Avionics Bending: L-1011 Autopilot - Pitch Mode and Heading Panel

The Avionic Flight Control System (AFCS) on the L-1011 is controlled via a number of panels located on the L-1011 glare shield. Most commonly these panels are referred to as the "autopilot" control panel. The autopilot on the L-1011 is a digital system that had analog inputs ... as you can see in the image above and the images following below. The later L-1011-500s had a digital AFCS panel also located on the glare shield. The digital version of the AFCS panel is not easy to find and there was one on eBay a few weeks ago and someone snatched it right from under my nose ... i am still sore about that one.

Anyway, in this posting I show you the status of my work with one of the panels ... the Heading/Pitch Mode Panel. The panel is located on the left hand side of the autopilot panel assembly and came in two version; one version that is like the one shown above and another that combined the Thrust and the Heading/Pitch Mode panel together (as seen below).

The right hand side of the panel has an engage button for heading control ("HDG") as well as a turn knob and a display for the selected heading. This side of the panel directly controls the L-1011's Roll Computer. In the image below the Roll Computer is engaged and the heading is set to 93º.

The left hand side of the same panel has the inputs for the aircraft's Pitch Mode. The L-1011 can pitch for 4 different modes:

• Vertical Speed (VS)
• Altitude 
• Indicated Airspeed 
• Mach Speed

The image below shows the Vertical Speed mode set on the L-1011's Pitch Computer and a target vertical speed for 1500 feet per minute climb.

There Vertical Speed controls on the panel are quite interesting. But more about them when I show you the schematic for the instrument later on. The ALT mode, when engaged holds the aircraft altitude at the moment of engaging the autopilot. The pitch for Indicated Airspeed and Mach is pretty self explanatory.

In the image below we would be holding the current altitude with the autopilot as well as the aircraft's heading. In other words, both the L-1011's Pitch and Roll Computers are engaged and, when the AFCS system is set to CMD will control the aircraft pitch and roll axis.

So now a few words about the VERT SPEED windows and the DN/UP switch. Prior to engagement of the VS mode, the tape in the the VERT SPEED window shows the aircrafts vertical speed. So in other words, unless "VS" is lit up, the VERT SPEED window will show the same indication as the vertical speed indicator. Once the VS mode is engaged the motor for the tape disengages and vertical speed adjustments can be made with the thumbwheel.

I have not gotten that tape motor part to work yet, however, it shouldn't be too hard to do. Below is the schematic for the VERT SPEED and DN/UP thumbwheel:

And a more enlarged view of the same schematic showing the ADC and Pitch Computer schematics as well: