After a turbulent launch, the Northrop Grumman Fire Scout vertical take-off and landing tactical unmanned air vehicle has been given a boost with the prospect of additional funding for an improved version

Within the next few months a diminutive Northrop Grumman RQ-8A Fire Scout VTUAV is expected to head out over the Pacific and land on a US Navy ship.

Although the planned autonomous landing on an LPD-9 Austin class amphibious transport dock vessel will be the first of its kind, Northrop Grumman hopes the event will become as routine as raising the anchor. It will also mark the culmination of efforts that began in mid-1999 when the pre-merged Northrop Grumman and Ryan Aeronautical started studying a new US Navy request for proposals (RFP) for a VTUAV. The navy wanted a rugged system to provide accurate situational awareness and precision targeting support for naval assets and the Marine Corps.

At the time neither company was able to meet the requirement as former Northrop Grumman Integrated Systems sector president Ralph Crosby recalled. "Ryan decided it couldn't bid, and Northrop Grumman didn't have a design, but in October the combined company said 'OK..let's go do it'. We had the financial weight of a large corporation and Ryan had the expertise. We learned from Ryan. Instead of just responding to the RFP we spent money on a demonstrator. We went out and bought a Schweizer 330 helicopter with our money, and developed the flight control system [FCS] to demonstrate vertical take-offs and landings," said Crosby.

The solution was a turbine-powered Schweizer Model 333, the latest variant of the 330, with the cockpit and nose section removed to provide room for large fuel tanks, flight control systems, sensor and targeting payloads. Northrop Grumman dubbed the new version the Model 379, and in February 2000 was awarded a $93.7 million US Navy contract to develop the concept.

A manned Model 379 demonstrator, AV-1, was developed to gather performance data and prove the basic suitability of the vehicle as a sensor platform. It first flew in September 1999 at Elmira, New York, and had completed 41h of tests by the following month. In December that year the first unmanned 379, P-1, achieved its first fully autonomous run up to 100% power and four weeks later, on 12 January 2000, it performed the first fully autonomous flight at Mojave, California, before moving on for trials at the nearby Naval Air Weapons Center, China Lake.

Despite several subsequent setbacks, including the crash of P-1 at China Lake later in 2000, threats to Schweizer's survival, changes in US Navy funding priorities and the cancellation of long-term plans for full-rate production, the Fire Scout has survived. In fact, such have its fortunes improved that, at the start of 2003, the US Navy is seeking an extra $45 million for further development of the system. Far from halting work on the programme by July 2003, the navy is pushing for production of six more vehicles, two ground stations and studies of an improved version dubbed the MQ-8 Sea Scout.

Extra lift

The key improvement for the MQ-8 will be a four-bladed rotor system, already developed for the Schweizer 333, in place of the Fire Scout's current three-blade unit. The extra lift means the Sea Scout can carry up to 45kg (100lb) of extra fuel, fly slightly faster and remain on station for up to 8h. The upgraded version, which is supported by a $5 million investment from Northrop Grumman and Schweizer, is also able to support more extensive payloads, including a tactical synthetic aperture radar. Two systems are being considered - Northrop Grumman's own TUAV Radar and General Atomics' APY-8 Lynx. Both offer moving target indication and Northrop Grumman is studying integrating the Affordable Moving Surface Target Engagement system into the vehicle.

Under the US Navy grey paint and revised lines of its VTUAV role, the Model 379 is a direct derivative of its civil Schweizer 333 counterpart, certificated in September 2000. The 333, in turn, evolved from the Model 330 and the preceding Hughes Model 269 series, production of which was taken over by New York-based Schweizer in 1983. Known to the US Army as the TH-55A Osage, 2,800 of all Model 269 versions were built before the line transferred to Schweizer, which delivered the 500th Model 300C derivative in 1994.

Built with a conventional steel tube structure and light alloy skin, the baseline machine differs from most other helicopters in using a belt drive between the Rolls-Royce Model 250-C20W turboshaft and the main gearbox. This was one of the main features that first attracted Northrop Grumman, as it not only eliminates the need for reduction gears - along with their associated lubrication and maintenance needs - but provided a lower vibration environment for the Fire Scout's payload of long-range electro-optical sensors.

The Fire Scout's three-blade, fully articulated main rotor is foldable and fitted with elastomeric dampers. The main blades have a cambered aerofoil section, and are mounted to a splined hub assembly which is larger than the Model 330 unit from which it is derived. The teetering, two-bladed tail rotor is made up of simple blades comprising metal spars and composite skins. Forward of the tail rotor are equally simple tail surfaces consisting of a horizontal stabiliser with endplates, as well as ventral and dorsal fins. The tail unit and rotor are mounted on a braced tubular tailboom.

The airframes arrive at Northrop Grumman Integrated Systems in San Diego, California, from Schweizer without the standard Model 333 nose and bubble canopy. In their place, structural modifications for the Model 379 include the provision of a large, 570 litres (150 USgal) fuel tank in a tall fairing around the rotor mast and in the upper fuselage section once occupied by the cockpit. The forward lower fuselage section and nose compartments house the flight control actuators, vehicle management system (VMS) and other avonics. The bulkhead separating the shielded avionics compartment from the nose cone also provides cantilevering support for the modular mission payload (MMP), which projects, turret-mounted, from beneath the nose.

The machined rigid forward bulkhead is a "higher-tech piece than Schweizer normally builds", says Fire Scout programme manager Scott Winship, adding that special attention is paid to the critical structure because the "slightest flexibility will put your sensors off boresight at 16 miles". The Northrop Grumman/Tamam-developed MMP attached to the bulkhead consists of a three-axis, four gimbal, gyro-stabilised ball providing 360¡coverage. The ball houses a diode-pumped laser rangefinder, zoom TV camera and a third-generation, midwave infrared thermal imaging system.

