Private Pilot Ground Course Lesson 8: Why Airplanes Have Flaps

Flaps are one of the most useful tools a pilot has during takeoff and landing, but new pilots often learn the flap settings before they really understand what the flaps are doing to the wing. In Lesson 8 of the Red Yeti Aviation Private Pilot Ground Course, we break down the aerodynamics behind flaps and explain why they let an airplane operate safely at slower speeds.

What Do Airplane Flaps Actually Do?

Flaps are high-lift devices normally located along the inboard trailing edge of the wing. When the pilot extends them, the shape of the wing changes. On a typical training airplane, flap extension increases the wing's camber, allowing it to produce more lift at a given airspeed and angle of attack.

That matters most during the low-speed portions of flight. A wing configured with flaps can generally produce the lift needed for flight at a lower airspeed than the same wing in the clean configuration. This is one reason published stall speeds are different between clean and landing configurations.

More Lift Comes With More Drag

Flaps do not simply create extra lift. They also create drag, and that drag becomes especially useful during landing. As flap deflection increases, the airplane can descend on a steeper flight path without allowing the airspeed to build the way it would in a cleaner configuration.

Think about a normal final approach. The goal is not simply to point the nose at the runway. The pilot needs to manage energy, maintain the proper approach speed, control the descent, and arrive in a position to flare and touch down at an appropriate speed. Flaps help make that possible by giving the pilot another way to manage both lift and drag.

Why Flaps Allow Slower Landing Speeds

Landing slower has an important practical advantage: less energy has to be dissipated during the landing roll. By increasing the wing's maximum lift capability, flaps reduce stall speed in the landing configuration and allow the airplane to approach and touch down at a lower speed when flown according to the aircraft's approved procedures.

The exact speeds and flap settings are aircraft-specific. Always use the Pilot's Operating Handbook or approved Airplane Flight Manual for the airplane you are flying rather than applying a flap procedure from another aircraft.

Flaps and the Approach Angle

One of the easiest effects to notice from the cockpit is what happens to the descent when additional flaps are selected. The extra drag can increase the angle of descent without requiring a large increase in airspeed. That is useful when setting up a stabilized approach and managing excess altitude.

However, flaps are not a substitute for good approach planning. Large configuration changes close to the ground can produce changes in pitch, trim, lift, and drag. A pilot should anticipate those changes instead of simply extending flaps and reacting afterward.

Common Types of Flaps

Private pilot applicants should recognize the basic flap designs commonly discussed in FAA training material: plain, split, slotted, and Fowler flaps. The designs accomplish the same general mission in different ways. Slotted flaps improve airflow over the flap, while Fowler flaps move aft as they extend, increasing effective wing area as well as camber.

You do not need to be an aerodynamic engineer to use flaps correctly, but understanding why different flap designs produce different combinations of lift and drag makes aircraft performance easier to understand.

What Student Pilots Should Remember

For the written exam, oral exam, and actual flying, remember the relationship: extending flaps changes the wing, increases lift capability, increases drag, generally lowers stall speed in the landing configuration, and allows a steeper descent without the same tendency to accelerate. The amount of each effect depends on the airplane and flap setting.

There is also an operational limitation every pilot needs to respect: flap operating speeds. Do not extend flaps above the limitations published for your airplane. Know the appropriate V_FE information and verify the limitations in the POH or AFM for the specific aircraft.

Watch Private Pilot Ground Lesson 8

Watch the complete Red Yeti Aviation lesson: WHY do Airplanes have FLAPS? (FREE PPL Ground Lesson 8).

Continue Your Private Pilot Ground Training

If you are preparing for the FAA Private Pilot knowledge test and want the complete Red Yeti Aviation ground-school program, the Affordable Online Private Pilot Ground School | FAA Written Exam Prep & Endorsement is available for $50. It is designed to take you beyond simply memorizing answers and help you understand the material you will use during flight training, the written exam, and your checkride.

Next lesson: Lesson 9 — How to Turn an Airplane.