* One of the latest trends in UAVs is the "uninhabited combat air vehicle (UCAV)", or robot strike aircraft. This chapter outlines current developments in UCAVs.
* If UAVs could be used for reconnaissance, it was obvious that they could also be used for active combat missions, at least in principle. In 1964, Ryan conducted experiments under "Project CeeBee" using a Firebee fitted with underwing pylons to carry two 115 kilogram (250 pound) bombs, later fitting the machine with longer wings to carry two 225 kilogram (500 pound) SUU-7 cluster munitions. The Firebee was ground-launched, using a hefty RATO booster taken from an ASROC antisubmarine rocket, with test flights performed in the White Sands missile range in New Mexico.
The CeeBee experiments didn't go anywhere because shooting at a specific target is much trickier than flying over an area and taking pictures, and it wasn't until 1971, when more sophisticated guided munitions were available, that the Air Force came back to the concept. The objective was to study an attack system to perform the dangerous "suppression of enemy air defenses (SEAD)" mission, or in other words to destroy enemy anti-aircraft gun and SAM sites. The project was known as HAVE LEMON, a somewhat odd choice of name, since in US slang a "lemon" is a troublesome and worthless automobile or similar disagreeable machine.
HAVE LEMON involved a number of Ryan Firebees equipped with a weapons pylon under each wing, a forward-looking TV camera, and a datalink mounted in a pod on top of the vertical tailplane. These UAVs were given the designation "BGM-34A" and used beginning in late 1971 to perform remote-control strikes on simulated air-defense sites with Maverick missiles and HOBOS TV-guided glide bombs. Both the weapons had imaging seekers, allowing a remote control "pilot" to target the weapons. The very first launch of a missile, a Maverick, from a UAV was on 14 December 1971. Experiments were also performed with Firebees carrying Shrike antiradar missiles.
The results were interesting enough to permit follow-on development, resulting in the "BGM-34B", which featured an extended nose to accommodate an infrared imaging system (some sources say low-light-level TV, maybe it could fit either) and laser target designator for targeting and control of laser-guided bombs. Tests performed with in 1973 and 1974 with the BGM-34B were also successful, and led Teledyne-Ryan to develop a "BGM-34C" as a conversion of existing Lightning Bug airframes. The BGM-34C could be used for reconnaissance or strike missions by swapping out nose modules and other elements.
The concept proved to be a little too far ahead of its time. Nobody in the Air Force hierarchy stepped forward to take ownership, and the HAVE LEMON exercise faded away. The test squadron was disbanded in 1979 and its roughly 60 UAVs were put into storage. However, in the summer of 2003 a UAV "airshow" of sorts was conducted, in which a Firebee was displayed carrying two Hellfire anti-armor missiles, as well as a pod for dispensing remote battlefield sensors; apparently Northrop Grumman was running the idea back up the flagpole to see if anyone would salute. It seems nobody did.
* UAV advocates claim the Air Force abandoned UAVs for strike missions because of inclination of "hotshot flyboys" to keep the mission for themselves, but in fact the concept has always suffered from "command and control" problems, such as the vulnerability of communications links to jamming and spoofing, along with the need to hit specific targets and not accidentally kill civilians or friendly troops. The fact that the Firebees had to be air-launched by a DC-130 and then recovered by a helicopter made them much more expensive to operate than they would seem on the face of it, and also resulted in a very long sortie turnaround time -- at least 24 hours, compared to three hours for an A-10 tank buster aircraft.
The US military had got off to a false start with the Lightning Bugs; UAVs proved useful in Vietnam but only for a very specific mission, and they were never as cheap as they seemed at first. US work on UAVs all but faded out in the 1980s. However, during the 1980s into the early 1990s a string of technological improvements were developed -- better communications links, GPS navigation, automated takeoff and landings, autonomous flight control -- and the military became much more comfortable with the idea of robot aircraft.
In the late 1990s, the concept of using UAVs for performing actual combat was revived in the form of various designs generally designated as "uninhabited combat air vehicles". One of the initial concepts was to develop a UCAV on a fast track for "air occupation". The idea was to use unpiloted aircraft to fly continuous patrols over hostile territory, with some of the aircraft fitted with sophisticated sensors to identify enemy activities and target them, and other aircraft following up with attacks. The idea was obviously inspired by USAF air patrols over Iraq and the Balkans. Lockheed Martin suggested rebuilding old F-16A fighters as UAVs, fitting them with a wide wing to provide additional fuel, and also permit carriage of six or more air-to-surface weapons to provide the air-occupation strike element. The modified F-16As would have had endurance of 8 hours over a target area, and three sets of them could maintain 24-hour coverage.
