In June 2000, the Defense Advanced Research Projects Agency (DARPA)
awarded the first study contracts for a carrier-based unmanned combat aircraft
- labeled UCAV-N (Unmanned Combat Air Vehicle - Naval) - to Northrop Grumman
and Boeing. At that time, Northrop Grumman was already privately developing
its Pegasus UCAV demonstrator, which was completed in July 2001. In
June, it had received the official military designation X-47A (Boeing's UCAV-N
was designated as X-46A).
The X-47A was extensively tested on the ground during 2001 and 2002 (including
taxiing), and the first flight finally occurred on 23 February 2003.
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X-47A |
The X-47A was a stealth design with no vertical control surfaces, yaw
control being achieved by differential movements of surfaces in the wings. The
all-composite airframe was powered by a single Pratt & Whitney JT15D turbofan.
The vehicle's computer-based control system performed flight control,
navigation, mission control and other tasks. The Pegasus was equipped
with a U.S. Navy Shipboard Relative GPS navigation system, which would have
been necessary for automatic pin-point landings on a moving aircraft carrier
deck. On its first flight, the X-47A tested that system by making an exact
landing on a pre-designated spot on the runway.
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X-47A |
As it turned out, the first flight of the X-47A remained the only one so
far. In April 2003, DARPA combined the UCAV-N program with the on-going USAF/DARPA UCAV
program into the joint DARPA/USAF/Navy J-UCAV program, later renamed J-UCAS
(Joint Unmanned Combat Air Systems). Northrop Grumman apparently decided that
further flight tests of the X-47A would not help the development of its
forthcoming J-UCAS demonstrator, designated X-47B.
The airframe of the X-47B has not much in common with that of the X-47A.
It is significantly larger, has a more powerful P&W F100 turbofan engine, and
redesigned outer wing sections and intake/exhaust configurations. The wing
extensions provide for longer range and better low-speed characteristics, and
are foldable to reduce parking space on the aircraft carrier. The payload
capacity for J-UCAS was to be 2040 kg (4500 lb), representing two GBU-31/B
JDAM (Joint Direct Attack Munition) GPS/INS-guided bombs. Northrop Grumman was
under contract to build two (originally three) X-47Bs, and flight testing,
together with the rival Boeing X-45C,
was expected to begin in 2007.
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X-47B |
The J-UCAS development effort was defined in terms of "spirals". The
X-45A
UCAV demonstrator was "Spiral 0", while the X-45C and X-47B represented
"Spiral 1". Later spirals were to further enhance the mission capabilities of
the system by integrating more sensor and weapon options. The ultimate goal
had been labeled J-UOS (J-UCAS Objective System) by DARPA.
In early January 2006, the J-UCAS program was cancelled in favor of
separate follow-on programs by the USAF and U.S. Navy, and - in case of the
Air Force - the development of new manned long-range bomber aircraft. The Navy
has since effectively taken over the J-UCAS program under a new label (first
N-UCAS, then UCAS-D (Demonstrator)), and parallel development of the X-47B and
X-45C vehicles as carrier-based UCAVs continued until mid-2007. In August
2007, the Navy announced the X-47B as the winner of the UCAS-D competition.
Primary goal of the six-year X-47B development and evaluation program is the
demonstration of launches and recoveries on an aircraft carrier at sea. The
first flight of the vehicle is tentatively scheduled for late 2008.
Specifications
Note: Data given by several sources show slight variations. Figures
given below may therefore be inaccurate!
Data for X-47A/B:
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X-47A |
X-47B |
| Length |
8.50 m (27.9 ft) |
11.6 m (38.2 ft) |
| Wingspan |
8.47 m (27.8 ft) |
18.9 m (62.1 ft) |
| Weight (gross) |
2500 kg (5500 lb) |
19000 kg (42000 lb) |
| Speed |
Subsonic |
High subsonic |
| Ceiling |
? |
> 12200 m (40000 ft) |
| Range |
? |
6500 km (3500 nm) |
| Propulsion |
Pratt & Whitney JT15D-5C turbofan; 14.2 kN (3190 lb) |
Pratt & Whitney F100-PW-220E turbofan; 105.7 kN (23770 lb) |
Directory of U.S.
