L-1011 Flight Controls: Active Controls Load Distribution (27-51)

In the illustration above the dotted line shows the basic wing lift design load distribution of the L-1011 wing. the solid line shows the redistribution produced by symmetrical upwards deflection of outboard ailerons. Both load distribution lines are for the same structural design wing lift but the redistribution line show how aileron deflection moved the center of pressure inboard thus lowering the wing root bending moments. During cruise, aileron deflection would be minimal.

the Active Control System (ACS) uses outboard ailerons symmetrical deflection to relieve wing loading. Aileron deflection is controlled by accelerometer and sensor signals delivered to the ACS computer and from there on to the aileron servo. The computer provides the following functions:

• Maneuvering Load Control (MLC) by redistributing air loads caused by maneuvering air gusts inward span wise toward the wing root. 
• Elastic Mode Suppression (EMS) - Reduces vibrations along the wing in response to the wings natural bending vibration frequency. 
• High Lift Control (HLC) or wing tip relief when in the high lift, high drag flaps and slats extended configuration. (Both outboard ailerons will be up 8º).

L-1011 Flight Controls: Active Controls -500 (27-50)

Here is something that is only relevant to the -500 model of the Lockheed L-1011. The active control system provides a means of relieving loads caused by the increase in wing span on the -500. Load relief is accomplished by outboard ailerons symmetrical deflections programmed by the Active Control System (ACS). The ACS is dual channel with either channel capable of performing the proper programming of aileron deflections. The system uses a revised outboard aileron servo with 2 ACS series servos (1 and 2) mounted to each outboard aileron servo . Triple accelerometers located in each wing tip and forward cargo compartment ceiling (9 total) provide the acceleration signals, and 3 impact pressure (Q) sensors provide airspeed affect for gain scheduling. 

L-1011 Flight Controls: DLC and Glide Slope (27-41/44)

The image above shows the aircraft on approach path. DLC spoilers 1, 2, 3 and 4L and 4R are up to null position of approximately 10º up. The spoilers will operate up to 20º or close to 0º from the null position with session of Pilot or Autopilot pitch inputs. 

Once panels have moved to a position from the 10º null position they drift back to the null position ready for the next excursion.

If the aircraft moves above the glide slope, DLC commands spoilers 1, 2, 3 and 4 open to 20º reducing approximately 10% of lift. 400,000 lb. of weight results in a -40,000 lb. of lift reduction. The airplane returns to approach path with only a minor pitch change. This provides increased passenger comfort. 

If the aircraft has drifted below the glide slope, pitch input causes the close the increasing lift and the aircraft flies back into approach path with only minor pitch changes. DLC serves one additional important function: its use reduces the size of the landing touchdown zone scatter. Thereby improving category III autoland precision.

The image above shows the Surface Position Indicator with DLC spoilers 4 and right 2 indices traveling also the speed brake lever traveling in the DLC range in response to pilot commanded stabilizer movements.

DLC automatically disengages under any one or all of the following conditions:

1. Stall Warning 
2. Go-Around Switch Activated
3. Any two Throttles Advanced 
4. Flaps Retracted less than 30º
5. Pilot-mnaual Override of Speed Brake Lever
6. Pilot Assist Disable Switch Pressed
7. System Failures

L-1011 Flight Controls: Direct Lift Control (DLC) (27-39)

Spoilers 1, 2, 3, and 4 are used for Direct Lift Control (DLC). The spoilers are driven automatically through the DLC/AGS servo. Here is the DLC engage logic:

• Flaps are set to more than 30º
• At least two throttles are below MCT
• At least two for the throttles are not in reverse. 
• There is no Airplane On Ground (AOG) signal received 
• The airplane is not in go-around mode 
• There is no stall warning 
• The DLC/AGS channels are powered and OK 

The DLC servo that controls spoiler panels 1, 2, 3 and 4 assists in pitch control by reducing the amount of pitch attitude change required to peek the airplane in the "slot" once landing flaps are selected. DLC servo inputs cause the spoilers to travel thereby increasing or reducing lift.

The spoiler handle located on the throttle quadrant follows all DLC inputs providing an indication to the crew of system operation.

