Discussion
An aeroplane pitches at \( 0.10 \ \mathrm{rad/s} \) with a tail arm of \( 12 \ \mathrm{m} \) at a true airspeed of \( 120 \ \mathrm{m/s} \). The incidence increment at the tail is about
Answer: D
The tail's vertical velocity from the rotation is \( q\,l_t \), so
\[ \begin{aligned} \Delta\alpha_t &= \frac{q\,l_t}{V} = \frac{0.10 \times 12}{120} \\ &= 0.010 \ \mathrm{rad} = 0.57^{\circ} \end{aligned} \]
a little over half a degree, and that small increment is the whole of the tail's damping contribution at this rate. 5.7 degrees is a factor of ten out, the commonest error being to forget that the result is in radians before converting. 0.06 degrees divides by the arm rather than multiplying. 1.2 degrees is \( q\,l_t \) itself, a velocity in metres per second, reported as an angle.
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