This month's AE presenter: James Aubuchon
Date of presentation: 17-Sept-2018 (not 100% certain of exact date)
Subject: The source of subsonic lift
Description:
Guest presenter James "Jim" Aubuchon delivered the September 2018
presentation on aerodynamics, explaining how the source of subsonic lift
is Van der Waals Forces, and not the Bernoulli Effect as commonly
believed.
The Bernoulli Effect is a valid observation made on
liquids and published in 1738. In some circumstances, it applies to
gases. However, it is an observed effect and not a fundamental cause.
Similarly, Newton’s Laws are statements of observed behavior and are not
fundamental causes. The fundamental forces of flight are gravity, which
must be overcome, and the electromagnetic force, which provides lift.
In subsonic flight, the electromagnetic force is applied to the aircraft
via Van der Waals forces. The popular explanation of lift in terms of
different airflow transit times above and below the wing is wrong.
The
most intuitive way to visualize lift is in terms of Newton’s Laws. The
wing directs airflow downward behind the wing, hence the air exerts an
upward force on the wing. For a Cessna 182, air within about 5 meters
above the wing is directed downward. Downwash and Van der Waals forces
cause lift, not Newton’s Laws or the Bernoulli Effect. The Bernoulli Effect is useful in aircraft design to calculate the pressure
distribution on aircraft surfaces, but, again, is not the proximal cause
of lift.