The US Navy also began studies for UCAVs at about the same time. The Navy saw that UCAVs had a number of potential benefits. They promised to be cheaper than manned aircraft, with a lower purchase cost and much lower operating costs, since operators could be given much of their training through simulations. UCAVs would also be smaller and so stealthier than manned aircraft, and could perform high-gee maneuvers impossible with piloted aircraft, allowing them to dodge missiles and enemy fighters.
Indeed, since the Navy found themselves increasingly committed to the use of expensive cruise missiles to perform punitive strikes and other "limited" military operations, UCAVs offered a potentially cheaper alternative, a "reusable cruise missile". One UCAV could carry a number of smart GPS-guided munitions and hit multiple targets on a single sortie, and then return home to be used again. Even with a high operational attrition rate, the cost would be less than that of a barrage of cruise missiles.
Lockheed Martin performed studies that envisioned a number of different naval UCAV configurations, including "short takeoff and landing (STOVL)" aircraft that could be operated off of aircraft carriers, or "vertical attitude takeoff and landing (VATOL)" or "pogo" aircraft that could be operated off destroyers and other surface combat ships, or even submarines.
Piloted pogo aircraft were flight-tested in the 1950s and proved a technological dead end at the time, since they couldn't carry a useful payload, and were extremely difficult to land even under benign conditions. The payload limitations can be addressed with lighter materials and RATO-boosted takeoff, and modern digital flight control systems can address the landing issue. The Navy envisioned using pogo UCAVs to arm a guided-missile destroyer "unmanned air wing" with 20 pogo UCAVs for strike, and five pogo UAVs for reconnaissance.
The submarine launch concept was even more speculative, since recovery was a problem. The Lockheed Martin UCAV concepts were in the 4.5 tonne (10,000 pound) weight class and carried a warload of 450 kilograms (1,000 pounds). Weapons were carried internally to improve stealth and consisted of 45 kilogram (100 pound) and 115 kilogram (250 pound) small smart bombs. Range would be about 1,100 kilometers (680 miles), with capability for probe-and-drogue aerial refueling. Top speed would be in the high subsonic range, and ceiling would be about 12.2 kilometers (40,000 feet). The UCAVs would be equipped with fairly simple radar or electro-optical sensors to give the operators imagery of the target. Long-range sensing would be provided by other platforms in air or space.
One Lockheed Martin UCAV concept was an arrowhead-shaped vehicle with no vertical surfaces and the air intake on top. A shaft-driven lift fan would exhaust through the nosewheel door for vertical landings, while the nose sensor array would pivot forward to expose the intakes for the lift fan. The UCAV would have a retractable refueling probe, communications antennas mounted on the aircraft's spine, and lights for navigation and refueling operations. Moveable wingtips and control surfaces along the sawtooth rear edge of the UCAV would eliminate the need for vertical stabilizers.
Another Lockheed-Martin UCAV concept envisioned a diamond-shaped tailless flying wing, with an engine buried down the centerline, and conformal weapons bays flanking the engine. For greater stealth, the UCAV would flip onto its featureless back and fly upside-down.
Such UCAVs could be available in several versions: one with an afterburning engine for maximum performance; one with a non-afterburning engine, but with a thrust-vectoring exhaust for better maneuverability; and one with a conventional non-afterburning engine for low cost. UCAV missions would be conducted by an operator in a ground vehicle, warship, or control aircraft over a high speed digital data link. The operator would not really be flying the UCAV directly, however, since the robot would be able to handle the details of flight operations by itself, leaving the operator in a supervisory role. The UCAV would be able to complete its mission autonomously if communications were cut.
BACK_TO_TOP* UCAV speculations were impressive for their imaginativeness, but had a taste of science fiction. Efforts quickly moved on to real-world UCAVs. In March 1999, DARPA awarded a contract to Boeing for two "X-45A" UCAV technology demonstrators. Northrop Grumman and Raytheon also submitted designs, but lost the bid. Boeing rolled out the first prototype for public presentation at Saint Louis, Missouri, in September 2000. First flight was on 22 May 2002, from Edwards Air Force Base in California, and was followed a few months later by the second prototype.
Boeing's X-45A was a stealthy tailless aircraft, with composite outer structures and an aluminum internal structure. It had a midbody-mounted wing with a straight leading edge and a sawtooth trailing edge, all with 45-degree sweep angles.
