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Navy Sailor Snapped a Picture of a Jet Fighter Breaking the Sound Barrier-Disputed!
This email features a picture of an F-18 jet fighter flying through
a cloudy circle of what is said to be visible evidence of breaking
the sound barrier. The story says the photo was taken by
Ensign John Gay when the plane swished past the U.S. aircraft
carrier Constellation at 750 miles per hour.
Ensign Gay is real and he did take the picture. There is
controversy among people who have seen the picture, however, as to
whether it is authentic. Some observers say that what Ensign
Gay has photographed is not a breaking of the sound barrier, but a
different phenomenon involving a combination of
the aerodynamics of the airplane, the atmospheric pressure, and the
temperature. Also, Ensign Gay says he took the picture at the
moment he heard the sonic boom. Critics have said that is not
likely since the plane was flying faster than sound, so any sonic
boom would have been heard after the plane passed.
To get a professional perspective on this, TruthOrFiction.com turned
to Professor James R. Frysinger of the Department of Physics and Astronomy
at the University/College of Charleston in Charleston, South
Carolina and who served in the United States Navy. He says
such pictures can be authentic and explains why. He also
describes why the person taking a picture of a supersonic jet would
indeed hear a sonic boom even if the jet had exceeded the sound
barrier long before arriving at the photographer's location:
Dr. Frysinger wrote:
The explanation A conically shaped high pressure surface is formed by objects
traveling faster than the speed of sound in a medium, e.g., a jet flying
through the air.
This cone is caused by the sound source (jet) traveling faster than the
sound waves that are produced by it can travel.
The result is an "envelope" of overlapping circles ("sound
wave crests"), each with its center lying ahead of the last sound
crest. That envelope is conically shaped with its point at the actual
sound source. Lying just inside this conically shaped sound pressure wave
(above ambient pressure) is a similar, conically shaped surface of
below-ambient pressure air ("sound wave trough").
This is a necessary result of the wave nature of sound waves. Any decent
physics text will have a sketch of this. If the humidity level is high
enough (e.g., just above sea surface on a warm Pacific Ocean afternoon),
the humidity in the air may condense in that trough of low pressure and
form a cloud, only to be reabsorbed by the air when pressure returns to
Such clouds tend to form on the noses, nacelles, an leading egdes or tips
of wings, canards, etc. These are not unlike contrails except that the
water vapor is present in the air before the jet passes, as opposed to
being the result of burning jet fuel.
The sonic "boom"
Pictures of these show the result of moisture condensing in the conically
shaped wave trough just behind the shock wave. The sonic "boom"
reported with these events is NOT caused at the time the jet's speed rises
past the speed of sound. It is in fact the continuous sound that the shock
wave "crest" represents. A person farther down the path of the
jet will hear the same "boom" but later than a person nearer the
jet's direction of approach. The speed of the sound crest is equal to the
speed of the jet in the direction of travel and equal to the speed of
sound perpendicular to the cone's surface. The movie clip on my website at
shows the jet approaching and at that moment it has not yet been heard by
the observer. Many of the stills being passed around are single frames
from similar video clips; the camera was rolling before the
"boom" was heard.
A personal account I was fortunate during my last tour of duty to be standing atop a
building at the end of the main runway at NOB Norfolk, a large naval base
during a show by the Navy Blue Angels. My height above ground was
equivalent to being on the fourth floor, but I was on top of it and
"in the elements". The announcer let us know that a jet was
coming in at a supersonic speed and would pass at that speed down the
length of the runway and "very close to the deck". I saw it
coming and aimed my camera slightly downward to its altitude and then
tripped the shutter on my tripod-mounted camera as it went by.
Immediately, I was blown over backwards and my camera and its tripod
landed on top of me. The sequence--all in a fraction of a second--was
click, boom, thud. Having been alerted I didn't need to "wait for the
boom" to tell when to take the picture. And since the shock wave is
NOT a momentary phenomenon, I could let my eye judge when he would be
"dead ahead". All this happened so fast that it seemed for a
moment to be simultaneous, but that was an illusion. Yes, I got the
picture, looking slightly down into the cockpit and with a clear view of
the pilot. Humidity levels that day were too low for a contrail-type cloud
to form as they did in the movie clip cited above.
The technical explanation The geometry works out such that the sine of the apex half-angle (half
the angle at the point of the cone) is equal to the ratio
of the speed of sound in air of that temperature,
pressure, and humidity to the jet's speed. That
speed ratio is called the Mach Number. So, sin(theta)
= V/v or sin(theta) = 1/(Mach Number) where v is the
speed of the jet, V is the speed of sound at that location,
and theta is half the angle made at the point of the cone.
Notice that if the speed of the jet equals the speed of sound, the
"cone" is actually a flat surface perpendicular
to the direction of travel. If the jet's speed is
less than the speed of sound, the equation is not
valid; there IS no superposition of crests taking place (although
there is a large pressure build up, similar to a bow wave on a
ship). Our thanks to Professor Frysinger
A real example of the story as it has been circulated:
Awesome - Wanna see a sonic boom?
Through the viewfinder of his camera, Ensign John Gay could see the
fighter plane drop from the skyheading toward the port side of the
aircraft carrier Constellation.
At 1,000 feet, the pilot drops the F/A-18C Hornet to increase his
speed to 750 mph, vapor flickering off the curved surfaces of the
plane. In the precise moment a cloud in the shape of a farm-fresh
egg forms around the Hornet 200 yards from the carrier, its engines
rippling the Pacific Ocean just 75 feet below, Gay hears an explosion
and snaps his camera shutter once.
"I clicked the same time I heard the boom, and I knew I had it",
Gay said. What he had was a technically meticulous depiction of the sound
barrier being broken July 7, 1999, somewhere on the Pacific between Hawaii
Sports Illustrated, Brills Content and Life ran the photo. The photo
recently took first prize in the science and technology division in
the World Press Photo 2000 contest, which drew more than 42,000
"All of a sudden, in the last few days, I've been
getting calls from everywhere about it again. It's kind of neat," he
said, in a telephone interview from his station in Virginia Beach, Va.
A naval veteran of 12 years, Gay, 38, manages a crew of eight
assigned to take intelligence photographs from the high-tech belly of
an F-14 Tomcat, the fastest fighter in the U.S. Navy. In July, Gay
had been part of a Joint Task Force Exercise as the Constellation
made its way to Japan. Gay selected his Nikon 90 S, one of the five
35 mm cameras he owns. He set his 80-300 mm zoom lens on 300 mm, set his
shutter speed at 1/1000 of a second with an aperture setting of
F5.6. "I put it on full manual, focus and exposure," Gay said.
tell young photographers who are into automatic everything, you
aren't going to get that shot on auto. The plane is too fast. The
camera can't keep up." At sea level a plane must exceed 741mph to
break the sound barrier, or the speed at which sound travels. The
change in pressure as the plane outruns all of the pressure and sound
waves in front of it is heard on the ground as an explosion or sonic
boom. The pressure change condenses the water in the air as the jet
passes these waves. Altitude, wind speed, humidity, the shape and
trajectory of the plane - all of these affect the breaking of this
barrier. The slightest drag or atmospheric pull on the plane
shatters the vapor oval like fireworks as the plane passes through,
he said everything on July 7 was perfect. "You see this vapor
flicker around the plane that gets bigger and bigger. You get this
loud boom, and it's instantaneous. The vapor cloud is there, and
then it's not there. It's the coolest thing you have ever seen."