1 aerodynamics Flashcards
maximum glide range
A maximum lift-drag ratio, obtained by the aircraft being flown at its optimal angle of attack and corresponding minimum drag speed (VIMD), produces an aircraft’s maximum glide range.
the effect of weight on the glide range
The glide range does not vary with weight, provided that the aircraft is flown at its optimal angle of attack and speed for that weight, because the glide range is proportional to the lift-drag ratio, which does not vary with weight.
Therefore, if a heavy aircraft were flown at the correct angle of attack and speed, it would glide the same distance as a lighter aircraft. However, the heavier aircraft would have a higher airspeed than the lighter aircraft, and therefore, although it would glide the same distance, it would take less time to do so.
rate of climb/descent
the time an aircraft will take to either climb or descend from a given height. It is normally expressed in terms of feet per minute.
effect of weight on rate of descent
The heavier the aircraft, the greater its rate of descent.
an aerofoil
a body that gives a large lift force compared with its drag when set at a small angle to a moving airstream, e.g., aircraft wings, tailplanes, rudders, and propellers.
an aerofoil chord line
a straight line from the leading edge to the trailing edge of an aerofoil
mean chord line
the wing area divided by the wing span
mean chamberline
line from the leading edge to the trailing edge of equidistance on the upper and lower surfaces of an aerofoil.
angle of incidence
the angle between the aerofoil’s chord line and the aircraft’s longitudinal datum.
angle of attack
the angle between the chord line of an aerofoil and the relative airflow
dihedral
the upward inclination of a wing from the root to the tip
anhedral
the downward inclination of a wing from the root to the tip.
lift
the phenomenon generated by an aerofoil due to pressure differences above and below the aerofoil.
the formula for lift
½ R V2 S CL ½R = half the value of the air density V2 = airflow velocity squared S = wing plan area CL = coefficient of lift
coefficient of lift (CL)
the lifting ability of a particular wing. It depends on both the shape of the wing section (fixed design feature) and the angle of attack.
center of pressure
a single point acting on the wing chord line at a right angle to the relative airflow, through which the wing’s lifting force is produced. The position of the center of pressure is not a fixed point but depends on the distribution of pressure along the chord, which itself depends on the angle of attack.
direct lift control
elevator/stabilizer
high lift devices
- Trailing edge flaps (Fowler flaps) increase lift at lower angles of deflection.
- Leading edge flaps (Krueger flaps) and slats increase lift by creating a longer wing chord line, chamber, and area.
- Slots (boundary layer control) prevent/delay the separation of the airflow boundary layer and therefore produce an increase in the coefficient of lift maximum.
Drag
the resistance to motion of an object (aircraft) through the air
two major types of drag
Parasite and induced drag = Total drag Parasite = zero-lift = profile drag 1. Form or pressure drag 2. Skin-friction drag 3. Interference drag
Parasite drag and speed relationship
Profile drag increases directly with speed because the faster an aircraft moves through the air, the more air molecules (density) its surfaces encounter, and it is these molecules that resist the motion of the aircraft through the air. This is known as profile drag and is greatest at high speeds.
Induced drag and speed relationship
Induced drag is caused by creating lift with a high angle of attack that exposes more of the aircraft’s surface to the relative airflow and is associated with wing-tip vortices. A function of lift is speed, and therefore, induced drag is indirectly related to speed, or rather the lack of speed. Thus induced drag is greatest at lower speeds due to the high angles of attack required to maintain the necessary lift.
Minimum drag speed (VIMD) is the speed at which induced and profile drag values are equal. It is also the speed that has the lowest total drag penalty,
high-drag devices
- Trailing edge flaps (in high-drag/low-lift position)
- Spoilers
a. In flight detent, used as a speed brake
b. On the ground, used as lift dumpers - Landing gear
- Reverse thrust (ground use only)
- Braking parachute
wing-tip vortices
a rotating flow created when the high-pressure area on the bottom of an airfoil pushed around the tip to the low-pressure area on the top, which causes turbulence
effects of wing-tip vortices
- Create aircraft drag (induced drag because the vortices induce a downward velocity in the airflow over the wing, causing a change in the direction of the lift force so that it has an induced drag component; therefore, it creates a loss of energy).