BOEING X-45A UCAV DEMONSTRATOR: _____________________ _________________ _______________________ spec metric english _____________________ _________________ _______________________ wingspan 10.3 meters 33 feet 10 inches length 8.08 meters 26 feet 6 inches height 2.94 meters 6 feet 8 inches empty weight 3,630 kilograms 8,000 pounds gross weight 5,528 kilograms 12,190 pounds maximum speed subsonic range 600 kilometers 375 MI / 326 NMI _____________________ _________________ _______________________
The X-45A was powered by an Allied-Signal F124 turbofan with a rectangular thrust-vectoring exhaust that swiveled in the horizontal plane, helping to compensate for the aircraft's lack of a tail assembly. The engine was mounted in the center of the fuselage.
The X-45A had two weapons bays. One of the bays was used to store a pallet of flight test systems, while the other bay was used to carry test stores, such as a single 450 kilogram (1,000 pound) Joint Direct Attack Munition (JDAM) GPS-guided bomb, or a "multipurpose bomb rack" to allow it to carry a wide range of smaller munitions, such as six 113 kilogram (250 pound) bombs. The rack allowed reloading the X-45A with a new set of munitions in about a half hour.
The first demonstrator was built to a "Block 1" standard, with a UHF control link and an L-band telemetry link. The second demonstrator was built to "Block 2" standard, with an added UHF satellite communications link and a "Link 16" high-speed data link, and the first machine was updated to that standard. The two demonstrators were then flown on cooperative test missions. The tests investigated operation of multiple UCAVs in military operations; integration of UCAVs with other military operations; and the feasibility of using reservists to fly the robot aircraft. The test program was completed in August 2005, with one prototype handed on to the USAF Museum in Dayton, Ohio, and the other handed on to the Smithsonian Museum of Air & Space in Washington DC.
BACK_TO_TOP* The US Navy did not commit to practical UCAV efforts until the summer of 2000, when the service awarded contracts of $2 million USD each to Boeing and Northrop Grumman for a 15-month concept-exploration program.
Design considerations for a naval UCAV included dealing with the corrosive salt-water environment, deck handling for launch and recovery, integration with command and control systems, and operation in a carrier's high electromagnetic interference environment. The Navy was also interested in using their UCAVs for reconnaissance missions, penetrating protected airspace to identify targets for the attack waves.
The Navy went on to hand Northrop Grumman a contract for a naval UCAV demonstrator with the designation of "X-47A Pegasus", in early 2001. The Pegasus demonstrator looks like a simple black arrowhead with no tailfin. It had a leading edge sweep of 55 degrees and a trailing edge sweep of 35 degrees. The demonstrator featured retractable tricycle landing gear, with a one-wheel nose gear and dual-wheel main gear, and had six control surfaces, including two elevons and four "inlaids". The inlaids were small flap structures mounted on the top and bottom of the wing forward of the wingtips.
Pegasus was powered by a single Pratt & Whitney Canada JT15D-5C small high-bypass turbofan engine with 14.2 kN (1,450 kgp / 3,190 lbf) thrust. The engine was mounted on the demonstrator's back, with the inlet on top behind the nose. The inlet duct had a serpentine diffuser to prevent radar reflections off the engine fan. However, to keep costs low, the engine exhaust was a simple cylindrical tailpipe, with no provisions for reducing radar or infrared signature.
NORTHROP GRUMMAN PEGASUS UCAV DEMONSTRATOR: _____________________ _________________ _______________________ spec metric english _____________________ _________________ _______________________ wingspan 8.48 meters 27 feet 10 inches length 8.51 meters 27 feet 11 inches height 1.74 meters 5 feet 8 inches empty weight 1,740 kilograms 3,835 pounds gross weight 2,495 kilograms 5,500 pounds maximum speed subsonic endurance > 1 hour _____________________ _________________ _______________________
The UCAV's airframe was built of composite materials, with construction subcontracted out to Burt Rutan's Scaled Composites company, which had the expertise and tooling to do the job cheaply. The airframe basically consisted of four main assemblies, split down the middle with two assemblies on top and two on bottom.
The Pegasus was rolled out on 30 July 2001 and performed its first flight on 23 February 2003 at the US Naval Air Warfare Center at China Lake, California. The flight test program did not involve weapons delivery. The Pegasus was used to evaluate technologies for carrier deck landings, though the demonstrator did not have an arresting hook. Other issues related to carrier operations involve adding deck tie-downs without compromising stealth characteristics, and designing access panels so that they wouldn't be blown around or damaged by strong winds blowing across the carrier deck. However, the Navy quickly shelved the Pegasus to work on more advanced concepts.
BACK_TO_TOP* While the US Air Force and US Navy had been proceeding with their UCAV demonstrator programs, the enthusiasm of the two services for the UCAV concept had grown by leaps and bounds. UAVs were star performers in the US intervention in Afghanistan in 2001:2002, with the Hellfire-armed Predator having a particularly high profile, and UAVs also proved their value during the US invasion of Iraq in the spring of 2003.
