Airplanes and Aerodynamics

VELOCITY v. G-LOADS - pg. 24

1. To determine the load acting on an airplane, multiply the load factor by the airplane's weight. -A level 60 degree bank imposes a load factor of approximately 2.0. 2. When an airplane is forced into an accelerated stall at twice its normal stalling speed, the load factor is approximately 4Gs. 3. Velocity/load factor charts have indicated airspeed on the horizontal axis and the load factor on the vertical axis. a. For various operation, one can plot the load factor and the possible impact on the airplane. Chart on 24. b. One can also plot gusts of various strengths against airspeed to find the resultant load factor. c. Point A to J is the stalling speed (Vs). d. Point C to H is the maneuvering speed (Va). e. Point D to G is the maximum structural cruising speed (Vno) f. Point E to F is the never exceed speed (Vne). g. The line from point C to point E represents the positive limit load factor. The lines from point I to point G and from point G to point F represent the negative limit load factor. The line from point E to point F represents teh never-exceed speed (Vne). --Exceeding the positive limit load factor, the negative limit load factor, or Vne would subject an airplane to structural damage or failure.

When the Center of Gravity in an airpane is located at the rear of the CG limit, the airplane

1. develops an inability to recover from the stall conditions, and 2. Becomes less stable at all airspeeds.

What frost does:

(A) Frost on wings disrupts the smooth airflow over the airfoil by causing early airflow separation from the wing. This: 1. Decreases lift and 2. Causes friction and increases drag. (B) Frost may make it difficult or impossible for an airplane to take off. (C) Frost should be removed before attempting to take off.

Bernoulli's Principle states:

(in part) the internal pressure of a fluid (liquid or gas) decreases at points where the speed of the fluid increases. i.e. high speed flow is associated with low pressure, and low speed flow is associate with high pressure. 1. This principle is applicable to an airplane wing because it is designed and constructed with a curve or camber. When air flows along the upper wing surface, it travels a greater distance in the same period of time (faster) than the airflow along the lower wing surface. 2. Therefore, the pressure above the wing is less than it is below the wing. This generates a lift force over the upper curved surface of the wing.

Stalls and spins.

1. An airplane can be stalled at any airspeed in any flight attitude. A stall results whenever the critical angle of attack is exceeded. 2. An airplane in a given configuration will stall at the same indicated airspeed regardless of altitude because the airspeed indicator is directly related to air density. 3. An airplane spins when one wing is less stalled than the other wing. -- To enter a spin, an airplane must always be stalled first.

AIRPLANE STABILITY

1. An inherently stable airplane returns to its original condition (position or attitude) after being disturbed. It requires less effort to control.

Ground effect must be considered during takeoffs and landings

1. If a pilot fails to understand the relationship between the aircraft and ground effect during takeoff, a hazardous situation is possible because the recommended takeoff speed may not be achieved. 2. due to the reduced drag in ground effect, the aircraft may seem capable of takeoff well below the recommended speed. As the aircraft rises out of ground effect with deficiency of speed, the greater induced drag may result in marginal initial ground performance. 3. In extreme conditions, the aircraft may be airborne initially with a deficiency of speed and then settle back to the runway.

AERODYNAMIC FORCES 4 Aerodynamic forces acting on an airplane during the flight are:

1. Lift: the upward acting force 2. Weight: the downward acting force 3. Thrust: the forward acting force 4. Drag: the rearward acting force

AIRPLANE TURN

1. The horizontal component of lift makes an airplane turn. -To attain this horizontal component of lift, the pilot coordinates rudder, aileron, and elevator. 2. The rudder of an airplane controls the yaw, i.e. rotation about the vertical axis, but does not cause the plane to turn.

Torque and P-Factor

1. The torque effect (left-turning tendency) is greatest at low airspeed, high angles of attack, and high power, e.g. on takeoff. 2. P-Factor (asymmetric propeller loading) causes the airplane to yaw to the left when at high angles of attack because the descending right side of the propeller (as seen from the rear) has a higher angle of attack (than the upward-moving blade on the left side) and provides more thrust.

3 Primary flight controls

Ailerons, elevator (stabilator), rudder

A.S.: Pitch Down

Airplanes (except a T-tail) normally pitch down when power is reduced (and the controls are not adjusted) because the downwash on the elevators from the propeller slipstream is reduced and elevator effectiveness is reduced. This allows the nose to drop.

Ailerons

Are control surfaces attached to each wing that move in the opposite direction from one another to control roll about the longitudinal axis. E.g. moving the yokes to the right causes the right aileron to deflect upward, resulting in decreased lift on the right wing. The left aileron moves in the opposite direction and increases the lift on the left wing. Thus, the increased lift on the left wing and decreased lift on the right wing cause the airplane to roll to the right.

