TECHNOLOGY PROTEUS
The Scaled Composites Proteus is a distinctive aircraft with a multipurpose capability. Mark Broadbent profiles this unique platform
In Greek mythology, Proteus was a sea god who changed shape at will and could predict the future. It is an apt name for the sole Scaled Composites Model 281 Proteus, which with its distinctive tandem wings and twin tails looks like very little else in commercial aviation. Proteus was initially conceived as a highaltitude long-endurance (HALE) platform for telecommunications relay, but from the outset it was designed to carry different payloads in a variety of locations around the aircraft. Payloads can be changed relatively easily, meaning that like its mythological namesake the aircraft’s form can change. The result is that Proteus is a multipurpose platform that can carry out different research roles, from atmospheric sampling and reconnaissance to commercial imaging and sensor testing.
It is now more than two decades since Proteus undertook its first flight from Mojave Air and Space Port in California on July 26, 1998, but the aircraft, N281PR (c/n 001), remains active and available for airborne research and testing.
Configuration
Proteus’ twin-wing double-boom layout looks unconventional. The main landing gear legs are spread wide apart and mounted in the tail booms in the rear section of the aircraft, which also contains the 77ft 7in (23.6m) main wings, the two Williams International FJ44-2 turbofan engines and the vertical stabilisers. The forward section contains the pressurised cockpit, forward canards and nose landing gear.
Proteus was designed to cruise at altitudes from 50,000ft to more than 63,000ft for up to 18 hours. Sam Henney, Scaled Composites Proteus Product Engineer, explained to AIR International this operating environment drove the aircraft’s unusual layout.
He said: “Because it’s a high-altitude longendurance platform you want long wings for efficiency. A lot of U-2 pilots talk about the stall up there at high altitude; it’s called the ‘coffin corner’. With Proteus’ configuration, more of a flying wing configuration, you have stall protection, so we can fly very comfortably.”
While Proteus looks unusual, what really makes it remarkable is the capability this layout provides. There is space for a barrel at the centre of the fuselage that, as it is well away from the wings, engines and other critical systems, can be modified quickly and easily to carry different instruments. The barrel can carry payloads of up to 2,000lb (907kg).
There are additional payload bays around the aircraft, including the nose, boom extensions, cabin and internal fuselage, and depending on the depth of the customer’s instrument, external pods can also be mounted directly to the fuselage using custom interfaces. The main wings and forward canards are extendable, thanks to removable tips (the main wings can extend to 92ft/28m) that are used as required to tailor Proteus’ handling according to the aerodynamic impact of the different external payloads.
The small cabin is pressurised to an equivalent altitude of 14,500ft when the aircraft is at 55,000ft (or pressurised to a 15,500ft equivalent altitude at 60,000ft), giving the two-person flight crew – one pilot, one crewmember operating the payloads – a measure of comfort despite the high-altitude operating environment. In other manned HALE platforms such as the U-2 pilots wear pressure suits; in Proteus, the crews are in shirt sleeves.
Proteus is a largely composite (graphiteepoxy sandwich) structure, although one of the removable wingtips is fibreglass, and the crew compartment has grid-stiffened solid laminate construction. The retractable tricycle landing gear is electro-hydraulically powered and the nosewheel steering is manually actuated by the crew’s rudder pedals. The flight controls operate on a conventional mechanical pushrod/cable system with sidestick controllers.
A user guide for the aircraft produced by Scaled Composites says Proteus’ autopilot can hold inertial or pressure altitudes to the accuracy of a couple of feet and, when coupled with the aircraft’s Garmin global navigation system (GNS), provides accurate course guidance to within a few hundred feet.
Semi-autonomous
Proteus has a semi-autonomous capability. The crew can fly the take-off , climb, descent and landing, but the aircraft can be operated on station at mission altitude remotely. There is a two-axis autopilot for hands-off flying when on station.
This capability resulted from co-operation between Scaled Composites and NASA’s Armstrong (formerly Dryden) Flight Research Center under the Environmental Research Aircraft and Sensor Technology (ERAST) programme, a NASA initiative that ran from 1994 to 2003 to develop new technologies for remotely operated systems.
NASA was interested in Proteus from the aircraft’s earliest days, according to Henney: “Proteus came about the same time as the Global Hawk, so for NASA it was a great platform to explore high-altitude longendurance [flight] at a really low cost.”
The primary focus of ERAST was to develop slow-flying unmanned systems able to perform long-duration science missions at altitudes above 60,000ft, such as remote sensing for earth sciences studies, hyperspectral imaging for agriculture monitoring, tracking of severe storms and serving as telecommunications relays. As well as the station-keeping autopilot system, the ERAST project also funded the development of a satellite communicationsbased (satcom) uplink/downlink data system for aircraft and payload data, giving Proteus a full over-the-horizon capability.
This enables the aircraft to be controlled remotely from a distant ground-based control station via the satcom uplink/ downlink and serve as a surrogate UAV in ‘detect, see and avoid’ flight test campaigns involving both cooperative, transponderequipped and non-cooperative, nontransponder- equipped aircraft.
NASA projects
NASA was the exclusive user of the aircraft for several years, flying it in many configurations with different payloads for various research projects beyond ERAST.
Early in 1999, Proteus carried an operating science-imaging payload, the Airborne Real- Time Imaging System, which was operated remotely by the flight crew and took visual and near-infrared photos of the California desert and provided near-real time images to a ground station from an altitude of 50,000ft.
