Avionics Bending: Inertial Navigation System (INS) - Part 4B

In my last blog posting I showed you position data from X-Plane displayed on the LTN-72RL CDU. The CDU showed the following:

LAT 47º43.1'N

LON 122º30.8'W

SEA Runway 34R - Incorrect Coordinates on Display!

So, after the blog posting I took the numbers to check the accuracy of X-Plane and plugged them into Google Earth. And to my surprise I was 21.49 miles to the North West of where I was supposed to be!! The simulator was set to the runway end of runway 34R at Seattle Tacoma airport. 

Google Earth Screenshot of Incorrect Data

Wow ... what happened? Could it be that X-Plane is this massively inaccurate!? Well, the answer is very simple, I made a very trivial and very basic mistake. I did not convert the fractions that X-Plane outputs on the longitude and latitude to arc seconds. Hence, what I showed on the display of the LTN-72RL CDU was the fraction and not the arc seconds. X-Plane handed me the data as 

LAT 47.431ºN

LON 122.308ºW

Which of course needed to be convert to arc seconds (multiply the fraction by 0.6) to result in  

LAT 47 25.88'N

LON 122 18.48'W

And, as you can see in the images below that puts me on the runway 34R at SEA with amazing accuracy when I reference X-Plane against Google Earth!

SEA Runway 34 R - Correct Data 

Google Earth - Correct Data

Google Earth - Correct CDU Data Showing Position on Runway 34R

Avionics Bending: Inertial Navigation System (INS) - Part 4

First Litton LTN-72RL CDU  Integration with X-Plane 

So far all of the data you have seen on the Litton LTN-72RL CDU was test data. Today I finally got around to integrate the Litton CDU with X-Plane. For this first setup i chose the data that is displayed on the POSITION DATA page of the CDU; this data is Latitude, Longitude and time in GMT (or Zulu).

Here are the X-Plane data refs that I feed to the CDU via the ARINC 429 interface using ARINC 575 data words:

gLongitude = XPLMFindDataRef("sim/flightmodel/position/longitude");

gLatitude = XPLMFindDataRef("sim/flightmodel/position/latitude");

gZuluHR = XPLMFindDataRef("sim/cockpit2/clock_timer/zulu_time_hours");

gZuluMIN = XPLMFindDataRef("sim/cockpit2/clock_timer/zulu_time_minutes");

gZuluSEC = XPLMFindDataRef("sim/cockpit2/clock_timer/zulu_time_seconds");

While X-Plane does not directly talk to the CDU (it talks to a CDU device driver that does the ARINC formatting and data transfer via UDP) I still chose to implement the data extraction out of X-Plane following the ARINC 429 label standard. The labels are 0310, 0311 and 0150. Below is the code snipped from the X-Plane plugin that builds the extract data:

    // Label 310 - Present Position Latitude

    sbuf.label = 0310;

    sbuf.value = XPLMGetDatad(gLatitude);

    msgsnd( msqidOut, &sbuf, 9,0);

    

    // Label 311 - Present Position Longitude

    sbuf.label = 0311;

    sbuf.value = XPLMGetDatad(gLongitude);

    msgsnd( msqidOut, &sbuf, 9, 0);

    

    // Label 150 - UTC

    sbuf.label = 0150;

    sbuf.value = XPLMGetDatai(gZuluHR)*10000 + XPLMGetDatai(gZuluMIN)*100 + XPLMGetDatai(gZuluSEC);

    msgsnd( msqidOut, &sbuf, 9, 0);    

Lets put all this in motion. Watch the short video below to see the LTN-72RL CDU display the LAT, LNG and GMT data from X-Plane in real time via the ARINC 429/575 data stream:

L-1011 - CPT Installation at the Museum - Pre-Installation Inventory

L-1011 Trainer Main Instrument Panel - Pre-Installation

Come January we are going to start the installation of a Delta Airlines L-1011 trainer at the National Museum of Commercial Aviation here in Atlanta. I went to the storage unit where the L-1011 trainer is currently stored to take an inventory of the pieces that will be moved to the simulator room that we have prepared at the museum. The image above shows the main instrument panel with the glare shield. Many of the instruments on the trainer are "simulated" instruments which are nothing more than empty shells with pictures in them. We will, of course, replace all the simulated instruments with the real flight hardware that I have worked on over the last few months and years.

