Or Spoilers/Speedbrakes?
DESCRIPTION
The term 'speedbrake' is used in a general sense to identify the spoiler/speedbrakes for the sake of brevity and to agree with the control markings. Where precise definition is necessary, 'spoiler' or 'speedbrake' is used.
The spoiler/speedbrakes are fitted in four independent sections, an inner and outer section on each wing. Each section is hydraulically operated by its own power control unit and linked by a pilot operated mechanical control system. No.1 hydraulic system powers the outer sections and No.2 system the inner sections, thus failure of one hydraulic system does not cause complete loss of speedbrakes.
Controls in Fuselage
On the centre console, the single control lever is fitted with a movable collar; a damper is attached to the control lever and the lever is linked by a push-rod to a cable quadrant. From the quadrant a cable circuit extends rearwards to a drum on the rear face of the fuselage torque box.
Controls in Wings
From the drum a cable goes to the upper of two pulleys on the mixing unit in each wing. From the lower pulley a second cable is led outboard around an idler pulley and back to the drum. On the port side only, the cables are crossed between the torque box pulleys and drum. A swinging arm, on which the mixing unit pulleys are mounted, is linked by rods and levers to a torque shaft assembly, comprising inner, centre and outer portions. The inner power control unit is connected to the outer portion of the torque shaft by links, bell-crank levers and the inner spring strut; the inner power control unit ram is attached to the inner section of the speedbrakes.
The outer power control unit is connected to the outboard end of the outer portion of the torque shaft by links, bell-crank levers and the outer spring strut; the outer power control unit ram is attached to the outer section of the speedbrakes. A follow-up mechanism cancels the input signal after the ram has moved to the selected position.
OPERATION
Speedbrake Control
The movable collar on the control lever is raised for take-off and landing, to allow full speedbrake (50°) to be selected for landing or for an abandoned take-off. The collar is pushed down in flight to prevent a speedbrake selection of more than 20°. This limited angle is not operationally embarrassing and improves lateral control in the event of inadvertent flight above VMO. Movement of the lever on the centre console is transmitted to the mixing unit pulleys in each wing. Pulley movement is changed to rotary movement in the torque shafts, and through spring struts operates the servo valves of the control units. Control system movement opens a rotary valve thus directing supply pressure fluid to one side or the other of a jack ram piston, which moves the ram body and consequently the control surface. Movement of the ram body is proportional to and in the same direction as the movement of the pilots' control input. When the control input ceases, a feed-back movement restores the rotary valve to a neutral (shut-off) position, thus preventing further control surface travel.
The control units regulate the flow of fluid to actuate the rams. If the aircraft exceeds the speed for speedbrakes extension they will blow back, but will gradually extend as speed is reduced. If a servo valve fails, the relevant spring strut will 'collapse' and operate the micro-switch, which will put on the associated fail warning light on the centre instrument panel. The warning lights are cancelled by moving the adjacent spoiler isolate switch to off. This will allow the affected spoilers to blow back.
Aileron/Spoiler Control Mixing
When used as spoilers, the appropriate surfaces move upward in conjunction with the upward moving aileron but remain stationary on the other wing. Mixing the aileron and spoiler control is achieved by input of the aileron control circuit being fed into the spoiler quadrants and of the mixing pulleys. Upward movement of the ailerons, above approximately 4° of aileron movement (11-15° of control wheel aileron movement), also moves the input lever of the control servo units which, due to the initial setting, delay the operation of the spoilers. With the spoilers extended as speedbrakes, application of aileron will retract the spoilers on the upward moving wing, and further extend them on the downward moving wing.
TCF