User`s guide

9 Design Case Studies
9-14
Plot the MIMO impulse response.
impulse(cloop,20)
Look at the plot from aileron (input 2)to bankangle (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 aircraft to 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
()