- Vortices create turbulence, which may affect the safety of other aircraft within approximately 1000 ft below or behind the aircraft.
- Downwash affects the direction of the relative airflow over the tailplane, which affects the longitudinal stability of the aircraft.
winglets
aerodynamic efficient surfaces located at the wing tips. They are designed to reduce induced drag. They dispense the spanwise airflow from the upper and lower surface often at different points, preventing the intermixing of these airflows
center of gravity
the point through which the total weight of a body will act.
center of gravity range
The center of gravity range relates to the furthest forward and aft center of gravity positions along the aircraft’s longitudinal axis, inside which the aircraft is permitted to fly.
Mach number
true airspeed indication, given as a percentage relative to the local speed of sound
critical Mach number (Mcrit)
the aircraft’s Mach speed at which the airflow over a wing becomes sonic.
Subsonic aircraft experience a rapid rise in drag above the critical Mach number, and because the aircraft’s engines do not have the available power to maintain its speed and lift values under these conditions, the aircraft suffers a loss of lift.
speed margins
the difference between the aircraft’s normal maximum permitted operating speed and its higher certified testing speed.
Vno
normal operating maximum permitted speed
Vne
higher, never exceeded operating speed
Vdf
the maximum demonstrated flight diving speed, established during design certification flight trials.
why an aircraft stalls
the streamlined/laminar airflow (or boundary layer) over the wing’s upper surface, which produces lift, breaks away from the surface when the critical angle of attack is exceeded, irrespective of airspeed, and becomes turbulent, causing a loss in lift
superstall
a stall from which the aircraft is unable to recover.
What systems protect against a stall
Stall warner’s and stick pushers.
Dutch roll
an oscillatory instability associated with swept-wing jet aircraft.
It is the combination of yawing and rolling (and sideslip motions
primary/main flight controls
Elevator. Controls the motion around the lateral axis, known as pitch/pitching.
Ailerons. Control the motion around the longitudinal axis, known as roll/rolling.
Rudder. Controls the motion about the normal/vertical axis, known as yaw/yawing.
adverse yaw
a yawing motion opposite to the turning/rolling motion of the aircraft. It is caused by the drag on the down-going aileron being greater than that on the up-going aileron. The imbalance of drag caused the aircraft to yaw around the normal/vertical axis. Since the yaw is adverse and is opposite to the turn, adverse yaw is detrimental to the aircraft’s performance.
spoilers
opening panels that extend from the upper surface of the wing and have the effect of spoiling/disturbing the airflow over the wing (drag), thereby reducing the lift.
three purposes of spoilers
- Roll control (usually in combination with the ailerons). Note that the primary purpose of spoilers is roll control.
- Air speed brakes
- Ground lift dumpers
Krueger flaps
leading-edge wing flaps used to increase the wing chamber and therefore increase the coefficient of lift maximum.
Fowler flaps
trailing-edge wing flaps (usually triple slotted) used to increase the wing area and chamber, which increases the coefficient of lift maximum for low flap settings, e.g., 1 to 25°. High flap settings increase drag predominately more than lift and therefore are used to lose speed and/or height, most commonly during an approach to land.
Moment
an aircraft’s tendency to rotate about its CG
Ground effect
the interference of the surface of the earth/water with the airflow patterns about an aircraft in flight
Lateral Stability
An aircraft’s tendency to return to its lateral level position along the longitudinal axis on the release of aileron in a sideslip.
Directional Stability
The tendency of the aircraft to regain it headings after it has been directionally disturbed (e.g. an induced yaw) from its straight path.
Longitudinal Stability
The ability of the aircraft to return to a stable pitch position along the lateral axis after disturbance
Straight-wing aircraft
Straight-wing aircraft experiences sonic disturbed airflow, resulting in a loss of lift at relatively low speeds,
Swept-wing design
Swept-wing design delays the airflow over the wing from going supersonic and allows the aircraft to maximize the jet engine’s potential for higher Mach cruise speed.
