Flight mechanics Flashcards
Forces on an aircraft
Lift generation
Air passing over the upper surface moves faster than the air passing over the lower surface. The upper surface has lower pressure than the lower surface. Integrating the pressure difference over the length of the aerofoil produces a lift force. Pressure drag is also produced.
Resolving for straight and level flight
T=D L=W
Definition of lift force
The component of the total aerodynamic force acting perpendicular to the relative airflow
Definition of drag force
The aerodynamic force that acts parallel to the relative airflow direction
Define angle of attack
Angle that the chord line makes with the incoming airflow
Factors that influence lift or drag force on an object
relative airflow velocity
planform area of lifting surface
air density
Lift coefficient
Drag coefficient
Factors that affect lift or drag coefficient of an object
air viscosity
AOA
aerofoil shape
Induced drag
drag caused by the formation of trailing vortices dependent on aspect ratio
How and why does airspeed affect induced drag?
As airspeed increases, induced drag decreases
the down-wash component of the incoming air-stream becomes proportionally smaller as the incoming air velocity increases
Ways to reduce induced drag on a wing
increasing aspect ratio adding winglets decreasing wing chord increasing wing span
What does parasitic drag consist of?
Parasitic drag is also known as profile drag
Parasitic drag = pressure drag + skin friction
Pressure drag
pressure differences from front to back of aerofoil
Total pitching moment
What happens when the moments about the centre of gravity equals zero?
there is no disturbing moment acting on the aircraft and flies along the desired flight path
Pitching moment coefficient
Define boundary layer
thin layer of air adjacent to the aerofoil’s surface
Types of boundary layer
Laminar Turbulent
Laminar boundary layer
low drag highly ordered
Turbulent boundary layer
high drag completely disordered
Define skin friction
equal and opposite force acting on the aerofoil, to the force retarding the air molecules
Wing geometry
Aspect ratio
Aerodynamic centre
It is a fixed point for which the pitching moment is invariant with incidence
Aerodynamic mean chord
Simpler and less accurate definition of wing chord is geometric wing chord. Equation for geometric mean chord
The power produced by an engine is converted into thrust by the propeller. Thrust produced is given by….
