Aircraft Performance, Propulsion and Wing – Key Vocabulary

Vocabulary flashcards covering fundamental terms, parameters and optimisation concepts introduced in the Aerospace Engineering II – Aircraft Performance, Propulsion and Wing lecture.

Aircraft Performance

Study of the extreme translational motions of an aircraft’s centre of gravity that affect its operational and economic use.

Aircraft Performance Analysis

Combination of analytical and experimental techniques used to predict performance quantities such as envelopes, range, endurance, climb and runway distances.

Operational Flight Envelope

Limits of airspeed, altitude and load factor within which an aircraft can safely operate.

Range

Maximum distance an aircraft can fly on a given amount of fuel; often estimated with Bréguet’s range equation.

Endurance

Maximum time an aircraft can remain aloft on a given fuel load; calculated with Bréguet’s endurance equation.

Lift-to-Drag Ratio (L/D)

Measure of aerodynamic efficiency; high values indicate more lift for less drag.

Thrust-to-Weight Ratio (T/W)

Available thrust divided by aircraft weight; key determinant of climb and acceleration performance.

Wing Loading (W/S)

Aircraft weight per unit wing area; influences stall speed and manoeuvrability.

Equation of Motion (3-DOF Point Mass)

Set of Newton’s second-law equations that govern aircraft translational motion using forces of thrust, drag, weight and lift.

Drag Polar

Relationship between drag coefficient (CD) and lift coefficient (CL) for a given aircraft configuration.

Drag Coefficient (CD)

Non-dimensional coefficient representing total aerodynamic drag over dynamic pressure and reference area.

Lift Coefficient (CL)

Non-dimensional coefficient representing lift force over dynamic pressure and reference area.

Zero-Lift Drag Coefficient (CD0)

Portion of drag that exists when lift is zero; dominated by skin-friction and form drag.

Induced Drag Coefficient (k·CL²)

Component of drag caused by lift generation; proportional to square of lift coefficient and influenced by wing aspect ratio and efficiency factor e.

Aspect Ratio (AR)

Ratio of wing span squared to wing area; higher AR reduces induced drag but may increase structural weight.

Elliptic Lift Distribution

Ideal spanwise lift shape that minimises induced drag and pushes efficiency factor e toward 1.

Minimum Drag Speed (V_MD)

Airspeed at which total drag is minimum; equals speed for best L/D in jet aircraft.

Minimum Power Speed (V_MP)

Airspeed requiring least propulsive power; about 0.76 of minimum drag speed for propeller aircraft.

Maximum Specific Range Speed

Speed at which distance per unit fuel is maximised; found where a line from origin is tangent to drag (or power) curve.

Specific Fuel Consumption (SFC)

Fuel flow per unit thrust (jets) or per unit power (props); key parameter linking propulsion and fuel burn.

Specific Range

Distance travelled per kilogram of fuel consumed; central metric in cruise optimisation.

Minimum Fuel-Flow Speed (Max Endurance)

Airspeed yielding lowest fuel burn rate, allowing longest time aloft for given fuel; equals VMD for jets and

Thrust-Versus-Velocity Curve

Plot showing required thrust as a function of airspeed during steady level flight, derived from drag polar.

Power Required Curve

Drag multiplied by airspeed; used for propeller aircraft to find speeds for minimum power and optimal range.

Flight Envelope (V-n Diagram)

Graph of allowable load factor (n) versus airspeed (V) defining structural and aerodynamic limits.

Gust Diagram

Overlay on the V-n diagram showing additional load factors due to atmospheric gusts.

Compressibility Effects

Changes in aerodynamic characteristics above about Mach 0.7 where CD and CL become Mach-dependent.

Mach Number (M)

Ratio of true airspeed to local speed of sound; key parameter in transonic and supersonic performance.

M(L/D) Optimisation

Technique for determining best cruise Mach and lift coefficient by maximising product of Mach number and L/D.

Step Climb

Series of altitude increases during long-range cruise to maintain optimal CL as aircraft weight decreases.

Propeller Efficiency (η_p)

Ratio of useful propulsive power to engine power output; links power required to fuel flow for prop aircraft.

Point Mass Model

Simplified performance model treating aircraft as a particle with forces applied at its centre of gravity.

Boundary Layer

Thin region of fluid near a surface where viscous effects dominate; its characteristics affect drag and lift.

Transonic Drag Rise

Rapid increase in drag coefficient experienced as Mach number approaches unity due to shock-wave formation.

Tailwind Effect on Specific Range

Tailwinds increase ground distance per fuel mass and lower optimal airspeed; headwinds have opposite effect.

Coursework Assessment (Drag Calculation)

15 % of module grade devoted to calculating drag characteristics as part of aircraft performance coursework.

Flight Test

Experimental method for validating analytical performance predictions through instrumented manoeuvres.