This is a very exciting phase in the L-1011 project because over the next few months the L-1011 simulator I have been working on will finally become an actual device that the museum will use as an education tool for young people as well as an experience for anybody who has a passion for wanting to fly a L-1011 in the simulator. The museum will offer guided tours on the simulator once it is open for business.

Anyway, back to the other components. The image below shows the upper and the lower section of the second officer station as it sits in storage:

L-1011 Trainer - SO Station Upper Section - Pre-Installation

L-1011 Trainer - SO Station Lower Section - Pre-Installation

The center pedestal below has the necessary motors mounted for the DLC operation as well as the Auto Spoilers and the Throttles. Much of the original cabling of the trainer can be re-used and will be directly interfacing with our I/O cards, synchro cards and for some of the instrumentation also with the ARINC 429 interface. Below is an image of the throttle quadrant with the center and forward electronics panels. All instruments that you see mounted on the pedestal are simulated but will be replaced with working devices such as the Litton LTN-72RL units that I am currently working on:

L-1011 Trainer Center Pedestal - Pre-Installation

The overhead panel and the the circuit breaker panel 1, 2 and 3 come as one piece. The image below shows the overhead panel in storage prior to moving it to the museum for installation and instrumentation retrofit.

L-1011 Trainer Overhead Panel and CB1, CB2 and CB3 panels - Pre-Installation

Over the next two weeks we will first move the platform for the trainer from storage to the simulator room at the museum. The pedestal is made from heavy iron square tubing to give the trainer stability. However, the heavy tubing also makes for considerable weight ... we estimate the platform to weigh about 500lb (~226kg). Below you can see the main section (right) and the forward section (left) of the L-1011 trainer platform:

L-1011 Trainer Platform - Pre-Installation

The trainer comes with many extra pieces and details, such as the pilot's and first officer's side panels and the rear circuit breaker panel.  

L-1011 Trainer Pilot's Side Panel with Nose Steering - Pre-Installation

Main Circuit Braker Panel - L-1011 Rear Wall - Pre-Installation

Avionics Bending: Inertial Navigation System (INS) - Part 3

Litton LTN-72RL CDU with Simulator Data

Took a few days off over the holidays. Hope everybody had a few nice days as well and is getting ready for 2013! I am now back to working on the Litton LTN-72RL implementation with the flight simulator using an ARINC 429 interface and the ARINC 575 characteristic. Before the CDU can talk to the simulator, however, the functions of the INS and IMU need to be simulated in software  as described in my previous blog posting.

The Litton INS is arranged into pages. Each page can have multiple lines and can also have sub-pages. The CDU, however, has room for 5 display lines with 16 characters each. In order to reach lines below the 5th line the up and down arrow keys are used. Litton referred to this as slewing the page up and down ... I guess today we would probably call it scrolling. The Litton CDU does not use ASCII code for the symbols but has a 6-bit character set defined by Litton. Therefore, in order to paint data on the screen the following needs to happen:

1. Translate each character from ASCII to the Litton Character set (this is done on the INS simulator side)
2. Package characters in groups of 4 into the 32bit ARINC 575 word. 
3. Transmit the ARINC 575 word to the LTN-72 CDU via the ARINC 429 interface. 

The same, of course, has to happen in reverse for every key entry. Again, for key entries, Litton encoded each key on the keyboard as a 6 bit character. 

In Litton's documentation, each screen and scroll sequence is sometimes represented by a stack of images (as seen below). So far I have worked on the database validation page as well as the position entry page. If you want to know more about the LTN-72RL document that I am using here for the blog, you can find it here: LTN-72RL Pilots Guide

Database Validation

From TP72RL-73-00 Litton Aero Products

Litton LTN-72RL CDU Simulator - Database Data Validation Entry

Once the database validates the INS will be ready for use. The LTN-72RL was originally not fully Y2K (there is blast from the past) compatible. However, it is now understood that "12" for the years does not stand for 1912 but for 2012. I also added the liberty of calling the version "72-73-CZ" instead of "72-73-00" as would have appears on the actual INS to assure that the screen I produce can not be mistaken for actual Litton screens. 

