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lecture_12 - Lecture # 12 Aircraft Lateral Autopilots...

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Unformatted text preview: Lecture # 12 Aircraft Lateral Autopilots Multi-loop closure Heading Control: linear Heading Control: nonlinear Fall 2004 16.333 101 Lateral Autopilots We can stabilize/modify the lateral dynamics using a variety of dif- ferent feedback architectures. a-- p 1- s r- G lat ( s )- r 1- s Look for good sensor/actuator pairings to achieve desired behavior. Example: Yaw damper Can improve the damping on the Dutch-roll mode by adding a feedback on r to the rudder: c = k r ( r c r ) r 3 . 33 Servo dynamics H r = s +3 . 33 added to rudder a = H r c r r System: 1 . 618 s 3 + . 7761 s 2 + . 03007 s + . 1883 G r c r = s 5 + 3 . 967 s 4 + 3 . 06 s 3 + 3 . 642 s 2 + 1 . 71 s + . 01223-3.5-3-2.5-2-1.5-1-0.5-2-1.5-1-0.5 0.5 1 1.5 2 0.94 0.86 0.16 0.34 0.5 0.64 0.76 3.5 0.76 0.985 0.16 0.34 0.5 0.64 1 0.86 0.94 0.985 0.5 3 1.5 2 2.5 Lateral autopilot: r to rudder Real Axis Imaginary Axis c r Figure 2: Lateral pole-zero map G r Fall 2004 16.333 102 Note that the gain of the plant is negative ( K plant < ), so if k r < , then K = K plant k r > , so must draw a 180 locus (neg feedback)-2-1.5-1-0.5 0.5 1 1.5 2-2-1.5-1-0.5 0.5 1 1.5 2 1 0.5 0.25 0.25 0.25 0.75 0.5 0.5 1 0.75 0.25 0.5 Lateral autopilot: r to r with k>0 Real Axis Imaginary Axis-3.5-3-2.5-2-1.5-1-0.5-2-1.5-1-0.5 0.5 1 1.5 2 1 0.25 0.25 0.5 0.5 0.75 0.25 0.5 0.75 Lateral autopilot: r to r with k<0 Real Axis Imaginary Axis Figure 3: Lateral pole-zero map. Definitely need k r < Root locus with k r < looks pretty good as we have authority over the four poles. k r = 1 . 6 results in a large increase in the Dutch-roll damping and spiral/roll modes have combined into a damped oscillation. Yaw damper looks great, but this implementation has a problem . There are various ight modes that require a steady yaw rate ( r ss = ). For example, steady turning ight. Our current yaw damper would not allow this to happen it would create the rudder inputs necessary to cancel out the motion !! Exact opposite of what we want to have happen , which is to damp out any oscillations about the steady turn. Fall 2004 16.333 103 Yaw Damper: Part 2 Can avoid this problem to some extent by filtering the feedback signal. Feedback only a high pass version of the r signal. High pass cuts out the low frequency content in the signal steady state value of r would not be fed back to the controller. New yaw damper: c = k r ( r c H w ( s ) r ) where H w ( s ) = s is the r s +1 washout filter. 10-2 10-1 10 10 1 10-2 10-1 10 Washout filter with =4.2 |H w (s)| Freq (rad/sec) Figure 4: Washout filter with = 4 . 2 New control picture p 1 a--- s G lat ( s ) c r 1 r r c----- H r ( s ) k r 6 s H w ( s ) Fall 2004 16.333 104-2-1.5-1-0.5 0.5 1-1.5-1-0.5 0.5 1 1.5 0.25 0.5 0.5 0.75 0.75 0.25 1 0.5 0.25 Lateral autopilot: r to rudder WITH washout filter Real Axis...
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This note was uploaded on 11/07/2011 for the course AERO 16.333 taught by Professor Alexandremegretski during the Fall '04 term at MIT.

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lecture_12 - Lecture # 12 Aircraft Lateral Autopilots...

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