Discussion
Consider the following pairs of change and its effect on the lateral modes.
More dihedral - Better spiral stability
Bigger fin - Higher Dutch roll frequency
Yaw damper - Better Dutch roll damping
More roll damping - Higher steady roll rate
How many of the pairs given above are correctly matched?
Answer: B
The first three are correct and the fourth is not, so three match. Dihedral helps the spiral, fin volume raises the Dutch roll frequency, and a yaw damper raises its damping. More roll damping, however, reduces the steady roll rate, since \( p_{ss} = L_{\delta a}\delta_a/(-L_p) \) has the damping in the denominator: it makes the response quicker to settle but slower in absolute rate. That tension between crispness and authority is worth carrying, because it is the reason roll requirements are written on both the time constant and the achieved rate.
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