I built a telemetry pair for a friend. An idea I used to have for a really long time, but I had lack of interest to do it only for myself.
All the system is based on arduino and NRF24L01 Transceiver module. (on the very begginings I had problems with the code on the atmega328 mcu on the TX side and so I was forced to used atmega2560 for TX which was very heavy for that application. After the code optimized runs fine on the atmega328)
The data that is transmitted at this point :
Speed (km/h)
Altitude(m)
Temperature (internal) (Celsius)
Battery Voltage of the battery of the plane (up to 4s battery) .
Looks very interesting, I see from your blog you have updated to the 4X20 LCD, Have you thought about using one of these,
**broken link removed**
They take less current and also have SD card built in for data logging.
Are you considering to make open source ?