Duo Discus QQ


In February of 2020, I performed a whole-panel upgrade of my Duo Discus.

I often get questions about all the stuff I installed, so here is a breakdown of all the diagrams I created to keep all the cables straight. I did all of the cabling and wiring, and all of it was with the close supervision of an FAA certified Aircraft Inspector (IA). After all the installation work was done, we filed a Form 337 to describe the installation of all the hardware. We also performed a weight and balance of the glider. The glider only gained 10 pounds from the installation of all this extra equipment.

Most of the components need electricity. I wired the system with two batteries in parallel. I used diodes to prevent one battery from trying to charge the other. All of the components are isolated with a circuit breaker of different maximum current levels. The back seat has a master switch to isolate all of the back-seat components from using electricity while doing solo flight in the front seat.

The front seat has the TRIG TC-20, the interface for the transponder and ADS-B. The front instrument panel also has the Becker AR 6201 radio, and the main flight computer. There is a bridge from the flight computer to the radio, so tuning the radio can be accomplished by the flight computer from the front seat or back seat, as well as by tuning the knobs on the radio unit. The variometer has connections to the total energy probes, total pressure (pitot tube) and static tubes. The flight computer relays information to the rear seat computer by teh RS485 cables. The flight computer can be controlled by the LXNav remote joystick. The altimeter is a digital altimeter. It's a TSO'd piece of equipment called an ACD-57.

These diagrams are printed out for the convenience of whoever has to figure out the interconnections of these devices. The printout contains QR-codes. Details about the Goddard cables interconnecting some of the devices can be viewed by following the QR-codes with a smart phone.

Avionics diagram for the rear pilot station. The rear pilot station contains the PowerFLARM Core unit, the Transponder's brain (TT22), the ADS-B information box (TN70). The PowerFLARM has two antennae, one for receiving and sending PowerFLARM signals, the other for receiving ADS-B information from other aircraft. In order to prevent guest pilots from feeling the temptation of touching the flight computer's screen (which is not a touch screen), the LXNav remote joysticks offer the easiest interface to the flight computer. The transponder antenna is mounted internally behind the main landing gear.

There are various tubes connecting the glider's instruments to the outside world. The glider originally came with capacity flasks for a mechanical variometer, but are no longer in use. (There's no room for a mechanical variometer after the upgrade!) The total energy probe only connects to the front seat variometer. Total energy information is relayed electronically to the variometer unit in the backseat. The Transponder has a squat switch, which changes the transponder's mode from GND to ALT, if there is enough airspeed entering the pitot tube, about 35 knots.