Born survivor - An in-depth look at the Northrop Grumman MQ-8B Fire Scout vertical take-off and landing UAV

Los Angeles
Source:
This story is sourced from Flight International
Subscribe today »

The Northrop Grumman MQ-8B vertical take-off and landing tactical UAV is finally poised to enter flight test - but will it play a role in Iraq?

Click here to see Flight International's Fire Scout MQ-8B cutaway drawing.

If the early years of Northrop Grumman's Fire Scout vertical take-off and landing tactical unmanned air vehicle (VTUAV) are anything to go by, its survivability appears already to be proven. Overcoming setbacks that would have killed off most programmes, the MQ-8B production version of the Fire Scout is entering flight tests for the US Navy and Army.

    
Using ARC-210 radios and datalinks Fire Scout will transmit its targeting data to US Navy ships and strike aircraft

Based on the Schweizer 333 light helicopter, the four-bladed rotorcraft will be one of the largest and most rugged UAVs yet flown. The MQ-8B is a strengthened, significantly redesigned derivative of the RQ-8A originally selected as the winner of the US Navy's VTUAV competition in 1999. The programme then fell victim to the budget axe in 2002 and seemed to be all but finished to the outside world.

"In early 2002 all funding was cut and the money beyond LRIP [low-rate initial production] curtailed," says Fire Scout programme director Doug Fronius. "So we had a programme that had some money left, but no future." The move was a blow to Northrop, which had achieved the first fully autonomous flight of the then-designated Model 379 VTUAV prototype in January 2000, followed by a $94 million LRIP contract to produce the first three systems.

The funding dried up just as Northrop was preparing the prototype RQ-8A for its first flight, which took place in May 2002. "So we decided to start demonstrating the system over 2002-3, and we moved it from China Lake [California] to Webster Field, near Patuxent River [in Maryland], so more people could see it fly - particularly as it was then in the navy's back yard for UAVs."

At the same time Northrop began to address the shortcomings of the original design that senior USN officials had pointed to in terms of payload limitations and the ability to perform missions beyond electro-optical/infrared(EO/IR) surveillance and target designation. "We began looking at what the RQ-8B should be," says Fronius. "It became clear that it was more desirable to increase payload or endurance, or both."

More weight

He adds: "Whatever combination of sensors were to be used added weight, and cut into the endurance. So we campaigned with Schweizer to increase the weight capability. The Rolls-Royce 250 turbine is a 420shp [335kW] engine, and we were only using about 280shp of it in the A model because of the rotor system, which was originally designed for a piston," Fronius says. "We had plenty of horsepower already in the vehicle, so to lift our weight we needed more wing area, and that was the rotor blade in our case. Rather than go for larger blades we opted to go for four blades, something that was made easier by the fact that Schweizer had already developed a four-bladed hub."

The transmission and drive-train were redesigned for the higher power, and parts of the structure strengthened. The heavily revised RQ-8B concept was publicly released in November 2002, and the following month the USN revealed it was thinking about a U-turn and exploring funding development of a more robust, multi-mission version tentatively designated the RQ-8B Sea Scout.

The following year was a turning point. In January 2003 the navy signalled its intention to develop the renamed Fire Scout in support of its new Littoral Combat Ship (LCS). March saw the first flight of the four-blade rotor on "P-5", a manned testbed aircraft, and in July 2003 programme funding was restored by Congress. More was to follow when, in August that year, the redesignated MQ-8B was selected as the Class IV UAV for the US Army's Future Combat System (FCS) - in which it would play a key role in the service's tactical intelligence, surveillance, reconnaissance and targeting architecture.

Recalling that memorable year, Fronius says: "It really marked the end of a two-year effort of desperately trying to find a home for it, from the programme going away to being reinstated."

By March 2004 the programme had reached firmer ground with the USN's formal contract to develop the MQ-8B for use on the LCS. By now it was also becoming clear that both the navy and army could use a common airframe, and that different communications systems and payloads could be adapted to the vehicle to suit the specific needs of each service.

