Chapter 1,3 and 6

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Questions and Answers

What is the definition of engineering design?

A random generation of specifications for artifacts without considering form and function

A haphazard process of artifact creation without any planning

A systematic, intelligent generation and evaluation of specifications for artifacts whose form and function achieve stated objectives and satisfy constraints (correct)

A trial and error process to create artifacts without any evaluation

What is the primary focus of conceptual design in aircraft design?

Configuration management, size, weight, and performance (correct)

Finalizing the manufacturing process

Detailed analysis of structural components

Testing the aircraft's propulsion system

What disciplines are involved in the preliminary design phase of aircraft design?

Only aerodynamics

Structures, controls, landing gear, etc. (correct)

Only propulsion systems

Electrical engineering and computer science

What is the role of a designer in aircraft design?

Creating the geometric description of an artifact to be built Signup and view all the answers

How many phases are described in generic engineering design?

3 Signup and view all the answers

What does the term 'configuration arrangement' refer to in aircraft design?

The type of tail, wing, etc. completed during conceptual design Signup and view all the answers

What is the iterative process primarily focused on during conceptual design in aircraft design?

Weight and size Signup and view all the answers

In which discipline is a designer not required to have knowledge while creating the geometric description of an artifact in aircraft design?

Marketing strategies Signup and view all the answers

What does aeronautical engineering primarily focus on?

Designing aircraft and spacecraft Signup and view all the answers

What is the lecturer's name for AERO470: Aircraft Design Laboratory Lecture 1: Introduction?

Dr Rafic Ajaj Signup and view all the answers

What percentage of a new aircraft cost can be attributed to avionics?

40% Signup and view all the answers

Which of the following is not part of the avionic systems mentioned in the text?

Engine control Signup and view all the answers

What is the purpose of wing flaps on an aircraft?

To provide extra lift during takeoff and landing Signup and view all the answers

Where are spoilers or air brakes located on an aircraft?

On the upper surfaces of wings Signup and view all the answers

What is the purpose of spring tabs on an aircraft?

To help pilot balance the plane without using a primary control surface Signup and view all the answers

Which group of controls includes ailerons, elevators, and rudder?

'Primary' group Signup and view all the answers

Which of the following is a type of civil aircraft?

Business jets Signup and view all the answers

What percentage of the total weight does the landing gear of an aircraft typically weigh?

4-5% Signup and view all the answers

Which type of engine is suitable for high-altitude, high-speed flight and has high fuel consumption and noise?

Turbojet engines Signup and view all the answers

What materials are commonly used for aircraft structures?

Aluminum, titanium, and carbon fiber Signup and view all the answers

What are the primary considerations in the design of aircraft wings?

$Lift$, $drag$, and $wing$ $loading$ Signup and view all the answers

Which organization regulates aviation safety requirements in Europe?

$EASA$ Signup and view all the answers

Which type of engine is suitable for medium-speed flight and has low fuel consumption and weight?

Turboprop engines Signup and view all the answers

What are the primary considerations in the design of aircraft engines?

Power, weight, efficiency, and fuel consumption Signup and view all the answers

Which type of engine uses a large fan for much of the thrust and is lighter and simpler than turbojet engines?

Turbofan engines Signup and view all the answers

What kind of testing is involved in aircraft design to optimize aerodynamic performance?

Wind tunnel testing Signup and view all the answers

What is the lift curve slope for a theoretical thin airfoil?

$2\pi$ Signup and view all the answers

What is the primary purpose of NACA four-digit airfoils?

Indicate percent camber, location of max. camber, and max. thickness Signup and view all the answers

What is the relationship between lift force and flight direction?

Perpendicular Signup and view all the answers

What is the equation for nondimensional section lift for a 2D airfoil?

$qcC_l = \frac{1}{2}\rho V^2 cC_l$ Signup and view all the answers

What does the pitching moment coefficient (CM) represent for a 3D wing?

Moment about the quarter-chord point normalized by dynamic pressure and wing chord length Signup and view all the answers

What does the term 'laminar bucket' refer to in airfoil design?

A range of Cl for which the flow remains laminar over most of the airfoil Signup and view all the answers

What are NACA four-digit airfoils mostly used for?

Tail sections Signup and view all the answers

What is the primary influence of a 10-degree aft wing sweep on dihedral angle?

