EASA ATPL 081 Principles of Flight flashcards

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

ISA sea-level values

Temperature 15 °C, pressure 1013.25 hPa, density 1.225 kg/m³. These are the reference conditions from which pressure altitude and density altitude are derived.

Continuity equation

For steady incompressible flow, A1V1 = A2V2. A narrowing streamtube speeds the flow up, while a divergent duct slows it down and raises static pressure.

Bernoulli equation

Total pressure p + ½ρV² stays constant along a streamline in ideal incompressible flow. Where velocity rises, static pressure falls, which is the basis of aerofoil lift.

Reynolds number

Re = ρVc/μ, the ratio of inertial to viscous forces. High Re gives a relatively thinner boundary layer, later transition and a greater resistance to separation.

Critical angle of attack

The angle at which CL reaches its maximum and the boundary layer can no longer stay attached. Exceeding it produces a stall at any speed, weight or attitude.

Boundary layer transition

Change from laminar to turbulent flow, promoted by high Reynolds number, surface roughness or an adverse pressure gradient. Turbulent flow has more friction but resists separation better.

Lift formula

L = CL ½ρV²S. Lift depends on the lift coefficient, dynamic pressure and wing area, so doubling speed quadruples the lift available at a given angle of attack.

Induced drag coefficient

CDi = CL²/(πAe), where A is aspect ratio and e the Oswald efficiency. Induced drag grows with the square of lift coefficient and falls with greater span.

Sweep and critical Mach

Sweep reduces the Mach number normal to the leading edge to about M cos Λ, delaying shock formation. It also lowers lift-curve slope and raises stall speed.

Dihedral effect

Sideslip produces a rolling moment that tends to level the wings, giving lateral static stability. Excessive dihedral causes Dutch roll and spiral instability.

Fowler flap

A trailing-edge flap that slides aft before hinging down, increasing both wing area and camber. It gives a large CLmax increase with relatively low drag at small deflections.

Load factor in a turn

In a level turn, n = 1/cos φ. A 60° bank gives n = 2, and stall speed rises by the square root of n.

Turn radius and rate

Radius r = V²/(g tan φ) and rate ω = g tan φ/V. For a given bank angle, higher speed increases radius and decreases rate of turn.

Manoeuvring speed VA

The speed at which full deflection of one primary control reaches the limit load factor without damage. It decreases as weight decreases, so it is not a fixed value.

Glide angle

In a steady glide tan γ = D/L, so the flattest glide occurs at maximum lift-to-drag ratio. Headwind steepens the glide and reduces range.

Static margin

The distance between the centre of gravity and the neutral point expressed as a fraction of mean aerodynamic chord. A forward CG gives a larger positive static margin.

Phugoid oscillation

A long-period, lightly damped oscillation of speed and altitude at nearly constant angle of attack. It is easily controlled by the pilot or autopilot.

Dutch roll

A coupled yaw-roll oscillation caused by strong dihedral effect and weak directional damping. Yaw dampers are fitted to meet handling-quality requirements.

Adverse yaw

The descending aileron produces more induced drag, yawing the nose away from the intended turn. Differential ailerons and coordinated rudder reduce the effect.

Trim tab function

A small surface hinged at the trailing edge that moves opposite to the main control. It reduces the hinge moment needed to hold a deflection but does not alter the aircraft's stability.

Fly-by-wire

Electrical signalling with computer control replaces mechanical linkages. It allows envelope protection, normal, alternate and direct law reversion, and g-command or C* laws.

Spoiler function

Spoilers spoil lift and increase drag. They provide speedbrake and lift-dump functions and, as spoilerons, can supplement roll control on some aircraft.

Stall recognition cues

Stall warning horn or stick shaker, airframe buffet, reduced control effectiveness, nose or wing drop, and a sink rate. The warning typically precedes the stall by a margin.

Spin recovery sequence

Close throttles, neutralise ailerons, apply full opposite rudder, push the column forward to break the stall, then centralise controls and recover from the dive.

Autorotation in a spin

One wing stalls more deeply than the other, so differential lift and drag sustain rotation about a vertical axis. Both stall and yaw are required for a spin.

Wing drop at stall

One wing stalls before the other and drops. Rudder, not aileron, is used to counter it because aileron deflection can increase the angle of attack on the descending wing.

Critical Mach number

The freestream Mach number at which local flow on the wing first reaches Mach 1. Thickness, camber and lift all lower it, and a shock wave then forms.

Mach tuck

A nose-down pitching moment at high Mach as the centre of pressure moves aft behind the shock wave. Mach trim systems and elevator input counter it.

Coffin corner

At high altitude the low-speed stall buffet and the high-speed Mach buffet boundaries converge, narrowing the usable speed range between them.

Advance ratio

J = V/(nD), the ratio of forward speed to rotational speed times diameter. It sets the blade element angle of attack and therefore thrust and efficiency.

P-factor

At high angle of attack the descending propeller blade takes a larger bite of air, producing a yawing moment toward the descending-blade side, most noticeable at high power and low speed.

Wake turbulence behaviour

Wingtip vortices sink about 100 to 150 feet per minute and level off a few hundred feet below the flight path. They persist longest in stable air with light wind.