How to build a synthetic airspeed sensor and estimate airspeed without a pitot tube: http://gallinazo.flightgear.org/uas/synthetic-air-data-an-afternoon-hack/
Great! By the way, MatrixPilot team (Bill Premerlani and Pete Holland) already went to a similar solution, for estimating air and relative wind speed just with the autopilot hardware (Uavdevboard).
Cool, I’ll have to track down their work and see how they approached this. I came up with my own simple system to estimate wind in flight, but it requires indicated airspeed as an input.