The Truth About Aerodynamics

(What Really Makes Airplanes Fly)

Most aeronautical engineers and the general public associate the lift generated by a wing with the differential pressure between the upper and lower surfaces of the wing. Nothing could be farther from the truth.

In reality, the lift required to cause a commercial aircraft to become airborne is furnished by the passengers and is inversely proportional to both the wing size and to the distance to be traveled. Furthermore, the distance to be traveled has a nonlinear relationship to lift, as will become clear in the following explanation:

1. How Passengers Provide Lift for Commercial Aircraft

The lift required for an aircraft to take off is furnished by the passengers pulling up on their seat armrests.

2. How Takeoff Lift is Initiated by the Pilot

After the aircraft reaches the end of the runway preparatory to takeoff, the captain will advance the throttles on the engines. This action has two purposes: a) to provide horizontal thrust to propel the aircraft down the runway, and b) to increase the Passenger Aggregate Fear Level (PAFL) by raising the noise level in the cabin. The consequent rise in PAFL causes the passengers to strenuously lift up on their seat armrests, thus imparting lift to the aircraft. As you can readily see, the engines have two purposes - to move the aircraft horizontally and to scare the bejeebers out of the passengers.

3. How the Duration and Degree of Lift Are Modulated by the Pilot

Once cruising altitude is reached, the pilot will throttle the engines back to lower the noise level. The reduction in noise level results in a reduction in PAFL, with a consequent decrease in lift. It is necessary for the pilot to make only minor changes in noise level to maintain straight and level flight. In some instances where the PAFL does not decrease sufficiently to prevent further climbing, the captain may order that free drinks be passed around, thus further relaxing the passengers and lowering the PAFL. One may observe that on most aircraft, the first-class passengers are automatically anesthetized by the use of free alcohol. Clearly, first-class passengers are a source of surplus lift and must be dealt with accordingly.

While the airline industry will never admit it, passenger seating assignment is governed by national characteristics. For instance, Italian males are hardly ever upgraded to first class since they are easily excitable, respond very quickly to outside stimuli, and cause abrupt and unpredictable changes in lift. Clearly, one would not want to get the Italians drunk. One difficulty associated with using Italians in this manner is their clannish nature; getting them evenly distributed (left and right, front and back) within the cabin can sometimes be difficult. Stewardesses will often resort to eyelash-batting and hip-wiggling to move the Italians about the aircraft.

While at first blush, it may seem that the French would also be a good source of lift, their uncooperative nature makes lift modulation difficult. One should never fly on an aircraft containing more than 45 percent (by volume) Frenchmen. Note that Lufthansa, SAS, and KLM fly only very large aircraft.

Raising the PAFL for the stolid Germans, Swedes and Dutch is notoriously difficult, requiring as many people as possible in each aircraft. The British never fly.

The high takeoff-accident rate for Aeroflot can be attributed to the fact that Russians are generally drunk before they get on the aircraft and are not a reliable source of PAFL-induced lift.

Descent and landing are accomplished using a combination of fatigue and passenger discomfort. It is a happy coincidence that travel over greater distances takes a correspondingly longer time. Even the most casual observer will note that after the aircraft reaches cruising altitude the plane will begin a slow and gradual descent for the balance of the trip. This descent is due to passenger fatigue and discomfort. A detailed explanation of the fatigue factor is unnecessary; suffice to say that with time one's arms get tired and the upward pull on the armrests is reduced. By reducing leg and hip room, passenger discomfort is increased with time; this distraction is also sufficient to reduce the Passenger Induced Lift, (PIL).
The common airline practice of showing only the most boring of in-flight movies is also a lift-modulation technique.

Note: The decrease in the amount and quality of airline food has not been found to be an effective method of PAFL modulation; biogas production offsets any decrease in lift. (See Hindenburg Disaster, reference no. 75.)

Several recent instances of sudden aircraft descent have been attributed to air pockets. The air pocket explanation is clearly a feeble attempt on the part of the aircraft crews to avoid blame. In reality, the crew neglected to closely monitor passenger fatigue, discomfort, or degree of inebriation. Luckily, sudden decreases in altitude are self-correcting due to the consequent rise in panic levels and increase in PAFL-induced lift.

Most passengers and the general public believe that the oft-experienced practice of circling the airport many times prior to landing is caused by the weather. This is not wholly the case. During bad weather, the PAFL increases as the aircraft reaches its destination. This undesirable increase in PAFL and consequent increase in lift must be dissipated by prolonging the flight and further tiring the passengers.

4. Historical Basis for This Theory and the Role of PAFL in Aircraft Design

As you may recall from early aeronautical history, the Wright Brothers' aircraft had four wings with a very large surface area. The large surface area of the wings inspired great confidence in Wilbur and Orville, decreasing their PAFL and, as a consequence, decreasing the altitude and flight duration capabilities of the Wright Flyer. As aircraft design advanced, it was found that smaller wing surfaces inspired greater PAFL, with a resultant increase in aircraft performance. Indeed it was not until the advent of the multi-passenger aircraft (with a higher PAFL factor) that increases in range and altitude were possible. The only reason wings (albeit very small ones) are still included on aircraft is that they look nice.

It is a little-known historical fact that the general unpopularity and eventual demise of the supersonic passenger aircraft were brought about by the fact that as soon as the aircraft reached supersonic speeds and altitudes, the passengers could no longer hear the engines, due to the high speed and thin air. No noise, no PAFL--and no PIL. The aircraft would drop like a rock, causing the PAFL to spike drastically, and the aircraft would then climb precipitously back to a high altitude, with the consequent loss of engine noise. As speed once again increased, the process would then repeat. The resultant sinusoidal altitude and speed changes thus rendered supersonic travel impractical.

While further research by highly annoying and pedantic people may bring this theory into disrepute, one must keep firmly in mind that, even with all of the airlines' efforts to reduce personal space aboard commercial airliners, they have yet to remove the armrests.

Art Lynch
Avid Aviator Pilot Supplies