Initial Position Data Entry 

Prior to INS alignment, the initial aircraft position has to be entered as a set of longitude and latitude coordinates. The POSITION DATA page allows for entry of this latitude and longitude data as well as GMT. 

From TP72RL-73-00 Litton Aero Products

The GMT line is actually on line 6 which is initially hidden from view. To get to the GMT line the display has to be moved up one line.

LTN-72RL CDU - Position Data Page

LTN-72RL CDU - Position Data Page scrolled to see GMT

Avionics Bending: Inertial Navigation System (INS) - Part 2

The Litton LTN-72RL implements a complete Area Navigation System (ANS). On the actual aircraft, the ANS consists of:

• Inertial Navigation Unit (INU)
• Computer Display Unit (CDU)
• Mode Selector Unit (MSU)

Litton LTN-72RL CDU and MSU

For the INS simulator integration I will emulate the INU and attach to the actual CDU and MSU. In a typical installation the CDU would be mounted on the center pedestal or the forward electronics pedestal. The MSU would be mounted on the overhead panel. Each INU on board (most aircraft have two or three INUs) has a corresponding MSU and CDU.

To create a simulation of the LTN-72 my simulation software needs to interact with the CDU in a way that appears natural to the way pilots interact with the LTN-72RL. Talking to the LTN-72RL CDU is actually quite simple. The CDU sends data in the form of keystrokes to the INU and the INU in return sends data on how to paint the screens back to the CDU. See the image below:

INS Simulator Topology

The Litton LTN-72 system has quite a large number of screens that need to be painted by the simulation software. Here are the data pages that need to be simulated and integrated in a way that they can interact with the flight simulator:

• Position (POS) - shows present position in Longitude and Latitude; Bearing and Distance from station; GMT and others 
• Course (CRS) - displays the TO and FROM waypoints; the desired track and the cross track 
• Track Leg Change (LEG) - permits the entry of FORM and TO waypoints; leg change entry; automatic and manual selection
• Waypoint (WPT) - provides pages for waypoint entry and route entry 
• Flight Plan (FPL) - here we will enter waypoints and compute the flight distance 
• Direct To (DIR) - enter data to fly direct to
• Instrument Data (DATA) - shows the INU data for heading; track; groundspeed; true airspeed; wind and along track acceleration
• Catalog (CAT) - provides pages displaying a station catalog; airport catalog; waypoint catalog; route catalog; location stations and a way to update catalog data
• Remote Ranging (RMT) - enables remote data from another INU unit, or the cross-filling of data from one INU to the others.  
• Status (STS) - Provides information on IMU alignment status, time to NAV mode and other action codes

Below is a short video showing a simple READ and WRITE test from the ARINC interface to the CDU. Data is being read on ARINC 575 label 030 and written with 21 labels starting at label 0200.

ARINC 429/575 Interface Development - Kickstarter

Commercial ARINC 429 interfaces tend to be be very expensive, therefore, myself and my team mates Javier and Himar in Spain are developing an ARINC 429 interface (it will also do ARINC 575 words) for the consumer market as a Kickstarter project. Our proposal is to develop a low-cost way of connecting ARINC 429 devices such as the ones you saw in many of my postings throughout this year. We are lovingly calling it the "ARINC42911" interface and it connects to x-plane and FSX via Ethernet. Please visit our project link on Kickstarter and support us! The site has a short video that shows the features of the interface and how it will enable you to use real world avionics in your home simulator setup.

http://www.kickstarter.com/projects/1753938984/flight-simulator-interface-to-real-avionics-instru

Avionics Bending: Inertial Navigation System (INS) - Part 1

Area navigation on the L-1011 was accomplished by the use of an Inertial Navigation System. Some L-1011s also used the now dismantled OMEGA system for area navigation. OMEGA was more or less the first global position indication system that used a network of terrestrial antennas to create signals that could be triangulated into a position with roughly 8 NM accuracy. OMEGA was replaced by the public version of GPS around 1996.