Forward of the turret is a pitot tube and an antenna for the Sierra Nevada-developed automated landing system. Fire Scout is designed to descend to 30ft (9m) above the sea surface and keep station off the port quarter until commanded to come aboard, guided by GPS and the UCARS (UAV common automatic recovery system). "If not commanded to come aboard it will stay there until it runs out of gas," says Winship.

Once ordered to land, the Fire Scout will move in towards the deck landing area until the probe of its Light Harpoon deck restraint system meshes with the deck-mounted grid. Mounted beneath the helicopter between the skids, the mechanical trapping system is automatically activated when the probe is in the grid and weight is sensed on both landing skids. On take-off, the controller releases the probe when power is sufficient for flight while, on deck, the plane captain manually engages the probe for movement to and from the grid. Despite the small size of the Fire Scout, the rotor height is 9ft (2.75m) above the deck and, as Winship says: "There are very few 9ft tall sailors!"

UCARS, radar altimeter and Light Harpoon form the core of the Fire Scout's launch and recovery system which, in turn, is connected to the two VMS units which form the "brains" of the UAV's dual-redundant avionics system. Using software architecture and redundancy management features developed for the RQ-4A Global Hawk, Northrop Grumman claims the system is 100 times more reliable than a single-string alternative.

The eyes and ears of the Fire Scout are three ARC-210 radios and the tactical control datalink (TCDL) which, by being integrated with the MMP, provide situational awareness to the UAV operators through the vehicle management computers at the heart of the VMS. The computers also work directly with the stability augmentation system which monitors and controls the engine throttle and the actuators for the collective, pitch and roll cyclic controls and yaw. An electrical power management unit also interfaces with the stability augmentation system as well as the computers.

Batteries, the Light Harpoon probe and its pneumatic bottles, pitch, yaw, roll and engine actuators are housed in the lower centre fuselage compartment. The forward avionics bay houses the ARC-210s, radar altimeter, identification friend or foe, UCARS transponder, VMS units, TCDL modem and a voice digitiser multiplexer.

The missions

As originally planned, Fire Scout is aimed at five main mission types: reconnaissance; target search and track; target designation; damage assessment; and communication relay. However, in common with other UAVs, the Fire Scout will also be demonstrated with air-launched missiles and rockets as part of studies of enlarged interdiction and precision strike roles. Tests with Lockheed Martin AGM-114 Hellfire missiles and possibly 2.75in (68.6mm) rockets are planned for later this year.

Each mission consists of five main segments: launch, ingress, target area operations, egress and recovery. For US Navy applications, the UAV is controlled throughout from a ground control station (GCS) either contained in a standalone land-based shelter that can be deck-mounted or integrated into the ship's combat information centre. For the Marines it will be mounted in a mobile shelter on the back of a Hummer wheeled vehicle. Each GCS has two operator workstations with four main displays, two each for the air vehicle operator (AVO) and the mission payload operator (MPO). Both see a map display, while the AVO has a primary flight display for monitoring and controlling the Fire Scout and the MPO has a payload monitor and display.

The GCS uses the L-3 Communications TCDL or a UHF datalink to transmit commands to the Fire Scout for mission and payload adjustments, take-off aborts, automatic landing and landing wave-off. The Fire Scout sends aircraft and payload status to the GCS over the same datalinks. Near real-time video and IR images are also passed to the GCS via the TCDL, while control can be passed from one GCS to another. Up to three UAVs can be controlled from one GCS simultaneously.

From launch to recovery the Fire Scout is autonomous, and during the launch sequence automatic checks are made of the aircraft systems and engine power. When ready, the Fire Scout takes off and continues to the planned mission departure waypoint. This is usually a latitude and longitude for shore-based launch, and a ship-based relative position for shipboard launch.

As the Fire Scout moves towards its target, the aircraft and mission systems are again checked and the mission plan is either confirmed or modified as needed. The mission plan is followed in the target area where data is gathered by the sensors. The aircraft will hover out of ground effect at 4,000ft (1,400m) at the design maximum gross weight of 1,160kg, although these figures will improve with the proposed Sea Scout. At lower weight the UAV is expected to fly above 15,000ft or "well out of the envelope of the classic anti-aircraft artillery and shoulder-launched anti-air missile launcher range", says Fire Scout business development director Rick Ludwig.

At the aircraft's current service ceiling of 20,000ft, it can achieve a maximum continuous speed of 90kt (167km/h) with 50% useable fuel, and 130kt at sea level. At maximum weight, these figures are 60kt and 125kt respectively.

Once at the ship or landing area recovery waypoint, the Fire Scout enters a preplanned holding pattern or starts the landing sequence. Shore-based landing is GPS and radar altimeter-assisted, while the UCARS will guide shipboard landings. Further developments will see transfer of more control from the ARC-210 radios to the datalinks, says Ludwig.

The joint US Navy/Northrop Grumman Fire Scout test team is now focused on envelope expansion and flight tests of the first engineering and manufacturing development (EMD) vehicle, E-1. The work has been performed at NAS Patuxent River, Maryland, and forms the first element of what the company hopes will be a busy phase of tests, including a joint operational assessment at NAS Fallon, Nevada, later in the year. "This will see how it fits as a joint asset," says Ludwig, who sees considerable potential for the Fire Scout in similar roles in Europe and the Asia-Pacific. In the shorter term, Ludwig believes Fire Scout is already operationally ready. "We are mature enough to go to war," he says.

Source: Flight International