Aircraft Basics and Performance

Air Basics and Performance

02 Sep 15II Lecture

Basic Aircraft Terminology

• Aerofoil: Cross sectional shape of a wing• Leading Edge (LE): Front edge of the wing• Trailing Edge (TE) : Back edge of the wing• Chord Line: Line connecting LE and TE• Camber : Centre line between top and bottom

of wing

Aerofoil

Axes of an AircraftLongitudinal: Parallel to the FuselageLateral : Parallel to the WingNormal : Perpendicular to the ground

Axes of an AircraftLongitudinal: Parallel to the FuselageLateral : Parallel to the WingNormal : Perpendicular to the ground

Six degrees of freedom

Wing Layout• Sweep: Angle between the lateral axis and the

wing• Taper: Chord decreases as you move towards

the wing tip• Incidence: Angle between the longitudinal axis

and the wing chord• Angle of Attack: Angle between the wing and

the relative wind• Twist : Bending of wings about lateral axis– Anhedral (downward)– Dihedral (upward)

Wing Geometry Definitions

Angle of Attack

Wing Layout

• Aspect Ratio (AR) = Span ^2/wing area• More efficient of slow moving aircraft• Typical values– Glider : 20-30– Trainer: 7 -9– Loadstar: 18.5

Control Surfaces

• Ailerons: Horizontal surfaces located on wing tips– Roll: rotation about the longitudinal axis

• Elevator : Horizontal surfaces located on the tail– Pitch: rotation about the lateral axis

• Rudder: Vertical surface located on the tail– Yaw: rotation about the normal axis

Stabilising Surfaces

• Vertical Stabiliser : The vertical part of the tail which prevents unwanted yaw

• Horizontal Stabiliser: The horizontal portion of the tail that prevents unwanted pitch

Flaps

• Changes the shape of Wing• Increases Lift and Drag• Used during takeoff and landing

Flaps

• Changes the shape of Wing• Increases Lift and Drag• Used during takeoff and landing

Forces of Flight

• Lift • Drag • Thrust• Weight

For steady and level flight these four forces and the moments they generate must be in equilibrium. An airplane is a force and moment balancing machine

Forces of Flight

Force of Flight

Lift

• Controlled by– Airspeed, angle of attack, altering aerofoil and

altering the planform area– Lift= ½ *p * V^2*A*Cl p- density V- Velocity A- wing area Cl – coeff of lift

Co-efficient of Lift

Magic no of lift; determined experimentally

Constant for any size wing with same aerofoil

Accounts for unkownVaries with AoA

There is an angle where the wing produces zero lift

Explains how airplane can fly upside down

Loss of Lift

• Every wing has a stall angle• Stall angle is angle of attack at which wing

losses lift• Stall angle ranges from 12-20 degrees

Drag

• Form Drag- shape of the object• Skin Friction Drag- surface of object• Induced Drag- Component of Lift• Parasitic Drag= Form Drag+ Skin Drag• Total Drag= Parasitic Drag+ Induced Drag• Total Drag= ½ *p*V^2*A*Cd Cd – Co-eff of Drag. Determined

experimentally

Drag Curve