In the middle of World War II
an American fighter plane fell out of
the sky without even being shot at.
That aircraft was the Lockheed P-38 Lightning 
- one of the fastest and most agile of its time -
and it was designed by a Michigan alum,
Clarence "Kelly" Johnson, one of the
world's top aircraft designers.
The P-38 was actually a great plane but these 
higher speeds brought new aerodynamic
challenges. When the P-38 entered a dive
from a high-altitude, a common flight
maneuver for fighter planes, it would
accelerate to a speed so fast that it's
elevators would effectively lock into
place making it impossible for the pilot
to recover. Many pilots died as a result.
This loss of control was attributed to
the onset of what we are called
"compressibility effects." This new phrase
was plastered all over popular magazines,
flight manuals, industry research papers
and even classified documents. But what
was really going on? The problem had to
do with the shape of a plane's wing, or
airfoil, and the speed of sound.
You see, the wing of an airplane is
designed to generate lift, and
the resulting shape causes air to
accelerate over the wing.
This means that the air flowing over the
wing will be traveling faster than the
plane itself. When this air hits the
speed of sound, or Mach 1,
big things happen. And for the P-38,
this would occur in a dive when the
plane hit an overall speed of about Mach 0.68,
or what's known as it's a critical Mach.
First a shock wave would form above the
wing, and sometimes below, and cause it to
stall because the drag would increase
and the lift would decrease. It would
also disrupt the airflow behind the wing.
And with the P-38, this disruption actually
increased the lift of the tail which is
what caused the nose of the plane to
pitch further and further down. The only
way for the pilot to recover was to be
patient. As the P-38 entered lower, denser
air where the speed of sound is higher,
the negative effects would wear off and
the pilot could pull up,
assuming he had enough altitude left to
work with. Johnson eventually limited
these effects on the P-38 by adding dive
flaps to the underside of the wings.
These flaps, designed by John Stack, helped
the wings maintain lift and stabilized
the downstream airflow for the pilot to
keep control. The P-38 went on to be
incredibly important for the Allied war effort,
but it was clear to Johnson that a new
generation of aircraft was needed.
Enter the jet age.
Johnson's next plane was a jet fighter
for two reasons. First, the jet engine was
a brand new technology that promised
higher top speeds and faster
acceleration compared to the propeller.
And second, the Germans already had one.
But the higher speeds from a jet engine
meant that the P-38's aerodynamic
problems were now more important than ever.
After the initial designs of the P-38,
federal research was conducted by Stack
and others into ways to improve wing
design that would increase a plane's
critical Mach, allowing a plane to fly
faster before it experienced problems.
And decreasing the thickness of the
airfoil would allow for increased
stability at high speeds.
Johnson implemented one of these
airfoils for his new jet fighter -
the P-80 Shooting Star - giving it a critical Mach
of 0.8. And once approved by the US military,
the P-80 became the first operational
American jet fighter and an influential
plane for the war to follow in Korea.
Further innovations in wing design
helped to eventually mitigate the
effects of shock waves, and the continual
improvement in jet engine design
allowed for speeds more than triple
that of the P-80, like Johnson's final
contribution to aircraft design - the
SR-71 Blackbird - which is still the
fastest and coolest-looking
air-breathing manned aircraft to date.
Way to go Kelly.
