Definitions Chapter 3 Standard atmosphere: A model of the atmosphere based on the aerostatic equation, the perfect gas law, an assumed temperature distribution, and standard sea level conditions. Temperature: Property of the atmosphere (τ). Function of altitude. Pressure: Property of the atmosphere (p). Function of altitude. Density: Property of the atmosphere (ρ). Function of altitude. Troposphere: Atmosphere from sea level to the tropopause (h =36,089 ft). Standard sea level conditions: Conditions at sea level used to define the standard atmosphere. Stratosphere: Atmosphere between h=36,089 ft and h=105,000 ft. Tropopause: Dividing line between the stratosphere and the troposphere, h=36,089 ft. Speed of sound: Property of the atmosphere (a). Function of temperature. Viscosity: Property of the atmosphere (µ). Function of temperature. Exponential atmosphere: An approximate standard atmosphere based on the assumption of constant temperature. ρ = ρ s exp( h/λ) Isothermal atmosphere: A constant temperature atmosphere. Same as exponential atmosphere. Lift coefficient: Nondimensional lift, C L = L/ qs. Drag coefficient: Nondimensional drag, C D = D/ qs.
Wing planform area: From the top view of an airplane, it is the area S of the wing extended from the fuselage centerline to the wing tip (outside of tip tanks if present). Mach number: Ratio of airplane velocity to speed of sound at the altitude the airplane is operating, M = V/A. Reynolds number: Ratio of inertia forces to viscous forces, R e = ρv l/µ Drag polar: The relationship between C D and C L, C D = C D (C L, M, R e ). Also called aero- Lift-to-drag ratio: Ratio of lift to drag E = L/D. dynamic efficiency. Aerodynamic efficiency: Lift to drag ratio, E = L/D. Zero-lift angle of attack: The angle of attack α 0L at which C L = 0, α 0L Lift-curve slope: The slope of the C L versus α curve, C Lα Basic symmetric airfoil: The thickness distribution of the airfoil without camber. Camber line: the line between the upper and lower sides of a cambered airfoil. Center of pressure: The intersection of the airfoil aerodynamic force line of action and the chord. Peak suction: The point on the chord where the minimum pressure occurs, x ps. Ideal lift coefficient: Lift coefficient of an airfoil where the minimum drag occurs. Thickness ratio: Ratio of the maximum thickness to the chord of an airfoil. 2
Root chord: The chord of the wing at the body reference line, c r. Tip chord: The chord at the tip of the wing (outside the tip tank if present), c t. Semi-span: The distance b/2 between the root chord and the tip chord. Sweep: The angle Λ that a particular chord line makes with the y axis. Aspect ratio: A nondimensional quantity which indicates the slenderness of a wing, A = b 2 /S Taper ratio: The nondimensional quantity c t /c r of a wing. Mean aerodynamic chord: The chord of an equivalent rectangular wing, c. Equivalent rectangular wing: A rectangular wing which has the same lift and the same moments about the x and y axes. Wing incidence: Angle i W between the wing chord plane and the body x axis. Wing chord plane: For a wing with no twist and the same airfoil shape along the span, the surface formed by the chords is a plane. Friction drag coefficient: The friction drag is the part of the drag caused by skin friction acting over the surface of the airplane, also called parasite drag. Wave drag coefficient: The wave drag is the part of the drag caused by the appearance of shock waves on a wing. The shock waves cause the boundary layer to separate. Induced drag coefficient: The induced drag is the component of the drag induced by the rotational flow about the wing tip vortices. Equivalent parasite area method: The parasite area is the area touched by the air flow over an airplane. Equivalent parasite area is parasite area 3
corrected for Mach number, interference, thickness, etc. Skin friction coefficient: The equivalent parasite area divided by the planform area. Compressibility factor: Gives the effect of Mach number on the equivalent parasite area. Interference factor. Gives the effect of interference effects on the equivalent parasite area. Form factor: Gives the effect of wing and body thickness on the equivalent parasite area: Fineness ratio: For a body shape, it is the length of the body divided by the maximum diameter. Wetted area: The wetted area is the surface area of an airplane which is touched by the air flow, S wet Mach number for drag divergence: The Mach number at which the drag begins to increase rapidly do to the appearance of shock waves, M D Oswald s efficiency factor: It gives the increase in induced drag due to the difference between an elliptic planform and another planform, e Parabolic drag polar: The drag polar that has the shape of a parabola, C D = C D0 (M) + K(M)C 2 L. Zero-lift drag coefficient: It is the drag coefficient C D0 the parabolic drag polar when C L = 0. associated with Induced drag coefficient: It is the drag coefficient KC 2 L associated with the parabolic drag polar. Induced drag factor: It is the term K in the parabolic drag polar. Corrected thrust: data. A nondimensional thrust used to represent thrust 4
Corrected specific fuel consumption: A nondimensional specific fuel consumption used to represent specific fuel consumption data. Corrected engine speed: A nondimensional engine speed used to represent engine speed data. Ideal subsonic airplane: A subsonic jet airplane characterized by a parabolic drag polar with constant coefficients, thrust independent of velocity, and specific fuel consumption independent of velocity and power setting. Ideal SBJ: The ideal representation of the airplane (SBJ) in App. A. 5