VFR · Lesson 14 · 8 min · ACS PA.VII · ACS PA.I.G

Ground Effect and Left-Turning Tendencies

Summary

Ground effect cuts induced drag near the surface and can mask a lack of climb speed. P-factor and the other left-turning tendencies yaw the nose left in the climb and are corrected with right rudder.

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What is the primary aerodynamic effect of flying within about one wingspan of the ground?

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Why this matters in flight

Ground effect explains why an overloaded airplane can lift off but fail to climb, and P-factor explains why you feed in right rudder on every climb. Both show up on every takeoff and landing.

Figure 5-17. Ground effect — reduced induced drag and altered downwash as the wing nears the surface.
Figure 5-17. Ground effect — reduced induced drag and altered downwash as the wing nears the surface.Pilot’s Handbook of Aeronautical Knowledge (FAA-H-8083-25C) · public domain
Figure 5-51. P-factor — the descending propeller blade meets a higher angle of attack, one of the left-turning tendencies.
Figure 5-51. P-factor — the descending propeller blade meets a higher angle of attack, one of the left-turning tendencies.Pilot’s Handbook of Aeronautical Knowledge (FAA-H-8083-25C) · public domain

Close to the ground — within about a wingspan — the surface interferes with the wingtip vortices and downwash, reducing induced drag. This is ground effect. It can let the airplane become airborne below normal flying speed, which is a trap: if you climb out of ground effect before reaching a safe climb speed, induced drag rises and the airplane may settle back or fail to climb. On landing, excess speed in ground effect causes floating. Separately, single-engine propeller airplanes have several left-turning tendencies. P-factor is the most cited: at a high angle of attack the descending right blade takes a bigger bite of air than the ascending left blade, so thrust is asymmetric and the nose yaws left. It is strongest at high power and high angle of attack — exactly the climb — and is held off with right rudder. Torque, spiraling slipstream, and gyroscopic precession add to the effect.

Key terms

Ground effect
Reduced induced drag near the surface, within about one wingspan.
P-factor
Asymmetric propeller thrust at high AoA that yaws the nose left.
Left-turning tendencies
Torque, P-factor, spiraling slipstream, and gyroscopic precession.

Sources & references · 2 · 2 linked

Every claim traces to a source — paraphrased knowledge elements pointing at the governing FAA publication. Items marked verified have been checked against the retrieved source text; the rest are pending verification. Where the exact page or regulation has been located in a retrieved document, the source links straight to it.

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