Specifications

10 Design Case Studies
10-14
Plot the MIMO impulse response.
impulse(sys,'b--',cloop,'r',20)
The yaw rate response is now well damped, but look at the plot from aileron
(input 2) to bank angle (output 2). When you move the aileron, the system no
longer continues to bank like a normal aircraft. You have over-stabilized the
spiral mode. The spiral mode is typically a very slow mode and allows the
aircraftto bank and turn without constant aileron input. Pilots are used to this
behavior and will not like your design if it does not allow them to fly normally.
This design has moved the spiral mode so that it has a faster frequency.
Washout Filter Design
What you need to do is make sure the spiral mode does not move further into
the left-half plane when you close the loop. One way flight control designers
have addressed this problem is to use a washout filter where
kH s()
Hs()
s
sa+
------------
=