Skunk Works ARES VTOL Project

The Pentagon’s Defense Advanced Research Projects Agency, better known as DARPA, has a reputation for demonstrating innovative solutions to practical problems.

Supplying and supporting dispersed troops in the field while getting personnel and vehicles off of roads with threats such as improvised explosive devices, or IEDs, is one such problem. DARPA is addressing this problem in a program called Aerial Reconfigurable Embedded System, or ARES. The reconfigurable part of the name describes multiple mission capability from a single vehicle and the embedded part refers to having this system operated by infantry soldiers and Marines.

“Transporting and resupplying troops in rugged, austere terrain has become a major challenge, especially as the US military shifts to using smaller and more distributed combat units,” explained Kevin Renshaw, Lockheed Martin Skunk Works lead on ARES.

The Skunk Works formed a team in 2010 with Piasecki Aircraft Corporation and Ricardo, Inc., that was selected for the DARPA Transformer program, as it was known at that time. In its original requirements, DARPA asked participants to “demonstrate a flyable/roadable vehicle that provides the warfighter terrain-independent mobility…. The vehicle will have VTOL capability with a minimum combat range of 250 nautical miles on a single tank of fuel.”

In the first phase of the program, the Skunk Works team performed trade studies and defined the concept of a modular VTOL UAV system with separable, independent flight and ground components.

The scope of the program has since been refined to delete the roadable capability and focus on the common VTOL lift module that could service multiple missions with interchangeable payloads, leading to the new program name — ARES. The program, currently in Phase 3, seeks to demonstrate a new generation of compact, high-speed, autonomous, unmanned vertical takeoff and landing, or VTOL, delivery systems.

“ARES will demonstrate several key technologies to achieve an operational VTOL system with a more compact footprint than those of conventional helicopters and couples this with higher cruise speeds,” Renshaw noted.

Preliminary Work
After being selected for Phase 2 of DARPA’s program in 2011, the Lockheed Martin team matured its concept and completed a preliminary design review with DARPA and other technical experts in 2012.

The preliminary design was the basis for the Phase 3 effort, which involves designing and building the prototype system. Lockheed Martin’s team won the Phase 3 contract in late 2012 to perform detail design work and risk reduction tests that led to a Critical Design Review in late 2013. Following this review, DARPA has decided to exercise a further option to build and then fly the ARES prototype in 2015.

Lockheed Martin has a head start in developing and fielding unmanned VTOL systems with the K-MAX unmanned cargo helicopter currently in operation with the United States Marine Corps in Afghanistan. K-MAX helicopters are flown by remote pilots with navigation automated between mission waypoints and payloads carried on an external cargo sling.
Engineers with Lockheed Martin Mission Systems and Training demonstrated the use of these unmanned helicopters to deliver more than three million pounds of cargo to the Marines. The system reduced their exposure of the military personnel to IEDs by tens of thousands of hours. The success of K-MAX in Afghanistan led the Marines to extend the demonstration indefinitely.

Mission Systems and Training is also under contract to the Office of Naval Research to demonstrate advanced sensors and controls for VTOL unmanned air systems, or UAS, under the Autonomous Aerial Cargo Utility System, or AACUS, program.

AACUS will test sensors and flight control software to allow the next generation of VTOL UAS to autonomously identify landing zones, avoid obstacles, and complete landings without a remote pilot. The system will be designed to be programmed by soldiers and Marines in the field, with simple, intuitive control interfaces, such as military smart phones or ruggedized tablet computers. This technology ties directly into ARES as part of the maturation path from the DARPA prototype to the fully operational system.

Design And Hardware
The ducted fan VTOL flight module designed for ARES could adapt to multiple missions with interchangeable payloads. The payloads could include cargo pods, medical evacuation units, delivering tactical ground vehicles, troops, and armed scout, reconnaissance, and strike capabilities.

The vehicle’s tilting ducted fans allow for a safer operating environment by combining faster transit speeds with a landing zone half the size of a typical helicopter with a similar payload. This also leads to a system that could fit into small ship hangars or into C-130 transports. The ducted fan design, with no exposed rotors, would also improve troop safety on the ground.