L-1011 Flight Controls: Spoiler Roll Assist (27-38)

When the Flaps on the L-1011 are set to 4º or more, spoilers 2, 3, 4, 5 & 6 assist roll on the up aileron or down wing in the turn. Travel can be as much as 40º up on the spoiler for roll assist. What's important to remember is that the spoilers are up with the aileron. They are dwelled or silent on the other wing. 

L-1011 Flight Controls: Speed Brakes - Flaps Up (27-37)

A rear view of the airplane shows spoilers L&R1 and L&R2 & 3 in their travel limited position with the corresponding Surface Position Indicator (SPI) indices. The inside right travel for number 2 & 3 spoilers is 30º while spoilers 4, 5 and 6 are up the full 60º speed brake travel. Also, number 1 spoilers L & R have no indication of the 20º up on the instrument in the image.

The B & D labeled indications on the SPI represent hydraulic systems powering the limiter actuators. 

L-1011 Flight Controls: Spoiler System (27-35)

The Lockheed L-1011 has six flat panels on each wing forward of the flaps. The panels hare hinged on the forward end and are driven up into the airstream by a single hydraulic actuator for each panel. The panels are numbered 1 to 6 from the fuselage toward the wing tip.

Here are the spoiler ranges for various flight conditions:

Flaps-Up - Speed Brakes
1 2 3 4 5 6
20º 30º 30º 60º 60º 60º

Flaps 4º to 33º - Speed Brakes 
1 2 3 4   5 6
N/A 60º 60º 60º 60º 60º

Roll Augmentation 

1 2 3 4 5 6

N/A 40º 40º 40º 40º 40º

Direct Lift Control (DLC)

1 2 3 4 5 6

10º 10º 10º 10º N/A N/A

Auto Ground Spoiler 

1 2 3 4 5 6

60º 60º 60º 60º N/A N/A

The spoilers have four modes of operation. They are:

1. speed brakes flaps up which are conventional
2. roll augmentation to assist aileron when flaps are extended
3. DLC during approaches and 
4. Automatic Ground Spoilers which operate on landings and rejected takeoffs. 

The System comprises of a speed brake lever either manual or boosted through ta DLC/AGS servo powered by hydraulic systems A and B. 

From the lever and servo, cable runs and roll systems deliver pilot or servo inputs to units called mixers located in the wheel wells. The mixers receive flap position and aileron position inputs and thereby shift accordingly setting up linkages causing the spoiler panels 2, 3 and 4 to work in the various modes. 

Another pair of right and left units called selectors located on the rear spars just inboard of the outboard ailerons receive pilot, flap and aileron inputs and schedule spoiler 5  and 6 right and left respectively from their two modes of operation. Number 1 spoiler control linkage is a bit different in that it uses a solid controller cable for inputs which cause it to work in its two modes. 

L-1011 Flight Controls: Aileron Control System (27-33)

Conventional wheels connected by roll disconnect. Two control cable paths, one on each side of the fuselage.

The main difference between the two control paths are - left path or Captain's side is the main or primary control path due to system design and lost motion device at bottom of the F/O column before inputs to right control path. F/O inputs cross over through Captain's; or primary path, under normal operation. Both paths incorporate roll monitor bungees. Also a bungee between inboard ailerons. No monitor in aft interconnect bungee between inboard ailerons. Conventional manual trim wheel on aft ENP of center console through cables to trim actuator in left primary or master aileron path trims feel forces, as in stabilizer and rudder trim systems.

Now continuing with primary path to left inboard aileron master servo we see that three hydraulic systems A, B & C power the aileron actuators controlled through the servo by pilot inputs. From the master inboard aileron one path goes to the spoilers input and on to the outboard aileron directly off inboard aileron movement to the outboard aileron servo. The outboard aileron is powered by two hydraulic systems B & C controlled by the servo.

Another control path from the left inboard, or master aileron movement crosses through the fuselage and aft interconnect bungee to the right inboard aileron servo which controls the three right inboard aileron actuators powered by hydraulic systems B, C & D.

From the right inboard aileron the primary control path continues directly from inboard aileron to the right wing spoilers and to the outboard aileron servo which controls the aileron's two actuators power by Hydraulic Systems B & D. Note again the hydraulic systems do not cross over as they power the ailerons. 