It creates an additional effective dihedral of 1 degree Signup and view all the answers

What is the primary purpose of high-mounted wings in aircraft design?

They provide increased dihedral Signup and view all the answers

What is the impact of rounded wing tips on drag?

They create more drag due to induced flow Signup and view all the answers

What is the main disadvantage of V-tail configuration in aircraft design?

Complex control mechanism and adverse roll-yaw coupling Signup and view all the answers

Which type of tail design is necessary for trim, stability, and control in aircraft?

T-tail, cruciform tail, and H-tail Signup and view all the answers

What is the impact of negative (anhedral) dihedral angle on aircraft stability?

It causes instability during turns Signup and view all the answers

What is the primary consideration for deciding the wing vertical location in aircraft design?

Operating environment and practicality Signup and view all the answers

What is the primary purpose of wing sweep in aircraft design?

To reduce the effects of transonic and supersonic flow Signup and view all the answers

How does airfoil thickness ratio (t/c) affect drag and weight in aircraft design?

Drag increases with increasing thickness due to separation, and structural weight increases with decreasing thickness Signup and view all the answers

What is the purpose of variable sweep in aircraft design?

To provide both swept and unswept wing benefits Signup and view all the answers

How does taper ratio affect lift distribution along the wing span?

Minimum drag occurs when the lift is distributed in an elliptical fashion Signup and view all the answers

What is the role of twist angles in aircraft design?

To achieve elliptic lift distribution and prevent tip stall Signup and view all the answers

What is the purpose of a Y-tail in aircraft design?

To reduce complexity and provide added rudder control Signup and view all the answers

Why might a twin tail be used in aircraft design?

To keep rudders away from the aircraft centerline and prevent ineffectiveness at high AOA Signup and view all the answers

What is the significance of tail positioning in stall recovery?

Low tails are best for stall recovery, especially for T-tail aircraft Signup and view all the answers

How should the horizontal tail sweep angle be selected to prevent stalling?

$5$ deg more than wing sweep angle Signup and view all the answers

For what type of aircraft is vertical tail sweep typically less than $20$ deg?

Low-speed aircraft Signup and view all the answers

How is tail surface area determined in aircraft design?

By considering historical guidelines for aspect ratio and taper ratio Signup and view all the answers

What is the primary purpose of a boom-mounted tail in aircraft design?

To allow utilization of pusher propellers or heavy jet engines located near CG Signup and view all the answers

What is a ring tail in aircraft design?

A round airfoil section acting as both horizontal and vertical tail surfaces Signup and view all the answers

How is the thickness ratio of a vertical tail determined?

Using historical guidelines for that of wings' thickness ratio Signup and view all the answers

What is the primary purpose of a V-n diagram in aircraft design?

To depict aircraft limit load factor as a function of airspeed Signup and view all the answers

What is the multiplier used on the limit load to determine the design load for aircraft?

Safety factor Signup and view all the answers

What does the term 'load factor' (n) express in aircraft maneuvering?

Maneuvering of an aircraft as a multiple of gravitational acceleration (g) Signup and view all the answers

What is the maximum lift load factor at stall speed for an aircraft?

$1.0$ Signup and view all the answers

What determines the maximum load factor at low speeds for an aircraft?

Aircraft maximum CL (coefficient of lift) Signup and view all the answers

6

Aircraft maximum CL. Signup and view all the answers

What does V-n diagram depict in aircraft design?

Aircraft limit load factor as a function of airspeed. Signup and view all the answers

What determines the maximum lift load factor at stall speed for an aircraft?

1.0. Signup and view all the answers

What determines the maximum load factor at low speeds for an aircraft?

Aircraft maximum CL (coefficient of lift). Signup and view all the answers

What is used to determine the design load for an aircraft?

Safety factor. Signup and view all the answers

What is the formula used by the FAA to determine the maneuver load factor for aircraft under 50,000 lbs?

$2.5 - (0.001\times W/S)$ Signup and view all the answers

At what speed does high AOA mark the slowest speed at which the maximum load factor can be reached without stalling?

Vc Signup and view all the answers

What represents the maximum allowed dynamic pressure for subsonic aircraft in dive speed (Vdive)?

$2\times V_c$ Signup and view all the answers

What affects the change in lift and load factor under strong gust or turbulence?

Statistical gust alleviation factor, K Signup and view all the answers

Where do critical loads occur based on information from the V-n diagram?

