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Ultimate CFI Flashcards > Aerodynamics > Flashcards

Aerodynamics Flashcards

1
Q

What is the planform?

A

A planform is the shape of the wing as viewed from directly above.

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2
Q

What factors go into the planform design?

A
  1. Aspect Ratio
  2. Taper Ratio
  3. Sweepback
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3
Q

What is Aspect Ratio?

A

The ratio of wing span to wing chord. Can be thought of as the length of the wing divided by the width of the wing.

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4
Q

What occurs if the Aspect Ratio is increased?

A

An increase in aspect ratio decreases the drag, especially at high angles of attack. High aspect ratio results in smaller wingtips, which decreases induced drag.

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5
Q

What is an important factor that needs to be remembered if you increase the aspect ratio?

A

With an increase in aspect ratio, there is an increase in the length of span, with a corresponding increase in the weight of the wing structure, which means the wing must be heavier to carry the same load. Part of the gain is lost because of the increased weight. A compromise is necessary to obtain the best results.

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6
Q

Do most GA aircraft have relatively high or low aspect ratios?

A

Most GA aircraft have relatively high aspect ratios. This is because they are operated at high coefficients of lift because they are typically slower compared to other aircraft.

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7
Q

What type of planes require low aspect ratios?

A

Airplanes that are developed to operate at very high speeds demand greater aerodynamic cleanness and greater strength and require lower aspect ratios.

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8
Q

What does a low aspect ratio result in?

A
  1. High wing loadings.
  2. High stall speeds.
  3. Coefficient of lift is generally lower, so the plane must be flying faster to compensate.
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9
Q

What is taper ratio?

A

Taper is the decrease from wing root to wingtip in wing chord or wing thickness. Can be thought of as the ratio of the root chord to the tip chord.

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10
Q

What does tapering cause?

A

Tapering causes a decrease in drag and an increase in lift. Smaller wingtips = less induced drag.

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11
Q

What are the benefits of a rectangular wing?

A
  1. Simpler to produce and repair.

2. The roots usually stall first, providing more warning of a stall with aileron effectiveness.

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12
Q

What is sweepback?

A

The rearward slant of a wing, horizontal tail, or other airfoil surface.

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13
Q

How is sweepback beneficial?

A
  1. Helps planes flying at very high speeds.

2. Contributes to lateral stability in low-speed planes.

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14
Q

What is controllability?

A

The capability of an aircraft to respond to the pilot’s control, especially with regard to flight path and attitude. It is the quality of the aircraft’s response to the pilot’s control application when maneuvering the aircraft, regardless of its stability characteristics.

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15
Q

What is maneuverability?

A

The quality of an aircraft that permits it to be maneuvered easily and to withstand the stresses imposed by maneuvers. It is governed by the aircraft’s weight, inertia, size and location of flight controls, structural strength, and power plant. It is an aircraft design characteristic.

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16
Q

What is stability?

A

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

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17
Q

What is static stability?

A

Refers to the initial tendency, or direction of movement, back to equilibrium. In aviation, this refers to the aircraft’s initial response when disturbed from a given pitch, yaw or bank.

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18
Q

Describe the three different types of static stability.

A
  1. Positive Static Stability: The initial tendency of the aircraft to return to the original state of equilibrium after being disturbed.
  2. Neutral Static Stability: The initial tendency of the aircraft to remain in a new condition after its equilibrium has been disturbed.
  3. Negative Static Stability: The initial tendency of the aircraft to continue away from the original state of equilibrium after being disturbed.
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19
Q

What is dynamic stability?

A

Refers to the aircraft response over time when disturbed from a given pitch, yaw, or bank.

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20
Q

Describe the three different types of dynamic stability.

A
  1. Positive Dynamic Stability: Over time, the motion of the displaced object decreases in amplitude and, because it is positive, the object displaced returns toward the equilibrium state.
  2. Neutral Dynamic Stability: Once displaced, the displaced object neither decreases nor increases in amplitude.
  3. Negative Dynamic Stability: Over time, the motion of the displaced object increases and becomes more divergent.
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21
Q

What is longitudinal stability?

A

Longitudinal stability is the stability about the aircraft’s lateral axis of rotation.

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22
Q

What contributes to longitudinal stability?

