NYT article -- NASA's X-43A jet (mach 7 speed)
May 22, 2001
Test of Revolutionary Jet Promises to Transform Flight
By WARREN E. LEARY
WASHINGTON, May 21 — After more
than four decades of promise and
speculation, a new type of jet engine is
about to power a small experimental plane at
speeds previously reserved for rockets.
Early next month, the unpiloted plane called
X-43A is to be shot to the edge of space on the
nose of a rocket before cutting loose for a short
dash on its own off the Pacific Coast at almost
5,000 miles per hour, seven times the speed of
sound.
If successful, the flight will be the first of an
air-breathing, nonrocket plane at hypersonic
speeds. This could lead to aircraft that can take
people anywhere in the world within two hours
or help boost cargoes into space at significantly
lower costs, proponents say.
To reach such speeds, the X-43A uses an
engine called a scramjet, which combines
features of a conventional turbojet with those of
a rocket. While the design and materials used to
make regular jets limit the speed of aircraft to
three or four times the speed of sound (2,000 to
3,000 m.p.h.), scramjets theoretically may push
planes to speeds of 18,000 m.p.h.
If scramjets work as engineers predict,
proponents say, it could bring an advance in
aircraft propulsion equal to that of jet engines
over motors driving propellers.
"This flight will make aviation history," said Joel
Sitz, X-43 project manager at NASA's Dryden
Flight Research Center in California, which is in
charge of the test flights.
Three X-43A's are to make hypersonic test flights over 18 months, starting on June 2,
from Edwards Air Force Base, Calif. Hypersonic speeds are those above Mach 5, or five
times the speed of sound. Mach 5 is about a mile per second, or 3,600 m.p.h. at sea
level. The first two X- 43A's are to try for Mach 7 and the last, Mach 10, about 7,000
m.p.h.
The aircraft are part of a six-year, $185 million program of the National Aeronautics and
Space Administration called Hyper-X, intended to refine hypersonic design and ground
testing and validate the results with flights. The program is being conducted jointly by
NASA's Langley Research Center in Hampton, Va., which is in charge of design and
ground testing, and Dryden.
The first hypersonic aircraft was the manned X-15, a rocket-powered craft that broke
speed and altitude records more than 30 years ago. The air-breathing X-43A hopes to
break the aircraft speed record of Mach 6.7 set by the X-15 in October 1967. The
fastest air-breathing plane is the SR- 71 "Blackbird" jet, slightly faster than Mach 3, or
2,100 m.p.h.
Conventional turbojets work by concentrating air with fan-like blades in a compressor,
combining it with fuel and burning the mixture to produce thrust. Faster speeds can be
attained using ramjets, which forgo the compressor and use a specially shaped inlet to
slow and concentrate air. But ramjets, which have been used in military missiles, do not
work unless the aircraft is already moving at high speed, usually with the initial
assistance of a rocket. Ramjets are also limited to about Mach 6 because their
combustion chambers overheat at higher speeds.
Scramjets, or supersonic-combustion ramjets, can attain higher speeds by reducing
airflow compression at the entrance of the engine and letting it pass through at
supersonic speeds. This reduces the temperature buildup in the combustion chamber,
overcoming the limits of regular jets but requires a rapid and tricky mixing and burning
of fuel and air.
Charles R. McClinton, technology manager for the Hyper-X program at Langley, said
researchers have worked on scramjets for more than 40 years, building mountains of
data from wind-tunnel and ground tests. Some early trials with limited prototypes led
some people to believe that hypersonic engines would not produce enough thrust to
overcome the atmospheric drag on the plane, Mr. McClinton said. "The X-43 flight is to
prove scramjets, once and for all, will work and will move an airplane."
Scramjet-powered craft are also different from other airplanes because the engine and
vehicle are integrated as one unit. The craft must be designed to capture large amounts
of thin air in the upper atmosphere, Mr. McClinton said, and the shape of the vehicle
must work like a giant air scoop.
The shock wave produced by the fast-moving aircraft helps guide the air into the engine,
and high pressure, trapped by the shock, on the bottom of the vehicle provides lift,
engineers said.
It has taken so long to develop scramjets because "the Apollo program came along, and
there was a shift to rocket technology," said Griff Corpening, chief engineer for the X-43
at Dryden.
There was a resurgence of interest in scramjets when President Ronald Reagan
announced the X-30 National Aero Space Plane, or NASP, project in 1986, intended to
produce a scramjet-powered craft that would revolutionize air travel and go into space at
25 times the speed of sound.
NASP never flew because it tried to combine too many untried technologies into a test
vehicle, Mr. Sitz and other experts said.
"We have taken NASP and chopped it up into more manageable chunks," Mr. Sitz said.
"This gets us a reasonable, mature technology base and gives us more confidence to step
up to a larger vehicle."
The X-43A is a 12-foot-long craft shaped like a flat blade with the engine sculpted into a
smooth pod on its bottom. The 2,700-pound vehicle, made by MicroCraft of Tullahoma,
Tenn., is 5 feet wide across its tail fins and made of aluminum and steel alloys, with a
special heat-resistant carbon material on its leading edges to withstand temperatures
expected to reach 2,200 degrees Fahrenheit.
The research craft is attached to a modified, air-launched Pegasus rocket booster made
by Orbital Sciences of Dulles, Va. The flight plan calls for a modified B-52 bomber to
drop the X-43A from 24,000 feet above the Navy's Pacific test range. The rocket is to
accelerate the craft to 95,000 feet and Mach 7 before the vehicles separate. Seconds
later, the scramjet is to fire for 7 to 10 seconds and propel the X-43A about 4,700 m.p.h.
Although engine burns of a few seconds may not seem significant, project engineers say
the data will be vastly superior to any from wind tunnels and will show how the engine
works under real conditions. More than 500 sensors will provide information about
almost every aspect of the flight, and chase aircraft also will be collecting data, officials
said.
Because of cost and complexity, there are no plans to recover any of the X-43's, which
will be maneuvered to crash into the ocean.
Copyright 2001 The New York Times Company |
