I've been testing the effect of different cruise airspeed settings on power consumption, but in the range that I've been testing (8m/s, 9m/s and 10m/s) it has almost no effect on actual airspeed (or power consumption).
I've been flying a lap about 1.5km long, and changing the cruise airspeed each lap.
Working with the log files afterwards the average of the airspeed for each lap shows little or no relation to the cruise airspeed setting.
(Before you ask, yes I changed the setting in the Arduplane Pids screen AND clicked Write. It is recorded in the tlog file with a mavlink_param_set_t entry).
Below is a table of measurements taken from the log file. The first column is the cruise airspeed setting for each lap. The next columns are the average values for the named variable taken from the tlog file. The final column (Watts) is just current * voltage.
The only reliable effect that I've measured is alt_error. It's lower at high speed settings. Obviously the plane doesn't fly any faster, or use significantly more power to achieve that. (I've done this test three times now and I got a similar result each time.)
Do I need to change the THROTTLE_CRUISE percent value too? What does this do? Why is there a THROTTLE_CRUISE (%) and AIRSPEED_CRUISE (m/s) setting?
(I'm flying a Bormatec Maja with APM 2.5 and airspeed sensor).