This blog documents a project to build a functional Lockheed L-1011 cockpit replica
using real flight hardware, NI labVIEW and the x-Plane software platform.
Today Jim Blasco and myself worked on doing ARINC 429 label integration tests with the Altimeter. The Altimeter uses Label 204 and due to the fact that it uses a slightly different variant of a ARINC 429 compatible protocol it has to run on it's own bus. The 204 Label for the Altimeter uses a 32bit word that does not have a SSM field or Parity Bit.
The short demo video bellows shows data being sent to the ADI, HSI, VSI and ALT. The next steps will be to send actual simulator from X-Plane to the instruments.
Besides the tests with the Altimeter we also installed the first of two audio side panels. The L-1011 Cockpit Procedure Trainer did not come with these side panels and we got them from an actual (British Airways) L-1011. The audio side panels provide the hookups for the headset (boom and headset) as well as a connector for the hand microphone. The side panel also has room to store the headset in.
We have reached another millstone with the L-1011 project. All of the cabling is complete for the ARINC 429 compatible devices. To test the correct installation of the cables and to make sure that there are no problems with the type of cable that we are using in the simulator we ran some tests by sending test data to the left hand side (captain's) ADI and HSI. Here is a short video showing ARINC 429 high speed and low speed data being transmitted to both instruments cabled to the same high speed and low speed bus.
Cable Type Used: AWG 24 2 Conductor Shielded
Over the next two weeks we will start sending all ARINC 429 labels needed for the simulator over a total of 16 TX and 16 RX lines. The instruments used in the L-1011 simulator that are ARINC 429 compatible are:
Attitude Direction Indicator (ADI)
Horizontal Situation Indicator (HSI)
Altimeter (ALT)
Vertical Speed Indicator (VSI)
Traffic and Collision Alert System (TCAS)
VHF Communication Radio Controller
ATC Transponder Controller
Ultimately we would like to replace the current RDMIs with ARINC 429 compatible ones.
The picture above is a good illustration of what most of the build sessions over the last few weeks have looked like. While there is lots of good progress, they are hard to really blog about. However, what you see in the image above is cabling work done on the Center Panel. The panel is home to the communication radios, the #3 INU CDU and the audio panels. There is also a controller for ATC as well the radar controller. The radios had been cabled to 24V DC and 440Hz 110V AC power a few weeks ago, however last night we installed the cabling for the ARINC 429 connections that will read data from the instruments and also send data to the displays.
The last few sessions working on the Lockheed L-1011 trainer at the museum have been very deep in the cabling trenches of the main instrument panel (MIP). Cabling takes a lot of patients and it is not particularly fast work either. In the image above and below you can see some of the new cable bundles introduced into the MIP on both the Captain's and the First Officers side. All this cabling is being done in preparation for the simulator being outfitted with the Ethernet based SIM429-11 ARINC interfaces.
L-1011 MIP Cabling
Saturday I also installed the second of 3 Ethernet switches into the simulator. This 5 port 10/100T switch will connect the SIM429 interfaces to the computer.
For the ARINC 429 integration of the L-1011 trainer at the museum we will be using bus interfaces made by V1 Avionics. For the integration testing V1 Avionics used the museum's L-1011 HSIs and ADIs. The video below shows the instrument preparation and testing prior to installation into the L-1011 trainer. The L-1011 sim will use the following ARINC 429 capable instruments:
After almost a month away from the L-1011, due to work constraints and other museum projects, it is finally time to get back into it. Today we powered up the first few elements of the aft electronics panel on located just aft of the throttle quadrant. To be exact, we powered up the 3 VHF/HF COM radio combinations.
L-1011 COM Radio Without Backlight
The radio faces operate of 3 difference 24VDC sources. The VHF1 radio receives power from the BATTERY bus, the VHF 2 radio uses the GROUND SERVICE bus and the VHF3 radio receives power from the NO.2 RADIO BUS. I have extensively blogged about these Gables Engineering devices before and you can find more info on them when you search for Gables Radio Heads here on the blog.
Below is an image of the radio face under low light conditions with back plate and display illumination.
L-1011 COM Radio With Backlight
These radio faces are ARINC 429 devices and will be controlled by ARINC 429 interface.
Powered the Collins DLC-800 up today. Thanks to Edo for helping me find the pinout for the Interactive Display Unit! The L-1011 has one of these installed on the aft electronics console (center pedestal) and is used to interact with the SatCom system. The display uses the ARINC 429 protocol for data exchange.
Collins DLC-800 IDU
Of course, all of the display logic will need to be programmed. I might also be able to to design a few pages that will allow general control of the flight simulator. This unit will replace the paper-mockup of the IDU in the image below:
L-1011 Trainer - IDU
Below is the general device pinout: A ... 115V AC 400Hz (H) B ... 115V AC 400Hz (C) C ... Chassis Ground T ... IDU Data Out (ARINC A) U ... IDU Data Out (ARINC B) H ... IDU Data In (ARINC A) J ... IDU Data In (ARINC B)
The simulation of the Litton INS system would not be complete without the simulation of the INS alignment. The Litton LTN-72 uses ultra precise gyroscopes with ring-lasers that need to be aligned with a known position prior to aircraft movement. The status of this alignment process is indicated by an "ALIGN" indication on the status page of the LTN-72RL CDU. The image above shows the the Mode Control Unit (MCU) that is typically mounted on the overhead panel of the aircraft. It is put there so it is out of the way because it really only needs to be touched during alignment prior to aircraft movement.
The INU starts the process once the switch is lifted out of a locked Standby (STBY) position and moved to the Alignment (ALIGN) position. In the image below you can see that the process starts with a status of 90 and counts down to a status of 2. The INU also estimates the time for alignment to be 14.6 minutes. This value also counts down as we work towards status 2. For the simulation it is important that the simulator does not report aircraft movement or the alignment will not complete or will be wrong.
