Aerodynamics and Atmospheric Pressure Quiz

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Questions and Answers

What is the pressure in the SRE when measured relative to atmospheric pressure?

44.7 psi (correct)

14.7 psi

30 psi

60 psi

How does temperature affect the density of air?

Temperature has no effect on density.

Density remains constant with temperature changes.

Density decreases as temperature increases. (correct)

Density increases as temperature increases.

What happens to the relative humidity (RH) of air when it is saturated?

RH is at its maximum. (correct)

RH fluctuates randomly.

RH becomes zero.

RH decreases significantly.

What instrument can be used to measure relative humidity?

Hygrometer Signup and view all the answers

What is the relationship between humidity and air density?

Higher humidity results in lower air density. Signup and view all the answers

If an aircraft flies through the air at 140 knots with a headwind of 30 knots, what is its ground speed?

110 knots Signup and view all the answers

At what rate does temperature generally fall from sea level upwards?

2 °C per 1000 ft Signup and view all the answers

How is relative humidity measured using the wet bulb method?

Comparing the readings of two thermometers, one wet and one dry. Signup and view all the answers

What is the role of a boundary layer in fluid flow around an aircraft?

It is the layer of fluid closest to a surface that slows down airflow. Signup and view all the answers

Which shape among the following would experience the least resistance in airflow?

Streamlined Form Signup and view all the answers

What happens to airflow around a non-streamlined object?

It becomes turbulent and creates eddies. Signup and view all the answers

How is a streamline defined in aerodynamic studies?

It's an actual path of a particle of fluid marked by arrows. Signup and view all the answers

What is the percentage of resistance associated with a flat plate shape in airflow?

100% Signup and view all the answers

What effect does the boundary layer have on the layers of molecules above it?

They move slower than the layers closer to the surface. Signup and view all the answers

Why are streamline patterns shown as smooth parallel lines?

They indicate consistent speeds and directions in airflow. Signup and view all the answers

What causes the airflow to swirl into eddies when it interacts with an object?

The object disrupts the laminar flow pattern. Signup and view all the answers

What happens to the center of pressure when the angle of attack increases?

It moves forward. Signup and view all the answers

In normal flight, what is the typical range of the angle of attack (AOA)?

2˚ to 4˚ Signup and view all the answers

Which wing shape is known to be aerodynamically the most efficient but difficult to manufacture?

Elliptical wing Signup and view all the answers

What is typically a characteristic of a rectangular wing?

Commonly found on older aircraft. Signup and view all the answers

Which type of wing planform is the most commonly used?

Tapered wing Signup and view all the answers

What is the primary design purpose of a sweepback wing?

To reduce drag at high speeds. Signup and view all the answers

Which of the following statements is NOT true about wings?

Elliptical wings are the easiest to manufacture. Signup and view all the answers

What is an airfoil primarily designed to do?

Provide lift while minimizing drag Signup and view all the answers

What distinguishes a symmetrical airfoil from an asymmetrical airfoil?

Asymmetrical airfoils create lift at zero angles of attack Signup and view all the answers

In low-speed aircraft, what type of camber is preferred?

Cambered shape that avoids excess lift and drag Signup and view all the answers

What does the mean camber line represent in an airfoil?

The imaginary line equidistant from the top and bottom surfaces Signup and view all the answers

What are the two parts into which camber is usually divided?

Upper camber and lower camber Signup and view all the answers

Why do medium and high-speed aircraft feature less curvature in their airfoil design?

To decrease drag due to increased speed Signup and view all the answers

At small angles of attack, which type of airfoil creates lift?

Only asymmetrical airfoils Signup and view all the answers

How is the chord line defined in the context of an airfoil?

The line connecting the leading edge to the trailing edge Signup and view all the answers

What is the boundary layer?

A layer of air that clings to the surface of an object. Signup and view all the answers

What characterizes laminar flow in the context of the boundary layer?

Air speed changes gradually with increasing distance from the surface. Signup and view all the answers

What happens to the airflow in a turbulent flow?

The flow becomes random and no longer adheres to the object's shape. Signup and view all the answers

What is meant by the transition point in the context of flow types?

The point where laminar flow changes to turbulent flow. Signup and view all the answers

How does friction affect the airflow in the boundary layer?

It causes each layer of air to experience retardation until a certain distance from the surface. Signup and view all the answers

What distinguishes turbulent flow from laminar flow?

Turbulent flow is characterized by flow separation and randomness. Signup and view all the answers

What is the profile of the airflow in the boundary layer close to the surface of an object?

The airflow comes to rest next to the surface. Signup and view all the answers

Which of the following statements about the boundary layer is false?

The boundary layer is a static layer of air that does not change. Signup and view all the answers

What is the characteristic of the stagnation point in relation to airflow?

It has zero airflow velocity. Signup and view all the answers

How does changing the angle of attack affect the stagnation point?

It moves down relative to the leading edge with increased angle. Signup and view all the answers

What is stagnation pressure in the context of aerodynamics?

The pressure at the stagnation point. Signup and view all the answers

Which direction does airflow under the wing generally move?

