DC8 Flight Controls
Hope this clarifies things.
AILERONS:
The DC8 has two (inboard, outboard) ailerons on each wing. The outboard ailerons are connected to the inboard aileron by a torque (slip clutch) linkage, and at low airspeeds and airloads, follow inboard aileron movement. To prevent over-controlling at higher airspeeds, airloads "freeze" the outboard aileron in the faired position, and all lateral control is accomplished with inboard aileron movement only.
The inboard ailerons have aerodynamic boost (control) tabs, which are directly connected to the control wheel through a manual reversion mechanism. When hydraulic pressure is available to the aileron, this tab is locked mechanically, and hydraulic pressure is routed through control valves to move the entire aileron. If hydraulic power is lost, the spring-loaded reversion mechanism allows the tab to operate by direct mechanical linkage from the pilot’s control wheel. When the wheel is moved, the tab is deflected and the aileron is "flown" to a new position to achieve the desired roll rate.
RUDDER:
The DC8 rudder is normally powered hydraulically by the left aircraft hydraulic manifold. A standby rudder pump is provided as an alternate hydraulic source. When powered hydraulically, the entire rudder is moved in response to pilot inputs. Should hydraulic power be unavailable, a rudder boost (control) tab is provided to "fly" the rudder to the required position.
The manual reversion mechanism determines whether the rudder pedal input will be mechanically linked to the hydraulic actuator, or the aerodynamic boost tab . Its operation is identical to that of the aileron. If hydraulic power is available, it is held in a POWER ON mode.
A rudder load limiter restricts the rudder to one third hydraulic pressure and travel to prevent over controlling in high speed (flaps up) flight.
ELEVATOR:
The elevator has no hydraulic input. It is strictly mechanical.
Two types of aerodynamic boost tabs are provided. The elevator control tabs, moved by the pilots, and the geared tabs, moved by the stabilizer when it is trimmed.
The elevator and control tabs are directly connected to the pilot's yoke. Initial movement of the yoke will reposition the aero_dynamic control tabs. When tab limits are reached, further yoke movement will result in limited movement of the entire elevator.
The geared tabs are designed to keep the elevator faired with the stabilizer to allow full control authority of the elevator as the stabilizer leading edge moves throughout the stabilizer trim setting range.