Steering

["James R. Cunningham" <jrccea@bellsouth.net>]

Matthew Bonnan wrote:

> Now that you have a tail that is independent of the hindlimb and can be used
> for "steering,"

I'd like to add a comment or two.  For the most part, modern birds (like
airplanes), don't generally use their tails for "steering".  They mostly use
them to provide command authority in yaw and pitch, and Matt's statement is
true, in that making the tail independent of the hindlimb enhances its ability
to provide that command authority. Most birds "steer" by use of asymmetric
flapping to command a bank to turn, then returning all controls to neutral or to
a symmetrical condition, thereby maintaining the bank in order to continue to
turn, and then commanding a roll out of the bank to end the turn.  Attempting to
turn by use of the rudder (tail) only, will often create adverse yaw due to the
consequent increased drag forces on the outer wing.  In order to coordinate the
turn, quite often while turning to the left, the tail will be used to command
yaw to the right, and vice versa.  Pitch control can be either by wing sweep, or
that function can be performed by the tail.

> I take no credit for these ideas: Gatesy, Padian, Dial, Middleton, and a
> number of others are all currently doing excellent work on this and other
> areas of bird and theropod locomotion.

I take no credit for these ideas either.  Dial and the others have indeed done
good work on the subject.  I particularly enjoyed the paper on the use of
asymmetric flapping to turn.Jim