From root to tip. Signup and view all the answers

What results from the airflow dynamics around an aerofoil?

The creation of a rotating flow. Signup and view all the answers

What describes the term 'Pitot pressure'?

The sum of static pressure and dynamic pressure. Signup and view all the answers

What is NOT a characteristic of a stagnation point?

It is always located at the leading edge. Signup and view all the answers

Study Notes

Aerodynamics Overview

Aerodynamics is the study of how air flows around objects.
Understanding airflow is crucial for aircraft design and flight.

Learning Outcomes

Students should be able to describe aerodynamics.
Students should be able to explain airflow around objects.
Students should understand basic aerodynamics terminology.
Students should know about airfoil characteristics.

The Atmosphere

Air is assumed to be dry.
Sea-level pressure is 1013.25 mb (milibar).
Sea-level temperature is 15°C.
The temperature lapse rate is 1.98°C per 1000 ft up to 36,000 ft.
The temperature remains constant above 36,000 ft.
Gravity is 9.81 m/s² at sea level.
The temperature lapse rate above 65,800 ft is approximately +0.33°C per 1000 ft to -44.6°C at 105,000 ft.

Airspeed

Airspeed is the aircraft's speed through the air.
Airspeed is not always the same as ground speed.
Ground speed considers wind.

Airflow Around a Body

When an object moves through air, the air molecules are disturbed.
The flow of air around the body affects flight.

Pressure

Pressure is force per unit area, measured in Pa, psi, or mb.
Sea-level pressure is 1013.25 mb (14.7 psi).
Pressure decreases with altitude non-linearly.
Pressure measurements are absolute pressure.
Gauge pressure will measure above atmospheric pressure.

Density

Density is mass per unit volume, measured in kg/m³.
Sea-level density is 1.2 kg/m³.
Density changes with temperature and relative humidity.
Lower temperature and lower relative humidity increase density.

Temperature

Sea-level temperature is 15°C.
Temperature decreases at a rate of about 2°C per 1000 ft.
High humidity lowers density.
Low humidity raises density

Humidity

Relative humidity (RH) falls with altitude.
RH is the amount of moisture in a volume of air compared to the maximum it can hold (saturated).
Higher humidity corresponds to lower density.
RH can be measured using wet-bulb and dry-bulb thermometers.

Boundary Layer

Layer of air next to a surface.
Molecules close to the surface are slowed by collisions.
Air speed close to the surface is slowed compared to free stream.
Layers in the boundary layer move faster than those closer to the surface.

Laminar Flow

Smooth, parallel airflow.
Follows the shape of the object without separation.
Airspeed changes gradually as distance from the surface increases.

Turbulent Flow

Rough, unsteady flow.
Airflow separates from the object.
Random airflow patterns.

Transition Region

Region between laminar and turbulent flow.

Free Stream Flow

The flow of air far from the object.
Clean flow unaffected by the object’s presence.

Upwash and Downwash

Changes in airflow direction at the leading and trailing edges.
Caused by airfoil design and angle of attack.

Wingtip Vortices

Rotating airflows behind the wing.
Created by high pressure on the bottom of the wing pushing air to the low-pressure area on top.

A380 Wake Turbulence

Large vortices produced by very large aircraft such as the Airbus A380.

Stagnation Point

Region where air is brought to rest at the leading edge.
Airflow velocity is zero relative to the airfoil.
Stagnation point stays constant relative to the leading edge regardless of angle of attack.

Stagnation Pressure

Pressure at the stagnation point.
This pressure is the same as total pressure (or Pitot pressure).
Total pressure = dynamic pressure + static pressure

Airfoil Characteristics

Shape of wings or blades.
Provides lift while minimizing drag.
Key features include leading edge, trailing edge, camber, chord, maximum thickness.
Symmetrical airfoils produce no lift at zero angle of attack.

Camber

Upward and downward curvature of the airfoil.
Critical in producing lift.

Mean Camber Line

Imaginary line halfway between upper and lower surfaces.

Chord Line

Straight line connecting the leading and trailing edges.

Chord

Distance along the chord line from leading to trailing edge.

Mean Aerodynamic Chord (MAC)

Imaginary chord length representing the average chord of a non-rectangular wing.

Centre of Pressure (C of P)

Point where the total force generated by air pressure acts.
Position changes with angle of attack.

Wing Shape

Common wing shapes include rectangular, elliptical, tapered, sweptback, and delta.

Aspect Ratio

Ratio of wingspan to mean chord.

Wing Area

The surface area of the wing.

Angle of Attack

Angle between the chord line and the oncoming airflow.
Positive angle of attack produces lift.

Separation and Turbulence

Flow separation occurs when the airflow detaches from the surface.
Turbulent flow happens at high angles of attack or low speeds.

Wash In & Wash Out

Variations in angle of attack along the wing span.
Causes wing tips to stall before root.
Maneuverability issue.

Finess Ratio

Ratio of wing length to wing breadth.

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Description

Test your knowledge on the principles of aerodynamics and atmospheric pressure. This quiz covers topics such as humidity, airflow resistance, and the effects of temperature on air density. Perfect for students studying physics or aviation science.