L-1011 Flight Controls: YAW SAS in Parallel (27-31)

Parallel mode provides runway alignment, rollout guidance, and engine out go-around capability during autopilot operation. Parallel mode is different in the the rudder pedals are now connected through the servo and the pilot receives rudder movement feedback. The YAW SAS system now also has the same authority as the Pilot or 30º. Manual inputs may be applied through the rudder pedals to override the servo, but ruder pedal forces will be approximately one hounded pounds of pressure or more. 

L-1011 Flight Controls: Rudder (27-28/29)

To get all the details, you might want to enlarge the picture above. The Rudder, on the L-1011, is a large single surface with servo and actuators near the lower end. There are no tabs on the L-1011 rudder. The rudder is fully hydraulically powered by the A, B and  C hydraulic systems.

The rudder is powered by two dual-tandem actuators (see image above) which operate as three in depended actuators and a controlling triple servo module. Hydraulic system A, B or C are capable of providing full rudder operation. Hydraulic power is manually controlled by the hydraulic limiting system.

The rudder servos are mechanically operated by the rudder peals through cables or electrically signaled by the Yaw Stability Augmentation System (YAW SAS).

Rudder Trim 

Pilot inputs can be made from either set of rudder pedals but control is provided by a cable run coming form the Co-Pilot's rudder pedals. Rudder trim is mechanical and simply establishes a new neutral position for the rudder feel mechanism. Rudder trim displease the ruder pedals.

Surface Position Indicator (SPI)

Top of the SPI, single indicator shows rudder position to 30º right and left.

Rudder Hydraulic Limiter 

The limit is controlled via a switch on the overhead that is normally latched in dark/no lights position. Amber "PUSH" with malfunction or loss of system pressure. White "OVRD" is switch pushed and unlatched. Powers back all available systems.

Rudder Power OFF Switch 

The Rudder Power OFF switch removes all power from the rudder. This also powers down the YAW SAS.


YAW SAS

The YAW SAS has two mods of operation. The first is called series and provides full time yaw damping and turn coordination. Series means that the YAW SAS is providing electric inputs to the rudder servo, but motion is not supplied to the rudder pedals - they remain in neutral. Manual inputs may be applied through the rudder pedals to override the servo with normal pedal forces. In this mode the YAW SAS has only 8º of authority over the rudder. The second mode is called parallel mode and provides runway alignment, rollout guidance and engine out go-around capability during autopilot operation. Parallel mode is different in that the rudder pedals are now connected through the servo and the pilot receives rudder movement feedback. The YAW SAS now also has the same authority as the Pilot ... or the full 30º.  Manual inputs may be applied through the rudder pedals to override the servo, but rudder pedal forces will be approximately one hundred pounds.

L-1011 Flight Controls: Stick Shaker (27-27)

A stall warning is provided by stick shakers which vibrate the control columns when airspeed drops to one hundred seven percent (107%) of the stall speed. the system is normally operated with both stall warn switches latched in. This will cause the first officer's, or number 2 stick shaker, to operate should a stall occur or the test switch be pressed while on the ground. The stick shaker will be felt in both control columns. The Captain's stick shaker only operates when number two system is unlatched/deactivated.

Each channel is controlled by an FCES Panel pushbutton switch. Inline monitoring is provided for sensor and power fault detections. Faults detect will annunciate an FCES Panel "FAIL" message, but will not automatically disconnect the affected channel. The pilot in all cases of indicated failures on the channel control switches, should disengage the faulty channel by depressing the appropriate switch. The second channel, whenever normally engaged, remains capable of providing stall waring. 

L-1011 Flight Controls: Stabilizer Control System (27-24)

To see all the described entails below, you might want to enlarge the picture above.

Conventional control columns operate through independent cable systems to control the two dual Hydraulic Servo Units. Each servo unit contains two hydraulically independent control valves. Each of the 4 servo units are supplied by a separate hydraulic system. Thus, two dual control and 4 hydraulic actuators provide maximum protection against system failure. Feedback links between the servos and the stabilizer signal position of stabilizer to the servos.

Stabilizer Servo Interconnect (Auto Transfer to System B.)