Military Rockets and Missiles,
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X-47 Pegasus Naval
Unmanned Combat Air Vehicle |
The airframe is a stealthy planform design. It is diamond-kite shaped
with a 55° backward sweep on the leading edge and a 35° forward sweep on the
trailing edge. The X-47A has a wingspan of 8.47m and is 8.5m long; the
dimensions of the X-47B have yet to be finalised.
Scaled Composites Inc of Mohave, California, were contracted to
manufacture the all-carbon composite airframe. The air vehicle has no tail or
vertical fin. Instead of a traditional rudder for yaw control, the upper and
lower surfaces are each fitted with two sections of moving surfaces. A large
elevon is clearly visible at the mid-section of each trailing edge.
"In April 2007, Northrop Grumman submitted a bid to the US Navy for the
Unmanned Combat Air System Demonstrator (UCAS-D)."
The vehicle is robustly built for carrier take-off and landings and uses
a conventional wheeled take-off and landing with an arrestor hook. The
retractable tricycle-type landing gear consists of a single nose wheel, twin
wheel main landing gear and a fully retractable arrestor hook. Smiths
Aerospace is providing the landing gear for the X-47B.
The Pegasus is equipped with an avionics suite supplied by BAE Systems
Platform Solutions of Johnson City, New York. The avionics and vehicle
management computer performs flight control processing, autopilot control,
engine control processing, mission command and control, navigation and other
functions.
The computer features an embedded, open-architecture CsLEOS real-time
operating system which uses 'brick-wall' time and memory partitioning to allow
multiple applications to run on the same system without interfering with each
other. The system also provides multiple scheduling modes, allowing users to
switch between different schedule profiles in real time.
The navigation systems include the United States Navy Shipboard Relative
Global Positioning System (SRGPS) automatic landing system.
The Pegasus is powered by a single Pratt & Whitney Canada JT15D-5C
turbofan engine rated at 14,19kN. The air vehicle carries 472kg of fuel but
has a maximum capacity of 717kg of fuel for long-range operations or for
increased loiter times.
US Air Force
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Flying Is
Easy; Landing Is Not! |
Smoothing the
landing
The Navy’s shipboard Joint Precision Approach and Landing System uses
Differential GPS to provide 3D navigation accurate enough for
hands-off autopilot landings on a carrier. Successfully demonstrated
by an F/A-18 on the USS Theodore Roosevelt in April 2001, the system
uses a base station on the carrier to broadcast error corrections to
the aircraft’s GPS receiver. The navigation processing equipment on
the aircraft uses the corrected signal to increase the plane’s
GPS-derived position.
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Northrop Grumman decided to focus its efforts
on landing characteristics, considered the toughest phase of flight, dictating
that the majority of the test flight activity be performed in the traffic
pattern. For that reason, the landing gear was pinned in the down position,
and speeds were limited to 175 kt, though Mazur says the plane would have been
capable of reaching Mach 0.8. If the aircraft experienced a communications
dropout—loss of a “heartbeat up and heartbeat down” signal—the on-board
software was designed to orbit the airport once while trying to reestablish
contact. If the link could not be restored, the aircraft would then fly to a
preestablished “waypoint,” try for 20 min to regain communications, and,
failing that, go land itself.
| Scaled
Composites built the X-47 from designs supplied by Northrop Grumman.
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Taxi tests are a “big step” for unmanned aircraft, says Mazur. For
Pegasus, this meant a series of “brakes off, brakes on” tests on the runways
at China Lake. Starting July 19, 2002, the team began towing the aircraft into
position on the taxiway, orthogonal to the runway, and commanding the vehicle
to taxi. Using GPS, Pegasus would line itself up on the runway centerline,
overshooting the turn in order to check steering in both directions. After
low-speed taxi tests at 3 kt and high-speed taxi tests at up to 85 kt, the
team put Pegasus through a series of 12-14 zigzag maneuvers for a mile down
the runway, making sure the nose wheel tracked the runway centerline. For
high-speed taxi tests, the team practiced autonomous takeoff aborts and ground
operator aborts.
