At the end of this lesson, you should be able to correctly:
A basic question – What Exactly is a Force?
A resultant force is the single force which represents the vector sum of two or more forces.
The ‘start’ of the second force needs to be moved to the ‘end’ of the first force, with the resultant going from the start of the first force directly to the end of the second force (as shown in the diagram).
A force acting on a point can be broken up into it’s horizontal (x) and vertical (y) components:
The moment of a force is a measure of its tendency to cause a body to rotate about a specific point or axis.
The magnitude of the moment of a force acting about a point or axis is directly proportional to the distance of the force from the point or axis. It is defined as the product of the force and the moment arm. The moment arm or lever arm is the perpendicular distance between the line of action of the force and the centre of moments.
When a system is in equilibrium, the TOTAL anticlockwise moment = TOTAL clockwise moment.
Consider the following system:
In this system, at this point in time, the system is in equilibrium!
The main forces acting on an aircraft in straight and level flight are lift and weight,which act in opposite directions, but not necessarily from the same point on the aircraft.
For STRAIGHT and LEVEL Flight:
The fluid on top of the wing is accelerated and the fluid on the bottom of the wind is slowed down compared to velocity of the aircraft itself because the wing geometry and angle narrows the flow area above the wing and widens the flow area below the wing. (Venturi Effect!)
As the Airfoil angle of attack changes, the pressure field changes. Due to this, the centre of pressure changes with variation in the angle of attack. In the airplane’s normal range of flight attitudes, if the angle of attack is increased, the centre of pressure moves forward; and if decreased, it moves rearward.
Relationship between Velocity & Pressure:
Total Pressure (H) = Dynamic Pressure (q) + Static Pressure (p)
H = q +p
Coanda effect is the tendency of a fluid jet to stay attached to a convex surface. It is named after Romanian inventor Henri Coandă, who described it as “the tendency of a jet of fluid emerging from an orifice to follow an adjacent flat or curved surface and to entrain fluid from the surroundings so that a region of lower pressure develops.”
When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction on the first body.
Weight = Mass x Gravity
The Centre of Gravity (CoG) is the average location of the weight of the aircraft components in total.