Atmospheric Relationships

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Questions and Answers

Which of the following is true about the density of the atmosphere with increased altitude?

The density fluctuates

The density remains constant

The density increases

The density decreases (correct)

What happens to pressure with increased altitude?

Pressure remains constant

Pressure fluctuates

Pressure increases

Pressure decreases (correct)

Which of the following best describes relative humidity?

The amount of water vapor present in the atmosphere

The amount of water vapor required to saturate the air

The ratio of water vapor to air pressure

The ratio of actual water vapor to saturated water vapor (correct)

If the temperature remains constant and the absolute humidity decreases, what will happen to the relative humidity?

It will increase Signup and view all the answers

If the temperature increases and the absolute humidity remains constant, what will happen to the relative humidity?

It will decrease Signup and view all the answers

Which of the following statements about absolute humidity is true?

Absolute humidity is the amount of water vapor in a mixture of air and water. Signup and view all the answers

What happens to the amount of water vapor the air is capable of holding with increasing temperature, assuming constant pressure?

The amount of water vapor increases. Signup and view all the answers

When is air said to be saturated with water vapor?

When it has all the water vapor it can hold at the prevailing temperature and pressure. Signup and view all the answers

Which of the following best describes the dew point?

The temperature at which water vapor begins to condense on a surface Signup and view all the answers

Why do people wearing eyeglasses experience moisture collecting on their glasses when transitioning from cold outside air to a warm room?

The glasses are below the dew point temperature of the air in the room Signup and view all the answers

How is the dew point determined?

By cooling the air until water vapor condenses on its surface Signup and view all the answers

What is vapor pressure and how is it related to atmospheric pressure?

Vapor pressure is the portion of atmospheric pressure exerted by moisture in the air. There is a direct relationship between vapor pressure and atmospheric pressure. Signup and view all the answers

What is the dew point and how does it depend on vapor pressure?

The dew point is the temperature at which the air becomes saturated with water vapor. The dew point depends on the amount of water pressure present, which is directly related to vapor pressure. Signup and view all the answers

Explain the relationship between relative humidity, absolute humidity, and temperature.

The relative humidity is the ratio of the amount of water vapor in the air to the maximum amount it could hold at a given temperature. Absolute humidity is the actual amount of water vapor in the air. As temperature increases, the maximum amount of water vapor the air can hold also increases, causing the relative humidity to decrease if the absolute humidity remains constant. Signup and view all the answers

What are the four forces acting on an airplane during flight?

The four forces acting on an airplane during flight are lift, weight, thrust, and drag. Signup and view all the answers

What is lift and what creates it?

Lift is the upward force created by the wing of an airplane. Signup and view all the answers

What is drag and what causes it?

Drag is the friction caused by the air flowing around the airplane. Signup and view all the answers

What is Bernoulli's principle and how does it relate to the study of airflow and aviation concepts?

Bernoulli's principle states that as the velocity of a fluid increases, the static pressure of that fluid will decrease, provided there is no energy added or taken away. This principle is applied in the study of air as it flows through converging or diverging passages, and is relevant to aviation concepts. Signup and view all the answers

Who discovered the concept of subsonic airflow and pressure differentials?

Daniel Bernoulli, a Swiss physicist, discovered the basic concept of subsonic airflow and the resulting pressure differentials. Signup and view all the answers

What is a direct application of Bernoulli's principle?

A direct application of Bernoulli's principle is the study of air as it flows through either a converging or a diverging passage, and relating the findings to some aviation concepts. Signup and view all the answers

In the venturi, velocity decreases and static pressure increases.

False Signup and view all the answers

The air flowing over the top of the wing moves at a greater velocity than the air flowing along the bottom.

True Signup and view all the answers

The difference in static pressures between the top and bottom of the wing creates lift.

