Basic Aerodynamics (Private Pilot)

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.

  • 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, 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.

 

Aircraft Design

Dihedral:

The dihedral is the upward angle of the wings, or where the outer tip of the wing is higher than that of the wing roots. When flying an aircraft with this wing design the pilot must be aware of the wing design and how the wind affects it.

When a gust of wind cause the airplane to, the dihedral design cause the airplane to sideslip. If the relative wind is from the side of the aircraft, the wing slipping into the relative will have an increase in the angle of attack (AOA), creating more lift and causing the aircraft to roll.

Sweepback Wings:

Sweepback wings are an advantage to aircraft. If an aircraft encounters a disturbance in flight, such as turbulence and one of the sweepback wings drops or slips, that wings leading edge becomes more perpendicular to the relative wind. As a result the low wing acquires more lift and the aircraft returns to its original flight attitude.

 

Torque & P-Factor

On single engine aircraft from the pilots’ prospective, “torque” is the left turning tendency of an engine aircraft. Torque is made of four types of twisting motion around one of the three axes of an aircraft.

  • Torque

  • Corkscrew slipstream

  • Gyroscopic Action

  • P-Factor

Torque:

Let’s take a look back at Newton’s third law, which is “for every action, there is an equal and opposite reaction”. As for aircraft the engine components and propeller are revolving in one direction, while an equal force is trying to rotate an aircraft in an opposite direction, this is called torque.

Corkscrew slipstream:

Corkscrew or spiraling slipstream is the air from the propeller rotating around the fuselage of the aircraft. During takeoff or when reaching a power-on stall, the rotating air impacts the left side of vertical tail surface, which causes a yawing motion on the aircraft.

Gyroscopic Action:

In this case when a force is placed on a rotating propeller to deflect it out of its plane of rotation, the result is a force 90 ahead and in the direction of rotation, which causes a yawing motion.

P-Factor:

P-Factor is caused by the aircraft propeller during high angle of attack (AOA). The downward moving blade takes a greater “bite” of air, than the blade that is moving upward. This causes the trust to move over to the right, causing the aircraft to yaw to the left around the vertical axis.

 

References

Private Pilot ACS PA.l.F.K3

PHAK FAA-H-8083-25 (Ch. 5) 

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