Sunday, November 11, 2018

Air Travel Science

Not often do we have the opportunity to travel by air twice in a ten day period. Two airline trips of several days each were separated by a few days at home. All told we traveled nearly 4000 miles via airline.  This entailed six flights, including two connecting flights. My former science students accused their teacher of framing many discussions during field trips through the lens of science—a characterization possessing a large measure of truth. Our goal, however, was that our teacher/student interactions included many relevant topics. Bear with us, readers, as we connect science with our recent air flights.

During the two trips described above, one a memorial service, another a celebration, many opportunities for reviewing the science and history of airline flights became apparent. Some facts announced by the pilot are fascinating. For example, the cruising altitude of 36000 feet at the speed of 600 mph and an exterior temperature of -66ºF on flights passing over several states enable passengers to muse about the progress of air flight science since the Wright Brothers’ initial 12 sec, 120’ flight on a heavier than air vehicle on December 17, 1903.

Our visions out of the undersized plane windows revealed mile after mile of the fascinating patchwork of civilization. Passengers interested in climatology could observe changing agricultural adaptations based on various zones of rainfall, temperature, and altitude. The Ohio River, a young river by geological standards, had its course changed somewhat by the fairly recent Wisconsin glaciation as the ice sheet retreated north upon melting. From the air, we see wonderful meandering rivers and remnants of long vanished rivers revealed by current patterns of vegetation.

Clouds visible from above or from their edges supply a stunning visual touch. Differing temperatures, water vapor content, and air currents provide a plethora of shape, beauty, and color. Knowledge of clouds helps forecast future weather. Often we fly through thick layers of clouds where pilots must entrust knowledge of their location to various electromagnetic phenomena such as radar (microwaves), radio frequencies, and GPS. They use instrument flight rules (IFR).

Understanding virtually every experience we have during air travel relates to scientific knowledge. Turbulence of one degree or another is caused by the interactions of air at different temperatures. Turbulence is a common experience of flyers but it seldom results in any harm. It may, however, cause unease.

Propeller flights provided the default air travel experience from 1928 until about 1960. After that, jet flight gradually replaced propeller flight. Jet air travel was cheaper, safer, and faster. In flight technology, we focus on four factors—all related to Newton’s famous laws of motion. Air travel technology must cope with the effects of (1) lift, (2) weight, (3) thrust, and (4) drag. These factors may be considered esoteric aeronautical knowledge, but most folks identify with these terms in a non-technical manner during air flight. 

In Newton’s First Law, we observe that an object at rest wishes to remain at rest unless acted on by an outside force. This is illustrated by our patient wait on the runway before take-off when directed by the control tower. After takeoff and when sufficient cruising speed has been achieved, there is no need for much additional force to be applied. The plane is speeding forward and tends to keep traveling in the same direction. We might say the airplane is on “cruise control,” minimally affected by the thin, high altitude air. The plane and passengers experience Newton’s First Law—the law of inertia.

In Newton’s Second Law, in order to change the motion of a heavy object, we must apply a force. As an example, if the pilot wants to move multiple passengers and a heavy airplane, he must apply a substantial force. In takeoff experiences, passengers experience an exhilarating force against their back when the pilot suddenly accelerates the heavy airplane at takeoff. The aircraft experiences thrust. In layman’s terms, we may say, “Full speed ahead!”

In Newton’s Third  Law, we observe that every action results in an equal and opposite reaction. In airline parlance, we observe that action in a forward motion is resisted by the force of air acting in the opposite direction. This is illustrated by the influence of drag during takeoff during which air resists forward motion.

Other terms apply to air flight. Lift is experienced when air is forced to travel over the upper curve of the aircraft’s wing. Air at the flat bottom surface of the wing exerts greater pressure. The pressure differential is greater the faster the airplane travels. This effect was described by Daniel Bernoulli in the 18th century. The Bernoulli effect applies to many other phenomena such as a moving frisbee which remains airborne in opposition to the frisbee’s weight as long as it is moving.

Laws of science govern our experiences each time we enjoy an air flight or a multitude of other life experiences. Laws of science are ordered and coherent. We live in a world governed by scientific laws. The Creator has established ordered and coherent laws for our benefit. They bring glory to Himself and enjoyment, order, and coherence to human life. We bow in worship for our Creator, the Author of order and coherence.