Forces of Flight Flashcards
What are the forces of flight and what do they do?
LIFT: Created primarily by airflow over / under wing.
WEIGHT: Created by downward pull of gravity, and opposes lift.
DRAG: Backward, retarding force opposite to the direction of flight.
THRUST: Force created by the powerplant to propel the airplane forward.
Why are the four forces of flight vectors?
- A vector represents a magnitude and direction.
- For example, velocity has a speed and a direction of travel, so it’s a vector. Speed is a scalar quantity (direction isn’t included).
What is the lift equation?
Lift = CL * 1/2p * V2 x S
Lift = total lift the airplance is producing
CL =Coefficient of lift, function of the shape of the wing and the angle of attach
p = “roe” air density
V = velocity or airspeed
S = surface area of the wing
What factors of the lift equation can be controlled by the pilot?
- Angle of attack
- velocity or airspeed
When are the four forces of flight in equilibrium?
These four forces are in equilibrium if NOT
- accelerating,
- decelerating,
- climbing, or
- descending.
During un-accelerated flight the four forces of flight are…
The Four forces are Equal and opposite during un-accelerated flight.
What is weight?
- Weight is the downward force due to gravity acting on the mass that is the aircraft and its contents (F = mg).
- Weight will decrease during flight as fuel is burned.
What is drag? Drag acts in the opposite direction of What?
- Drag is the term describing resistance to airflow.
- Drag acts in the opposite direction to thrust
How is drag created?
- Drag is unavoidably created in the process of creating lift.
- Drag is also created by all outward parts of an airplane, or any object moving through air for that matter!
What are the 2 types of drag?
- Parasite drag
- Induced drag
What causes induced drag?
Induced drag results directly from the production of lift
Name the 3 types of parasite drag
Parasite drag is the sum of
- form drag,
- interference drag, and
- skin friction drag
What is form drag?
- When a structure (like an airplane) disrupts airflow, the air flows around the structure adhering to its surface for a short distance.
- When this airflow separates from the structure, it causes a turbulent wake (like the wake behind a speed boat).
- This turbulent wake results in form drag.
The amount of form drag is dependent on what?
the size and shape of the object disrupting the airflow
The ______ of an airfoil minimizes the wake, and, therefore, minimizes form drag
shape
What is the boundary layer?
A thin layer of air next to the surface of the wing in which airflow accelerates from zero to free air stream velocity
What are the two types of boundary layer?
Two types of boundary layer:
- A laminar flow layer in which air flows in smooth layers; usually found near leading edge of wing where friction has not overcome energy of airflow.
- Turbulent flow caused by friction overcoming energy of airflow and “tripping” airflow into turbulent flow.
- Turbulent flow has higher kinetic energy
The air touching the airfoil surface _______ and has a ______ ________
- The air touching the airfoil surface “sticks,” and has a zero velocity
- This layer transitions from zero velocity at the surface to the free air stream velocity
On a propeller, where is the angle of attack greater and why?
On a propeller the angle of attack is greater at the center because because the speed of that part of the propeller is slower than near the tips
A _____ angle of attack at a ______ airspeed can create the same amount of lift as a ________ angle of attack at a ________ airspeed
A larger angle of attack at a slower airspeed can create the same amount of lift as a shallow angle of attack at a higher airspeed
The _________ changes along the length of the propeller to produce ______________?
The angle of attack changes along the length of the propeller to produce a uniform amount of thrust along the blade
For an airplane with a constant pitch propeller, the power from the engine is controlled with the_____ and displayed on the _________
For an airplane with a constant pitch propeller, the power from the engine is controlled with the throttle and displayed on the tachometer in RPM
What is the drag curve?
- As airspeed increases, parasite drag increases.
- As airspeed decreases, induced drag increases
What is skin friction drag?
Caused by friction between the air and surface of an airplane
Skin Friction Drag
The _______ the boundary layer, the greater the skin friction drag
The thicker the boundary layer, the greater the skin friction drag
Skin Friction Drag
What happens if the surface is not completely smooth?
- If the surface is not completely smooth (rivets, dirt, frost, etc.), the air is “tripped” and separates from the surface causing turbulent flow.
- Turbulent flow results in a thicker boundary layer which results in more skin friction drag
Form drag occurs when?
Form drag occurs as a result of the wake formed at some point behind a moving object.
Form Drag
The ________the airflow remains “attached” to the surface (laminar flow) of the object, the smaller the resulting wake
The longer the airflow remains “attached” to the surface (laminar flow) of the object, the smaller the resulting wake
Form Drag Vs. Skin Friction Drag
When does one stop and the other begin?
Once the airflow completely separates from the surface (turbulent flow), skin friction drag is not generated, but that’s where the wake, and form drag, begins
Skin friction drag is the result of what?
Skin friction drag is the result of the air “sticking” to the surface of an object moving through it
Turbulent airflow within the boundary layer results in a ______ boundary layer = _______ skin friction drag.
Turbulent airflow within the boundary layer results in a much thicker boundary layer = more skin friction drag.
What’s the point?
But reducing ______ drag increases ______ drag
The point is that we don’t want either form or skin friction drag, but reducing one of these two types increases the other
But reducing skin drag increases form drag
The shape of an airfoil minimizes _____ drag, so _______ drag is the biggest concern.