NASA’s Office of Earth Science, joined by the National Oceanic and Atmospheric Administration and the Department of Defense, subsequently funded a series of flights as part of its evaluation of Proteus as an airborne platform for atmospheric science and remote sensing missions at altitudes up to 60,000ft. The result, in October 2000, was Proteus setting three world altitude records over California’s high desert for Class C-1E, Group III aircraft (those with gross weights of 12,500lb/5,669kg or less). These were a peak altitude of 63,245ft, sustained horizontal flight at 62,385ft and a peak altitude of 55,994ft while carrying a 2,204lb (1,000kg) payload.
Other NASA research missions in which Proteus was involved included the Transport and Chemical Evolution over the Pacific) mission above the North Pole, the Chesapeake Lighthouse and Aircraft Measurements for Satellites programme to measure ocean characteristics and the Crystal-FACE (Cirrus Regional Study of Tropical Anvils and Cirrus Layers–Florida Area Cirrus Experiment) campaign.
As Scaled Composites maintains and flies Proteus, the company has over time opened access to the aircraft to other customers beyond NASA and it is available for research and evaluation to support science campaigns and test new flight systems.
Among others, Angel Technologies and Raytheon used the aircraft to test a 1,100lb (499kg) telecommunications dish measuring 13ft (4m) in diameter by 3ft (0.9m) in depth; a joint US Department of Energy and Sandia National Laboratories programme saw Proteus equipped with sensors to study cirrus in the upper atmosphere; while the US Air Force used the aircraft for its Multi-Platform Radar Technology Insertion Program and Airborne Laser projects.
Proteus has been very well-used over the last two decades: it has carried around 30 different payloads and amassed more than 4,000 flying hours. Henney noted Scaled Composites originally intended to use the aircraft only for a couple of hundred flying hours as a proof-of-concept demonstrator, and the fact that it has been used far more than first planned is perhaps the ultimate testament to its capabilities.
Payload integration
How are new payloads put on to Proteus? As the aircraft’s designer, manufacturer and operator, Scaled Composites says it is “extremely flexible when it comes to payload integration and has the ability to rapidly accommodate many customers’ requirements”.
According to the company’s user guide, a typical flight test for a payload consists of the following stages: pod design, pod fabrication, sensor/system integration, ground testing, flight-test planning, payload checkout flights and data collection/demonstration flights. The company’s engineers and technicians work with a client to understand its objectives, asking tailored questions to define the scope of the testing effort, before going through the phases from design to data collection.
Scaled Composites stresses the availability of the aircraft: “Due to the modular payload approach, changing payloads can be a simple task. This capability enables [the company] to support multiple customers during concurrent test programmes.”
With Proteus offering a modular capability, power is an important aspect of the aircraft. Electrical connections from the front and rear fuselage sections provide power lines for the payloads in the belly and the other locations.
There are two starter/generators supplying up to 800 amps of 28-volt direct current (although output is nominally limited to 200 amps per starter/generator to preserve life) and inverters. A 55-pin 38999 connector and two ethernet connections provide the crew with the ability to control payloads. The Scaled Composites user guide says: “Everything from custom boxes to PC laptops have been used for payload interface and control.”
Other systems aboard are two VHF (118.000–136.975MHz) radios and one UHF (225.000–399.975MHz) radio providing line of sight communication within approximately 150 nautical miles (277km) of a base station radio and a bi-directional line of sight data link (rated at up to 4.5Mb per second).
A NovAtel SPAN GPS-aided inertial navigation system mounted in the lower cabin forward of the aft pressure bulkhead shows attitude, position and rate information over serial data lines, which is collected by an onboard data acquisition system.
Navigational information is provided by all-in-one GPS/navigation/communications packages in the form of two Garmin GNS units. A GPS source splitter provides GPS signals to the various aircraft payloads, receiving its signal from a Sensor Systems Antenna P/N S67-1575-39. If necessary, other GPS antennas can be adapted to existing mounts on top of the fuselage.
Future usage
In the time Proteus has been flying, there have of course been significant advancements in HALE operations with the evolution of unmanned systems. Most obviously there is the Northrop Grumman RQ-4 Global Hawk, but a brace of new unmanned HALE systems such as the Airbus Zephyr HAPS and Aurora Flight Sciences Odysseus is emerging from the commercial sector just now.
These and other pseudo-satellite systems are being designed to offer persistent capabilities in surveillance, reconnaissance, commercial imaging and communications relay – exactly the type of work for which Proteus is designed. A question therefore arises: what is the future for this aircraft?
Scaled Composites firmly believes Proteus still has a role. Henney said customers can deploy systems on Proteus more easily than on an unmanned system: “The high-altitude, long-endurance regime is complex and expensive. It’s actually cheaper to operate a platform manned than unmanned [and] you can develop autonomous systems much more safely and cheaply.”
Henney added unmanned systems for the HALE environment generally require more resources on the ground in flight support and engineering. He said: “The number of people it takes to operate an unmanned platform is a lot compared to Proteus. It’s built like a general aviation aircraft: very simple systems. We can go all over the world with a team of three or four. There are savings right there.”
Despite the new generation of highflying unmanned systems, therefore, the shape-shifting Proteus is likely to remain in the skies. Moreover, Henney told AIR International the aircraft continues to be well-used: “Generally, we don’t share what our customers are up to unless they want us to. I can say though that the aircraft is busy; we fly multiple customers a year, three, four or five payloads. We’re busy all this year and into next year. It remains a cost-competitive and relevant platform.” AI
