Aircraft involved in GPS triangle racing typically carry a GPS. Data is transmitted to a ground station using some form of telemetry. There are commercially available systems that include air and ground based components and show the pilot where he is, where the four waypoints (3 triangle, start line) are, flight direction, time elapsed and so on. These systems are built for purpose and are relatively expensive.
Much of the functionality involved seems to exist in Ardupilot GCS systems.
I’m wondering what the issues would be in using something like Mission Planner to collect data from the aircraft GPS and show the pilot where his aircraft is, his heading, where the waypoints are and measure time elapsed since crossing a “start line”.
Aircraft could carry airspeed sensors if necessary.
Aircraft would carry FRSKY receivers and transmit telemetry SPORT data to the pilot’s control transmitter. The data would need to get from there to a nearby screen - phone or tablet - running Mission Planner or equivalent using bluetooth, cable or something else developed for the purpose. Some FRSKY transmitters have BT capability inbuilt, others do not. There will be other additional requirements around recording distances and timing - these would be documented if the concept is feasible.