The shape of an airfoil minimizes form drag, so skin friction drag is the biggest concern.
What are the four turning effects of propellers?
There are four turning effects due to propellers you need to know about:
Slipstream effect
Propeller torque effect
Gyroscopic effect
Asymmetric thrust (P-factor)
How do you compensate for the 4 left turning effects of the propeller?
Hold a little Right rudder
4 left turning effects of the propeller
What is torque effect?
The propeller turns clockwise. Using Newton’s Third Law - “every action has and equal oppostite reaction” the torque reaction is the airplane tends to rotate counter clockwise along the longitudinal axis
4 left turning effects of the propeller
gyroscopic procession?
Usually occurs in tail drags
The resultant force is 90 degrees from the applied force
airplace yaws left around the vertical axis
4 left turning effects of the propeller
propeller slip stream
- Most propellers rotate in a clockwise direction when viewed from the cockpit.
- Slipstream from the propeller not only flows rearward in a straight line, it also spirals rearwards around the fuselage.
- As this spiraling airflow strikes the rear of the aircraft on the tail it pushes the tail to the right.
- This is observed by the pilot as a yaw to the left.
4 left turning effects of the propeller
Asymmetric Thrust = P-Factor
- Occurs At high angle of attack
- the ascending and descending propeller blades have differing, individual angles of attack.
- The descending propeller blade will have a greater AoA as compared to the ascending blade
- The descending blade (the blade on the right for a propeller rotating clockwise as viewed from inside the cockpit)
- Because the descending propeller blade has a greater angle of attack (AoA) as compared to the ascending blade, it creates more thrust than the ascending blade.
- The greater thrust produced by the descending propeller blade results in a left yawing tendency.
4 left turning tendencies
Asymetric Thrust - P factor
Is most noticeable when?
P-factor is most noticeable at high angles of attack with high power settings
4 left turning tendencies
Why is Asymetric Thrust - P factor is not noticeable at lower airplane angles of attack
P-factor is not noticeable at lower airplane angles of attack as the blades will have almost equal blade angles of attack.
4 left turning effects of the propeller
With Asymmetric Thrust = P-Factor which propeller blade has the greater angel of attack?
The descending propeller blade (the blade on the right for a propeller rotating clockwise as viewed from inside the cockpit) will have a greater AoA as compared to the ascending blade.
Define the term aspect ratio
The term aspect ratio was invented to help describe the effect of changing the wing span and the wing area separately with respect to wing planform
What is the formula for aspect ration?
Aspect Ratio = wing span / average chord length
OR
Aspect Ratio = (wing span)2 / wing area
What is L/D Max?
- It is the airspeed at which the best range glide will occur
- (maximum distance forward per foot of altitude loss).
The Drag Curve
As airspeed increases, parasite drag________?
What happens to induced drag at high airspeeds?
As airspeed increases, parasite drag increases.
And induced drag decreases.
What is the minimum drag point?
The point where the parasite drag curve crosses the induced drag curve is the airspeed where TOTAL drag is minimized (L/Dmax).
What is ground effect?
- While flying very close to the ground (within a wing’s span), the airflow around the airplane is altered.
- This alteration results in a reduction in wingtip vortices, because the earth restricts the downward deflection of the air behind the wing
How does ground effect - effect takeoff?
- this means that an airplane is capable of lifting off at a slower airspeed than it can fly out of ground effect.
Ground Effect
What does a reduction in wingtip vortices do to relative wind?
lift vector?
Induced drag?
Reduction in wingtip vortices:
- -- Less “tilting” of the average relative wind downward and rearward - -- Less “tilting” of the lift vector - -- Less induced drag
How does Ground Effect landing?
On landing, ground effect may cause “floating,” which increases the landing distance
What do flaps do?
To increase lifting ability of wing.
To increase drag.
Flaps allow the wing to produce the required lift at a _____ airspeed when landing
Flaps allow the wing to produce the required lift at a lower airspeed when landing
Flaps also allow _______ descent for landing
Flaps also allow steeper descent for landing
Why and how would you use flaps for takeoff?
- Flaps are Primarily, a lift altering device.
- The first 1/3 of deflection will change the camber of the wing such that lift will increase more than drag will increase.
- Useful for maximum performance takeoffs
- This is where Bill said he would use them just a little for takeoff.
How should you recover from a stall?
- Lower angle of attack
- and apply maximum allowable power to break stall
- climb, because you have probably lost altitude
Explain how and why and airplan stalls(angle and airflow)
- An airplane stalls when it reaches it’s critcal angle of attack
- A stall is caused by separation of airflow from the wings upper surface which results in a rapid decrease of lift
Define Bernoulli’s principle(the formula and the meaning)
- static(still) pressure + dynamic(in motion) pressure = constant
- The total energy in a steadily flowing fluid stream is a constant along the flow path
- When the velocity of a fluid increases, it’s pressure decreases
Bernoulli’s principle
Explain what is happening.
When air moves over the wing….
- When air moves over the wing it must move faster over the top of the wing because the length of the top of the wing is longer
- The faster air means lower pressure on top of the wing
- the higher pressure below the wing and the lowerpressure above the wing causes lift
What is the angle of incidence?
The angle between the chord line and the longitutinal axis of the plane
