On October 14, 1947 over California’s Mojave Desert, U.S. Army Air Force Captain Charles
E. “Chuck” Yeager became the first person to fly faster than the speed of sound, piloting the Bell
X-1 experimental rocket plane. It was a stunning achievement, paving the way for routine supersonic
flight and earning Yeager the prestigious Collier Trophy and a place in the history books. Yet
strange as it may seem, Yeager may actually have beaten to the punch a full two years earlier by
a German jet pilot during WWII. And stranger still, it happened completely by accident.
In the 1930s and 40s, as aircraft began flying ever faster and higher,
pilots began encountering a disturbing phenomenon. At speeds above 600 km/h,
their controls would freeze up and the nose of their aircraft would suddenly pitch down,
sending them into a lethal, unrecoverable dive. This problem, known as compressibility,
was a particularly acute in high-performance fighters like the Lockheed P-38 Lightning,
which during flight trials in 1941 killed test pilot Ralph Virden when the tail ripped
off in a high-speed dive. As this phenomenon occurred near the speed of sound, or Mach 1,
pilots began to speak of a “sound barrier” - an invisible upper limit to manned flight.
Engineers, however, were not so sure. While the P-38’s compressibility issues were
solved by installing special dive-recovery flaps, this was only a temporary solution;
if aircraft were to fly safely above 600 km/h, the aerodynamics of flight at transonic and
sonic speeds had to be understood. It was soon discovered that the strange phenomena encountered
by pilots were caused by the formation of shock waves on their aircraft. Shock
waves form at the speed of sound, but as airflow varies widely over the surface of an aircraft,
they will form in certain areas before others. When they form on the wings, this creates a
change in pressure distribution that causes a sudden pitching down of the nose - what pilots
call “Mach tuck.” And when shock waves form on the hinges of elevators and other control surfaces,
it can cause them to lock up and become unresponsive, making the resulting dive
unrecoverable. While all these problems were theoretically soluble, there was another,
major hurdle to achieving supersonic flight: shock waves also form on propeller blades, making them
less and less effective the faster they turned. This meant that no matter how powerful an engine
was installed, no propeller-driven aircraft could exceed the speed of sound. However,
the Second World War saw the introduction of two brand new propulsion technologies - the
rocket engine and the jet engine - and in these lay the key to practical high-speed flight.
On April 9, 1945 - barely a month before the end of the war in Europe - Cadet Sergeant Hans Guido
Mutke took off from Lagerlechfeld in Germany flying a Messerschmitt Me-262. The Me-262 was
the world’s first operational jet fighter, entering service with the German Luftwaffe
in April 1944. Powered by two Junkers Jumo (yunkers you-moh) 004 turbojet engines,
the aircraft was capable of then-unheard of speeds of 900 km/h and had superb handling
which German ace Adolf Galland to describe as “like angels pushing.” Far outclassing anything
the Allies could field, it could have been a war-winning weapon were it not for one man:
Adolf Hitler. Obsessed with remaining on the offensive even as enemy forces closed in on all
sides, Hitler insisted that the Me-262 be developed into a high-speed bomber,
a role for which it was ill-suited. By the time he changed his mind and authorized full-scale
production of the jet fighter, the war was already lost, and the bombing of German factories combined
with chronic shortages of spare parts and jet fuel kept most Me-262s grounded and prevented
them from having a major impact on the war. Nonetheless, in its single year of operational
use the Me-262 racked up a total of 542 confirmed kills, with 28 jet pilots attaining ace status.
On that April morning in 1945, Cadet Sergeant Mutke was on his
third training flight in the Me-262, along with several other cadets and an instructor,
Lieutenant Colonel Heinz Bär (“Bear”). Mutke had just reached an altitude of 12,000 metres
when the flight was attacked by group of American P-51 Mustangs. Racing to his comrades’ aid, Mutke
opened the throttle and pushed his aircraft into a 40-degree dive. As Mutke accelerated through
11,000 metres, he began to experience the telltale signs of compressibility,
his aircraft buffeting and swinging side-to-side and his controls growing increasingly stiffer.
His airspeed indicator, which only went up to 870 km/h mph, jumped off the scale. When Mutke
tried to pull out of the dive, the controls would not respond. The aircraft became uncontrollable,
shaking violently and threatening to break apart as it hurtled towards the ground.
Then, something strange happened. The buffeting suddenly stopped. The cockpit went eerily quiet,
and Mutke discovered he had full control of the aircraft. Yet he was still accelerating,
his airspeed indicator needle stuck against the stop peg. But Mutke had little time to
ponder this strange phenomenon, as a few seconds later both his engines flamed out. The aircraft
decelerated and the buffeting returned, not dissipating until Mutke had dropped below
the aircraft’s maximum rated speed of 870 km/hr. Mutke immediately returned to base,
and upon landing was shocked to discover the condition of his aircraft. Dozens of rivets
had been ripped out of the airframe, and his wings were bent and twisted. Due to this damage,
Mutke did not report the dive to his superiors, as exceeding 900 km/hr was strictly forbidden.
But Mutke didn’t quite know what to make of the strange phenomena he’d encountered
during the flight, and he put it out of his mind. It was not until three years later,
when Mutke learned of the pioneering flights of Chuck Yeager, that he came
to a startling realization: that he had broken the sound barrier.
The facts certainly seemed to fit: when an aircraft exceeds the speed of sound,
the multiple shockwaves forming all over the airframe coalesce into a single shock cone,
leading to smoother airflow. The sudden quiet Mutke experienced is also consistent
with supersonic flight, as at such speeds an aircraft effectively outruns the sound from its
own engines. The Me-262’s engines, however, were not designed to ingest air at supersonic speeds,
and breaking the sound barrier would have caused them to flame out just as Mutke experienced.