The ability to use the same flight module to perform multiple missions with a common system could reduce fleet costs. ARES could supplement more expensive specialized helicopters that require trained crews. “The modular concept enhances the original DARPA vision by enabling a variety of roles, offering versatility now and adaptability in the future,” Renshaw added.

The transitions to and from vertical flight for takeoffs and landings would be done automatically. The operational version would autonomously navigate to the desired delivery site while avoiding obstacles en route or in the landing zone.

The ARES Flight Control System design is taking full advantage of the digital fly-by-wire VTOL control work that Lockheed Martin has done in the past fifteen years with the X-35 and F-35 programs. The design also benefits from the team’s previous experience with autonomous control of unmanned air systems. “Operating this type of system in VTOL, transition, and cruise flight requires a sophisticated fly-by-wire flight control system,” said Renshaw.

Piasecki Aircraft, a long established helicopter and VTOL research company, is responsible for the flight module design, including the design of the lift system drivetrain. Frank Piasecki invented the dual rotor system for helicopters in the 1950s. Dual rotors are used today on the CH-46 Sea Knight and CH/MH-47 Chinook helicopters. The company’s previous ducted fan VTOL experience includes its VZ-8 AirGeep series of demonstrators. Piasecki has also studied the potential for lift system modularity under the US Army Combat Medic casualty evacuation project. 

“The operational system was always meant to have the capability to be flown as a highly autonomous UAS with the flight module able to return to base after dropping off the payload,” Renshaw explained.

In Phase 3 during 2013, the Lockheed Martin team created detailed drawings of the hardware for a full-scale prototype flight module. The hardware design includes the structure, drive shafts, propellers, control actuators, and lift system drivetrain gearboxes. Those items were in hand or are in fabrication to support assembly in 2014.

The team has selected existing flight control computers to be used for the digital flight control system. The team has also identified sensors, GPS navigation aids, and datalinks for the UAS operation, based on other Skunk Works UAV efforts. The team is creating the digital flight control laws and flight control software to manage hover, transition, and cruise flight.

Simulations of the control and handling qualities of the system are now running in the flight controls labs. These simulations are designed to test the software package for hardware-in-the-loop tests and flight test.

Long lead items, such as gears and bearings, have been delivered to support initial drivetrain tests scheduled for late 2014. “Existing helicopter turboshaft engines will power the prototype,” explained Renshaw. “The team is selecting available components wherever possible to minimize the cost of the prototype.”

The team has built and tested a one-third-scale powered wind tunnel model to test in the fall of 2013 and summer of 2014. The wind tunnel tests measured the aero and propulsion effects across the full range of thrust, duct angle, and control inputs. This data is being used to finalize the flight control laws and software for the prototype.

Construction of the prototype has begun with the ducted fan drivetrain, propellers, and duct structure in mid-2014. Subsystems, flight controls, and electronics will be added next. Tests of the complete system on a ground test stand will be used to measure thrust and UAV control responses. The test stand will also allow tests of failure modes and emergency procedures with flight hardware and software in a controlled environment.

The program will conclude with demonstrations of the flight module’s ability to perform vertical takeoffs, hover, make smooth transitions between hover and forward flight, and meet predicted flight performance. After the prototype proves that it can fly as predicted, additional tests with a variety of payload types could be performed. Specifics of those tests would depend on service user requirements. “We’re contacting operators from the United States Marine Corps, US Army, and Special Operations Command to help identify how they would use this system in the field,” said Renshaw.

“Once fully developed, ARES could provide future commanders increased flexibility and options for transporting personnel, performing reconnaissance missions, and supporting troops in the field,” Renshaw concluded. “The ability for small units in the field to get in and out of compact, austere forward bases and to move supplies or evacuate wounded troops without having to schedule high demand helicopters could revolutionize dispersed operations.”

This article was updated on 12 August 2014.