A

The CG, CL, and tail. The CG and tail are downward forces, while the CL is an upward force. The CG and tail balance each other out, keeping the aircraft level.

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23
Q

What is lateral stability?

A

Lateral stability is the stability about the aircraft’s longitudinal axis of rotation.

24
Q

What design factors contribute to lateral stability?

A
  1. Dihedral
  2. Sweepback
  3. Keel Effect
  4. Weight Distribution
  5. Wing Location
25
Q

What is dihedral?

A

Dihedral is when the outer tips of the wings are higher than the wing roots. An upward angle of the wing.

26
Q

How does dihedral contribute to lateral stability?

A

When a gust causes a roll, a sideslip will occur. The wing slipping into the wind is subject to an increase in AOA and develops an increase in lift. The wing away from the wind is subject to a decrease in AOA and develops a decrease in lift. The changes in lift create a rolling moment that raises the windward wing.

27
Q

How does sweepback contribute to lateral stability?

A

10 degree of sweepback on a wing provides about 1 degree of effective dihedral. When a disturbance causes an aircraft to slip or drop a wing, the low wing presents its leading edge at an angle that is more perpendicular to the relative airflow. The low wing acquires more lift, rises, and the aircraft is restored to its original flight attitude.

28
Q

How does wing location effect lateral stability?

A

A high wing configuration can provide about 5 degrees of effective dihedral over a low wing configuration.

29
Q

Name the four turning tendencies.

A
  1. Torque Effect
  2. Gyroscopic Precession
  3. Spiraling Slipstream
  4. P-Factor
30
Q

Explain torque effect.

A

Involves Newton’s Third Law: For every action, there is an equal and opposite reaction.
While the internal engine parts & propeller are revolving in one direction, an equal force is trying to rotate the aircraft in the opposite direction.

31
Q

What does torque effect cause when airborne?

A

The aircraft to rotate about the longitudinal axis to the left.

32
Q

What does torque effect cause when on the ground?

A

It wants to roll the airplane to the left, but can’t since both wheels are on the ground. This causes the left main landing gear to have more weight applied to it, making the friction greater than the right landing gear. This causes the aircraft to yaw to the left.

33
Q

Explain spiraling slipstream.

A

The rotation of an aircraft propeller gives a corkscrew or spiraling rotation to the slipstream. The slipstream strikes the vertical fin on the left side, causing the aircraft to yaw towards the left.

34
Q

When is spiraling slipstream strong? Weak?

A

At high propeller speeds and low forward speeds, this spiraling rotation is very compact and exerts a strong sideward force on the aircraft’s vertical tail surface. As forward speed increases, the spiral elongates and becomes less effective.

35
Q

Explain gyroscopic precession.

A

Precession is the resultant action, or deflection, of a spinning rotor when a deflecting force is applied to its rim. When a force is applied, the resulting force takes effect 90 degrees ahead of and in the direction of rotation. The rotating propeller makes for a very good gyroscope. Any yawing around the vertical axis results in a pitching moment. Any pitching around the lateral axis results in a yawing moment.

36
Q

Explain P-Factor.

A

When an aircraft is flying with a high AOA, the “bite” of the downward moving blade is greater than the “bite” of the upward moving blade. This moves the center of thrust to the right of the propeller, causing a yawing moment to the left.

37
Q

Explain P-Factor more in depth in regards to velocity.

A

This asymmetric loading is caused by the resultant velocity. The right downward swinging blade, is passing through an area of greater resultant velocity than that affecting the left upward swinging blade. Since the propeller blade is an airfoil, increased velocity means increased lift.

38
Q

What is the general definition of load factor?

A

Load factor is the ratio of the total load acting on the airplane to the gross weight of the airplane.

39
Q

How is load factor measured?

A

Load factor is measured in the acceleration of gravity, or “Gs”. A LF of 3 means that the total load on the structure is 3x its gross weight, expressed as 3 G’s.

40
Q

Why is load factor important?

A
  1. It is possible for a pilot to impose a dangerous overload on the aircraft structures.
  2. An increased load factor increases the stalling speed and makes stalls possible at seemingly safe flight speeds.
41
Q

What are the category system, maneuvering load factor limits?

