Aerodynamics Flashcards
Definition of Lift:
The upward force that opposes weight and supports an airplane in flight
Angle of Sweepback of a wing
Angle between the lateral axis and a line represented by 25% root chord and 25% wing tip chord
Stagnation Point
Point on the leading edge of an airfoil where the airflow splits to either follow the upper or lower surface of a wing
Coefficient of Lift (Cl)
Wings ability to produce lift as a product of Angle-of-Attack (AOA) and the shape of the camber line
Definition of Drag
Component of the total aerodynamic force, which resists the motion of body moving forward through the air
- Parasite and Induced
V(smin) vs V(s1g)
V(smin): stall speed for conventional aircraft. Will stall with a load factor slightly below 1g
V(s1g): stall speed for fly-by-wire aircraft. V(smin) = 0.94 x V(s1g)
Free Stream Airflow
Airflow that is far enough away from an aircraft that the aircraft does not disturb it
What is Mach number?
The relationship between the speed of the aircraft through an air mass (TAS) and the speed of sound for the same air mass (LSS)
same atmospheric conditions
M = TAS / LSS
What is Critical Mach Number?
Speed at which airflow over any part of the aircraft or structure first reaches (but does not exceed) the speed of sound (Mach 1.0) and results in shockwaves forming on the structure
Speed of sound is not exceeded
Highest speed without reaching supersonic flow
Shock waves, buffet, and airflow separation take place above critical Mach number
Speed Spectrum
Subsonic: < 0.75M
Transonic: 0.75M - 1.2M
Supersonic: 1.2M - 5.0M
Hypersonic: > 5.0M
Stability of an aircraft
the characteristic of an airplane in flight that causes it to return to a condition of equilibrium (steady state flight) after being disturbed.
Static Stability vs Dynamic Stability
Static stability: What the airplane will do right now
Dynamic Stability: What an airplane will do in time
Center of Pressure
Point where all aerodynamic forces act on the chord line
Wing Dihedral
The upper angle of a wing which increases its lateral static stability
Angle of Attack
Angle between the chord line of a wing and the relative wind
Critical Angle of Attack (Clmax)
For any given aerofoil a stall always occur at the same angle regardless of IAS, flight attitude and/or weight
Advantages of sweptback wings
- less drag
- higher cruise speeds
- higher critical Mach number
- greater lateral stability
- less sensitive to turbulence
- delay the onset of compressibility effects (boundary layer and shock waves)
Disadvantages of sweptback wings
- tendency at low speed to stall at the wing tip first (center of pressure moves forward contributing to nose up pitch, less stall warning, and reduced lateral control)
- Dutch roll tendency
- reduced coefficient of lift (more of effect in subsonic flight)
“Coffin Corner”
At some point, the stall speed of the aircraft in Mach number could equal the MMO of the aircraft, and the pilot could neither slow down (without stalling) nor speed up (without exceeding the max operating speed of the aircraft)
*with an increase in altitude at a constant Mack number KTAS reduces
