I had a successful flight with the EagleTree airspeed module connected to my TWOG. I did not have to do any hardware modifications, the sensor has an I2C interface that I connected directly to the TWOG I2C port. I was able to figure out the slave address and decode the raw output of the sensor. The results are quite good, the module is low cost and comes with a very good pitot tube (Prandtl style, pitot-static tube) that includes static and dynamic ports. For now I am simply sending the airspeed through the telemetry, the next step would be to modify the autopilot code to regulate the throttle in order to keep the airspeed constant (and a minimum ground speed). I am also working on interfacing with the EagleTree altimeter sensor.
Following is the data from my last flight, there was no wind and I tried to keep the pitch close to zero for most of the flight in order to be able to compare ground and air speed.
I will release the source code as soon as I have both airspeed and altimeter tested.