At velocities of high AOA and max q Signup and view all the answers

What factors are considered for finding the best material for aircraft structures?

Yield and ultimate strength, stiffness, density, fracture toughness, fatigue crack resistance, creep, corrosion resistance, and temperature limits Signup and view all the answers

At what stress level does stress corrosion occur in materials exposed to moisture, salt, etc.?

1/10th the ultimate stress Signup and view all the answers

What does 'producibility' indicate in terms of material selection?

Both ease of fabrication and material availability Signup and view all the answers

Which of these factors is not considered when finding the best material for aircraft structures?

Aircraft fuel consumption Signup and view all the answers

Which material was used in all early aircraft but is not popular anymore?

Wood Signup and view all the answers

Which material has the highest strength-to-weight ratio and stiffness better than aluminum?

Titanium Signup and view all the answers

Which material is suitable for hypersonic and re-entry vehicles, but is heavy and difficult to form?

Ni alloys Signup and view all the answers

What type of composites have short strands of fibers randomly distributed in the matrix?

Whisker-reinforced composites Signup and view all the answers

What is the primary issue with composites in terms of carrying concentrated loads?

They cannot carry concentrated loads at all Signup and view all the answers

What is the primary role of the core in a sandwich construction using composites?

Carry shear loads and loads perpendicular to the faces Signup and view all the answers

What is a major drawback of composites in terms of damage inspection?

Mild damage occurs internally, making it impossible to inspect Signup and view all the answers

What is the primary reason for using a structural sandwich with face sheets and a core in aircraft construction?

To carry tension and compression loads due to bending Signup and view all the answers

What is anisotropic material in the context of aerospace materials?

A material that has different properties in different directions Signup and view all the answers

What is the primary issue with composites in terms of material properties?

Material properties are sensitive to manufacturing process, temperature, and exact ratio of fiber to composite Signup and view all the answers

What is the primary purpose of a V-n diagram in aircraft design?

To depict aircraft limit load factor as a function of airspeed Signup and view all the answers

What does the term 'load factor' ($n$) express in aircraft maneuvering?

It expresses maneuvering of an aircraft as a multiple of gravitational acceleration Signup and view all the answers

What determines the maximum load factor at low speeds for an aircraft?

Aircraft maximum CL Signup and view all the answers

What represents the maximum allowed dynamic pressure for subsonic aircraft in dive speed ($V_{dive}$)?

$q_{max} = 1/2 \rho V_{dive}^2$ Signup and view all the answers

What is the formula to determine the design load for an aircraft?

$D = 1.5L$ Signup and view all the answers

What is the multiplier used on the limit load to determine the design load for aircraft?

$1.5$ Signup and view all the answers

What are typical maneuvering load factors experienced by fighters during flight?

Up to 9 times the level flight conditions Signup and view all the answers

What does a V-n diagram depict at stall speed?

Max. lift load factor is 1.0, meaning aircraft cannot fly below that speed. Signup and view all the answers

What does a V-n diagram illustrate at low speeds?

The maximum load factor constrained by aircraft maximum CL. Signup and view all the answers

What does 'ultimate load' represent in aircraft design?

The highest load an aircraft is designed to withstand. Signup and view all the answers

What is the formula used by the FAA to determine the maneuver load factor for aircraft under 50,000 lbs?

$n = 2.5 + 15000/(W + 10000)$ Signup and view all the answers

What represents the maximum allowed dynamic pressure for subsonic aircraft in dive speed ($V_{ ext{dive}}$)?

$1.5q_{ ext{max}}$ Signup and view all the answers

At what stress level does stress corrosion occur in materials exposed to moisture, salt, etc.?

$1/10$th the ultimate stress Signup and view all the answers

What does 'producibility' indicate in terms of material selection?

Ease of fabrication Signup and view all the answers

What factors are considered for finding the best material for aircraft structures?

All of the above Signup and view all the answers

Where do critical loads occur based on information from the V-n diagram?

@High AOA and max q velocities Signup and view all the answers

What is the primary purpose of wing sweep in aircraft design?

To delay the onset of shock waves at high speeds Signup and view all the answers

What is high AOA indicative of in an aircraft?

Slowest speed at which maximum load factor can be reached without stalling Signup and view all the answers

What determines the required maneuver load factor at all speeds up to Vc?

