Fixed-Wing Flight Basics

A fixed-wing aircraft stays up because air flowing over its wing makes lift, and lift grows with speed and with the wing's angle to the airflow. Push the angle too far and the airflow separates from the wing: lift collapses, called a stall. Fixed-wing drones fly far longer than quadrotors on the same battery, but they must keep moving.

Throttle Angle of attack Bank angle

Lift and the turn

Lift depends on air density $\rho$, speed $v$, wing area $S$, and the lift coefficient $C_L$, which rises with angle of attack $\alpha$ until the stall:

$$L = \tfrac{1}{2}\rho\,v^2 S\,C_L(\alpha) \qquad R_{\text{turn}} = \frac{v^2}{g\tan\phi}$$

Banking at angle $\phi$ tilts the lift sideways, which turns the aircraft, but leaves less lift holding it up.

What to notice

Raise the angle of attack and lift grows, so the aircraft climbs, until about 15° where the curve drops and it stalls and sinks. Low throttle means low speed, so the wing needs more angle for the same lift, bringing it closer to the stall. A steeper bank turns tighter, but needs more lift to stay level. This is why fixed-wing drones must keep a minimum airspeed and cannot hover, the trade-off they make for their long range.