A potential role for bat tail membranes in flight control

Wind tunnel tests conducted on a model based on the long-eared bat Plecotus auritus,
indicated that the position of the tail membrane (uropatagium) can significantly influence flight control. Adjusting tail position by increasing the angle of the legs relative to the body, has a two-fold effect; increasing leg-induced wing camber (i.e. locally increased camber and angle of attack of the inner wing surface) and increasing the angle of attack of the tail membrane. We also used our model to examine the effects of flying with and without a tail membrane. For the bat model with a tail membrane increasing leg angle increased the lift, drag and nose-down pitching moment produced. However, removing the tail membrane significantly reduced the change in pitching moment with increasing leg angle, but it had a much smaller effect on the level of lift and drag produced. The tail membrane, therefore, is potentially important for controlling the level of pitching moment produced by bats and an aid to flight control, specifically improving agility and manoeuvrability. Although the tail of bats is different from that of birds, in that it is only divided from the wings by the legs, it nonetheless, may, in addition to its prey capturing function, fulfil a similar role in aiding flight control.