FAA formula unless limited by stall Signup and view all the answers

What are gust loads primarily affected by on an aircraft?

Statistical gust alleviation factor (K) Signup and view all the answers

Study Notes

The aircraft design process includes five phases: concept, configuration, detail design, production, and full-scale development.
Aircraft can be civil or military types. Civil types include passenger aircraft, cargo planes, business jets, agricultural aircraft, and light aircraft for recreational use. Military types include fighter planes, bombers, trainers, reconnaissance planes, and military cargo planes.
Other types of aircraft include rotorcraft and vertical takeoff and landing (VTOL/STOL) aircraft.
Aircraft structure must be strong, stiff, resistant to fatigue and corrosion, and lightweight.
Flying and stabilizing surfaces include wings, tails, and canards. Wings generate lift and carry the aircraft, while tails and canards ensure stability.
Landing gear supports the aircraft on the ground and weighs about 4-5% of the total weight.
Aircraft propulsion can come from air-breathing engines or rockets. Air-breathing engines include piston engines, four-stroke engines, turbojet engines, turbofan engines, and turboprop engines.
Turbojet engines are suitable for high-altitude, high-speed flight and have high fuel consumption and noise.
Turbofan engines use a large fan for much of the thrust and are lighter and simpler than turbojet engines. They are available in a wide range of sizes and have high efficiency.
Turboprop engines are suitable for medium-speed flight and have low fuel consumption and weight. They are powered by a jet engine and have high efficiency.
Structural materials for aircraft include aluminum, titanium, and carbon fiber.
The design of aircraft wings involves considerations for lift, drag, and wing loading.
The design of aircraft engines involves considerations for power, weight, efficiency, and fuel consumption.
Aircraft testing includes wind tunnel testing, flight testing, and structural testing.
Military aircraft often have more complex designs and require more advanced technology due to their unique requirements.
Aircraft design must consider factors such as aerodynamics, propulsion, structures, and materials.
The design process involves collaboration between engineers, designers, and manufacturers to ensure the aircraft can be built on time and at the estimated cost.
Aircraft design must also consider regulatory requirements, such as those from the Federal Aviation Administration (FAA) and European Aviation Safety Agency (EASA).
Aircraft design involves the use of computer-assisted design (CAD) software and wind tunnel testing to optimize aerodynamic performance.
Aircraft design must consider maintenance and repair costs, as well as the costs of fuel and other operating expenses.
Aircraft design involves the use of materials such as carbon fiber, aluminum, and titanium to optimize strength and weight.
Aircraft design must consider safety features such as fire suppression systems, emergency power systems, and backup systems.
Aircraft design involves the use of advanced technology such as fly-by-wire systems, digital avionics, and aerogels for insulation.
Aircraft design must consider the needs of the passengers or cargo, such as comfort, temperature control, and cargo handling systems.
Aircraft design involves the collaboration of various teams, including engineering, manufacturing, marketing, and finance, to bring the aircraft to market.
Aircraft design is an ongoing process, with regular updates and improvements made to existing designs and the development of new technologies.
Airfoils are designed for maximum lift with laminar flow and minimal stall at the trailing edge.
The design lift coefficient (Cl) is a key factor in selecting an airfoil for an aircraft.
For level flight, the lift equals the weight, with wing lift coefficient equal to airfoil lift coefficient.
To select the airfoil at conceptual design, look up catalogs of Cl-Cd curves for airfoils with the desired Cl value.
Three types of stall occur in airfoils: trailing edge stall in fat, round leading edge airfoils, and leading edge stall in thinner airfoils.
To prevent and delay stall, use different angle of attacks (AOA) throughout the wing, twist the wing, and incorporate different airfoils with varying stall angles.
Airfoil thickness ratio (t/c) affects drag, lift, stall, and weight. Drag increases with increasing thickness due to separation, and structural weight increases with decreasing thickness.
Thickness is usually selected based on the trends in the figure, and may be varied from root to tip.
Wing geometry includes a trapezoidal wing shape with a root airfoil at the centerline of the aircraft. The wing shape depends on aspect ratio, taper ratio, and sweep.
High aspect ratio wings have greater wing span and efficiency, but also increased wing weight.
Wing sweep is used to reduce the effects of transonic and supersonic flow, with swept wings providing structural divergence issues.
Variable sweep provides both swept and unswept wing benefits, but is complex to design and adds weight.