While three of the original RQ-8A Fire Scout vehicles (built under the LRIP contract) continued to undergo test and development work, Northrop began preparations in April 2004 for production of the MQ-8B at a new unmanned systems centre at Trent Lott International airport in Moss Point, Mississippi. The new site, which formally began production of the MQ-8B when it received the first airframe from Schweizer in January this year, is also responsible for subassembly work on the RQ-4B Global Hawk.

Just two weeks after MQ-8B production began, the first of nine autonomous shipboard landings was made by an RQ-8A on board USS Nashville. The landings, which were conducted by two vehicles over 16-17 January, marked the first time a USN UAV had performed vertical landings on a moving ship without guidance from a pilot. In February, the RQ-8A was again used as a demonstrator, this time at the army's Yuma Proving Ground in Arizona, where it proved its utility as a beyond-line-of-sight tactical communications relay.

More range

Changes from the RQ-8A to the MQ-8B are all about increasing range and payload, says FCS Class IV UAV programmes chief engineer Michael Roberts. "Endurance with full fuel and a baseline 55kg [120lb] payload is more than 8h, and flight time with a 250kg payload is more than 5h, and to get more out of the engine we've upgraded the main rotor transmission," he says. The upgraded transmission is rated for 320shp continuous power from the Rolls-Royce 250-C20W turboshaft, with a 5min emergency rating of 340shp.

The Fire Scout's primary structure has been strengthened for a design weight of up to 1,545kg, although the maximum take-off gross weight will be 1,430kg, compared with 1,160kg on the RQ-8A (Flight International, 28 January-3 February 2003). Most of the major structural changes associated with the increased weight are in the landing gear, which has larger-diameter, thicker-walled skid tubes and heavier duty fore and aft cross-beams running transversely beneath the fuselage. The gear retains the existing RQ-8A struts and high-capacity dampers. The MQ-8B also features a new quick-fold link at the outer ends of the landing gear cross-beams that enables the skids to "articulate down to load on a C-130, because we had a rotor mast height problem before with the -8A", says Roberts.

The landing gear sponsons have also been completely redesigned to provide extra space for equipment relocated from the main fuselage and engine area, as well as to provide mounts for weapons, tie-downs and vertical replenishment loads. Based around a box-beam structure, the aerodynamic sponsons are made of standard formed and riveted sheet metal. "We've added support braces and hooks so the vehicle can be lifted by the sponsons, and it gives quicker access for the weapons systems," he adds.

Another characteristic of the MQ-8B is the larger rotor pylon, which is extended forward to increase fuel capacity from 570 litres (150USgal) to 720 litres. "We extended the forward edge of the 'dog house' to increase the fuel load while keeping it close to the centre of gravity, and structurally we added a new horse collar strut to handle the extended dog house," says Roberts.

Within the pylon housing is a relocated and redesigned flight-control actuator. "We had a fairly large actuator, which we've reduced in size by around 50% and which provides full redundancy with a single motor," says Roberts. The new actuator is based on a switched reluctance (SR) motor, which is a rotating electric machine in which the stator is made up of a set of coils. The motor is kicked off by a sequence of current pulses applied at each phase. The individual phases are sequentially excited, forcing the motor to rotate. The MQ-8B SR design has six independent phases for dual redundancy.

Redesigned nose

The nose section is redesigned to accommodate a larger avionics bay, additional fuel and bigger payloads. The lower part of the redesigned forward structure is supported at the rear by a new canted aft bulkhead connected to the lower avionics floor and sponson transverse box beam. At its upper end the bulkhead is bolted to an enlarged space frame, which has itself been significantly altered to fit with the enlarged pylon, redesigned nose, sponsons and aft tailcone. The fuel deck is strengthened and connects at the forward end to a strengthened payload bulkhead, which has additional mounting pads for future growth. A new composite nose cone, provided by California-based Formula 1 auto-racing specialists Swift Engineering, replaces the former laid-up glassfibre unit. An antenna for the UAV common automatic recovery system (UARS) is mounted to the lower fairing, which is separated from the nose cone by a simplified split line.