True Signup and view all the answers

According to Newton's third law, for every force there is an equal and opposite __________ force.

reacting Signup and view all the answers

The reacting force created by the air traveling around a wing and leaving the trailing edge is called __________.

lift Signup and view all the answers

To calculate lift based on Newton's third law, Newton's second law and the formula 'Force = Mass × Acceleration' would be used. The mass would be the weight of air flowing over the wing every second, and the acceleration would be the change in velocity the wing imparts to the __________.

air Signup and view all the answers

The air is forced to move in a downward direction when it travels around a wing and leaves the trailing edge because a force is required to make something change direction, according to Newton's third law. This force is the equal and opposite __________ force.

reacting Signup and view all the answers

Bernoulli's principle and Newton's third law can both be used to explain the lift being created by a wing. While Bernoulli's principle focuses on the change in __________ along the wing, Newton's third law emphasizes the equal and opposite reacting force.

pressure Signup and view all the answers

What is the angle of attack?

The angle between the chord line and the relative wind Signup and view all the answers

What is the aspect ratio of a wing?

The relationship between the span and the chord of the wing Signup and view all the answers

What happens to lift on a wing when the angle of attack becomes too great?

The lift is destroyed Signup and view all the answers

Which of the following devices can be considered an airfoil?

All of the above Signup and view all the answers

What is the purpose of the camber on an airfoil?

To increase velocity of the air on the top surface Signup and view all the answers

What is the angle between the chord line and the longitudinal axis of the airplane called?

Angle of incidence Signup and view all the answers

What is the purpose of washout in the design of an airplane's wing?

To improve the stall characteristic of the wing Signup and view all the answers

What is the relationship between aspect ratio and drag on a wing?

Higher aspect ratio produces less drag Signup and view all the answers

What is the initial flow of the boundary layer over the airfoil called?

Laminar layer Signup and view all the answers

What is the main reason for the boundary layer to adhere to the wing surface?

Air viscosity Signup and view all the answers

Which statement best describes the boundary layer as it approaches the center of the wing?

It loses speed due to skin friction and becomes thicker and turbulent. Signup and view all the answers

What is the point at which the boundary layer changes from laminar to turbulent called?

The transition point Signup and view all the answers

What happens to the transition point as the speed and angle of attack of the wing increase?

It tends to move forward. Signup and view all the answers

Which of the following best describes wingtip vortices?

The air beneath the wing flows over the wingtip and creates a spiral or vortex that trails behind the wingtip. Signup and view all the answers

What is the significance of wake turbulence caused by wingtip vortices?

It can cause a smaller airplane following too closely to be thrown out of control. Signup and view all the answers

Which flight control causes the airplane to move around the longitudinal axis?

Ailerons Signup and view all the answers

What is the center of gravity also referred to as?

Center of rotation Signup and view all the answers

What flight control causes the airplane to move around the lateral axis?

Elevator Signup and view all the answers

What is the movement described as when the airplane moves around the vertical axis?

Yaw Signup and view all the answers

Study Notes

Atmospheric Density & Pressure

Atmospheric density decreases with increased altitude.
Atmospheric pressure decreases with increased altitude.

Relative Humidity

Relative humidity describes the amount of moisture in the air relative to the maximum amount it can hold at a given temperature.

Relative Humidity Changes

If the temperature remains constant and the absolute humidity decreases, relative humidity will decrease.
If the temperature increases and the absolute humidity remains constant, relative humidity will decrease.

Absolute Humidity

Absolute humidity refers to the actual amount of water vapor present in the air.

Water Vapor Capacity

The amount of water vapor the air can hold increases with increasing temperature, assuming constant pressure.

Saturated Air

Air is considered saturated with water vapor when it can hold no more moisture at a given temperature and pressure.

Dew Point

Dew point is the temperature to which air must be cooled to become saturated with water vapor.
The dew point is an indication of the actual amount of moisture present in the air.

Moisture on Eyeglasses

When transitioning from cold outside air to warm room, moisture collects on eyeglasses because the warm room air is saturated with water vapor, and the cold eyeglasses cause the vapor to condense.

Dew Point Determination

Dew point can be determined using a psychrometer or a hygrometer.

Vapor Pressure

Vapor pressure is the partial pressure exerted by water vapor in the air.
Vapor pressure is directly proportional to the amount of moisture in the air.

Dew Point and Vapor Pressure

Dew point is dependent on vapor pressure.
Higher vapor pressure leads to a higher dew point.

Humidity Relationships

Relative humidity is a ratio of the actual amount of moisture in the air (absolute humidity) to the maximum amount it can hold at a given temperature.
Temperature influences the relationship between absolute and relative humidity.

