NCAA PPL Principles of Flight flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Four Forces of Flight

Lift, weight, thrust, and drag. In unaccelerated flight lift equals weight and thrust equals drag; any imbalance causes acceleration in the direction of the net force.

Angle of Attack

The angle between the wing chord line and the relative wind. It is the primary control of lift and the direct determinant of the stall, independent of airspeed.

Critical Angle of Attack

The angle of attack at which the wing stalls, regardless of airspeed, weight, or bank. Exceeding it causes airflow separation and loss of lift.

Lift Equation

L = ½ρV²SC_L, where ρ is air density, V true airspeed, S wing area, and C_L lift coefficient. Lift varies with the square of airspeed.

Induced Drag

Drag created by lift production, from wingtip vortices and downwash. It increases at low airspeed and high angle of attack and decreases as airspeed rises.

Parasite Drag

Drag from form, skin friction, and interference, unrelated to lift. It increases with the square of airspeed and dominates total drag at high airspeeds.

L/D Max

The angle of attack giving the best lift-to-drag ratio and minimum total drag. It yields the farthest glide distance and occurs where induced equals parasite drag.

Load Factor

The ratio of total lift to aircraft weight. In a level turn, n = 1/cos(bank); at 60° bank the load factor is 2.

Stall Speed in Turn

V_S in a level turn equals straight-and-level stall speed times the square root of load factor. A 60° bank raises stall speed about 41 percent.

Adverse Yaw

Yaw opposite the turn direction caused by higher induced drag on the rising, slower-moving wing. Rudder pressure in the turn direction counteracts it.

P-Factor

Asymmetric thrust in a propeller aircraft at high angle of attack, where the descending blade takes a larger bite of air. It yaws the nose left in a climb.

Torque Effect

The reaction of the engine and propeller turning one way, rolling the airframe the opposite way. It is most noticeable at high power and low airspeed.

Gyroscopic Precession

A force applied to a spinning propeller acts 90 degrees later in the direction of rotation. In a tailwheel pitch change this produces yaw.

Spiraling Slipstream

Propeller wash corkscrews around the fuselage and strikes the vertical tail on the left side, yawing the nose left at high power and low airspeed.

Center of Pressure

The point where total lift acts. It moves forward as angle of attack increases and backward as it decreases, creating a pitch change tendency.

Static Stability

The initial tendency of an aircraft to return to equilibrium after disturbance. Positive static stability resists displacement; negative static stability amplifies it.

Dynamic Stability

The tendency of an aircraft to damp out oscillations over time after a disturbance. Positive dynamic stability decreases oscillation amplitude until equilibrium returns.

Dihedral Effect

Wing upward angle that creates more lift on the lower wing in a sideslip, producing a rolling moment away from the slip and contributing to lateral stability.

Aileron Adverse Yaw

The down-going aileron wing generates more lift and induced drag, yawing the nose opposite the turn. Coordinated rudder prevents a slipping turn.

Elevator Trim

A tab or adjustable surface that relieves control pressure by holding a set elevator position. It sets airspeed tendency, not a fixed pitch attitude.

Flap Effect on Lift

Extending flaps increases camber and wing area, raising C_L and lift at a given airspeed, lowering stall speed, but adding drag and reducing climb performance.

Flap Effect on Stall

Flaps lower stall speed by increasing maximum lift coefficient, but the critical angle of attack is unchanged. Full flaps may also reduce aileron effectiveness near the stall.

Ground Effect

Reduced induced drag and downwash within about one wingspan of the surface. Lift increases and the aircraft may float or lift off prematurely.

Wingtip Vortices

Swirling air from high pressure below to low pressure above the wingtip. They are strongest when heavy, clean, and slow, and create wake turbulence.

Bernoulli Principle

Faster-moving air over the curved upper wing has lower static pressure than slower air below. The pressure difference contributes to total lift.

Newton's Third Law

Deflecting air downward produces an equal upward reaction on the wing. Downwash and the resulting momentum change account for much of lift.

Aspect Ratio

Wingspan squared divided by wing area. High aspect ratio wings reduce induced drag and improve glide and climb efficiency.

Swept Wing Characteristics

Swept wings delay shock-wave formation at high speed but tend to stall at the tips first, reducing aileron effectiveness and altering pitch behavior.

Tapered Wing Stall

A tapered wing tends to stall at the tip first because the tip reaches critical angle before the root, causing loss of aileron control and pitch-up.

Secondary Stall

A stall occurring during recovery when back pressure is reapplied before the wing regains flying speed, or when recovery is abrupt and angle of attack increases again.

Spin Aerodynamics

An aggravated stall with one wing more stalled than the other, producing autorotation. Recovery requires reducing angle of attack, then applying rudder against rotation.

V_G Diagram

A plot of load factor versus airspeed showing positive and negative limit loads, the maneuver speed, and the never-exceed speed where structural limits are reached.