A
  1. Normal : 3.8 to -1.52
  2. Utility (mild acrobatics, including spins) : 4.4 to –1.76
  3. Acrobatic : 6 to –3
42
Q

How are vortices created?

A

Whenever the wing is producing lift, pressure on the lower surface of the wing is greater than the upper surface. The high-pressure air wants to reach the low-pressure air. The path of least resistance are the wing tips. The high-pressure air under the wing tends to flow laterally outward on the wingtip and swirl up to the top of the wingtip and equalize with the low-pressure air. This causes a clockwise vortex on the left wing and a counterclockwise vortex on the right wing.

43
Q

What governs the strength of vortices?

A

The strength of the vortex is governed by the weight, speed, and shape of the wing. The AOA directly affects the strength.
1. As weight increases, AOA increases.
2. A wing in the clean configuration has a greater AOA than with flaps.
3. As airspeed decreases, AOA increases.
As AOA increases, the pressure gradient steepens between the air below and above the wing, making the vortices stronger.

44
Q

What is the behavior of vortices?

A

Vortices tend to sink and travel with the wind. When larger aircraft vortices sink to the ground, they tend to move laterally (2-3 knots). A wind will decrease lateral movement of the upwind and increase movement of the downwind.

45
Q

How can you avoid wake turbulence when landing and taking off?

A
  1. Landing: Stay above/land beyond the preceding aircraft’s touchdown point.
  2. Takeoff: Lift-off before the preceding aircraft’s lift-off point.
46
Q

Name and give a general definition of the four forces of flight.

A
  1. Lift : The upward force created by the effect of airflow as it passes over and under the wing.
  2. Weight : Opposes lift, and is caused by the downward pull of gravity.
  3. Thrust : The forward force which propels the airplane through the air.
  4. Drag : Opposes thrust, and is the backward force, which limits the speed of the plane.
47
Q

Explain how lift is created using Newton’s Third Law.

A

Newton’s Third Law states, “For every action has an equal and opposite reaction”. As an airfoil has air flowing over the top and bottom of it, the air gets deflected off the trailing edge in a downward motion called “backwash”. The equal and opposite reaction is an upward motion, hence lift. Also as you increase the angle of attack, air is hitting the bottom of the airfoil at a more perpendicular angle, causing the airfoil to get deflected upwards. If you think of putting your hand outside a car window on the highway and subjecting it to an angle, your hand gets blown upwards.

48
Q

What is Bernoulli’s Principle?

A

Daniel Bernoulli did an experiment using a Venturi tube. He measured the internal pressure and velocity of a fluid going through the Venturi. What he discovered was that as the fluid increased in velocity, the internal pressure of that fluid decreased.

49
Q

How does Bernoulli’s Principle relate to lift?

A

The curvature or “camber” of the airfoil causes the airflow over the top surface to travel at a higher velocity than the lower surface. The air pressure on top of the airfoil is a lower pressure than the bottom since the airflow is at a higher velocity on the top than the bottom. High pressure always seeks out low pressure. The high pressure under the wing causes a force to push the wing up as it tries to get to the lower pressure on top of the wing. This is called a “pressure gradient”, and produces lift.

50
Q

What is an airfoil?

A

An airfoil is a surface designed to create an aerodynamic force by the use of an airstream.

51
Q

What is a chord line?

A

The chord line of an airfoil is when you draw an imaginary line from the leading edge to the trailing edge of the airfoil.

52
Q

What is angle of attack and why is it important?

A

The angle of attack is the angular distance between the chord line of the airfoil and the relative wind. It is important because it directly affects the coefficient of lift, which affects the product of lift. It is also important when discussing stalls.

53
Q

What is the relative wind?

A

The relative wind is the oncoming direction of airflow in respect to the airfoil. Relative wind is always opposite and parallel to the flight path.

54
Q

What factors affect lift?

A
  1. Density of the Air
  2. Surface Area of the Airfoil
  3. Coefficient of Lift
  4. Velocity
55
Q

What is the lift equation?

A

L = (1/2)rhoV^2S*CL

56
Q

Which factors affect the coefficient of lift?

A

The coefficient of lift is effected by the shape of the wing and the angle of attack.

Ultimate CFI Flashcards (9 decks)

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