PT2 CHP5 Basic Aerodynamics Flashcards
What is the upward force that opposes weight?
Lift
What is the downward force that opposes lift?
weight
What is the forward force that opposes drag?
thrust
What is the rearward force that opposes thrust?
drag
In unaccelerated, level flight, describe the balance of all four forces
they are all equal
Lift = Weight
Thrust = Drag
What is weight?
- The result of gravity
- Applied at the Center of Gravity (CG)
- Always pointed towards the center of the Earth, opposite of Lift
- If the weight of the aircraft exceeds the maximum allowable weight, the airfoil won’t be able to generate enough lift to counteract the weight
- Will change throughout the flight due to fuel being burned
What is the Center of Gravity?
the point at which, if a string was attached, the object would be in equilibrium
What is Lift?
- The upward force produced by the wing (airfoil) on a fixed wing aircraft
- It is applied at the center of pressure (also called center of lift)
- Lift will always be perpendicular to the relative wind
The lift vector is always perpendicular to what?
the relative wind (parallel to the path of the aircraft, not the nose)
What part of the of airfoil does the air hit first and last?
The air hits the leading edge first then the trailing edge last
The line drawn through the leading edge and the training edge is know as what?
Chord line
What is the angle of attack?
The angle between the chord line and the relative wind
If lift is generated, what else is generated?
drag
What is the simplified lift equation?
L = V * α
V = velocity
α = angle of attack
What is the full lift equation?
L = (CL * ρ * V² * S)/2
CL = coefficient of lift
ρ = air density
V = velocity
S = surface area of the wing
What is the breakdown of each variable for the full lift equation?
(CL * ρ * V² * S)/2
CL = coefficient of lift
ρ = air density
V = velocity
S = surface area of the wing
What are the two principles that create lift?
- Newton’s 3rd law
- Bernoulli’s principle
What is Newton’s 3rd law?
For every action, there is an equal and opposite reaction
(the propeller moves air backward, and causes the airplane to move forward)
What is Bernoulli’s principle
As air moves through a venturi, the speed increases in the middle, which decreases pressure
- Lower pressure above the wing
- Higher pressure below the wing
* Pressure wants to move from high to low*
What is thrust?
- Created by the propeller that is attached to the motor
- ## The propeller is an airfoil that generates horizontal lift
What is the blade angle?
- Blade angle is measured between the chord line and plane of rotation
- Angle of attack is measured between the chord line and the relative wind
- If the aircraft is not moving forward, the blade angle equals the angle of attack
- As the aircraft moves forward, the relative wind changes
- As a result, the angle of attack changes as well
What is drag?
- Opposes thrust generated
- During unaccelerated flight, thrust = drag
What are the types of drag?
- Parasite drag
- (Lift) Induced drag
What is Parasite drag?
- The byproduct of flying through the air
- Increases as speed increases
What are the three types of parasite drag?
- Form drag
- Interference drag
- Skin friction drag
What is form drag?
- Based on the shape of the object (airplane)
What is the type of drag that is based on the shape of the object?
form drag
What is interference drag?
- Occurs at surfaces with sharp angles
- Varied currents meet and interact
What is the type of drag that is occurs at surfaces with sharp and varied angles when they meet and interact?
interference drag
What is skin friction drag?
aerodynamic resistance due to the contact of moving air with the aircraft surface
The aerodynamic resistance due to the contact of moving air with the aircraft surface is which type of drag?
skin friction drag
The byproduct of flying through the air is which type of drag?
parasite drag
What is (lift) induced drag?
- Generated as soon as lift is created
- Increases as speed decreases
- Greater angle of attack = greater induced drag
What type of drag is created as soon as lift is created, when speed decreases, and with a greater angle of a attack this drag increases as well?
Induced drag
Describe the relationship between drag and airspeed for parasite and induced drags.
- Parasite drag: increase as the speed increase
- Induced drag: increased at slower airspeed, reduces at higher airspeeds
- Parasite and induced drag added up equals total drag; in the middle is where the least amount of drag is created (Vglide)
Describe the relationship between Coefficient of drag or lift and angle of attack.
- The coefficient of drag increases as the angle of attack increases
- The coefficient of lift increases to a certain point as the angle of attack increases
- The point that the coefficient of lift decreases at a certain angle of attack is when the critical angle of attack has been reached and the airplane begins to stall
- The coefficients of drag and lift added up equal a curve that signify at which point is the best angle of attack for the best ratio of lift and drag
What are wingtip vortices?
- Created due to the difference of pressure below the wing (high pressure) and above the wing (low pressure)
- Due to pressure wanting to go from high to low, the high pressure moves upward to the low pressure, then outward at the wingtips
- the size of the aircraft will affect the size of the wingtip vortices
Wingtip vortices are greatest for which types of aircraft?
- Heavy: generating more lift = more wingtip vortices
- Clean: no flaps used (flaps allow aircraft to generate more lift while flying at slower speeds, if no flaps are used, then the aircraft will need to fly faster, which will create more lift and result in more wingtip vortices)
- Slow: will have a higher angle of attack, which will create more lift, which will create more wingtip vortices
Why does an aircraft in a clean configuration create wingtip vortices?
- No flaps are used
- Flaps allow aircraft to generate more lift while flying at slower speeds
- If no flaps are used, then the aircraft will need to fly faster, which will create more lift and result in more wingtip vortices
Why does an aircraft in a heavy configuration create wingtip vortices?
- More lift is being generated, which will result in more wingtip vortices
Why does an aircraft in a slow configuration create wingtip vortices?
- Will have a higher angle of attack
- Will create more lift
- Will create more wingtip vortices
When wingtip vortices are generated, where do they go?
They will “fall”/sink under the aircraft’s flight path
In order to avoid the area/path where the wingtip vortices will fall/sink under, how do you maneuver the aircraft when on takeoff?
- Fly above the other (larger) aircraft
- Wait several minutes to pass
In order to avoid the area/path where the wingtip vortices will fall/sink under, how do you maneuver the aircraft when on landing?
- Touchdown before the path where the other (larger) aircraft took off
When a large aircraft generates large wingtip vortices and there is wind, what do you need to consider?
The wind can push the wingtip vortices over into the other runway where the smaller airplane is trying to takeoff/land
What is ground effect?
The result of the interference of the surface of the Earth with the airflow patterns about and airplane
The result of the interference of the surface of the Earth with the airflow patterns about and airplane is known as what?
ground effect
When is ground effect most prevalent?
At an altitude that is less than the length of the wingspan above the ground
Describe the sensation of ground effect and why it occurs?
The aircraft will feel as if it’s floating at an altitude that is less than the length of the wingspan due to less lift but more induced drag
How will ground effect affect an aircraft when on takeoff?
The aircraft become airborne before the proper takeoff speed
How will ground effect affect an aircraft when on landing?
The aircraft will float on landing
What is one maneuver that ground effect can be used?
Soft field landing, get to the speed to be in ground effect until enough airspeed is gained and then full take off