Inertial Navigation Systems (INS) are still very much in use today. I will not go too much into detail on how INS technology works, but trust me, it is super cool. Read about it on Wikipedia by following the link. Present day Inertial Reference Units (IRUs) use lasers and are ultra precise. One of the main manufactures of INS and OMEGA systems was Litton Aero Products which got acquired by Northrop Grumman in 2001. 

The image below, taken from airliners.net, shows three Litton CDUs installed in the RAF L-1011 tanker. 

from. airliners.net (C) Duncan Monk

Over the next few weeks I will be creating a simulation of the Litton LTN-72RL INS. The LTN-72RL CDU basically acts as a terminal for the INS unit and in a triple system installation, as in the image above, all 3 INS units can be synchronized with each other. Here is the test setup on the workbench:

Litton LTN-72RL CDU and INS MODE SELECTOR on DZUS Rails

Litton LTN-72RL CDU and INS MODE SELECTOR on DZUS Rails

Litton LTN-72RL CDU and INS MODE SELECTOR on DZUS Rails

Litton LTN-72RL CDU and INS MODE SELECTOR on DZUS Rails

For this series of avionics bending I will be using the ARINC 575 protocol format. ARINC 575 is electrically identical to ARINC 429 however the general word format is different. ARINC 575, just like ARINC 429, uses an 8bit label and a 24bit data filed. However, unlike ARINC 429 the 575 format does not compute parity, does not have a SID or a defined SSM filed. The Litton CDU uses ARINC 575 words for data between the CDU and the INS unit in both directions. In the next posting we will take a look at the general system architecture and how I will go about creating and INS system and then integrating it with x-plane. 

Field Trip: B727 Avionics

FedEx B727 Cockpit - National Museum of Commercial Aviation

The National Museum of Commercial Aviation here in Atlanta, the museum that I do volunteer work at, has this awesome FedEx Boeing 727-22C N113FE. Yes, of course this is the L-1011 blog but the B727 happens to be my 2nd favorite aircraft and also an awesome tri-jet. Anyway, I do have access to the B727 and that allows me to study a lot of the avionics stuff that I would otherwise have only pictures of.

FedEx B727 Cockpit - National Museum of Commercial Aviation

What makes the FedEx B727 so awesome is that the aircraft avionics an electrical systems are complete. Below is a shot of the first officer station of the B727.

FedEx B727 Flight Engineer Station - National Museum of Commercial Aviation

Since the aircraft was in service with FedEx it was configured for freight. Actually this particular aircraft was a version of the B727 that could be frequently configured between freight and passenger operations. However, the extra weight of the floor re-enforcement gave this type of B727 the nickname "led sled" and most airlines walked away from the re-configuration scheme and operated them as freighters only. By doing so the "passenger" friendly interior was removed and replaced with insulation sheets only, as you can see in the image blow.

FedEx B727 Cargo Configuration - National Museum of Commercial Aviation

But now for the good part and my favorite hangout in the B727.  The avionics bay. The avionics bay on the B727 is accessible from a plug door just behind the front landing gear on the underside of the aircraft fuselage. The next three images show how the door opens and rolls back into the fuselage. (she really needs a bath!)

FedEx B727 Avionics Bay Access Door - National Museum of Commercial Aviation

FedEx B727 Avionics Bay Access Door - National Museum of Commercial Aviation

FedEx B727 Avionics Bay Access Door - National Museum of Commercial Aviation

The avionics bay in the B727 is complete. All instruments and devices are present which makes this avionics bay an amazing way to explore L-1011 ear avionics, devices, mounting and cabling techniques. What you see on the right hand side are black-boxes that are part of the B727s autopilot system. The large whit container on the right hind side of the image is a protective cover of the gyros.

