Aviation 2100 OSU Final Exam

Four forces of flight

lift, thrust, weight, drag

Relationships between forces of flight

in straight and level, unaccelarated flight, lift= weight, thrust= drag. Flight is subjected to acceleration when forces aren't balanced

Distance

Feet, nautical miles 1.15 sm = 6067 ft

Speed

knots

force

Pounds, LBS

Power

horsepower, pounds of thrust, volts

Newton's Laws

A body will maintain its state of motion until a force is applied to it.

A. body will accelerate at any rate proportional to the force applied to it, and inversely proportional to its mass.

For every action there is an opposite reaction.

How is lift generated?

1. Air keeps moving in one direction until forced to change direction.

2. Force (action) must be applied to change direction.

3. A reaction is generated (lift).

What is an airfoil?

A slice of a wing

Leading edge

the front of the airfoil

trailing edge

the back of an airfoil

chord

straight line connecting the leading and trailing edge (imaginary)

Camber

curvature of an airfoil

Relative Wind

the average direction of the airflow impacting the airfoil

Angle of attack

angle between the relative wind and the wing chord line

What is Static Pressure?

pressure of the fluid at rest.

Dynamic Pressure

pressure exerted by a fluid in motion.

Pd= 1/2 p V^2

Equation of total pressure

(Pt)= Ps+ Pd

Bernouili's Principle

The mass of the fluid, flowing through a duct, remains the same regardless of the duct cross-section. if the area of the cross section decreases, the speed of flow must increase to keep the flowing mass the same. *For the water to pass through in the same amount of time, the water must speed up.

Bernouilli effect on airfoils

Air is being squeezed around the airfoil, therefore it must speed up, making dynamic pressure rise and static fall. Less static pressure on top, the movement of air underneath pushes the airfoil up.

Center of Pressure

The point at which a single resultant force (that replaces all forces of pressure distribution) is applied.

Pressure Distribtion

Changing the angle of attack causes the center of pressure to move over the airfoil.

Lift equation

Lift = (1/2)(density of air)(velocity ^2)(surface of wing)(coefficient of lift)

What affects air density?

-Altitude (Pressure- less pressure higher up means less dense air)

-Temperature (colder air is more dense)

-Humidity (lesser degree, more water vapor= less air)

What affects velocity?

Power, path, drag.

What happens to lift when speed is doubled?

lift quadruples if airspeed doubles

As angle of attack increases, what else increases?

Lift

Coefficient of Lift

How efficiently the wing converts dynamic energy to pressure energy. Dependent on the shape of the airfoil and the AOA

Critical Angle of Attack

The angle of attack at which an airfoil stalls (loses lift) regardless of the aircraft's airspeed, attitude, or weight.

Surface Area

Larger wing surface= more lift

Flaps

increases chord increased cambar. Increase the critical AOA, increase drag.

Clean Wing, dirty wing

clean wing= no flaps

dirty wind= flaps extended

Turbulent Flow

As the angle of attack increases, the boundary layer of the airflow begins to separate from the wing surface (detached airflow) and becomes turbulent rather than laminar.

Stall Characteristics are

-How the stall manifests

-How the airplane behaves during a stall

-How controllable is the airplane during stall recovery

Stall characteristics depend on

-Wing planform

-Wing washout

-Airplane Balance

Wing Planform

Shape of the wing when viewed from above

Rectangular Planform

- simple contruction, stalls at the root first, good for slow speed.

-high drag

elliptical planform

-uniform lift distribution, low drag

-complex structure, poor stall characteristics

Tapered Planform

-compromise between rectangular and elliptical. Easier than elliptical to manufacture, less drag than rectangular.

-stall characteristics similar to elliptical

Sweptback Planform

-delayed onset of sonic eave at high speed.

-stalls at wing tip first.

Delta Planform

-low drag in all flight regimes, very strong (able to handle high wing loads)

-stall characteristics similar to sweptback (wingtip first), requires high AOA at low speeds.

Wing Contamination

- changes the shape of the airfoil.

-anything that disrupts the smooth airflow reduces the coefficient of lift.

What must happen when coefficient of life is reduced?

to maintain lift equal to weight, airspeed must be increased.

What are wing contaminants?

snow, ice, frost

What is aspect ratio?

(span of the wing from tip to tip)/ length of the chord)

The higher the aspect ratio...

the lower the drag, better glide ratio. The more efficient the wing is.

