What are the forces acting on the Aircraft?
Thrust, drag, lift and weight are the forces that act upon all aircraft in flight.
What four forces acting on an aircraft in straight and level unaccelerated flight?
Thrust, Drag, lift, and Weight.
Define Thrust
The forward force produced by the Powerplant/propeller or rotor. It opposes or overcomes the force of drag. As a general rule, it acts parallel to the longitudinal axis. However, this is not always the case, as explained later.
Define Drag
A rearward, retarding force caused by disruption of airflow by the wing, rotor, fuselage, and other protruding objects. As a general rule, drag opposes thrust and acts rearward parallel to the relative wind.
Define Lift
Is a force that is produced by the dynamic effect of the air acting on the airfoil, and acts perpendicular to the flight path through the center of lift (CL) and perpendicular to the lateral axis. In level flight, lift opposes the downward force of weight.
Define Weight
The combined load of the aircraft itself, the crew, fuel, and the cargo or baggage. Weight is a force that pulls the aircraft downward because of the force of gravity. It opposes lift and acts vertically downward through the aircraft’s center of gravity (CG).
In steady flight, the sum of these opposing forces are…
Always zero. There can be no unbalanced forces in steady, straight flight based upon newtons 3rd law of motion. Every action is an equal and opposite reaction.
Does this mean in steady flight all four forces are equal?
It means that the opposing forces are equal to, and thereby cancel, the effects of each other.
In unaccelerated flight, it is true that the opposing lift/weight forces are equal. They are also greater than the opposing forces of thrust/drag that are only to each other. Therefore, in steady flight:
The sum of all upward components of forces (not just lift) equals the sum of all downward components of forces (not just weight)
• The sum of all forward components of forces (not just
thrust) equals the sum of all backward components of
forces (not just drag)
This formula explains that a portion of thrust is directed upward in climbs and slow flight and acts as if it were lift while a portion of weight is directed backward opposite to the direction of flight and acts as if it were drag. In slow flight thrust has an upward component. But because the aircraft is in level flight, weight does not contribute to drag.
How are the forces acting on the plane while it’s gliding?
A portion of the weight vector is directed along the forward flight path and, therefore, acts as thrust.
In other words, any time the flight path of the aircraft is not horizontal, lift, weight, thrust, and drag vectors must each be broken down into two components.
What is the Angle of Attack?
The AOA is defined as the acute angle between the chord line of the airfoil and the direction on of the relative wind.
