Fig. 3. Average acceleration-compensated pressure measurements for inner and outer tail positions (red lines) and two positions along the wings (blue lines), with non-acceleration compensated results (black lines) underlying. The synchronising accelerometer trace (green lines throughout; black lines indicate ±1 S.D.; N=3 pigeons) from an accelerometer placed at the base of secondary S3 allows signals from separate flights to be combined; each cycle is defined by the peak in accelerometer signal, relating to rapid upwards acceleration of the wing towards the end of downstroke. The time-base for each raw signal is normalised to the wing stroke cycle (thus slight differences in frequency do not result in increasing variation through the cycle). In each trace, the signal is split into a take-off flap followed by three full flaps, three full flaps at the middle of the flight, and three full flaps prior to landing followed by a landing flap. Underlying grey bars indicate periods of downstroke throughout.