Parasite Drag

caused by movements through the air

induced drag

byproduct of lift generation, any time the plane generates lift

What are the types of parasite drag?

form, skin friction, interference

Form Drag (shape drag)

caused by the shape of the obkect

Skin Drag

caused by rubbing of air molecules against a rough surface, happens with any surface, no matter how smooth. Depends on viscosity (density) of air and roughness of the surface. increases the faster we go

Interference Drag

Caused by mixing of airflow that causes a wake. Minimized by creating a smooth transition between joining surfaces.

Effect of Speed on Parasite Drag

parasite drag increases with the square of airspeed. if airspeed is doubles, parasite drag is increased by a factor of 4.

Wing Downwash

air that emits after the wing passes through

induced drag is

a byproduct of lift

how to increase induced drag?

increase the angle of attack

the total lift force is...

perpendicular to the effective relative wind

Components of lift

total lift has a vertical component (opposes weight) and rearward component (induced drag) added to drag

Where is induced drag applied?

center of pressure

Effects of speed on induced drag

the faster we go, the lower angle of attack we have. PARASITE DRAG increases with speed. Induced drag is inversely proportional to the square of airspeed. If airspeed is doubled, induced drag is REDUCED by a factor of 4.

Total Drag

The sum of parasite drag and induced drag

What is the Best Glide airspeed (BG)?

the airspeed at which total drag is minimum.

What determines the severity of wake turbulence?

Airspeed, weight, configuration

How to avoid wake turbulence?

What is ground effect?

caused by downwash and wingtip vortices blocked by ground. Total lift becomes more vertical. Effective lift increases, induced drag decreases

What are the consequences of ground effect?

-Takeoff: airplane may become airborne prior to reaching a safe takeoff speed. If climb is inititated too soon, the aircraft could suddenly lose lift and settle back onto the ground, or stall.

-Landing: Airplane will gain lift close to the ground, resulting in longer floating, especially if airspeed is higher than normal.

Thrust

Thrust is generated by the engines to neutralize drag

Propellor

generates thrust the same way a wing develops lift

Three axes of flight

longitudinal, lateral, vertical

Aileron

roll, longitudinal

elevator/stabilizer

pitch, lateral

rudder

yaw ,vertical

Primary flight controls

elevator, ailerons, rudder

secondary flight controls

flaps/slats, trims, air breaks/spoilers

Elevator

controls pitch about the lateral axis (nose up/down)

operated by yoke or stick

stabilizer: a moveable horizontal that combines elevator and trim

Pushing forward moves the elevator down and causes the tail to rise (nose drops).

Pulling aft moves the elevator up and causes the tail to lower (nose rises)

Ailerons

control roll (bank) about the longitudinal axis. operated by yolk or stick from left to right. Moving control to the left deflects the left aileron up and the right aileron down, causing bank to the left.

Rudder

controls yaw about the vertical axis.

Operated by the rudder pedals.

Pushing the right pedal deflects the rudder to the right and causes yaw to the right, pushing the left pedal deflects the rudder to the left and causes yaw to the left.

Slats

similar to slotted flaps, accelerate airflow to the top of the wing surface, thus delaying the separation of airflow. Increases camber.

Practical Application of Flaps

Increasing drag, enables a steeper approach angle to the runway, without the increase of airspeed. By increasing camber and surface area, increase the critical AOA, and enable slower landing or takeoff airspeed.

Slots

Permanent openings on the wing; function exactly like slats. The shape of the wing is not altered.

Spoilers

Lift destroyers. Cause a separation of airflow on the upper wing surface and increase drag. Function as air brakes.

Trim Tabs

fixed tabs, controllable tabs

Stability

inherent quality of an aircraft to correct for conditions that may disturb its equilibrium and to return or to continue on the original flight path.

Static Stability

Initial tendency of the airplane to return to its original position after being displaced

Dynamic Stability

Response of the aircraft to return to its original position over time, through a series of oscillations

What must you have for dynamic stability to exist?

Must have positive static stability to have dynamic stability at all

What is static stability?

the tendency of the airplane to return to the origina state after being displaced.

Positive Stability

Aircraft returns by itself. Nose goes up- will go right back down

Neutral Stability

Remains in displaced position, nose goes down, stays where it is

Negative Stability:

moves farther away, nose goes down, will continue to move down