LEM
HD and 411A have answered your query but whilst cleaning out my old computer the other day I found an old file which may be of use if you have a broader interest in the Tristar....
All of the flight controls on the Tristar are hydraulically actuated and none has any form of manual reversion. This simply means that, in the event of the failure of all hydraulic systems, the aeroplane would be completely uncontrollable. Before you blacklist all airlines flying Tristars, remember that the flight crews are all made well aware of this fact during their conversion and that they are all only too happy to operate the aeroplane. Prior to going on to the hydraulic actuation of these controls, and all of the rest of the hydraulic services, I will briefly run through these flight controls with particular reference to those that may not be quite so familiar to all of us.
Pitch control is maintained by the use of an all flying tailplane to which is attached a relatively normal elevator. They move in conjunction, and the elevator is mechanically linked to the tailplane. Control is by two servos and if either jams it can be disconnected. Trim is automatic and is achieved by the positioning of both surfaces Each time trim is used the control column takes up a new neutral position. The rate of movement of the trim is automatically varied for different speeds.
The rudder is reasonably conventional and incorporates a yaw damper whose purpose is to help eliminate "Dutch Roll". A series of "stops", which are actuated by speed sensitive switches, automatically limits arc of travel of the rudder in various conditions of flight.
Most jet airliners are equipped with two ailerons on each wing and the norm has been for the outboard aileron to be automatically locked central at high speed. The Tri Star differs in that all ailerons are operating at all stages of the flight. Extra control in the rolling plane at slow speed is needed and is provided by differential operation of the spoilers.
Six spoilers are fitted to each wing and their functions are many and wonderous to behold. They operate in a multitude of combinations to achieve these functions which are as follows:-Speed Brakes (at any time in the flight), Roll control assistance (when flap is extended), Lift control (on approach), and automatic extension after landing. When spoiler extension is demanded the aircraft decides which ones will extend and which ones will not. To make these decisions it gathers information from a series of speed sensitive switches, flap position indicating switches, Throttle position switches, and "squat" switches on each of the three U/C. legs.
Four double-slotted Fowler flaps are fitted to the trailing edges of the wings and alternate between the spoilers, while there are seven slats, or leading edge flaps, fitted to each wing. The slats go out with the first extension of the flaps (3 degrees), and are responsible for the very marked difference in the stall, and approach, speeds when either flapped or clean.
Hydraulic Systems.
There are four hydraulic systems in the Tristar. They are completely independent of each other. Each has is own reservoir and pressure source, and a loss of fluid in one will not affect any other. Pressure is provided by E.D.P.'s, P.T.U.'s, A.T.M.'s , electrically powered pumps and a R.A.T.
"A" System is powered by an E.D.P. on No. 1 engine and has, as an alternate power source, a PTU from System "B".
"B" System is powered by an E.D.P. on No. 2 engine and, as alternate power source, has an A.T.M. and an electric pump,
"C" System is exactly similar to "B" System but in addition may be powere by the R.A.T.
"D" System is exactly similar to "A" System.
The RAT is extended automatically when needed, and can be manually extended on the ground. It is normally "pinned", for safety reasons, when the aircraft is on the ground.
The most important hydraulically operated services are the flight controls and each of them is supplied with a multitude of alternate pressure sources, either by extra jacks to the same control surface or to mated surfaces (ie spoilers). There are two independent sets of wheel brakes. U/C. can be free falled, and flaps can be done without .
Flight Director/Auto Pilot, Area Navigation, & Auto Land.
Equipment includes, two Auto Pilots. two Flight Directors. three computors, two Inertial Nav. Systems and two VORTAC's.
The information used by the autopilot is the same as used by the corresponding flight director. Only one autopilot may be operated at a time, except in "Autoland" mode, but the flight directors may be operated in conjunction or independently and either automatically or by manual input. The third nav. computor monitors the other two at all times and any one of the three that is "odd man out" is automatically discarded. VORTAC stations are automatically tuned as the a/c. moves along track. As an alternate to automatic navigation the autopilot in use may be manually controlled
Movement along track may be monitored on a C.R.T. type display, a complete sector flight plan may be fed into the computer, automatic interceptions of VOR radials and ILS's can be made, an auto throttle is fitted, and either height or speed may be maintained.
Auto landings are available wherever there is a suitable ILS. Interception of both the ILS and the G/S. are automatic. A "Go Around" facility is incorporated, it is armed when flap in excess of 33 degrees is selected and it is activated when a button is pressed.