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Lift and Drag
An aircraft has four forces acting upon it, thrust, drag, lift, and weight. Balancing these
forces against each other can result in flight. It is important to note that the angle of attack
(AOA) of an aircraft has a significant effect on both lift and drag. A low AOA can cause the wing
to underperform, where an angle past the critical AOA will cause the wing to lose laminar flow
across the wing, which will result in the loss of sufficient lift and subsequent stall. In
unaccelerated flight, Sir Issac Newton’s 3rd law “A body in motion will remain in motion, in a
straight line, unless acted upon by an unbalanced force.” (Badick. 2021.), is demonstrated by the
aircraft’s engine producing thrust, which pushes air backward and propels the aircraft forward.
Bernoulli’s principle is demonstrated as the wings of an aircraft move through the air. The air
traveling over the top of the wing travels farther than the air going beneath, in the same amount
of time, this creates a low pressure above the wing and a high pressure below, which creates lift.
Regardless of airspeed, if lift is produced, drag is produced as well. Induced drag is most
prominent when an aircraft is in a heavy, clean, and slow configuration. “Induced drag occurs
because the distribution of lift is not uniform across the wing as it varies from the wing root to
the wingtip.” (Badick. 2021.). As airspeed increases, induced drag is reduced because a lower
AOA is required to maintain level flight. However, parasitic drag is not dependent on the
production of lift, instead it is directly proportional to the increase in airspeed. “As speed
increases, parasite drag will increase because the ‘solid body’ is moving through the ‘fluid’ with
greater force and thus experiences the force of drag in a greater capacity.” (Badick. 2021.).
Parasitic drag is caused by aircraft skin friction, form drag, interference drag, and leakage drag.
These forms of drag increase along with airspeed. “Parasite drag varies directly as the velocity
2
squared, so if the airspeed doubles then the parasite drag quadruples” (Badick. 2021.).
References:
Badick, J. R., & Johnson, B. A. (2021). Flight Theory and Aerodynamics (4th ed.). Wiley
Professional Development (P&T). https://libertyonline.vitalsource.com/books/9781119772415
