Brunei DCA CPL(A) 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 density

Standard sea-level density is 1.225 kg/m³ at 1013.25 hPa and 15 °C. Density ratio σ compares local density to this value and drives the TAS/IAS relationship.

Dynamic pressure formula

q = ½ρV², measured in pascals. All aerodynamic forces scale with q, so doubling true airspeed quadruples lift and parasite drag at a constant lift coefficient.

Angle of attack

The angle between the wing chord line and the relative airflow. It is not the pitch attitude; it depends on flight path and is the variable that determines lift coefficient and stall.

Aerodynamic centre

The point on an aerofoil about which the pitching moment is essentially constant as angle of attack changes. For subsonic sections it lies near 25 % chord.

Zero-lift angle

The angle of attack at which a cambered aerofoil produces no lift. It is negative for cambered sections and about zero for symmetric sections.

Centre of pressure

The point where the resultant aerodynamic force acts. On a cambered aerofoil it moves forward as lift coefficient increases, approaching the aerodynamic centre near the design lift.

Lift equation

L = ½ρV²S CL. Lift equals dynamic pressure times wing area times lift coefficient; CL rises with angle of attack up to the critical angle.

Lift slope

The rate of change of lift coefficient with angle of attack, about 2π per radian (0.1 per degree) for thin aerofoils in incompressible flow.

Steady level flight condition

Lift equals weight and thrust equals drag. Any increase in weight at fixed speed requires a higher lift coefficient, hence a higher angle of attack.

Induced drag formula

Di = L²/(½ρV²πb²e). It falls as speed rises and dominates total drag at low speed, high weight and high load factor.

Minimum total drag condition

Total drag is minimum where parasite drag equals induced drag. This occurs at CL = √(CD0/(πAe)) and coincides with maximum lift-to-drag ratio.

Best glide ratio

Maximum L/D gives maximum glide range. Glide angle satisfies tan γ = 1/(L/D), and minimum sink occurs at a lower speed than best range.

Excess power

Excess power is power available minus power required. Maximum excess power determines the best rate of climb speed Vy for a propeller aircraft.

Propeller efficiency

η = THP/BHP, the ratio of thrust power to shaft power. It peaks near the design advance ratio and is near zero at zero airspeed.

Static margin

The distance from centre of gravity to the stick-fixed neutral point, expressed as a fraction of mean aerodynamic chord. A larger margin gives stronger stability.

Dutch roll

A coupled lateral–directional oscillation in which the aircraft yaws and rolls out of phase. It is usually lightly damped and is countered by yaw dampers.

Phugoid oscillation

A long-period longitudinal mode in which the aircraft exchanges speed and altitude at nearly constant angle of attack. It is usually lightly damped.

Adverse yaw

The yaw away from a turn caused by greater induced drag on the down-going aileron. Differential or Frise ailerons reduce it, and rudder coordinates the turn.

Control effectiveness

The force a control surface produces depends on dynamic pressure at that surface. Effectiveness therefore falls as indicated airspeed falls, regardless of altitude.

Critical angle of attack

The angle at which the wing stalls, typically 15–16° for a plain wing. Stall occurs at this angle regardless of speed, weight or attitude.

Load factor and stall speed

Stall speed rises with the square root of load factor: Vs(n) = Vs × √n. At 60° bank, load factor is 2 and stall speed rises about 41 %.

Spin recovery sequence

Reduce power, neutralise ailerons, apply full opposite rudder, then ease the elevator forward to break the stall. Centralise controls as rotation stops.

Manoeuvring speed VA

The speed at which full control deflection produces the limit load factor. Below VA the wing stalls before the structure reaches its limit load.

Limit and ultimate load

Limit load is the maximum expected in service. Ultimate load is 1.5 times limit load, and the structure must withstand it without failure.

Level turn load factor

In a level turn, n = 1/cos φ. A 60° bank gives 2 g, and a 75° bank gives about 3.9 g, raising stall speed accordingly.

Critical Mach number

The flight Mach number at which local airflow first reaches Mach 1 somewhere on the airframe. It falls as lift coefficient and wing thickness increase.

Mach tuck

At high Mach numbers the centre of pressure moves aft, producing a pitch-down tendency. Mach trim systems and high-speed elevator designs counter it.

Sweep and critical Mach

Sweep delays the onset of shock waves because the effective Mach number normal to the leading edge is M cos Λ. Sweep also reduces lift slope.

Propeller advance ratio

J = V/(nD), where V is true airspeed, n revolutions per second and D diameter. Thrust and power coefficients vary with J.

Feathering

Aligning the propeller blades with the relative airflow to minimise drag and stop rotation after an engine failure. It reduces asymmetric drag and yaw.

Critical engine

For a conventional clockwise-turning propeller pair, the left engine, whose failure produces the greatest adverse yaw and control difficulty.

VMC definition

The minimum control speed with the critical engine failed and the other at maximum take-off power, gear up, take-off flaps and rudder fully applied.