Avionics Bending: L-1011 Autopilot - Pitch Mode and Heading Panel - Part 3

L-1011 Autopilot - Vertical Speed Select

The VERT SPEED window and Vertical Speed Select thumb wheel are two pretty interesting components of the Heading/Pitch Mode Panel oft he Lockheed L-1011 autopilot. The Vertical Speed is indicated using a tape that is motorized and the thumbwheel allows adjustment of the value once the VERTICAL SPEED (VS) mode is selected on the panel.

The module takes +12 and -12V bipolar power. For todays hack I have worked on reading the vertical speed select values as output by the panel. The values are between -5V for 4000 feet per minute climb and -10V for 8000 feet per minute descent. I love the face that 8000 fpm can actually be selected on the L-1011 autopilot ... makes sense for an emergency descent ... of course, would probably also make about 80% of the 280+ people behind you loose their lunch. :)

Here is short video of the values produce by the panel ... for detail information please also see the chart below:

Avionics Bending: L-1011 Autopilot - Pitch Mode and Heading Panel - Part 2

Over the holidays I have been working on the digital input/output integration of the L-1011 panels using the Interbus components that I chose a few months ago. The project is not going quite as fast as I had hope it to progress due to chronic funding problems. However, every week I am making are small steps towards breathing live back into this great machine. After all, it is the largest project I have ever undertaken.

Here is a test setup for the Ethernet to Interbus I/O testing. The test setup consists of a single 32 port Digital Input and one 32 port Digital Output element. The Interbus terminal, DI-32 and DO-32 modules are made by Phoenix Contact.

Phoenix Contact Interbus Test Setup

Slowly the autopilot is becoming clearer to me and how to interface it with X-Plane. Below is a short video that demonstrates the initial digital integration between the Heading/Pitch Panel mode selectors and X-Plane.

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: