NCAA CPL Principles of Flight flashcards

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

Critical angle of attack

The angle of attack at which the wing reaches maximum lift coefficient; exceeding it causes stall regardless of airspeed, weight or attitude.

Induced drag

Drag caused by lift, arising from downwash tilting the lift vector rearward; it varies with the square of the lift coefficient and inversely with aspect ratio.

Boundary layer separation

Detachment of the slow-moving boundary layer from the surface under an adverse pressure gradient, causing loss of lift and a large increase in pressure drag.

Aspect ratio

Wing span squared divided by wing area; a higher aspect ratio reduces induced drag for a given lift coefficient and improves glide performance.

Equivalent airspeed

True airspeed multiplied by the square root of the density ratio; it reflects dynamic pressure and therefore structural loads and indicated stall behaviour.

Mach number

The ratio of true airspeed to the local speed of sound; it governs compressibility effects and rises with altitude for a fixed true airspeed.

Critical Mach number

The free-stream Mach number at which local airflow first reaches the speed of sound somewhere on the airframe, usually on the upper wing surface.

Speed of sound

The speed at which pressure waves propagate, equal to the square root of the product of the specific heat ratio, gas constant and absolute temperature.

Downwash

The downward deflection of air behind a lifting wing; it reduces the effective angle of attack and produces the rearward component of lift called induced drag.

Tip vortices

Rotating airflow trailing from wingtips where higher-pressure air flows to the lower-pressure upper surface; they create downwash and are strongest when slow, heavy and clean.

Washout

A wing design in which the tip has a lower incidence than the root, so the root stalls first and aileron effectiveness is preserved at high angle of attack.

Ground effect

Reduction in induced drag and downwash when flying within about one wingspan of the surface, caused by interference of the wing's flow field with the ground.

Lift formula

Lift equals lift coefficient times half the air density times true airspeed squared times wing area; in steady level flight it equals weight.

Best glide speed

The speed at which the aircraft achieves its maximum lift-to-drag ratio, giving the greatest still-air glide distance from a given altitude.

Minimum drag speed

The speed at which parasite drag equals induced drag and total drag is lowest; flying slower places the aircraft on the back side of the drag curve.

Fowler flap

A trailing-edge flap that translates aft as it extends, increasing both wing camber and wing area and giving the largest increase in maximum lift coefficient.

Vortex generators

Small vanes that mix high-energy free-stream air into the boundary layer, delaying separation and improving control effectiveness at high angle of attack.

Spoiler

A surface that disrupts lift by spoiling the upper-surface flow and adding drag; used for descent control, roll control and ground deceleration.

Static margin

The distance between the centre of gravity and the neutral point, expressed as a fraction of mean aerodynamic chord; positive margin gives longitudinal static stability.

Dihedral effect

The rolling moment produced by sideslip: a wing with dihedral rolls the aircraft away from the slip, providing lateral stability.

Dutch roll

A coupled yaw-roll oscillation, usually lightly damped, in which the aircraft sideslips and rolls while yawing back and forth.

Stall speed formula

Level-flight stall speed equals the square root of twice the weight divided by the product of air density, wing area and maximum lift coefficient.

Accelerated stall

A stall occurring at a higher speed than the one-g stall because increased load factor raises the angle of attack required to produce the needed lift.

Spin

An autorotation in which one wing is more deeply stalled than the other, sustained by yaw; recovery requires breaking the stall with opposite rudder and forward elevator.

V_MC

The minimum control speed in the air: the slowest speed at which full rudder can maintain control after one engine fails with the other at takeoff power.

Critical engine

The engine whose failure produces the greatest yawing moment, usually because its propeller slipstream or rotation direction most assists directional control.

Load factor

The ratio of total lift to weight; in a level turn it equals one divided by the cosine of the bank angle, so sixty degrees of bank doubles it.

Best angle of climb

The speed that maximises height gained per unit horizontal distance, used for obstacle clearance; it is lower than the best rate of climb speed.

Advance ratio

Propeller forward speed divided by the product of rotational speed and diameter; it defines the operating point at which propeller efficiency is measured.

Feathering

Rotating propeller blades to an edge-on position to minimise drag and asymmetric yaw after an engine failure, preventing the propeller from windmilling.

Mach tuck

A nose-down pitching moment at high Mach caused by aft movement of the centre of pressure as shock-induced separation develops over the wing.

Manoeuvring speed V_A

The design speed at or below which full control deflection stalls the wing before exceeding the limit load factor, protecting the structure from overstress.