A new centre web runs fore-and-aft across the avionics bay floor, connecting the payload and aft bulkheads, while further aft external stiffening is provided by structural fillet assemblies. Aft bulkhead stiffening ribs also tie directly to the sponson box beam, providing additional strengthening forward of the space frame.

The new forward structure design allows the fuel tank to be removed through the top of the vehicle, and incorporates a relocated pressure refuelling port with an integrated fold-down step. In the RQ-8A this was located higher up on the main pylon, and the new port is lower and more easily reached from deck level, says Roberts. A new centreline splice joint sits between the forward bulkhead and the new skin and rib assembly supporting the horse collar. The splice joint area provides a housing for the repositioned forward tactical control datalink (TCDL) antenna.

Just behind the TCDL antenna, the sloping forward edge of the extended pylon is supported by two bolt-on mast braces that have been added to the original space frame. Other changes include cluster fittings fore and aft that attach the frame directly to the new sponson box beam and a mount for the rotor brake, which can now be removed for improved maintenance access. A new aft strut also ties the mast to the redesign aft fuselage.

Stiffer tail

Compared with the original Schweizer 330-based braced tubular tailboom, the MQ-8B adopts the Model 333-style monocoque tailcone. "Before, we had shafts back there to support the tailboom. Now the tailcone skins take the load, which gives a stiffer tail and a lighter structure," says Roberts. The existing RQ-8A empennage and teetering, two-bladed tail rotor is retained. The redesigned structure is attached to a new mid-tailcone transition section, forward of which is a revised barrier filter over the engine inlet.

System changes, largely driven by lessons learned on the RQ-8A, include repositioning several items to make them more easily accessible, or to provide additional space for avionics. The nitrogen bottle and manifold, formerly located in the engine bay by the aft TCDL antenna and harpoon deck-landing system, is moved into the tail cone, while the batteries are moved down to a site just aft of the port sponson. A new space-saving combined pitot-static probe is sited on the upper side of the pylon.

A ground control panel has been moved to a more easily accessed area formerly used for an environmental control vent, freeing up extra space for the enlarged avionics bay. Within the bay itself are new processors, "which are the biggest change to the vehicle management computer [VMC] capabilities", says Roberts. "We've changed from a PC-104+ CPU architecture to Power PC 500Mhz processors, and we're now interfacing through a single-channel Ethernet on a dedicated connector," he says, adding that the changes maintain the same system weight while "dramatically increasing processing speeds and flash memory".

First flight of the USN's MQ-8B in December kicks off "a fairly extensive test programme", says Fronius, who adds: "It will gradually build up with additional payloads and using the datalink." System development and demonstration (SDD), covered by a $136 million navy contract awarded in August, has three major phases over 18 months - technical evaluation, operational evaluation and actual operations aboard the LCS. "It is scheduled to finish by the end of October 2008," says Fronius, who adds: "Northrop Grumman's test team is fully integrated with the US Navy test team, so the line between tech and opeval is very grey."

Although contracted for seven MQ-8Bs under the most recent SDD contract, Northrop expects to have orders for nine vehicles by the end of December. The first MQ-8B, N1, was due to be completed by mid-November, allowing preparation time for first flight in early December. Vehicles N2 through N6 are expected to come off the Mississippi line by the end of 2007, with a further three vehicles following in 2008.

Initial operational capability (IOC) with the navy is expected in late 2008, when the MQ-8B is due to be deployed alongside Sikorsky MH-60R/S helicopters on anti-surface/anti-submarine warfare and mine interdiction missions. "Fire Scout will play a part in each, and will not be replacing the H-60," says Fronius. "It will adding to the overall capability, and when operated by the navy will be operated by a common aviation crew. The Fire Scout will be fully networked with the H-60s."

