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FOUR FORCES



Understanding how these forces work and knowing how to control them with the use of power and flight controls are essential to flight.


There are, four force’s that act on an aircraft during straight-and-level and un-accelerated flight, they are:

  • Thrust

  • Drag

  • Weight

  • Lift


​But, for an aircraft to move one force must be greater than the other. For an example, for an aircraft to move forward thrust must be greater than drag. An aircraft will continue to gain speed until thrust and drag become equal. The same goes for lift and weight. For an aircraft to maintain altitude lift and weight must be equal.

Thrust – This is the forward force from the powerplant/propeller and is opposite of drag.

Drag – Is the rearward force caused by disrupted airflow from the wings, fuselage, etc. and is opposite of thrust. There are two types of drag:

  • Parasite Drag – Is not associated with the production of lift. It is basically caused by rough skin creating friction and anything sticking out of the aircraft, such as rivet heads/common hardware (nuts, bolts, screws, etc.), antennas, even ridges used to reinforce flight control surfaces, non-retractable gear aircraft.


  • Induced Drag – Is when an airfoil is producing lift. When airfoils produce lift the air flows from the high pressure, below the wing to the low pressure are above the wing creating vortices. Induced drag can be something that is induced into the airflow, such as: lowering flaps, lowering landing (retractable gear aircraft, only), raising spoilers, etc.

Weight – Is the downward force caused by gravity and additional items such as fuel, cargo, crew, etc. and is opposite of lift.

Lift – Is the upward force created by the airflow around the wings and is opposite of weight.



​Remember:

Four forces:

  • Thrust

  • Drag

  • Weight

  • Lift

References:




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