Fundamentals of Structural Analysis

Reference Wing

The 'trapezoidal' wing used as the basic geometry layout to start the design process.

Leading-Edge Sweep

The angle critical for supersonic flight, while the quarter-chord line sweep is more relevant for subsonic flight.

Aspect Ratio

For rectangular wings, it is the span divided by the chord; for tapered wings, it is the span squared divided by the area.

Taper Ratio

The ratio of the tip chord to the centerline root chord, affecting lift distribution along the wing span.

Dihedral/Anhedral Angle

The angle the wing makes with the local horizontal, with dihedral for roll stability and anhedral for roll rate.

Airfoil Camber

Refers to the curvature of most airfoils, with the mean camber line equidistant from upper and lower surfaces.

Bernoulli's Equation

States that higher velocities result in lower pressure, causing the airfoil to generate lift by pressure differences.

Design Lift Coefficient

The lift coefficient at which the airfoil has the best lift-to-drag ratio, crucial for initial airfoil selection.

Airfoil Thickness Ratio

Directly impacts drag, maximum lift, stall characteristics, and structural weight of the wing.

Wing Twist

Adjustment (2-3 degrees) to prevent tip stall and approximate an ellipse lift distribution.

Geometric Twist

Twist when tip and root incidences differ.

Aerodynamic Twist

Twist when tip and root airfoil sections differ.

Wing Incidence

Angle between fuselage axis and wing's airfoil chord-lines.

Incidence Angle

Angle chosen to minimize drag, typically 2 deg for general aviation.

Thrust

Force generated by propulsion system to overcome drag.

Drag

Aerodynamic resistance force opposing flight direction.

Lift

Force perpendicular to flight direction, mainly generated by wings.

Weight

Force directed towards the center of the earth, dependent on mass and payload.

Design Takeoff Gross Weight

Total weight at the start of the mission, not necessarily the maximum takeoff weight.

Empty Weight

Weight including structure, engines, avionics, not crew, payload, or fuel.

Fuel Weight Fraction

Fraction of fuel weight to total takeoff weight, mission fuel dependent.

Mission Segment Weight Fractions

The aircraft weight at the end of a mission segment divided by its weight at the beginning of that segment.

Total Fuel Weight Fraction

The ratio of the aircraft weight at the end of the entire mission divided by the initial weight.

Specific Fuel Consumption (SFC)

The rate of fuel consumption divided by the resulting thrust, usually measured in pounds of fuel per hour per pound of thrust.

Propeller Engine SFC (C)

Given as Cbhp, the pounds of fuel per hour to produce one horsepower at the propeller shaft.

Lift-to-Drag Ratio (L/D)

A measure of the design's overall aerodynamic efficiency, highly dependent on the configuration arrangement.

Wetted Aspect Ratio

Defined as the wing-span squared divided by the total aircraft wetted area, considering total wetted area instead of wing reference area.

Fuel Weight Fraction Equation

Equation to find takeoff gross weight iteratively

Statistical Empty Weight Equation

Equation to find takeoff gross weight iteratively

First-Order Sizing Process

Iterative process to estimate takeoff gross weight

Fuselage Sizing Constraints

Determines fuselage size based on real-world limitations

Fuselage Fineness Ratio

Ratio of fuselage length to maximum diameter

Takeoff Wing Loading

Ratio of takeoff gross weight to wing area

Tail Volume Coefficient

Method to estimate tail size based on volume

Vertical Tail Volume Coefficient

Relationship between vertical tail and wing size

Horizontal Tail Volume Coefficient

Relationship between horizontal tail and wing size

Tail Moment Arm

Distance from tail quarter-chord to wing quarter-chord

Control Surface Flutter

Rapid oscillation caused by airloads, mitigated by balancing methods