Having finished the modification of the FMS/CDU bay, I continued my top-to-bottom avionics installation. One of the most critical components, the Boeing throttle quadrant, is located just aft of the FMS/CDU bay.
The TQ I have was purchased several years ago from Art May-Alyea at Northern Flight Sim. Art has a wealth of experience converting old TQs from classic models to closely resemble those used in the NG. He completely disassembles the units, refinishes and paints all the components, installs microswitches to detect every switch position including every detent on the flap lever, then fits the assembly with motors for the trim wheels and throttle levers, as well as servos for the speed brake lever and trim indicator.
Art supplies the TQ conversion with bare wires coming out the front, and interfacing is up to the user. Full details of how I chose to complete the interface will be described in a later post, but the short version of the story is that most of the TQ is connected to a BU0836X joystick controller card from Leo Bodnar. The 12v motor driving the trim wheels are connected to a PhidgetsMotorControl HC card. The throttle levers are driven by two 12v motors fitted with slip clutches and interfaced to two Pololu Jrk 12v12 cards.
The pedestal itself is a Boeing OEM unit that came with the full cockpit I purchased from eBay in 2010. The frame was removed, fully stripped, restored and repainted in the colors of a typical NG model prior to reinstallation. All of the radios and other avionics in the pedestal were provided by FDS, and are purpose built for the simulation market. The one exception is the fire panel in the most forward part of the pedestal frame: this is a Boeing OEM unit that I reverse engineered and will describe in a future post.
Prior to proceeding with installation of the trim pieces and back wall, I spent several months checking avionics functionality to determine whether I would need to run any additional wires behind any of the panels. Access to the back of the overhead panels is fairly easy thanks to FDS mimicking the OEM design . I didn’t think of everything, but I got most of the major kinks worked out prior to proceeding with the finish work.
In this post I will describe how I figured out the wiring diagram for a real Boeing 737 landing gear lever mechanism, including the solenoid and Korry lights.
I’ve seen (and even owned) several landing gear levers that were designed and marketed for the home simulation market, but they just don’t have the heavy tactile feel of the real thing, and I’ve never seen any that have a working solenoid or override lever. The cockpit I bought fortunately still had the original gear lever still in place, complete with the six Korry annunciators that serve as gear position/transit lights.
The solenoid is a 28 volt device that, when energized, allows the lever to be pulled up to initiate a gear-up cycle. In the real aircraft, a number of logical conditions must be met for the solenoid to be activated, which prevents the gear from being raised while the aircraft is on the ground. The gear handle itself is equipped with an override trigger that allows to pilot to raise the handle in the event that the solenoid fails.
The solenoid wiring was easily determined as there were only two wires, one of which had to be 28 volt and the other a ground. The position switch wires were also easily traced back to the cannon plug. I was surprised on initially removing the assembly that only the gear down position had a switch installed. Although holes were present for mounting a gear up switch, the switch itself was missing. I can only assume that in the real aircraft the up position is read somewhere along the cable that runs to the actuator. For my simulator I just added an identical switch scavenged from another part of my project.
There are several manufacturers of annunciators for the home simulation market, but once again, there’s nothing quite like the real thing which have the press-to-test function available.
The wiring of the model 319 type 1 Korry annunciators have been described by David Allen. These are ground-seeking type circuits with 4 terminal lugs. Terminal 1 is the 28 volt input voltage. Ground terminal 2 to illuminate the indicator. Terminal 3 is grounded for a ‘test all’ function that lights the indicator, but extinguishes the light when pressed. Terminal 4 is grounded for a press-to-test function.
The wiring scheme is as follows:
24-pin cannon plug:
Pin 3: common to all terminal 3’s (test all function)
Pin 4: nose red terminal 2
Pin 5: nose green terminal 2
Pin 6: right red terminal 2
Pin 7: left red terminal 2
Pin 8: right green terminal 2
Pin 9: left green terminal 2
Pin 10: common to all terminal 4’s (press-to-test function)