For the first flight, Mazur says a test pilot with Global Hawk flight
experience pushed the takeoff button while a company King Air provided
air-to-air photographic coverage. Pegasus accelerated to the rotation speed of
110 kt, lifted off, climbed out of ground effect, and then accelerated to 150
kt. On downwind, the aircraft climbed to 3,300 ft and slowed to 110 kt to test
the flight characteristics in landing configuration.
Next it accelerated to 130 kt and began preparations for landing,
deploying the inlays, and slowing to 110 kt with the arresting hook in place.
Mazur says the goal was to set up a carrier-style landing—2.5° glideslope and
no flare touchdown—using the spot where the arresting hook touched down as the
pass/fail criterion. After a “very smooth” landing, the team found that
Pegasus had landed 18 ft downrange and 16 ft to the left of the planned
touchdown point, close enough that it would have caught an arresting cable on
a carrier landing, Mazur notes.
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Under the new joint UCAV program, Northrop
Grumman’s work on the X-47B will be more closely aligned with Boeing’s UCAV
work. For now, however, it appears that both companies will build and deliver,
in the 2006 time frame, their own versions of demonstration aircraft, each
capable of flying 1,300 n.mi. with a 4,500-lb payload. Boeing, which has
completed dozens of flights with its X-45A, is currently working on larger
models. The company is scheduled to deliver three aircraft under its
$140-million contract with DARPA.
Aside from the limited number of demonstration aircraft coming later
this decade, will UCAVs be big business in the future? That depends whom you
ask. Weatherington has said the potential number of UCAV systems to be
deployed is very large, and that the joint program office will not have the
winner-take-all policy that the Joint Strike Fighter program had. He would not
comment on what he thinks the mix between manned and unmanned systems in the
future is likely to be, however.
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Boeing X-45 (Top) and Northrop X-47 (Bottom) |
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Larry Dickerson, senior analyst with Forecast International, says
military opinions on unmanned missions are divergent—some think strike
missions are too complicated for UAVs and that cruise missiles will suffice,
while others would rather see the funding go to reconnaissance platforms such
as Global Hawk and Predator.
Teal’s Zaloga says the value of UCAVs must be weighed against the cost
of alternatives. “Most traditional programs have suffered from extremely high
cost growth,” he says, adding that Global Hawk costs grew from $10 million to
$40 million. “If the UCAVs end up with high procurement costs and low
reliability, the competition will not come from the manned side, but from
missiles,” he says. If the “threat environment” from surface-to-air missiles
increases, says Zaloga, the military will have the options of using cruise
missiles, at up to $1 million each; manned aircraft with standoff missiles,
for about $300,000 each; or unmanned stealthy platforms, theoretically at half
the price of fighter aircraft, carrying $40,000 GPS-guided bombs. “UCAVs are
attractive if you can get into the target area with cheaper munitions,” he
says, adding that there is likely to be less “political fallout” from losing
an unmanned aircraft.
In the long term, visions of hunter/killers roaming the skies with
nothing but integrated circuits behind the wheel are probably best left to
Hollywood. “At this stage, the UCAV is a technology demonstration,” Zaloga
says. “It’s such a novel concept that until you try doing it, you can’t answer
the questions. It’s by no means clear what the unmanned vs. manned mix will
be,” he says. “I don’t personally believe unmanned will replace manned in the
next decade, if ever.”
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The Northrop Grumman X-47 Not A Concept
Anymore |
Writing by Evan Ackerman
on Thursday, 29 of November , 2007
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Back in August, the Pentagon chose Northrop Grumman’s X-47 UCAV for
a major airforce contract, pretty much killing off
Boeing’s X-45 drone
program. It’s not even December yet, and already Northrop Grumman has a
“100% structurally complete” X-47 UCAS-D (that would be, Unmanned Combat
Air System Demonstrator). All that’s left to do before it’s ready to go is
subsystems installation, lots and lots of testing, and figuring out how to
get it to land and take off on an aircraft carrier. Huh, looks easy enough
in the video…