Both the Air Force and the Navy had been developing plans for operational follow-ons to their respective demonstrator programs, but pressures rose for the two services to merge their efforts, resulting in the formation of the "Joint Unmanned Combat Air System (J-UCAS)" program in October 2003 under DARPA direction.
DARPA and Boeing had been working on the "X-45B", a scaled-up X-45A that was seen as the prototype for an operational machine that would reach service in 2008, and would carry a 1,590 kilogram (3,500 pound) warload to a combat radius of 1,665 kilometers (900 nautical miles). Two were to be built, but before any metal could be bent for the two X-45B prototypes planned, the Air Force redirected the effort to an even more capable machine, the "X-45C".
Partly because of the pressure from Boeing, in the summer of 2003 Northrop Grumman formed an alliance with Lockheed Martin to help develop the "X-47B", a follow-on to the X-47 that would compete against Boeing efforts. The alliance was focused on building a modular stealthy UCAV that could be adapted to a wide range of missions.
A Navy UCAV would have a stronger airframe and landing gear for carrier takeoffs and landings; an arresting hook; and avionics for automated carrier approach and landing, along with a "relative navigation system" that will tell the UCAV where it is relative to the carrier.
* However, as it turned out, the joint program was doomed. In an abrupt turnaround, in late 2004 the J-UCAS program was reassigned to the Air Force, removing DARPA from the driver's seat. Then, in early 2006, the USAF decided that requirements had changed and dropped out of the program, canceling the X-45C prototypes. That killed the J-UCAS program. The Air Force is currently defining the service's new requirement.
The UCAV program had been noted by shifts in definition and requirements from the early days, and the abrupt collapse of the J-UCAS program didn't come as any big surprise. In early 2007, the Navy began a competition for a "UCAS Demonstrator (UCAS-D)" program, with Boeing and Northrop Grumman jumping in. The Northrop Grumman X-47B won the competition in August 2007. The first of two X-47Bs was rolled out in early 2009, and performed its initial flight in early 2011; the second followed late in the year. The X-47B is highly stealthy, with a low radar cross section over a wide range of radar bands; it stows an inflight refueling probe in a landing gear well and has a connection over the wing fold to ensure it doesn't compromise stealth.
Unlike the X-47A, the X-47B actually has distinct wings, extended from a diamond-shaped fuselage like that of the X-47A. The wings improve handling and range. The body's leading-edge sweep is 55 degrees, with the wing sweep reduced to 35 degrees. The wings fold up 135 degrees for carrier hangar storage; preventing the wing fold from compromising stealth was a tricky design challenge. Flight control surfaces include elevons, ailerons, and a spoiler on top of each wing. It is powered by a Pratt & Whitney F100-PW-220U bypass turbojet, a marinized and non-afterburning version of the same engine used on F-15 and F-16 fighters, providing up to 76.6 kN (7,805 kgp / 16,000 lbf) thrust.
NORTHROP GRUMMAN X-47B: _____________________ _________________ _______________________ spec metric english _____________________ _________________ _______________________ wingspan 18.9 meters 62 feet 1 inch wingspan (folded) 9.42 meters 30 feet 11 inches wing area 91.7 sq_meters 935 sq_feet length 11.6 meters 38 feet empty weight 12,975 kilograms 28,610 pounds gross weight 20,080 kilograms 44,275 pounds maximum speed high subsonic ceiling > 12,200 meters > 40,000 feet range > 3,885 km > 2,415 mi / 2100 NMI _____________________ _________________ _______________________
The X-47B will be able to operate from a carrier in weather too foul for piloted flight, will have an endurance with inflight refueling of up to a hundred hours, and will be able to carry a total of 12 SDBs in two weapons bays. Work is also being done on plugging fuel tanks into the two weapons bays to permit the UCAV to be used as an inflight refueling tanker -- a scheme which has been greeted with enthusiasm by Navy F/A-18 Super Hornet pilots, who are currently tasked with the tanker mission.
A number of piloted surrogates -- an F/A-18D, a Beech King Air, and a Learjet -- are being used in the development program, mostly for software evaluation. The X-47B evaluation will culminate in carrier trials in 2013. The Navy is expecting to then follow with a development program for an operational carrier-based UCAV system, to be fielded before the end of the decade. However, the service is planning an open competition and is not necessarily focused on an X-47B derivative -- though of course the X-47B work will give Northrop Grumman an edge.
Boeing did not get out of the UCAV business after the cancellation of J-UCAS, with work continuing with company funds for a demonstrator named the "Phantom Ray" derived from the X-45C work. The machine was rolled out in 2010 and performed its initial flight in April 2011.
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