RBAK - Basic Aviation Knowledge
Lift, Drag and Angle of Attack
See how changes in airspeed and angle of attack affect lift, drag, stall margin and endurance.
Lesson references
- Last reviewed
- 2026-05-18
- Lesson references
- RePL Study Guide pp. 200-213; Part 101 MOS C10 p. 93.
Lift changes with speed and angle
Increasing airspeed or angle of attack can increase lift up to a point. Beyond the useful range, airflow can separate and lift can reduce sharply.
For fixed-wing RPA, that point is tied to stall awareness. For multirotors, the same general idea still helps explain rotor loading, translational lift and why disturbed airflow matters.
Three steps. Step 1, aerofoil: air flows past an aerofoil section from left to right. This is the relative airflow, opposite to the direction the aerofoil moves. A dashed chord line runs from the leading edge to the trailing edge. The angle of attack (AoA) is the angle between the chord line and the relative airflow, and it opens and closes slightly. Step 2, hover: a multirotor seen from the side. Lift acts up and weight acts down through the centre of gravity, and they are equal (L = W). Step 3, forward flight: the multirotor tilts forward, so the rotor thrust tilts and gets longer. Its upward part is still equal to weight and its forward part is thrust. Drag acts rearward, opposite to the motion, and in steady level flight thrust equals drag (L = W, T = D). The Climb button shows lift greater than weight (L > W). The Descend button shows weight greater than lift (W > L). Arrow lengths are schematic. The still frame shows step 3.
Drag is not one thing
Parasite drag includes form drag, interference drag and skin friction. Induced drag is associated with producing lift. Different types dominate at different speeds.
The practical lesson is that flying too fast or too slow can both waste energy. Mission planning should account for the aircraft's efficient operating speed, wind and payload.
Left: a multirotor flying forward, with air streaming past it. Right: a schematic graph of drag against airspeed, with no numbers. Step 1, parasite drag: as airspeed increases, the turbulent wake behind the aircraft grows and the parasite drag curve rises with the square of airspeed. Step 2, induced drag: at low airspeed the rotor tip vortices are large and induced drag is high; as airspeed increases the vortices shrink and the induced drag curve falls. Step 3, total drag: total drag is parasite plus induced. It is high at low speed and at high speed, with a minimum in between, marked min drag. The Airspeed slider moves the aircraft's speed along the graph. Curves are illustrative.
Endurance comes from balance
Maximum endurance is not simply maximum speed or minimum speed. It is the point where the aircraft can stay airborne longest for the available energy.
Remote pilots see this as battery margin. Wind, climb, turns, payload and poor route design all move the operation away from the ideal.
A schematic graph of power required against airspeed, with no numbers. Induced power is high at low speed and falls as speed increases. Parasite power is low at low speed and rises steeply at high speed. Added together they make a U-shaped total power curve. A marker slides along the curve: flying too slow or too fast needs more power, so the time-aloft bar shrinks. At the bottom of the U, minimum power, the time aloft is longest: best endurance. A line from the origin touches the curve at a slightly higher speed: minimum drag, best range. Payload raises the curve and moves the best endurance point; climbing raises the whole curve, so time aloft falls.
Practice Questions
Which type of drag is associated with producing lift?
- Induced drag
- Skin friction only
- Form drag only
- Magnetic drag
Answer: Induced drag
Induced drag is lift dependent and is one of the drag types remote pilots should recognise.
Next step after study
Complete your Remote Pilot Licence training
The free study guide is a strong theory foundation. To actually be issued with a RePL, students still complete approved training, practical flying and assessment with a certified provider.