A mechanical interconnect device between the A/B and D/C stabilizer servos prevent shutdown of all 4 servos simultaneously. The unit allows only paired servos to be depressurized at any onetime. The mechanical device gives the B Servo priority. Since the Ram Air Turbine (RAT) will supply pressure the the B Hydraulic System in case of loss of all other sources, it is logical to have a mechanical interlock which gives the B Stabilizer Servo priority.

The separate control paths from the Captain's and Co-Pilot's stations are coupled at both the forward and the aft ends of the aircraft by the pitch disconnect mechanism and the aft coupler. The Pitch Disconnect can be separated manually by using the T-handle in the center console. The Aft Coupler is disconnected electrically and automatically if both servos on one side are turned off. A pitch monitor is used to continually monitor the Pitch System for possible jams. Each Stabilizer Servo has two switch lights located on the Primary Flight Control System (PFCS) panel which display a loss of hydraulic pressure or a jam condition by illuminating INOP.

Bungee cartridges, one in each control path and one int he Aft Coupler path act as solid links during normal operation. If either control path should jam, Pilot forces exerted on the control path will apply breakout forces to the affected bungee. Switches attached tot he bungee will sense the breakout and signal the monitor system the fault condition which then illuminates the PUSH lights on the PFCS.

Pitch Trim/Feel 

The Pitch Feel and Trim Force System is comprised of two units, one in each cable path which provides artificial feel forces and trim inputs for the Pilot and reaction forces to the autopilot. The Captain's path has an electric unit one the Co-Pilot's path has a mechanical unit. These feel/trim unit are coupled with a Trim Synchronizing Shaft so any inputs into one side will be transferred to the other. Manual trim inputs are made to the mechanical trim unit in the Co-Pilot's side cable path. Electric trim input go to the two electric motors in the Electric Path. These inputs are kept synchronized by a shaft connecting the two units. Loss of one channel reduces Electric Trim Rate to half normal rate.

Mach Trim 

The Mach Trim system is a two-channel system as well, one is active - the other one is standby. The system provides speed stability compensation in the pitch axis trim when operating under manual control in the high speed region. Engagement of the autopilot does not disable the Mach Trim system function. Mach Trim can be overridden by electric trim, manual trim and autopilot trim inputs. Mach Trim remains in the existing condition should both channels fail.

The two channel switches located in the FECS overhead panel provide the Mach Trim control and fault annunciators.

Mach Feel 

The Mach Feel system is a two-challen active-standby system which operates together with stabilizer trim angle and Mach number to provide pitch control force changes in stabilizer effectiveness as a function of Mach.

The system normally controls one of two electrical motors which are integrated into the pitch feel/trim mechanism. The pitch control force gradients are scheduled from Mach data derived from the two Central Air Data Computers (CADC). Engagement of the autopilot does not remove the function of the Mach Feel system.

The meter on the Mach Feel panel indicates position status of the Mach feel system, calibrated in Mach. The feel system position meter also provides pilot indication of proper system operation. The indicated Mach number should match the Mach number on the Airspeed Indicator.

Autopilot Servo 

The two autopilots powered by hydraulic systems A and B provide pitch inputs to the Control Path through the Aft Cross Tie. Trim follow-up is brought the mechanical Feel/Trim Unit. Therefore, the Stabilizer servos receive the input signals the same way from the autopilot as they would from pilot inputs.  The Electric Trim Thumbwheel on the control column, however, is de-energized when the autopilot is in operation, except in Control Wheel Steering (CWS) mode when then Pilot applies the necessary force to the control column.

L-1011 Flight Controls: Flying Stabilizer (27-23)

The L-1011 has a flying stabilizer that is powered by all four hydraulic systems. However, any one of the hydraulic systems alone is capable of controlling the airplane. The advantages of a flying tail/stabilizer are:

• No mistrim problem 
• No stalling drive mechanisms 
• The elevator is mechanically slaved 
• Non-linear controls 
• Column remains in position 

The feeling on the column is created by springs. There is no direct force feedback, it is created through the stabilizer position and the Mach number. Everything is done fully by hydraulics, there is no electrical power required. 

L-1011 Flight Controls: Rudder and Aileron Manual Trim (27-21)

On the L-1011 neither the Rudder nor the Aileron trim is electronic, they are considered conventional. The Aileron is trimmed by rotating the trim wheel that is protruding from console to either Left Wind Down (LWD) or Right Wing Down (RWD). The will is marked in 10 units which equals to 7º  of authority.

