发信人: Lsquirrel (demon), 信区: MilitaryTech
标 题: 美国人说：J20隐身战斗机是脆弱的
发信站: 水木社区 (Sun Jan 16 16:48:31 2011), 站内
因为随着AESA和L等长波段雷达的飞速发展，隐身飞机的隐身能力越来越不可靠了:-)
Stealthy Chinese J-20 Vulnerable
Jan 14, 2011
By David A. Fulghum, Bill Sweetman, Bradley Perrett, Robert Wall
Washington, Washington, Beijing, London
China’s newest combat aircraft prototype, the J-20, will require an intense
development program if it is going to catch up with fast-moving anti-stealt
h advances.
In fact, anti-stealth will bring into question all stealth designs: How much
invulnerability will current low-observability techniques offer as air defe
nse systems adopt larger and more powerful active, electronically scanned ar
ray (AESA) radars? From the early days of AESA development, a key goal was t
o build a radar that could detect very small objects—such as a cruise missi
le at a distance great enough to target and shoot it down—or a larger objec
t like a fighter with a very low-observable treatment.
Airborne detection of stealth aircraft may already be an operational capabil
ity. In a series of tests at Edwards AFB, Calif., in 2009, Lockheed Martin’
s CATbird avionics testbed—a Boeing 737 that carries the F-35 Joint Strike
Fighter’s entire avionics system—engaged a mixed force of F-22s and Boeing
F-15s and was able to locate and jam F-22 radars, according to researchers.
Raytheon’s family of X-band airborne AESA radar—in particular, those on u
pgraded F-15Cs stationed in Okinawa—can detect small, low-signature cruise
missiles.
Moreover, Northrop Grumman’s lower-frequency, L-band AESA radar on Australi
a’s Wedgetail airborne early warning and control aircraft is larger and pot
entially more capable of detecting stealth aircraft at longer ranges.
Lockheed Martin also hinted at a JSF anti-stealth capability in 2009 in a re
ference to combat with sophisticated, foreign aircraft. “The F-35’s avioni
cs include onboard sensors that will enable pilots to strike fixed or moving
ground targets in high-threat environments, day or night, in any weather, w
hile simultaneously targeting and eliminating advanced airborne threats,” s
aid Dan Crowley, then-executive vice president and F-35 program general mana
ger.
Better images emerging from China point clearly to the J-20’s use of stealt
h technology, but major uncertainties and questions remain unresolved.
The overall shape resembles that of the F-35 and F-22, which have a single “
chine line” uniting the forebody, upper inlet lips, and wing and canard edg
es with a curved surface above that line and flat, canted body surfaces belo
w it. The wing and canard edges are aligned: The wing and canard leading edg
es are parallel and the trailing edge of each canard is aligned with the opp
osite wing’s trailing edge. The same basic philosophy also has been adopted
in British, Swedish and Japanese studies for stealth fighters.
The aim in all cases is to endow a practical, agile fighter configuration wi
th a “bow-tie” radar signature, with the smallest signature around the nos
e and the greatest (still much lower than that of a conventional aircraft wi
th curved or vertical-slab sides) to the side. The fighter’s mission planni
ng system, using a database of known radar locations, then derives a “blue
line” track that weaves between radars and avoids exposing the side-on sign
ature to those radars more than transiently.
The “diverterless” supersonic inlet avoids a signature problem caused by a
conventional boundary layer diverter plate. For example, the F-22 has a con
ventional inlet, which is likely to require extensive radar absorbent materi
al (RAM) treatment.
The biggest uncertainty about the Chinese design concerns the engine exhaust
s, which as seen on the prototype are likely to cause a radar cross-section
(RCS) peak from the rear aspect. One possibility is that a stealthier two-di
mensional nozzle will be integrated later in the program; however, the nozzl
es on the current aircraft show some signs of RCS-reducing sawtooth treatmen
t, suggesting that the People’s Liberation Army has accepted a rear-aspect
RCS penalty rather than the much greater weight and complexity of 2D nozzles
.
Other features are less clear. Stealth development has been dogged by detail
-design challenges. All the antennas on the aircraft have to be flush with t
he skin and covered with surfaces that retain stealth properties while being
transparent in a specific frequency. Maintainability becomes a complex trad
eoff: Some systems requiring frequent attention will be accessed via landing
gear and weapon bays, and others by latched and actuated doors that can ope
n and close without affecting RCS—but the latter involves a weight penalty.
Perhaps the toughest hurdle is managing radio-frequency surface currents ove
r the skin. Early stealth designs used heavy, maintenance-intensive RAM. The
F-22 introduced a much lighter surface treatment, but it has proven unexpec
tedly difficult to maintain, causing corrosion issues. Lockheed Martin now a
sserts that the F-35 will be robust and affordable to maintain in service, w
ith a combination of a high-toughness, sprayed-on topcoat and a conductive l
ayer cured into composite skin panels.
The Chengdu J-20 design has struck many analysts and observers as familiar a
nd somewhat different from the F-22, F-35 or Sukhoi T-50.
“The J-20 is reminiscent of the Russian MiG-1.42 both in terms of planform
and also with regard to the rear fuselage configuration,” says Douglas Barr
ie, senior fellow for military aerospace at London’s International Institut
e for Strategic Studies. “The most obvious difference is the greater forwar
d fuselage shaping as the basis for low-observable characteristics, along wi
th the different engine intake configuration. The MiG program was canceled b
y the Russian government around 1997,” he notes. However, the similarity to
the MiG concept may suggest some collusion with the Russian aviation indust
ry.
The J-20 made its first flight shortly before 1 p.m. Beijing time on Jan. 11
. The flight ended three weeks of anticipation that began in late December w
hen the new design started taxi tests.
The discussion about the program will now shift to the aircraft’s mission (
fighter or, more likely, long-range strike), sensors (strike missions would
require a high-resolution, long-range radar) and communications (which would
demand high-speed data links and sophisticated integration).
Conventional radars have only one-half to one-third of the range of an AESA
radar. Moreover, the movement of a conventional, mechanically scanned radar
antenna provides a tell-tale glint of radio-frequency reflections to enemy a
ircraft with advanced radars. Such reflections undercut the effectiveness of
a stealth airframe. China is known to be pursuing newer radar technology.
“It’s too early to tell the true status of the Chinese AESA program,” say
s a Washington-based intelligence official. “We’ve seen lots of press and
air show information on the program, but that doesn’t automatically transla
te into a robust development or give us an accurate look at where [China] is
as far as fielding one anytime soon.
“Like the [high-performance] engine, it’ll be a challenge to take the step
from older radars to one designed for a fifth-generation fighter,” he says
. “Again, though, the J-20 is just the first or second—depending on whom y
ou believe—prototype in a very long development program.”
If the Chinese conduct a few months of flight tests and there are no more ai
rcraft involved in the program, this might indicate that the J-20 is a proof
-of-concept or technical demonstrator. If there are several aircraft eventua
lly, a prototype program would be a more likely conclusion.
The flight occurred during a visit to China by U.S. Defense Secretary Robert
Gates, who says Chinese President Hu Jintao confirmed the event to him in t
alks. However, Gates still believes the U.S. will retain a preponderance of
stealth fighters through 2025. |
显身卡