Taper ratio (tip chord to centerline root chord) affects lift distribution along the wing span. Minimum drag occurs when the lift is distributed in an elliptical fashion.
Twist angles are used to achieve elliptic lift distribution and prevent tip stall, with usual values of 0-5 degrees and 3 degrees typical.
Wing incidence is the pitch angle of the wing relative to the fuselage, chosen to minimize drag during operation.
For unwisted wings, angle of incidence is as shown, with twisted wings defined relative to the chordline at the wing-fuselage intersection.
At high speeds, the maneuver load factor may be restricted according to FAR Part 23 or 25.
The maneuver load factor for subsonic aircraft is usually +2.5, but for aircraft under 50,000 lbs., the load factor is determined by the FAA using a specific formula.
The required maneuver load factor at all speeds up to Vc is determined by the FAA formula, unless the maximum achievable load factor is limited by stall.
High AOA marks the slowest speed at which the maximum load factor can be reached without stalling.
The forward component of the load at high AOA creates an extra load on the wing structure.
Dive speed (Vdive) represents the maximum allowed dynamic pressure and is about 50% higher than level flight cruise speed for subsonic aircraft, and M0.2 higher than level speed at engine max. continuous power for supersonic aircraft.
Gust loads are the loads acting on the aircraft under a strong gust or turbulence, and the change in lift and load factor is affected by the statistical gust alleviation factor, K.
Design requirements for gust velocities are derived from equivalent airspeed.
The V-n diagram shows the gust load factors, and the intersection of the maximum achievable load factor curve and the gust load factor curve defines the velocity at which the gust load factor is applied.
Information from the V-n diagram is used to calculate loads on the lifting surfaces, and critical loads occur at velocities of high AOA and max q, and where the gust load factor exceeds the assumed limit load factor.
Factors considered for finding the best material include yield and ultimate strength, stiffness, density, fracture toughness, fatigue crack resistance, creep, corrosion resistance, and temperature limits.
Corrosion occurs when materials are exposed to moisture, salt, aircraft fuel, oils, battery acid, engine exhaust, etc., and can cause stress corrosion at stress levels 1/10th the ultimate stress.
Producibility indicates ease of fabrication, and material availability increases with the possibility of obtaining the material when desired.
Common aerospace materials include wood, which was used in all early aircraft but is not popular any more, and is still used in homebuilt aircraft.
At high speeds, the maneuver load factor may be restricted according to FAR Part 23 or 25.
The maneuver load factor for subsonic aircraft is usually +2.5, but for aircraft under 50,000 lbs., the load factor is determined by the FAA using a specific formula.
The required maneuver load factor at all speeds up to Vc is determined by the FAA formula, unless the maximum achievable load factor is limited by stall.
High AOA marks the slowest speed at which the maximum load factor can be reached without stalling.
The forward component of the load at high AOA creates an extra load on the wing structure.
Dive speed (Vdive) represents the maximum allowed dynamic pressure and is about 50% higher than level flight cruise speed for subsonic aircraft, and M0.2 higher than level speed at engine max. continuous power for supersonic aircraft.
Gust loads are the loads acting on the aircraft under a strong gust or turbulence, and the change in lift and load factor is affected by the statistical gust alleviation factor, K.
Design requirements for gust velocities are derived from equivalent airspeed.
The V-n diagram shows the gust load factors, and the intersection of the maximum achievable load factor curve and the gust load factor curve defines the velocity at which the gust load factor is applied.
Information from the V-n diagram is used to calculate loads on the lifting surfaces, and critical loads occur at velocities of high AOA and max q, and where the gust load factor exceeds the assumed limit load factor.
Factors considered for finding the best material include yield and ultimate strength, stiffness, density, fracture toughness, fatigue crack resistance, creep, corrosion resistance, and temperature limits.
Corrosion occurs when materials are exposed to moisture, salt, aircraft fuel, oils, battery acid, engine exhaust, etc., and can cause stress corrosion at stress levels 1/10th the ultimate stress.
Producibility indicates ease of fabrication, and material availability increases with the possibility of obtaining the material when desired.
Common aerospace materials include wood, which was used in all early aircraft but is not popular any more, and is still used in homebuilt aircraft.

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Test your knowledge on aircraft design with this quiz covering the introductory concepts of engineering design and the definition of design according to Merriam-Webster dictionary.