Airplane Forces

The four forces acting on an airplane during flight are lift, drag, thrust, and weight.

Lift

Lift is the upward force that opposes gravity and keeps the airplane in the air.
It is generated by the shape of the wing, creating a pressure difference between the upper and lower surfaces.

Drag

Drag is the force that opposes the motion of an airplane.
It is caused by friction between the air and the airplane's surfaces.

Bernoulli's Principle

Bernoulli's principle states that as the speed of a fluid increases, its pressure decreases.
It relates to airflow over an airplane wing, causing lift by generating pressure differences.

Subsonic Airflow

The concept of subsonic airflow and pressure differentials was discovered by Daniel Bernoulli in the 18th century.

Bernoulli's Application

Venturi is an example of a direct application of Bernoulli's principle.

Venturi

In a venturi, the velocity of the fluid increases while the static pressure decreases.

Airflow Over a Wing

The air flowing over the top of the wing moves at a greater velocity than the air flowing along the bottom.
This difference in velocity creates a difference in pressure between the top and bottom of the wing, resulting in lift.

Newton's Third Law and Lift

According to Newton's third law, for every action, there is an equal and opposite reaction.
The reacting force created by the air traveling around a wing and leaving the trailing edge is called lift.

Lift Calculation

To calculate lift, Newton's second law and the formula 'Force = Mass × Acceleration' are used.
The mass is the weight of air flowing over the wing every second, and the acceleration is the change in velocity the wing imparts to the air.

Downward Force

The air is forced to move in a downward direction as it travels around a wing and leaves the trailing edge because a force is required to make something change direction, according to Newton's third law.
This force is the equal and opposite reacting force.

Lift Explained

Bernoulli's principle and Newton's third law both explain the creation of lift by a wing.
Bernoulli's principle focuses on the change in pressure along the wing, while Newton's third law emphasizes the equal and opposite reacting force.

Angle of Attack

Angle of attack is the angle between the chord line of the wing and the relative wind.

Aspect Ratio

Aspect ratio of a wing is the ratio of its wingspan to its average chord length.

Lift and Angle of Attack

As the angle of attack increases, lift increases until it reaches a critical angle.
Lift decreases if the angle of attack exceeds the critical angle, leading to stall.

Airfoil

Any surface designed to produce lift in a moving fluid, such as airplane wings, helicopter blades, and wind turbine blades, can be considered an airfoil.

Camber

Camber on an airfoil is the curvature of the upper and lower surfaces of the wing.
It helps generate lift at low speeds by increasing the pressure difference between the top and bottom surfaces.

Dihedral

Dihedral is the angle between the chord line of the wing and the longitudinal axis of the airplane.

Washout

Washout in the design of an airplane's wing is a slight decrease in angle of attack from the root of the wing to the tip.
It helps to improve the stall characteristics of the wing by ensuring that different sections of the wing stall at different angles of attack.

Aspect Ratio and Drag

A higher aspect ratio generally leads to lower drag, improving the efficiency of the wing.

Boundary Layer

The initial flow of the boundary layer over the airfoil is called laminar flow.

Boundary Layer Adherence

The boundary layer adheres to the wing surface due to the viscosity of the air.

Boundary Layer Behavior

As the boundary layer approaches the center of the wing, it loses its laminar flow and transitions to turbulent flow due to the increased friction and turbulence.

Transition Point

The point at which the boundary layer changes from laminar to turbulent is called the transition point.
The transition point shifts towards the leading edge of the wing as the speed and angle of attack increase.

Wingtip Vortices

Wingtip vortices are swirling masses of air generated at the tips of the wings due to the difference in pressure between the upper and lower surfaces.

Wake Turbulence

Wake turbulence caused by wingtip vortices creates hazardous conditions for aircraft following closely behind.

Flight Controls

The elevator is the flight control that causes the airplane to move around the longitudinal axis, affecting the pitch of the airplane.
The center of gravity is also referred to as the CG.
The ailerons are the flight control that causes the airplane to move around the lateral axis, affecting the roll of the airplane.
The rudder is the flight control that causes the airplane to move around the vertical axis, affecting the yaw of the airplane.

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Test your knowledge on the relationship between altitude, temperature, pressure, and density in the atmosphere. Learn why density decreases as altitude increases in this informative quiz.