Fundamental Thoughts - Engineering and Physical Science Language

Engineering Definition

• Engineering is the application of scientific principles to practical ends.
• The word "ingenium" means inborn talent and skill, ingenious.

Language of Engineering

• A logical collection of symbols, definitions, formulas, and concepts.
• Often esoteric and incomprehensible to the average person.
• Intended to convey physical thoughts and describe natural phenomena.
• Evolved over at least 2500 years; for example, Democritus introduced the atom concept in 400 BC.

Book Overview & Roadmaps

• The book provides road maps to guide understanding.
• Figure 2.1 is an overall road map.
• Begins with preliminaries (fundamental thoughts).
• Discusses the properties of the atmosphere (Ch. 3).
• Explores aerodynamics (Chs. 4 and 5).
• Covers flight dynamics, including airplane performance (Ch. 6) and stability/control (Ch. 7).
• Addresses space flight (Ch. 8) and propulsion (Ch. 9).
• Touches on flight structures (web page).
• Considers advanced vehicle concepts (Ch. 10).
• Figure 2.2 is a roadmap for Chapter 2.

Chapter 2 Purpose

• To help the reader get started with learning about airplanes and space vehicles.
• Emphasizes basic definitions for describing, discussing, analyzing, and designing these vehicles.
• Explores the concept of aerodynamic force and its sources.
• Stresses the importance of dimensions and units in engineering and science.
• Provides a brief description of the anatomy of airplanes and space vehicles.

Fundamental Physical Quantities of a Flowing Gas

• Airflow over an airplane's surface is the primary source of lift.
• Aerodynamics deals with the flow of air or gasses.
• Applications include rocket and jet engines and planetary entry vehicles.
• Four fundamental quantities are pressure, density, temperature, and velocity.

Pressure

• Pressure is the normal force per unit area.
• Exists due to air molecules striking a surface and transferring momentum.
• Defined as: Pressure is the normal force per unit area exerted on a surface due to the time rate of change of momentum of the gas molecules impacting on that surface.
• Defined at a point and can vary.
• Expressed mathematically as: $p = lim_{dA \to 0} (\frac{dF}{dA})$

Density

• Density is the mass per unit volume.
• Designated by the symbol $\rho$ (rho).
• $\rho = \frac{mass}{volume}$
• Defined at a point and can vary.
• Expressed mathematically as: $\rho = lim_{dv \to 0} (\frac{dm}{dv})$

Temperature

• Temperature is a measure of the average kinetic energy of the particles in the gas.
• Expressed as: $KE = \frac{3}{2}kT$, where $k$ is the Boltzmann constant. $k = 1.38 \times 10^{-23} J/K$
• High-temperature gas: particles move randomly at high speeds.
• Low-temperature gas: particles move relatively slowly.

Flow Velocity and Streamlines

• Velocity includes both speed and direction.
• Flow velocity is a point property that can vary.
• Defined as: The velocity at any fixed point B in a flowing gas is the velocity of an infinitesimally small fluid element as it sweeps through B.
• A streamline is the path traced by a moving fluid element in steady flow.

Source of Aerodynamic Forces

• Aerodynamic force on an object stems from:
  • Pressure distribution on the surface.
  • Shear stress (friction) on the surface.
• Pressure always acts normal to the surface.
• Shear stress acts tangentially on the surface.
• Theoretical and experimental aerodynamics aim to predict and measure these forces.

Equation of State for a Perfect Gas

• A perfect gas has negligible intermolecular forces.
• Air under normal conditions behaves as a perfect gas.
• The equation of state for a perfect gas is: $p = \rho R T$
  • R is the specific gas constant.
  • For normal air, $R = 287 \frac{J}{kg \cdot K} = 1716 \frac{ft \cdot lb}{slug \cdot ^\circ R}$.
• The universal gas constant $\Re$ is related to $R$ through $R = \frac{\Re}{M}$, where $M$ is the molecular weight. For air, $M = 28.96 \frac{kg}{kg \cdot mole}$
• Modified Berthelot equation of state (for real gasses): $(p + \frac{a}{v^2})(v-b) = RT$
• At very high speeds and temperatures (e.g., Apollo capsule entry), air becomes chemically reacting, and $R$ becomes variable $R = R(p,T)$.

Discussion of Units

• Units are vital to the language of engineering.
• SI units (Systeme International d'Unites) are the accepted norm.
• The United States is moving toward the voluntary implementation of SI units.
• Engineering students must be familiar with both engineering units and SI units.

Consistent Units

• Consistent sets of units allow physical relationships to be written without conversion factors.
• Newton's second law: $F = ma$
  • SI units: 1 newton = (1 kilogram)(1 meter/second^2).
  • English engineering system: 1 pound = (1 slug)(1 foot/second^2).
• Non-consistent sets of units require a conversion factor: $F = \frac{1}{g_c} \times m \times a$
• The weight of an object is $W = mg$, where $g$ is the acceleration of gravity.
• Always deal with a consistent set of units in calculations.

Specific Volume

• Specific volume (v) is the volume per unit mass.
• $v = \frac{1}{\rho}$
• From the equation of state: $pv = RT$
• Units: $m^3/kg$ and $ft^3/slug$.

Anatomy of the Airplane

• Fuselage: the center body.
• Wings: the main lift-producing components.
• Horizontal and vertical stabilizers: provide stability.
• Nacelle: a shroud housing the engines.

Control Surfaces and Flaps

• Flaps: increase lift.
• Ailerons: control rolling motion.
• Elevators: control pitching motion.
• Rudder: controls yawing.
• Three-view diagrams convey the shape of an airplane.
• Cutaway drawings illustrate the internal structure.

Anatomy of a Space Vehicle

• Space vehicle configurations vary greatly depending on the mission.
• Common launch vehicles include multistage rockets (e.g., Delta), air-launched rockets (e.g., Pegasus), and reusable boosters (e.g., X-34).
• The Space Shuttle is a partially reusable system with an orbiter, solid rocket boosters (SRBs), and an external tank.
• Satellite example: FLTSATCOM communications satellite (geostationary orbit).

Historical Note: The NACA and NASA

• The National Advisory Committee for Aeronautics (NACA) was created in 1915 to advise the government on aeronautical research and development.
• The Langley Memorial Aeronautical Research Laboratory was the first major U.S. aeronautical laboratory.
• The dawn of the space age led to the creation of the National Aeronautics and Space Administration (NASA) in 1958.
• NACA's programs, people, and facilities were transferred to NASA.
• NASA has been fundamental to the technology of flight.