And as the aircraft decelerated through the transonic regime, the single shock cone would
have broken up into multiple shock waves, causing the violent buffeting to return.
But the most compelling piece of evidence was the fact that unlike most aircraft,
the Me-262 had an all-moving horizontal stabilizer, which instead of having
separate hinged elevators rotated as a single unit. This feature was later added to the Bell
X-1 supersonic rocket plane to get around the problem of shock waves forming on the elevator
hinges and freezing up the controls. The Me-262’s design would thus have
made it uniquely capable of maintaining pitch control at transonic and supersonic speeds.
But many are highly skeptical of Mutke’s claims. When designing the Me-262,
engineer Willy Messerschmitt conducted a series of wind tunnel tests to determine the aircraft’s
maximum speed. He concluded that the 262 could not exceed Mach 0.86 without experiencing pitch-down
forces so powerful no pilot could recover from the resulting dive. Post-war test flights
of captured 262s conducted by the British Royal Aircraft Establishment confirmed this,
with RAE engineers pinning the aircraft’s maximum speed at Mach 0.84. Engineers have
further argued that the 262’s engines were too underpowered and its wings and its airframe
insufficiently aerodynamic to allow for supersonic flight, and that the phenomena
Mutke encountered - like his airspeed indicator jumping off the scale - can occur at lower speeds.
However, several early jets not designed for supersonic flight - such as the North
American F-86 Sabre and Hawker Hunter - still managed to break the sound barrier in a dive,
the combination of engine thrust and gravitational acceleration being just enough to overcome the
drag of the airframe. This fact has prompted a reevaluation of Hans Mutke’s claims. In 1999,
Professor Otto Wagner of Munich’s Technical University carried out a series of computer
simulations and determined that the Me-262 could, theoretically, reach Mach 1.02 in a
dive and remain controllable. However, Wagner admitted that the aerodynamic data available
on the Me-262 was unreliable, and that obtaining Willy Messerschmitt’s original wind tunnel data
from 1941 would allow for a more definitive analysis. And theoretical models are about
the only available way of testing Mutke’s claims. No original Me-262s remain flying,
and the few flying replicas in existence use completely different, modern engines. Plus,
sending an aircraft into a supersonic dive is far too dangerous just to test an 8-year-old anecdote.
And in any case, whether or not Hans Guido Mutke actually broke the sound barrier is irrelevant.
Official aviation records are administered by the Federation Aeronautique Internationale,
a governing body based in Lausanne, Switzerland, and every record must be
confirmed using onboard FAI recording equipment. Due to the unmonitored wartime nature of his
1945 flight, Mutke was ineligible to claim an official record, while the October 14,
1947 flight of the X-1 - which carried FAI recording equipment - was. Thus,
the title of first pilot to break the sound barrier still belongs to Chuck Yeager.
Bonus Facts
1. Another pilot often claimed to have broken the sound barrier before Chuck Yeager is test pilot
George Welch, perhaps best known as one of the few American fighter pilots to make it into the
air and engage the Japanese during the attack on Pearl Harbour. In his 1998 book Aces Wild:
the Race for Mach 1, fellow test pilot Al Blackburn claimed that Welch broke the sound
barrier in a dive two weeks before Yeager while test-flying the North American XP-86,
the prototype of the famous F-86 Sabre. According to Blackburn, Welch was reprimanded for this act,
as official Air Force orders at the time forbade pilots of other aircraft from breaking the sound
barrier before the X-1. This was allegedly because the Air Force had poured vast resources
into the X-1 project and did not want a regular - and less expensive - aircraft beating them to
the punch. However, the historical record does not support this claim. While Welch did begin
test-flying the XP-86 in late September 1947, he immediately ran into problems extending the
aircraft’s landing gear. It was thus decided to carry out subsequent test flights with the
wheels extended, making it impossible for it to fly supersonically. The XP-86 would not fly
with its wheels retracted until after the X-1’s record-breaking flight on October 14. Furthermore,
many engineers and pilots at the time doubted that the XP-86’s J35 jet engine had enough power
to push the aircraft past Mach 1 even in a dive and with the wheels retracted. There is evidence,
however, that Welch broke the sound barrier on October 19 - a barely month after Yeager
and the X-1. However, this claim is based on data from ground tracking equipment and
not sensors mounted aboard the aircraft itself. According to Air Force records,
the XP-86 did not officially fly faster than sound until May 21, 1948 - a full seven months
later. So once again, Chuck Yeager’s claim to the title remains indisputable.
2. Yeager’s claim to being the first to break the sound barrier was also challenged by the
U.S. Navy - though this time on the basis of a technicality. At the time,
FAI rules stated that to qualify for an official record, an aircraft had to take off and land under
its own power. According to the Navy, this disqualified the X-1, which was air-launched
from a B-29 mothership. It also meant that the first supersonic aircraft was, conveniently,
the Navy’s own jet-powered Douglas D558-1 Skystreak. The Air Force did not take kindly
to this challenge, and on January 5, 1949 Chuck Yeager performed the first - and only - ground
takeoff in the X-1. The acceleration was so powerful it ripped off the aircraft’s flaps,
but Yeager managed to maintain control and pull the X-1 into a near-vertical climb.
90 seconds later Yeager broke the sound barrier at an altitude of 7,000 metres,
not only proving the Navy wrong but setting a long-standing time-to-climb record in the process.