Why Do Airplane Wings Angle Backwards?

Straight winged airplanes always had stability issues when flying at high speeds, but research into the aerodynamics of straight winged airplanes did not start until after the death of a Lockheed test pilot named Ralph Virden in 1941.  John Stack pioneered the study of airflow over airplane wings using a special kind of photography called Schlieren Photography.

Schlieren photography

This photography allowed him to see the airflow moving over the top of the wings.  He noticed that in straight wings, small pockets of air moving faster than the speed of sound were creating small shockwaves.  These shockwaves disrupted the flow of air over the wings, causing increased drag and decreased lift.  By angling the wings backwards, air is able to move diagonally along the front of the wind.  This results in less air moving over the wings and less shockwaves when traveling at high speeds.

John Stack

But he did not angle the wings back right away.  His first idea was to place a small flap on the underside of the wing.  This flap increased the lift of the plane during high speeds to prevent an uncontrolled dive.  Then during the production of the Bell X-1 he used very thin wings and raised the tail wing above the height of the wings.  This kept the tail out of the disrupted airflow of the wings, allowing for better speed and control.  The Bell X-1 became the first manned vehicle to break the sound barrier even with straight wings.

Bell X-1 (1946)

The Bell X-5 was the first plane that could change its sweep angle during flight.  It was able to sweep its wings farther back based on how fast the plane was flying.  Although John Stack was not on the primary development team for the X-5 his research was crucial to its success.

Bell X-5 (1951)

John Stack’s creativity came mainly from motivation.  He was externally motivated by the death of test pilot Ralph Virden.  This pushed him and his field to develop safer ways to fly at high speeds,  but also created the problem for him.  We discussed how often finding the problem was the hardest part of creativity.  Ralph Virden’s crash showed John Stack that the problem was in the wings of the aircraft.  He was also a pioneer in his field.  As Collins and Amablile explored, “creativity is motivated by the enjoyment and satisfaction that a person derives from engaging in creative activity.”  As a pioneer he was intrinsically motivated to push the limits of his field because he enjoyed his work.

Sources:

http://www.popularmechanics.com/flight/a19875/why-airplane-wings-angle-backwards-explainer/

Week 5: Motivation, Collins&amabile

http://crgis.ndc.nasa.gov/historic/John_Stack