Flaps

Attached to the trailing edge of the wing and are used during approach and landing to increase wing lift. This allows an increase in the angle of descent without increasing airspeed. (1) the most common flap used on general aviation aircraft today is the slotted flap. 2) When the slotted flap is lowered, high-pressure air from the lower surface of the wing is ducted to the upper surface of the flap, delaying airflow separation.

Movement of primary flight control surfaces

Changes affect the airflow and pressure distribution over and around the airfoil These changes affect the lift and drag produced and allow a pilot to control the aircraft about its 3 aces of rotation

Rudder

Controls movement of the aircraft about its vertical axis. 1) When deflecting the rudder into the airflow, a horizontal force is exerted in the opposite direction; this motion is called YAW. 2) Rudder effectiveness increases with speed because there is more airflow over the surface of the control device.

These forces are at equilibrium when the airplane is in unaccepted flight:

Lift=weight thrust=drag

Load Factor Examples

Load factor (or G units) is a multiple of the regular weight or, alternatively, a multiple of the force of gravity. 1. Straight-and-level flight has a load factor at 1.0 (verify on the chart at pg. 23) 2. A 60 degree level bank has a load factor of 2.0. Due to centrifugal force, the wings must hold up to twice the amount of weight. 3. A 50 degree level bank has a load factor of about 1.5.

LOAD FACTOR

Load factor refers to the additional weight carried by the wings due to the airplane's weight plus the centrifugal force.

Stabilator - Elevator

One piece horizontal stabilizer and elevator that pivots from a central hinge point

Load Factor Chart - Pg. 23

See pg. 23 Compute load factor by multiplying plane's weight by load factor that corresponds to the given angle of the bank.

Canard - Elevator

Similar to the horizontal stabilizer but is located in front of the main wings. An elevator is attached to the trailing edge of the canard to control pitch. The canard, however, actually creates lift and holds the nose up rather than the aft-tail design that prevents the nose from rotating downward.

Excess Load

The amount of excess load that can be imposed on an airplane's wings varies directly with the airplane's speed and the excess lift available. 1. At low speeds, very little excess lift is available, so very little excess load can be imposed. 2. At high speeds, the wings' lifting capacity is so great that the load factor can quickly exceed safety limits. An increased load factor will result in an airplane stalling at a higher airspeed. As bank angle increases, the load factor increases. The wings have to carry not only the airplane's weight but the centrifugal force as well.

Angle of attack

The angle between the wing chord line and the direction of the relative wind. The angle of attack at which a wing stalls remains constant regardless of weight, airplaine loading, etc.

A.S.: Longitudinal Stability

The location of the center of gravity (CG) with respect to the center of lift (or center of pressure) determines the longitudinal stability of an airplane. --changes in the center of pressure in a wing affects the aircraft's aerodynamic balance and control.

Elevator

The primary control device for changing the pitch attitude of an airplane, changing the pitch about the lateral axis. It is usually located on the fixed horizontal stabilizer on the tail of the airplane. E.G. Pulling back on the yoke deflects the trailing edge of the elevator up. This position creates a downward aerodynamic force, causing the tail of the aircraft to move down and the nose to pitch up.

What happens in ground effect:

The vertical component of the airflow around the wing is restricted, which alters the wing's upwash, downwash, and wingtip vortices.

FROST Frost forms

When the temperature of the collecting surface is at or below the dew point of the adjacent air and the dew point is below freezing. -- the water vapor changes its physical state through deposition and immediately forms as ice crystals on the wing surface.

Secondary flight controls

Wing flaps, leading edge devices, spoilers, trim systems

The reduction of wingtip vortices:

alters the spanwise lift distribution and reduces the induced angle of attack and induced drag. --Thus, the wing will require a lower angle of attack in ground effect to produce the same lift coefficient, or, if a constant angle of attack is maintained, an increase in the lift coefficient will result.

Ground effect may cause:

an airplane to float on landings or permit it to become airborne with insufficient airspeed to stay in flight above the area of ground effect. --an airplane may settle back to the surface abruptly after flying through the ground effect if the pilot has not attained recommended takeoff airspeed.

AOA. Wing chord line:

an imaginary straight line from the leading edge to the trailing edge of the wing.

Spoilers

are high-drag devices deployed form the wings to reduce lift and increase drag. They are found on gliders and some high speed aircraft.

Trim Systems

are used to relieve the pilot of the need to maintain constant back pressure on the flight controls. They include trim tabs, antiservo labs, and ground adjustable labs. (1) Trim tabs are attached to the trailing edge of the elevator. e.g. If the trim tab is set to the full nose up position, the tab moves full down. This causes the tail of the airplane to pitch down and the nose to pitch up.

AOA. Relative wind:

the direction of airflow relative to the wing when the wing is moving through the air.

GROUND EFFECT

the result of the interference of the ground (or water) surface with the airflow patterns about an airplane.

An airplane is affected by ground effect:

when it is within the length of the airplane's wingspan above the ground. The ground effect is most often recognized when the airplane is less than one-half the wingspan's length above the ground.