Tests will prove the ability of the MQ-8B and its sensor and communications suite to scout out targets and provide precision engagement data up to 200km (110nm) away from its launch point. The vehicle will be equipped with a three-axis, four-gimbal, gyro-stabilised ball housing a laser rangefinder/designator, zoom TV camera and a mid-wave infrared thermal imaging system. Target and other intelligence information will be passed back to the fleet using the TCDL.

Awaiting IOC

Two out of three LCS vessels are to be equipped with up to three Fire Scouts per ship. This equates to an expected production requirement for around 100 MQ-8Bs, plus additional vehicles for attrition and shore-based training. "But the real answer will depend on the results at IOC. That's when they see what its real capabilities are, so we could be looking at between 100 and 200," says Fronius. He believes the LRIP tally for 2007 could total 13 vehicles.

While the navy development effort marches on, Northrop is working to manage the impact of the slow down to the FCS Class IV UAV programme, for which it is a subcontractor to Boeing and SAIC. Due to software and hardware (JTIRS radio) development delays, the entire Class IV UAV element has been delayed around 25 months, with first flight now not due until November 2010. The latest projections now put limited user testing and long lead for LRIP in 2012 and IOC in 2014.

News of the "budget realignment" on FCS first came in April this year, and Northrop is reorganising its production schedule at Moss Point to accommodate. "We're currently going through that," says Army FCS Class IV UAV programme director Joe Emerson. "We've moved tasks to the right, and descoped some tasks to equal the contract value," he says, adding that is made more complex by "things like inflation and other disconnects," such as alignment with the navy production schedule. Assembly is still planned, meanwhile, for the initial eight vehicles covered by the FCS SDD contract. "The current plan is to have a very slow integration of avionics and cabling to make it into a UAV when it comes out of Schweizer," he adds. Integration work on the first Army Fire Scout started in June, but "it's continuing at a crawl", says Emerson.

Iraq role

In the meantime, Northrop is working on plans to use some of these early-built vehicles in an alternative, and more pressing role. It hopes to know by the end of December if trials will go ahead of an MQ-8B equipped to search for mines, booby traps and roadside bombs in Iraq. The decision will be made by the US Department of Defense's (DoD) Joint Improvised Explosive Devices Defeat Office (JIEDDO)." It would be a phased approach, beginning with testing at Yuma, Arizona for an 18-month effort. If that was acceptable, it would go overseas for around 90 days of demonstrations," Emerson says.

Assuming an early 2007 start, the planned schedule could see the first MQ-8B deployed to Iraq by the end of 2008. In its anti-IED role, the MQ-8B would carry Northrop's Airborne Standoff Minefield Detection System, incorporating an electro-optical/infrared sensor and a quad prism aperture-splitting sensor. The system, which was developed under an army contract in 2003, also includes a laser illuminator and rangefinder/designator.

In the meantime, other potential Fire Scout applications could include the US Marine Corps, which saw its requirements for a new unmanned aircraft system, called VUAS, endorsed by the DoD earlier this year. With a contest expected as early as 2008 or 2010, the VUAS is planned to be in service by 2015, to replace the USMC's Pioneer unmanned air vehicle.

Northrop expects stiff competition from Bell Helicopter with its Eagle Eye unmanned tiltrotor, and from Boeing with either the A160 Hummingbird, Unmanned Little Bird or even the Canard Rotor Wing.

However, the Fire Scout's existing place in the UAV inventory could already be an advantage. Speaking recently at UAV conference in Panama City, Florida, the USN's programme executive officer for strike weapons and unmanned aircraft, Rear Adm Tim Heely, said the Fire Scout is as "a good symbol of army and navy and possibly USMC co-operation on a vehicle".