L-1011 Trainer Installation: Interbus Installation into S/O Station

L-1011 Trainer - Interbus Installation

The Lockheed L-1011 cockpit has literally hundreds of switch positions and an even larger number of annunciator lights. For the computers receiving switch data and driving the annunciator lights we use Interbus components. Interbus is a relatively old bus format but is perfect for the use on the simulator since this is a field bus system that readily works in the 24VDC domain. In a few previous postings we talked about installing Interbus Terminal stations in the Flight Engineer's (SO Station), the Overhead and the Main Instrument Panel. All the Interbus components we selected for the simulator mount onto DIN rails and will be fully field replaceable.

In order to get the DIN rails added to the simulator we are blessed to have the master of all hardware mounting, Mr. Jim Blassco, create custom mounts for the simulator. 

First we had to find a good position in the simulator's Flight Engineer station to mount the devices. We picked a spot towards the top of the station for two reasons: a) there was really a lot of space there and b) we would get good airflow over the components for cooling. 

L-1011 Flight Engineer Station - Digital I/O Bracket

Then the fun started, Jim made some custom designed brackets and introduced me to the use of an angle drill ... an amazing piece of hardware that looks like a gigantic dentist tool.

Jim Manufacturing Brackets for the L-1011 Trainer

With the brackets in place we installed the steel DIN rail (they flex a lot less than aluminum rails) and mounted the Interbus modules right onto it.

L-1011 Trainer - Digital I/O Bracket

L-1011 Trainer - Digital I/O Buildout

Every day is a step towards the finishing of this project. However, as Kevin pointed out ... in sim building a lot of the fun is actually in the journey of putting such a complex machine together. Thanks to everyone for their awesome support!

L-1011 Trainer Installation: Switch (Digital) Input Modules

Interbus Input Module Preparation

Cables, Cables and more Cables. The next few weeks are going to be filled with lots of postings on the digital cabling process of the L-1011 Trainer at the museum. The digital cabling connects all of the hundreds of trainer switches and lights to the computers. Today, I started building out the first of many digital input modules for the simulator. As described in a few earlier postings, I will be using a PLC system based on Interbus for the switch input and for the annunciator and switch light output on the L-1011 trainer.

interbus 8-bit Switch Input

Each of the digital input (DI) modules has 32 inputs that are arranged in 8 channels + 1 GND signal per group. The image above shows the 8 digital input lines that will be coming from switches. Each cable represents a bit and together each connector represents one Byte of information on the Interbus. 

L-1011 Trainer Installation: Ethernet and Interbus Cabling

L-1011 Trainer - Ethernet

Today was one of those "got a lot done .. but have little to show" kind of installation days. Today I installed Ethernet cabling into the simulator for both the instrumentation control as well as the simulation computer network. In the diagram below you can see the different cables installed into the simulator for both of the main data systems; Ethernet and Interbus:

L-1011 Trainer: Interbus and Ethernet Cabling

All cables are built to custom length, so it took a while to get them all laced in, cut and ends crimped on them. All Ethernet connections are now point to point tested from the simulator computers to the switches. The Interbus tests are to follow.

Simulation Platform - Network Tests

L-1011 Trainer: Digital and Analog Bus Integration

Digital and Analog Integration Planning

L-1011 Digital I/O Bus

To make the simulator work there are a number of hardware integration methods that we need to put in place to allow the actual flight hardware to interact with the simulator software and vice versa. We need to be able to do the following:

Digital Input and Output (I/O)

Digital I/O is used to read switch states (on/off) as well as setting of annunciator lights. A large amount of digital I/O channels are needed to drive the L-1011 cockpit. All in all, there will be a need for 530 Output Channels as well as 582 Input Channels. The digital I/O bus also needs to be highly distributed across the sim (FE Station, MIP, Overhead, etc) and it needs to be resistant to electrical noise and power transients. Since everything in the simulator operates on either 24VDC or 115V AC ... the Digital I/O system needs to be able to directly interface with 24VDC without much need to do signal conditioning prior to entering the I/O interface (e.g. TTL level conversion). Digital Output will also need to be done mostly on 24VDC and will need to be able to be sourced as well as sunk.

Analog Input and Output (AIO)

The simulator instruments will required a number of analog signals to be generated. These generated analog signals will simulate the aircraft sensors. For example, engine tachometer signals need to be generated the same way they would be sent from the engine transducers to the instruments. Also, many of the flight controls will, of course, produce analog input signals to the simulator software which need to be digitized. For example, movement of the yoke or the flight control trim. So there is a need for a great amount of Digital to Analog (DAC) as well as Analog to Digital (ADC) conversion.

ARINC 429 Protocol 

Some of the primary navigation as well as attitude control instruments use the ARINC 429 bus protocol. The correct protocol needs to be generated and sent to the simulator hardware to display the right navigation and attitude data.

Overall

Since the simulator will be used in a museum and public setting where safety and reliability is of most  importance, it is critical that we use industrial strength, serviceable and commercial off-the-shelf (COTS) hardware. While building a lot of custom hardware might be more fun and perhaps a lot less expensive, it also makes it hard to maintain the sim in the future. When custom built components break down ... they can be very difficult or impossible to replace. So, at the current we are looking at using the following COTS technologies:

• Digital I/O -- Phoenix Contact Interbus (old, but very very reliable and trusted)
• Analog I/O -- National Instruments DAQ Equipment and Phoenix Contact Interbus 
• ARINC 429 -- V1 Avionics Simulator Interface 

Again, the key is to use as much off-the-self and easy to replace hardware as possible.