Einstein’s Wing Flops

Einstein once took an interest in aviation and tried to design an improved wing. He wrote a technical article in August 1916 in which he proposed a new shape for wings that he hoped would improve lift.

His proposal was a wing with a large mid-chord arch.

His paper began with the question, “Where does lift come from that allows airplanes and birds to fly?” To answer the question, he searched the existing published literature on the subject and concluded that not even a primitive answer was to be found.

He evidently didn’t have the Wright brothers’ 1902 wind tunnel data or he probably would have pursued a different idea.

Einstein used Bernoull’s theorem as a basis for the design of his improved wing. Lift is created by the pressure differential created by the flow of air over a wing.

Bernoulli’s Theorem developed by Daniel Bernoulli, an eighteenth century scientist discovered that as the velocity of a fluid (such as air) increases, its pressure decreases.

In the case of an airplane, the theorem postulates that the wing is shaped to force the air flowing over the upper surface of a cambered wing to flow faster to cover a longer distance than the air flowing over the lower surface. The faster air on the top surface creates a pressure differential resulting in an upward force on the wing.

The hump on the top of the wing surface, Einstein thought, would create an even longer path for the air to travel, resulting in additional lift.

Einstein’s proposal for a wing design was given to Paul Ehrhardt who had flown for two-minutes as a passenger with Orville in 1909. He was the technical manager of an aircraft company in Berlin. He forwarded the proposal to his engineering group for evaluation.

Engineering consulted with Einstein and subsequently compared 99 conventional airfoils in a wind tunnel with Einstein’s foil. All but two the conventional foils had higher lift-to-drag ratios.

This was not a result that Einstein envisioned.

Einstein’s proposal didn’t work because the Bernoulli explanation of lift that he relied upon is incorrect when applied to airplane wings even though it still can be found in popular literature.

A better explanation of lift is based on Newton’s Third Law that postulates that for every action there is an equal and opposite reaction. Issac Newton has been regarded for over 300 years as the founding exemplar of modern physical science.

As applied to a wing, the thrust of the airflow passing over the trailing edge of a wing is bent downward. The downward thrust of the air creates an equal upward force that is lift.

Other determinants of lift in addition to the shape of the wing include the size of the wing, velocity of the air flowing over the wing, the density of the surrounding air and the angle of attack.

Following the German wind tunnel tests on the Einstein wing, they constructed a full-size prototype airplane consisting of a WW I German biplane with “Enstein’s wings” attached.

Ehrhardt decided to be the test pilot. After a long takeoff run, the plane went in to an unintended roll as he took-off. Ehrhardt said that he landed quickly and safely and “was overjoyed to find himself on firm ground and still in one piece.”

Ehrhardt further elaborated on his experience, saying that the plane was hard to control tending to “waddle while flying something akin to the flight of a pregnant duck.”

Einstein accepted the failure of his wing design with good humor. He wrote to Ehrhardt, “That is what can happen to a man who thinks a lot, but reads little.

The year 2005 is the 100th anniversary of Einstein’s extraordinary year in which he published five scientific papers that fundamentally changed our knowledge of space, time, light and matter. His genius made possible the development of computers, satellites, telecommunication, lasers, television and nuclear power. Not bad for someone who never learned to drive a car.

The year 2005 also is important time for the Wright brothers and to society. It is the 100th anniversary of the time when they developed the first practical airplane. It took the genius of Wilbur and Orville to accomplish that.

Reference: Einstein’ Wing, Air & Space, April/May 2005.