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 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 Autoflight: Go-Around Mode (22-44)

When the GO-AROUND button is pressed, the autopilot will roll "wings level" and pitch the airplane to maintain 1.25Vs minimum speed or 17.5º maximum pitch attitude whichever produces the higher airspeed. The speed command system automatically provides these computations for autopilot use. The direct lift control (DLC) function is disabled andy he YAW SAS system remains in a parallel mode of operation in which rudder pedal movements may be felt.

Verification of GO-AROUND mode selection is made by checking for GO ARND message on both AFCS MODES annunciators.

If the flight directors were on at the initiation of GO AROUND, they should be left on until a positive rate of climb is achieved or a 17.5º pitch attitude is reached.

L-1011 Autoflight: Glideslope Capture and Track (22-31)

Glideslope capture cannot be initiated until after localizer capture is initiated, but localizer track status is not a pre-capture requirement. Nearly simultaneous capture of localizer and glideslope is poossible. The glideslope is normally captured from below the beam, but it can also be captured from above using vertical speed as pitch pre-capture guidance. When glideslope capture starts, the GS ARM annunciation changes to GS, and the pre-capture pitch mode is released, removing its annunciation on the AFCS MODES panel. A glideslope capture timer also start with initiation of glideslope capture.

When 25 seconds have elapsed on the glideslope capture timer and the glideslope deviation is 1/6 dot or less, the status changes from glideslope capture to glideslope track. This change in status it not annunciated. When these conditions have been satisfied, a glideslope gain change takes place reducing sensitivity of the autopilot/flight director system by 75 percent. This gain change is to partially compensate for glideslope beam convergence as the airplane approaches the transmitter.

Direct Lift Control (DLC) becomes active when the flap handle is moved through the 30 degree position.

L-1011 General Aircraft Characteristics: Approach Visibility at 50 Feet (25-33)

In an approach configuration, at 50 feet altitude, 334 feet of the ground will be obscured by the nose of the aircraft. Therefore, in a Category IIIA landing, with an RVR of 700 feet only 366 feet of the runway would be visible in front of the aircraft.

The use of direct lift control (DLC) during the approach will maintain a relative constant deck angle. Therefore, the visibility range will also remain quite constant.

L-1011 General Aircraft Characteristics: Control Surfaces (25-4)

The primary flight control system includes controls for the horizontal stabilizer, rudder, ailerons, and the spoilers. Conventional control wheels, columns and rudder pedals are provided in the flight station for the Captain and First Officer. These controls are linked to (and govern) hydraulic actuators which determine the positioning of hydraulic servos. Thus the control surfaces are fully powered by the hydraulic system. The L-1011 has a flying stabilizer and slaved elevator. Other flight controls include the ailerons and spoilers. Both the inboard and outboard ailerons are full time ailerons. The spoilers, in addition to being speed brakes, are used in a Direct Lift Control System (DLC). The DLC is used in approach to Landing and modulates the spoilers, changing wing lift, greatly increases approach and touchdown accuracy.