FedEx B727 Avionics Bay Access Door - National Museum of Commercial Aviation

The image below show the backside of the avionics rack and the cabling for the individual device holders. The system is pretty clever with a power-bus on the bottom of each rail and individual connector cables bundled together on top.

FedEx B727 Avionics Bay Access Door - National Museum of Commercial Aviation

It would actually be pretty neat to get my hands on an actual avionics rack for the workbench here at the house. 

Avionics Bending: VHF/HF COM Radio Integration with X-Plane (Part 9)

Gables Radio Controller, Audio Panel and Lexicon Multi Channel Audio Interface

Up until now all the audio you heard on the previous blog postings had been live streaming ATC traffic from the Internet. While that is very cool, it is not really useful in the simulator. In the sim we want to be talking to real air traffic controllers. The good thing is that there are several large virtual flight traffic controller communities out there and VATSIM is one of them. Vatsim is a very active community, especially here around Atlanta, and you can connect to it from many different flight simulators. For this blog posting I use X-Plane as the simulator and the XSquawkbox plugin to connect to VATSIM. The video below shows a short demonstration of the end-to-end implementation of the actual flight hardware made by Gables using ARINC 429, the Laminar Research X-Plane simulator and XSquawkbox:

Avionics Bending: VHF/HF COM Radio Integration with X-Plane (Part 8)

As you probably know, navigation aids, such as VOR, DME, ILS and ADF, are identified by Morse code (CW). Typically they are identified by a 3 or 4 letter identifier like: PDK, JFK, CHA, etc. The standard frequency for the CW signals is 1020Hz. However, in some cases NAV aids also carry a voice signal that can give weather or AWOS or other information. In the case of ADF stations, that signal can also be co-located with AM radio stations. So most audio panels provide the ability to "filter" out Morse code to provide a clear and uninterrupted voice signal. To enable this filter most panels, like the one that I use from Gables Engineering, have a "VOICE ONLY" type setting. The audio panel that I am intending to use for the L-1011 simulator has a large orange momentary switch that toggles the CW filter on and off. The video below shows the Voice Only filter for CW in action:

I used the Kennedy VOR (JFK) as the Morse code and the Kennedy International D-ATIS information as the voice ... this is a combination that does not really exist in reality and I just combined them for this demonstration. Just doing a rough measurement it appears the filter covers a frequency range between about 920 - 1120Hz. The filter has very little to no impact on the voice signal, however, the effect on the CW is very obvious.

Below is a quick refresher on Morse Code:

International Morse Code

Avionics Bending: VHF/HF COM Radio Integration with X-Plane (Part 7)

The last two days I have been mostly working on the integration of the Gables radio head with x-plane. In particular the two VHF COM channels simulated on x-plane. Over the next few days this will then further control VATSIM and the respective VHF COM channels on VATSIM. The video above shows the integration between the original flight hardware and x-plane.

The integration architecture is pretty straight forward as you can see in the image below.

ARINC 429 to X-Plane Data Integration

The data flows from left to right in the diagram. The Gables multi function radio head outputs ARINC 429 data as described in the previous blog postings. The ARINC429 data is read by an ARINC 429 interface and then sent via UDP (Ethernet) to the computer running the simulator (in the video above that is my laptop). The system running the simulator (on the right hand side of the diagram above) also runs a device driver that receives the UDP packets, formats them for x-plane and sends them on to the TAP plugin running under X-Plane.

Next, the VATSIM integration and then we will get back to creating all the necessary audio channels for a radio experience that is close to the real thing as possible.

By the way, today I was asked by someone on the Internet if I modify the original flight hardware (such as the Gables radio heads) to work with my setup. The answer is no, all of the original flight hardware remains in its state as it was flown on the actual aircraft and is not modified at all.

