as a scale rocket, its all-flying tail was tested on the Miles Falcon. The contemporary American supersonic project, the Bell X-1, adapted its variable incidence tailplane into an all-moving tailplane (based on the Miles M.52 project data) and was operated successfully in 1947. Entering service in 1951, the Boeing B-47 Stratojet was the world's first purposely built jet bomber to include one piece stabilator design. A stabilator was considered for the Boeing B-52 Stratofortress but rejected due to the unreliability of hydraulics at the time. The North American F-86 Sabre, the first U.S. Air Force aircraft which could go supersonic (although in a shallow dive) was introduced with a conventional horizontal stabilizer with elevators, which was eventually replaced with a stabilator. When stabilators can move differentially to perform the roll control function of ailerons, as they do on many modern fighter aircraft they are known as tailerons or rolling tails. A canard surface, looking like a stabilator but not stabilizing like a tailplane, can also be mounted in front of the main wing in a canard configuration (Curtiss-Wright XP-55 Ascender). Stabilators on military aircraft have the same problem of too light control forces (inducing overcontrol) as general aviation aircraft. Unlike light aircraft, supersonic aircraft are not fitted with anti-servo tabs, which would add unacceptable drag. In older jet fighter aircraft, a resisting force was generated within the control system, either by springs or a resisting hydraulic force, rather than by an external anti-servo tab. For example, in the North American F-100 Super Sabre, springs were attached to the control stick to provide increasing resistance to pilot input. In modern fighters, control inputs are moderated by computers ("fly by wire"), and there is no direct connection between the pilot's stick and the stabilator. Airliners Most modern airliners do not have a stabilator. Instead they have an adjustable horizontal stabilizer, and a separate elevator control. The movable horizontal stabilizer is adjusted to keep the pitch axis in trim during flight as the speed changes, or as fuel is burned and the center of gravity moves. These adjustments are commanded by the autopilot when it is engaged, or by the human pilot if the plane is being flown manually. Adjustable stabilizers are not the same as stabilators: a stabilator is controlled by the pilot's control yoke (or stick), whereas an adjustable stabilizer is controlled by the trim system. In the Boeing 737, the