior set the pattern for gunship designs|
With the turbine-powered Bell UH-1 Iroquois "Huey" utility helicopter offering a quantum leap in capability for the US Army over previous, cumbersome, piston-driven rotorcraft, it was a natural progression that the UH-1s would be armed for aerial fires support for the growing conflict in Vietnam. But Bell's engineers in Fort Worth were steps ahead of the military with studies as early as 1958 for a tandem-seat purpose-built helicopter gunship that used the transmission and engine systems of what would become the UH-1. Bell's first offering had the in-house designation D-245 and was named "Warrior" which laid down the standard layout of gunships that followed- a slim fuselage with tandem seating for a pilot and gunner, stub wings for weapons, and nose-mounted gun turret. But despite its potential, the Army had yet to determine operational doctrines for the use of attack helicopters and the D-245 Warrior was quietly shelved.
Despite official disinterest from the US Army, Bell decided to embark on internally-funded development to further refine the D-245 Warrior design. In June 1962 Bell unveiled the D-255 Iroquois Warrior to the Army at its Fort Worth facility. The D-255 was a bit larger than the earlier D-245 but retained the tandem seating for pilot and gunner in stepped layout with the pilot sitting behind and higher than the gunner in the forward seat. Again, the tail boom, rotor transmission and engines were adapted from the UH-1. While the mixed reaction from the US Army was an improvement over the official disinterest that the earlier D-245 design elicited, it still wasn't enough to get a production contract from the Army. Again the D-255 was quietly shelved, but this still wasn't going to discourage the Bell team from staying ahead of the game. In December 1962 a brainstorming session of the engineering team resulted in a decision to build a flying demonstrator to prove the US Army what Bell's gunship concept could accomplish.
|The Sioux Scout was quite small for a two-seat gunship|
Designated the Model 207 and named the Sioux Scout, the demonstrator combined the engine, rotor, and drive systems of the proven Bell OH-13 Sioux (the bubble-cockpit helicopter made famous in the introduction to the TV series M*A*S*H) with its civilian counterpart, the Bell 47. The six-cylinder Lycoming 435 engine of the OH-13/Bell 47 was supercharged to deliver 220 horsepower driving the main rotor system from the OH-13 and the tail rotor/tail boom of the Bell 47. An all-new slim fuselage was created that used box beams to create a rigid structure to which were attached the stub wings that could carry external stores on six hardpoints on each side as well as house an additional 43 gallons of fuel which gave the Sioux Scout a range of 200 miles. At high speeds, the stub wings helped offload the main rotor as well. An Emerson Electric TAT-101 gun turret was installed under the nose (the rigid fuselage structure dampened recoil) housing twin 7.62mm machine guns that were adaptations of the M60 gun. With 1,100 rounds of ammunition, the gunner in the forward seat used a pioneering hand controller to operate the gun turret 100 degrees side to side, 15 degress upward, and 45 degrees downward. Under each stub wing were six round, 2.75 inch rocket launchers on each hardpoint.
|The gunner had an outstanding field of view from the front seat|
The Sioux Scout made its first flight from Bell's Fort Worth facility in Hurst on 27 June 1963, in the process becoming the first pure gunship in the world to take flight. Since the demonstrator program was somewhat secret, the helicopter was painted red and white to not so blatantly give away its military purpose. After several weeks of testing with Bell that added up to 65 flight hours, the Sioux Scout was repainted in more Army-like olive drab and began a series of weapons tests at Fort Sill, Oklahoma, northwest of Fort Worth. In November of that year, the Sioux Scout was taken on the road, touring Army bases and being flown by both Army and even NASA test pilots with over 300 flight hours that included firing over 83,000 rounds of ammunition from the chin turret. Finally, in 1964, B Troop, 3rd Squadron, 17th Cavalry of the 11th Air Assault Division spent a month flying the Sioux Scout in operational conditions and in field exercises. At the time, the 11th Air Assault Division was tasked by the Army commanders with experimenting and creating operational doctrines in helicopter assault at Fort Benning, Georgia.
|The Model 209 prototype had retractable landing skids|
Other than the Sioux Scout being underpowered and the reliability of the experimental gun turret being less than ideal, Army evaluators were overwhelmingly pleased with the outcome of the 11th Air Assault Division's operational evaluation of the demonstrator. The recommendation was issued that a turbine-powered, more capable version be developed as quickly as possible for operational use. In late 1964 the Secretary of the Army created the Advanced Aerial Fire Support System (AAFSS) with invitations to industry to submit designs. With the quick realization that the AAFSS design would take time to field, the Army decided that an interim design was needed that would field the gap until the AAFSS became operational. Bell dusted off its D-255 Iroquois Warrior design and with further refinements based on the Sioux Scout evaluation, designated it the D-262. However, in 1965 the Army rejected the D-262 design. But, as Bell had done before, they quietly went about refining the design further on company funds- within several months of the rejection of the D-262, the situation in Vietnam worsened and the US commander in Vietnam, General William Westmoreland, advised the Pentagon that either the AAFSS needed to fielded quickly or some interim design was needed as soon as possible. In March 1965 Bell just happened to finish the full-scale mockup of its refined gunship designated the Model 209 and "leaked" to Army commanders what it was up to. Before long, the Army issued a formal requirement for an interim design. Beating out submissions from Sikorsky, Kaman, Piasecki and Boeing Vertol, the Model 209 was selected on 11 March 1966 for production as the AH-1 Cobra.
And the AAFSS? That became the Lockheed AH-56 Cheyenne and was a classic case of wanting too much out of a design. It ended up getting cancelled in August 1972. That same month, the Army created the Advanced Attack Helicopter program (AAH) which became the AH-64 Apache. And what become of the Sioux Scout? The grand daddy of gunships can be seen today in the Army Aviation Museum in Fort Rucker, Alabama. And of course, Bell's interim design is still in production today for the US Marine Corps as the AH-1Z Viper.
Source: Helicopter Gunships: Deadly Combat Weapon Systems by Wayne Mutza. Specialty Press, 2010, p56-60. Images from aviatstar.org