Avionics Bending: VHF/HF COM Radio Integration with X-Plane (Part 6)

The Gables G6984 multi function radio head transmits 3 different ARINC 429 label. The labels are:

• Label 030 - VHF Frequency
• Label 205 - HF Frequency
• Label 207 - Additional Software information

For the flight simulator integration, only Label 030 and 205 are of interest to me right now. There are three (3) VHF frequencies and two (2) HF frequencies on the radio. Here are the details on the labels:

Label 205 - HF Word - From ARINC 429 Specification

Label 030 - VHF Word - From ARINC 429 Specification

All three VHF and both HF frequencies that can be set on the radio head are transmitted on the ARINC 429 bus with the same label. Each radio is identified with a unique SDI in the ARINC 429 word. The SDI is a 2 bit field.

VHF SDIs

01 -- VHF Radio 1
10 -- VHF Radio 2
11 -- VHF Radio 3

HF SDIs

01 -- HF Radio 1
10 -- HF Radio 2

Below is a short video that shows the radio head transmitting ARINC 429 data to a test program. Currently the ARINC data is read by a debug code and output to the screen. Over the next two days I will connect the Radio head data to the x-plane flight simulator.

Avionics Bending: VHF/HF COM Radio Integration with X-Plane (Part 5)

Today is all about the Gables audio selector panel and seeing it in action. For the test setup I have configured 3 audio channels that are fed to the VHF-1, VHF-2 and VOR-1 channel on the audio panel. Here is a description from the L-1011 flight manual on how the audio panel works (taken from a Delta Airlines L-1011 Operating Manual):

1. Microphone Switchlights 

Push to select desired transmitter. Integral light illuminates. VHF switch lights also select respective receive function without independently selecting the corresponding receive switch. A mechanical interlock prevents the selection of more than one transmitter at the same time.

2. Control Knobs

Push to monitor audio. Push again to discontinue monitoring audio. All receivers may be simultaneously monitored. Rotate knob to adjust volume.

3. Voice Only 

Filters out the out the Morse code (CW) signal.

Below is a short video demonstrating the features of the Gables audio selector panel that I intend to use for the L-1011 project:

Note: The computer voice that says "This is VHF one" and other is there for testing only. I mix it into the audio channel that is connect to help me assure that I am cabled correctly. Also, the ATC feeds are not from X-plane or VATSIM quite yet ... they are live ATC audio feeds from the Internet. 

Avionics Bending: VHF/HF COM Radio Integration with X-Plane (Part 4)

Each crew member has three different ways of sending microphone input to the audio system.

1. There is a microphone attached to the headset worn by each crew member. 
2. A hand microphone is provided for the Pilot and First officer, and,
3. A microphone is installed in the oxygen mask

Each microphone is routed to the respective radio via the Mic Select switch on the audio panel. A radio will transmit when Push To Talk (PTT) switch is pressed. The pilot an First officer have 3 ways of keying the PTT:

1. The pilot and first officer yoke have a Push To Talk (PPT) switch on each yoke. The following two images show a typical Boeing 737 yoke with the PPT switch located on the forward facing side of the left hand grip.

B737 Yoke and PTT

B737 Yoke and PTT

2. Each crew station in the cockpit is also equipped with a hand microphone. The image below shows a typical Telex hand microphone as used on the L-1011 and many other aircraft type. The push button on the top of the hand mike has the same function as the PPT switch sown in example 1.

Hand Microphone PTT Switch 

3. The microphone can also be keyed with a small switch located directly on the audio selector panel. In most cases, this PPT switch would be used in conjunction with the Oxygen Mask microphone.

Audio Selector Panel PTT

For the simulator project, all three ways of keying the microphone results in a "transmit" setting on the flight simulator. 

Avionics Bending: VHF/HF COM Radio Integration with X-Plane (Part 3)

Now that I have decided on a basic architecture for the audio integration it is time to do a power up test of both the Gables radio head as well as the audio selector panel. Both components take 24-28VDC power input. I am driving them with 24VDC and that works just fine.

Gables Radio Head and Audio Selector Powered

At this point the radio head is powered but not yet connected to an ARINC 429 receiver or transmitter. The audio panel is powered and the built in amplifier and "Voice Only" selector are working. I also cabled a temporary L-1011 Headphone and Hand-Mike break-out panel ... this way I am able to connect the David Clark headset for testing. 