Once the INU reaches Status 2, the last alignment status, the green READY NAV light comes and indicates that the INU can now be put into navigation mode. Navigation mode should not be entered until we are ready to move the aircraft.
Once the INU is in navigation mode (see image below) the timer starts counting up to give us an indication for how long the INU has been running. For a precision INU, such as the LTN-72, i think the average error is 2NM over a 4 hour period.
Below is the display sequence as published by Litton in the LTN-72 Pilots Operating handbook.
Litton LTN-72RL CDU Development Setup with X-Plane
Still working on the Instrument Data page of the Litton LTN-72RL CDU. The data page actually incorporates a great number of X-Plane data refs and I finally got them all to work. A few of them, like drift angle, turned out to be a bit of head-scratcher.
Here is the list of X-Plane data refs that feeds the CDU's Instrument Data page:
The first image shows the aircraft sitting on the runway end, ready for take-off. You see that the "Wind Data" line is blanked because we have not reached the minimum target speed of 100KT yet. The wind data is only really relevant in flight and is used on this page to compute the Drift Angle. The track heading that is dialed into the INS is a course from Seattle Tacoma direct to JFK (a bit unlikely ... but good enough for the test.
Litton LTN-72RL - On Ground
In the image above you see that on the HSI we are expecting the course pointer to point to 063º for our track and the the compass card to indicate a heading of 161º. Both are magnetic as indicated by the "M". You see that we have a ground speed of 0 but a True Air Speed indicated of 2KT ... that's our headwind component that points directly into the pitot :)
Once we are airborne the Instrument Data page can be used as a cross reference to the HSI, the Airspeed Indicator and the Altimeter. In the real aircraft installation, the INS would actually send all this data to the HSI if it is selected as the source for the HSI.
X-Plane ADI and HSI showing the corresponding INS data.
In the image above and below you see the direct correlation between the X-Plane simulated ADI and HIS as well as the output on the Litton LTN-72RL CDU. This is a few minutes into flight and we are climbing through an altitude of 5600ft on a heading of 034º magnetic towards our track of 064º magnetic. I tried to take the two images as close to each other as possible, but you see that the LTN-72RL indicates a ground speed of 244KT and X-Plane shows roughly the same (246KT).
Litton LTN-72RK showing heading and speed data.
The Instrument Data page of the LTN-72RL has more than 5 lines of data. To reach the additional data the display needs to be scrolled down with the down arrow. The additional lines give data for body acceleration along the track (G's) as well as Drift Angle and Altitude in Feet and Meters (this data is not corrected for pressure). The image below shows the X-Plane rendered altitude, data and the corresponding data output on the Litton LTN-72RL Instrument Data page.
X-Plane ADI Altitude Band Output
LTN-72RL Altitude Information on Instrument Data Page
On climb-out and as we are approaching our target altitude of FL200 (20,000ft) the simulated weather outside gets smoother and the LTN-72RL indicates a longitudinal axis acceleration of 0.095 Gs. You are probably familiar with this when you fly on a regular commercial jet, it's that gravity pull that makes you feel just a little heaver in your seat. However, 0.095Gs you would probably not feel and it would be quite comfortable. Given the wind at 18,400ft we have also computed a Drift Angle (DA) of 6.4º nose right ... as indicated by the "R" in the DA line.
Litton LTN-72RL Track Acceleration and Drift Angle
Writing the integration for the LTN-72RL is really a lot of fun. Again, the device uses ARINC 575 as the data transfer from the computer simulated INS to the display. The INS simulation runs on the same computer as x-plan ... so all it really requires is my laptop and the ARINC 429/575 interface.
Worked on the implementation of the Instrument Data page. The instrument data page shows the INS data that is sent from the INS to the flight displays. There are still a bunch of challenges with the display refresh method ... i am thinking about using line blanking which is available to the CDU via a specific data label.
Litton LTN-72RL Data Field Examples
The instrument data page can show heading and track data as Magnetic or True. All speed data is shown in Knots. Here is the data page from the Litton manual showing the flow of ANS data to the HSI as well as the layout of the first 5 lines of the Instrument Data page:
Litton ANS Data and the HSI (from Litton LTN-72 Pilot Reference)
Litton LTN-72 Instrument Data Page (from Litton LTN-72 Pilot Reference)
Below is a short video showing the Instrument Data page in action:
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
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:
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:
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:
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.
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.
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:
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.
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.
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.
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.
Perhaps one of the bigger challenges in using older avionics is that most of them are deeply rooted in analog technology. More precisely, many avionics instruments form the 70s and 80s extensively use synchros and resolvers. Here is a picture of what a typical set of synchros in an instrument from the early 70s looks like:
Synchros are actually pretty old technology but are super resilient to noise and other external factors. They are still pretty common on just about all aircraft today, however, digital avionics have pretty much pushed them out of the cockpit. However, for the L-1011 sim project I will need a lot of synchro input to drive the avionics with. The good thing is that there are quite a lot of digital to synchro converters out in the surplus market that can be used for testing. The ultimate goal, of course, is to build some basic converters.
Below is a short video of my reference Digital to Syncrho converter. It's made by Shadin and actually designed to drive DME indicators ... however, it can be bent to control just about any synchro. It takes ARINC 429 data packets on one side and outputs an X, Y, Z synchro signal on the other side. What you see in the video is Label 251 data from 0 to 360". The really tall wave (enlarged by a factor of 2x) is the reference wave, I use it to trigger the scope with. The two small waves show the phase shift on the X and Y phase:
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