Chu Chu :
Could control effectiveness be used to calculate airspeed? For example, perhaps the FBW system could induce a small, brief, rudder deflection and measure the resulting yaw rate?
Skyjob:
Due to the inertia on large(r) aircraft this yaw rate would not be noticeable, so I suspect this is not a good option and no real alternative.
Reminded me of an idea I had a while back:
I believe some AOA sensors have an integral test driver (think analog meter movement coil) to move the vane, in normal use this is part of an end to end test of the system.
My idea was to use the test driver to force a small defiection (up and down) of the AoA vane, the drive current required for the deflection should be proprotional to airspeed. (actually density and speed?)
Way beyond my knowledge to specifiy other parameters that would be needed to calculate air speed but should be possible.
One nice thing about this is that it would require no additional HW, probably would need a enhanced AoA sensor (calibrated drive) but that would be a direct replacement.
Just a thought, will wait patiently for the royalty checks :-)