Original L-1011 Hand-Mike and Headset Connector Panel

Below is a short video that show the setup in action. I connected a scanner radio listening to Atlanta Center to the Gables Audio Selector's VHF-1 input. The audio is not yet coming from the simulator. 

Avionics Bending: VHF/HF COM Radio Integration with X-Plane (Part 2)

Overview

There are quite a large number of audio sources that pilots use during flight and on the ground. Not all audio sources are really meaningful in a simulator cockpit, however, I will attempt to create and implement as many as possible. So here are the radio sources, as well as other sources that produce audible signals, most commonly found on large transport aircraft:

1. Very High Frequency (VHF) radios are mostly used for communication and navigation. VHF COM is used both in the air and on the ground to talk to controllers as well as listening to weather services like AWOS. VHF NAV is used for navigation, however, also carries audible signals in the form of Morse Code (for VOR and ILS identification and sometimes DME) and/or voice signals for other automated signals. 
2. High Frequency (HF) is used for company communication from the ground to aircraft and the other way around. HF really has not much of use in a simulator, however, I will still cover it as part of this effort because maybe there is something fun that can be done with it (maybe SELCAL integration).
3. Automatic Direction Finder (ADF) uses a band that is in many cases also used by AM radio broadcasts. The NAV aids are also known as Beacons and also have Morse Code for Beacon identification. 
4. Marker Beacons are part of the Instrument Landing System (ILS) and typically consist of 3 radio Beacons called; Outer-, Middle- and Inner-Marker. Each of them has a different frequency that is represented in the cockpit by goth a visual queue (a blue, orange and white light) as well as an audible signal in the form of 3 different tones. 
5. Passenger Address (PA) System allows the cockpit and cabin crews to make those lovely announcements about keeping your seat belts on until at the gate and look out the left window to see the Grand Canyon. 

The most interesting sources to implement with the simulator are the VHF, ADF, Marker and PA sources. VHF COM is most frequently by using either a synthetic ATC system or by connecting to a simulator service like VATSIM run by real people who act as flight controllers. My plan is to implement with VATSIM for the VHF COM radios. 

Technical Implementation

One of the core issues is that most flight simulators output a stereo-mix of audio, however, for the Audio Panel I need discrete output from each simulated audio source. Some of the audio output will need to be created from scratch, here are some thoughts on the signals:

• VHF Voice - use the VATSIM output.
• VHF NAV - generate Morse code based on the NAVAID name
• ADF - generate Morse code and mix in some type of radio or other signal
• AWOS - use text to speech generator 
• Marker - use sound generator to create marker beacon signal

All in all the integration for each of the 3 radio head/audio selector panel combinations will look as follows:

Avionics Bending: VHF/HF COM Radio Integration with X-Plane (Part 1)

Now that we have at least one primary flight instrument, the HSI, under our belt (see the previous 15 postings) I will now move on to something very interesting, which is radio integration into X-Plane. Here is the stack that I will be working with for the next few weeks:

Gables Multi Function Radio Head and Gables Audio Selector Panel

The two instruments in the picture above are a GABLES G6984 radio head and a GABLES G2930 audio selector panel. The G6984 uses the ARINC 429 protocol for radio data and is a perfect next step for the ARINC 429 work I have been doing lately. Unlike the the HSI, which only required sending ARINC 429 data to the device, the G6984 will require bi-directional traffic; radio frequencies from the radio and FMS data to the radio head.

In the L-1011 cockpit there are three identical audio selector and radio head combinations; one for the Pilot, one for the First Officer and One for the Second Officer. For the test setup I will also use a Hand Mike and a David Clark Headset (rather have a Telex, but I don't have access to one). Below is a picture of the input and output:

Gables VHF COM, Hand Mike and David Clark Headset

The L-1011 cockpit has two overhead speakers that can be used for monitoring audio without the need for a headset. For the test setup I will only use one of the two speakers. The speaker is powered and has an amplifier built in.

Original L-1011 Cockpit Overhead Speaker

Tomorrow, we will look at t detail analysis of the audio signals needed for a realistic integration of X-Plane and a simulated ATC system.