The Rudder is trimmed by rotating the when on top of the the rear console. This wheel also contains a crank. The Trim authority for the Rudder trim is 10º left or right. 

L-1011 Flight Controls: Center Console Flight Controls (27-19)

The L-1011 center console has a number of flight controls besides the thrust levers. Here is a summary of those controls:

• Flap/Slat Lever on the right hand side - for selecting various flap positions (see yesterday's Flap Position indicator posting)
• Speed Brake Lever on the left hand side - for manual spoiler/speed brakes. This lever also travels automatically with DLC/AGS. The lever also has one switch and two indicator lights. The disable switch is to unpower boosted spoilers and the two amber DLC/AGS spoiler channel disable indicators. The two lights come on when disabled through the handle switch.
• Pitch/Roll Disconnect Handles - located in the left and right forward corners of the console illuminate amber when pulled and rotated to disconnect the two control columns. 
• Stabilizer Manual Trim Wheels - to the left and right of the console.

L-1011 Flight Controls: Flap Indicator (27-17)

The L-1011 had at least two different variants of the Flap Indicator. The variants depended on the type of L-1011. The one in this posting is from a -500 that has a different flap range than the -1 or -100 for example. So you might see a different flap indicator in other postings here on the blog:

The Flap Indicator is located on the right side of the Pilots' center instrument panel above the landing gear lever. The instrument has two tapes - one for each set of wing flaps left and right. Flap positions are are:

• 0º/UP
• 4º (maximum extend speed 250K)
• 10º (maximum extend speed 230K)
• 14º (maximum extend speed 225K)
• 18º (maximum extend speed 220K)
• 22º (maximum extend speed 215K)
• 33º (maximum extend speed 200K)

The OFF Flag shows loss of power (on other indicators the tapes will roll half way to an OFF marker). The SLAT Lights are indicators for the status of the leading edge slats

• RED SLAT light - will illuminate when the slats are not in position 
• GREEN LE/SLATS light - indicates are slats are fully extended
• GREEN FLASHING LE/SLATS light - the slats are in transit 

L-1011 Flight Controls: Surface Position Indicator (27-16)

The surface position indicator is located on the main instrument panel. It indicates the position of the:

• Rudder
• Stabilizer
• Ailerons, inboard and outboard (the button switches from inboard to outboard)
• Spoilers
• DLC
• Auto Pilot 
• Mis-Trim Flags

L-1011 Flight Controls: Mach Feel and Rudder Limiter Panel (27-15)

The L-1011 Mach Feel/Rudder Limiter Panel is located on the overhead panel.

MACH FEEL

• Two Channels 
• Mach Feel Force Comparison indicator. 

RUDDER LIMITER

• Override switch to power all available hydraulic systems back to rudder. 

Typically there is also a chart of hydraulic rudder limiting for various speed conditions. 

L-1011 Flight Controls: Primary Flight Controls Systems (27-14)

The Primary Flight Controls Systems (PFCS) panel on overhead forward of FCES.

The controls on the panel contain:

• Switches for Pitch and Roll Monitors (two channels each).
• Rudder Power (Off Switch)
• Stabilizer Servo Controls
• Aileron Controls 
• Spoiler Controls 

L-1011 Flight Controls: FCES Panel (27-13)

L-1011 cockpit controls have a conventional layout. There are two control columns with wheels, rudder pedals for both the captain and first officer, there is electric and manual stabilizer trim and manual aileron and rudder trim.

Various switches and indicators are located in the forward, overhead and Flight Engineer's Panels. One of them is the Flight Controls Electronic Systems (FESC) Panel located on the overhead. It contains controls for:

• ACS (not on all aircraft)
• Yaw Stability Augmentation system (YAW SAS)
• Stall Warning Computer (STALL WARN)
• Pitch Trim Computer (PITCH TRIM)
• Direct Lift Control and Auto Spoiler Computer (DLC/AUTO SPLR)
• Automatic Throttle Systems (ATS)
• Mach Trim (MACH TRIM)

Each of the systems has two channels, hence there are two switches for each system.