Title: FlightPerformanceCalc Aviation / Aerodynamics & Lift
Tags: aerodynamics-lift

Tag: Four Forces
Question: Name the four forces acting on an airplane in flight.
Answer: Lift (up), Weight/gravity (down), Thrust (forward), and Drag (rearward). In unaccelerated straight-and-level flight they balance: lift = weight and thrust = drag.
Ref: AERODYNAMICS · 01

Tag: Lift
Question: How does a wing produce lift? (two complementary explanations)
Answer: It deflects air downward — Newton's third law gives an equal and opposite upward reaction — AND it creates lower pressure over the curved upper surface than beneath (Bernoulli). Both describe the same net upward force.
Ref: AERODYNAMICS · 02

Tag: Lift
Question: State the lift equation and its variables.
Answer: L = C_L × ½ρV² × S. C_L = coefficient of lift (airfoil shape and angle of attack), ρ = air density, V = velocity, S = wing area. Lift varies with the SQUARE of airspeed.
Ref: AERODYNAMICS · 03

Tag: AOA
Question: Define angle of attack.
Answer: The angle between the wing's chord line and the relative wind. It is NOT the same as pitch attitude — a wing can be at a high angle of attack at any pitch or airspeed.
Ref: AERODYNAMICS · 04

Tag: Stall
Question: What is the critical angle of attack, and what is a stall?
Answer: The critical AOA (about 16–18° for many airfoils) is where airflow separates and lift drops sharply. A stall is ALWAYS the result of exceeding the critical angle of attack — it can happen at any airspeed, weight, or attitude.
Ref: AERODYNAMICS · 05

Tag: AOA
Question: Distinguish chord line, relative wind, and flight path.
Answer: The chord line runs from the leading to the trailing edge. The relative wind is the airflow opposite the flight path. Angle of attack is the angle between the chord line and the relative wind.
Ref: AERODYNAMICS · 06

Tag: Drag
Question: Induced drag vs parasite drag — and where each dominates.
Answer: Induced drag is a by-product of producing lift (wingtip vortices); it is greatest at low speed / high AOA. Parasite drag (form, skin friction, interference) rises with the square of airspeed; it dominates at high speed.
Ref: AERODYNAMICS · 07

Tag: Performance
Question: What is L/D max?
Answer: The angle of attack (and corresponding airspeed) that gives the greatest lift-to-drag ratio — the point of minimum total drag. It yields best glide range and underlies best-endurance/economy speeds.
Ref: AERODYNAMICS · 08

Tag: Ground Effect
Question: What is ground effect?
Answer: Within about one wingspan of the surface, wingtip vortices and induced drag are reduced. It can let an airplane lift off below normal flying speed or float during landing.
Ref: AERODYNAMICS · 09

Tag: Left Turn
Question: Name the four left-turning tendencies.
Answer: Torque (reaction to prop rotation), spiraling slipstream (strikes the tail on the left), P-factor (descending blade makes more thrust at high AOA), and gyroscopic precession (felt during pitch changes, e.g., a tailwheel takeoff).
Ref: AERODYNAMICS · 10

Tag: Left Turn
Question: What is P-factor?
Answer: Asymmetric propeller thrust. At a high angle of attack the descending (right) blade takes a larger bite of air than the ascending blade, producing more thrust on the right and yawing the nose left.
Ref: AERODYNAMICS · 11

Tag: Turns
Question: What is adverse yaw and how do you counter it?
Answer: When rolling into a bank, the rising (outside) wing has more lift and therefore more induced drag, yawing the nose away from the turn. Counter it with coordinated rudder into the turn.
Ref: AERODYNAMICS · 12

Tag: Load Factor
Question: How does stall speed change with load factor in a level turn?
Answer: Stall speed increases with the square root of the load factor: V_s(new) = V_s × √n. At a 60° bank the load factor is 2 G, so the stall speed rises about 41% (× 1.41).
Ref: AERODYNAMICS · 13

Tag: Load Factor
Question: Define load factor and give the values at 30°, 45°, and 60° of bank.
Answer: Load factor = lift ÷ weight (in G). In a level turn n = 1/cos(bank angle): 30° ≈ 1.15 G, 45° ≈ 1.41 G, 60° = 2.0 G.
Ref: AERODYNAMICS · 14

Tag: Stability
Question: Center of gravity vs center of pressure?
Answer: The CG is the airplane's weight balance point. The center of pressure is where the wing's total lift acts, and it moves fore/aft with angle of attack. Their relationship drives pitch stability.
Ref: AERODYNAMICS · 15

Tag: Stability
Question: Effects of a forward vs an aft CG?
Answer: Forward CG: more stable, higher stall speed, heavier control forces, more tail-down force and drag. Aft CG: less stable, lower stall speed, lighter controls — and if too far aft, dangerously unstable and hard to recover from a spin.
Ref: AERODYNAMICS · 16

Tag: High Lift
Question: What do flaps do aerodynamically?
Answer: They increase wing camber (and, on some types, area) to raise the coefficient of lift — allowing slower flight and steeper approaches. They also add drag, which is greatest at high flap settings.
Ref: AERODYNAMICS · 17

Tag: Stability
Question: Name the three stability axes and their control surfaces.
Answer: Longitudinal stability = pitch about the lateral axis (elevator, CG, horizontal stabilizer). Lateral stability = roll about the longitudinal axis (dihedral). Directional stability = yaw about the vertical axis (vertical fin).
Ref: AERODYNAMICS · 18

Tag: Spins
Question: What is a spin, and what is the PARE recovery?
Answer: An aggravated stall with autorotation — one wing more deeply stalled than the other (yaw present at the stall). PARE: Power idle, Ailerons neutral, Rudder full opposite the spin, Elevator forward to break the stall, then recover from the dive.
Ref: AERODYNAMICS · 19

Tag: V-speeds
Question: What is maneuvering speed (V_a), and why does it change with weight?
Answer: The maximum speed at which full, abrupt control deflection won't overstress the airframe — the wing stalls before it breaks. V_a DECREASES as weight decreases, so a lighter airplane has a lower maneuvering speed.
Ref: AERODYNAMICS · 20

Tag: AOA
Question: Angle of incidence vs angle of attack?
Answer: Angle of incidence is the FIXED angle at which the wing is mounted to the fuselage (built in by the designer). Angle of attack is variable and set by the pilot through pitch relative to the relative wind.
Ref: AERODYNAMICS · 21

Tag: Stall
Question: Why is stall speed (in indicated airspeed) about the same at any altitude?
Answer: A wing stalls at a fixed angle of attack, which corresponds to a fixed INDICATED airspeed (dynamic pressure). So the stall IAS stays nearly constant with altitude even though true airspeed increases.
Ref: AERODYNAMICS · 22

Tag: Wake
Question: What are wingtip vortices, and when are they strongest?
Answer: Circulating air spilling from the high-pressure area below the wingtip to the low-pressure area above — the source of induced drag and wake turbulence. They are strongest when an aircraft is heavy, clean (no flaps/gear), and slow.
Ref: AERODYNAMICS · 23

Tag: Performance
Question: What is the region of reversed command ("behind the power curve")?
Answer: The low-speed, high-AOA regime where MORE power is required to fly SLOWER because induced drag dominates. On approach it means correcting a low, slow condition may require adding power rather than only pitching down.
Ref: AERODYNAMICS · 24