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 installed a number of items into the simulator. We installed several computer components that will be used to drive the digital I/O as well as the ARINC 429 I/O. We also put power to all 3 of the Litton INU CDUs in the cockpit. There are two CDUs in the forward center console as well as a third on in the aft center console. You can see the #1 and #2 INU CDU in the image above. The picture below shows the cabling in progress.
L-1011 Litton INU CDU Cabling
We also powered up the ATC Transponder head as you can see in the image below. The ATC Transponder head that we have has facilities for TCAS. However, we will initially not build out the simulator for TCAS.
Taking a short break from the SFENA HSI today and tested ARINC 429 receive words with the DDC card. So far all the stuff you saw with the SFENA HSI had been ARINC 429 transmit words. The receive mode used in this example is called "mailbox" mode in which the channel on the card only remembers the last word received for a specific label. I had a Skype discussion with Edo from Italy today who is building a B767 simulator and we talked about the difference of using 2-of-5 and ARINC 429 label encoding. In 2-of-5, which is typical for ARINC 500 class devices, an ATC code or a radio frequency would be sent over 18 ore more discrete pins. Here is an example of how 2-of-5 encodes individual digits on individual pins:
2 of 5 Code used in ARINC 500 Series
The ARNC word still encodes the individual digits, but, does so in BCD format. The ARINC 429 Label also has some status information as part of a 32bit word that is being transmitted. All this data is transmitted on just two pins.
ARINC 429 Word for ATC Transponder
Typically BCD encoding uses 4 bits, however, since each position in the Transponder code only goes from 0 to 7 each digit can be encoded in 3 bits only. The video below shows a short introduction to reading the ARINC 429 label as shown above and doing a simple dump to the screen. The code is written in C.
The Gables ATC Transponder head that I would like to use for the L-1011 project has powered up successfully. The instrument had not been in use for several years and came out of obsolete surplus. I was uncertain if it would actually work.
The device powered up fine from a 115V 400Hz source and the head consumes roughly 43 mA.
The data-output form the head is in the ARINC 429 format.
In the Lockheed L-1011 cockpit the transponder is located on the center console. A three-position transponder select switch is provider in most cases:
#1, #1 transponder is being used, #2 Standby
Standby, both transponders are warmed up (as long as power on aircraft) but neither is operating.
#2, #3 transponder is being used, #1 in Standby
The mode select switch determines whether A domestic or B international coding is being used. (More modern devices include other modes as well as TCAS).
A three-position altitude reporting switch is provided:
#1, ADC #1 is being used for altitude reporting
OFF ... the system is off
#2, ADC #2 is being used for altitude reporting
The fault light indicates a fault within the selected system (amber). This should prompt the pilots to select the other transponder. The IDENT button provides an additional pulse reply. IDENT pulse lasts for 20 seconds after IDENT button is release.
Pushing the test button also illuminates the REPLY light.
For the Lockheed L-1011 project, I picked a old Gables 4096 Transponder that I restored a few months ago. Don't have the electronics retrofit for it yet, but it will be one of the first ones I work on. The ATC Transponder is located on the center console of the Lockheed L-1011. The panel that I will use is not a TCAS panel.
The elements of the ATC TRNASP panel are.
TRANSPONDER SELECTOR SWITCH - OFF .. turns the transponder off, STBY .. puts the transponder subsystem into a non-transmitting standby mode, ON .. is the normal operation of the transponder system and LO SENS .. puts the transponder into low sensitivity mode.
SYS SWITCH - switches between two different transponder systems .. one acts as primary the other as standby
CODE SELECTOR - there are two double stacked knobs; one for each digit
IDENT - momentary pressing button increases output signal for about 10 seconds
MODE SELECTOR SWITCH - The panels supports ATC transponder modes A, B, C and D.
ALT RPTG - when in the OFF position, the altitude reporting function is turned off.
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