V/STOL TECHNOLOGIES

Innovation offers needed lift for the rotorcraft of tomorrow

Strong commitment to R&D and inspired concepts are key to advancing the forefront of vertical lift capability.




Airframe design

EcoMotors diesel motor on display at Heli-Expo 2011.

• Morphing aircraft structures (MAS). The major function of a structure is to carry load or provide shape. The idea of equipment that can change its shape isn't science fiction. NASA has developed a carbon nanotube polymer composite that bends when a voltage is applied. NASA research using nanotechnology is well under way to develop aircraft wings, propellers and transport vehicles that can literally change shape to improve performance and efficiency.

This type of morphing material or "smartskin" may be used in various ways, including actuation, electrical/thermal (either to insulate or conduct), health monitor/control, stealth (managing electromagnetic or visible signature), self-healing/repairing localized damage and sensing physical and chemical variables.

Also, less MAS deflection is required for equivalent hinged control or tab operation. The flexibility allowed by MAS could result in huge savings and much im­proved efficiency.

• Wireless alternatives. The amount of wire installed on a typical aircraft has nearly tripled over the past 15 years with the introduction of glass cockpits, new sensors, health and usage monitoring, and active vibration control. Sikorsky is researching wireless alternatives for use in combination with other technologies having the potential of reversing the wire growth trend.

• Design alternatives. Some innovations are deceptively simple. The BLR Aerospace FastFin system in­corporates dual tailboom strakes (to reduce any translating tendency) with a reshaped vertical fin that improves tail rotor management, resulting in increased performance and greater stability in all flight regimes, including hot-and-high hover.

EADS Innovation Works is researching the possibility of tilting the main rotor forward to provide forward thrust in cruise while the body of the helicopter is in the minimum-drag position. The tail rotor could also be turned off in cruise flight as an aerodynamic surface can be used to maintain directional control.

Since many civil helicopter features began with military innovations, it is noteworthy that the DARPA Transformer (TX) program will examine the feasibility and approaches for developing vertical-takeoff-and-landing (VTOL) roadworthy vehicles that carry a 4-person payload more than 250 nm on a single tank of fuel, are able to safely travel on roads and can be operated by 1 person.

Technical areas that will be explored include the following—hybrid electric drive ducted fan propulsion system, ring motors, energy storage methods such as batteries and ultra capacitors, morphing vehicle bodies, and advanced flight controls and flight management systems.

Propulsion

Record-setting first flight of e-volo all-electric "multicopter" in 2011.

Many of the most significant advances in aviation have been enabled by transformations in propulsion technology. Diesel engines for rotorcraft feature excellent fuel consumption, good high-altitude performance and accommodation of multiple fuel types. Electric propulsion simplifies the propulsion system by reducing the number of moving parts and increases reliability while reducing direct operating costs.

• Diesel. Eurocopter is currently considering applications for the EcoMotors (US) 2-stroke opposed piston, opposed cylinder (OPOC) diesel engine with a goal to improve on the power-to-weight ratio of turbine engines.

• Electric. The pure electric motor stores energy in batteries and ultracapacitors. The hybrid turboelectric concept uses gas-powered generators to supply electricity to motors, driving fans that produce thrust.

Sikorsky Innovations built the Firefly, a 2-seat Schweizer S300C, powered by a 191-hp electric engine, which was scheduled to fly this year. However, in Oct 2011, German company e-volo achieved the world's first all-electric manned rotorcraft flight.

• Ring motor. In 2011, ThinGap an­nounced a 14-in diameter ring motor weighing just 25.6 lb and delivering 163 hp, allowing a ducted fan to develop as much thrust as with a gas turbine.

Environment

Helicopters make noise by interference of rotor blade tip vortices from one rotor blade with those of the following blades.

This blade/vortex interaction (BVI) is typically a "slap" sound created during normal descent. Vibration is another effect which fatigues the airframe as much as it does the flightcrew.

Finally, degraded visual environment (brown­out, whiteout, sea spray, fog) is a major safety hazard causing loss of situational awareness. This also makes helicopters and tiltrotors with high-set rotors, engines and transmissions prone to catastrophic rollovers.

• Noise. Eurocopter is developing a new kind of main rotor blade, called Blue Edge, which uses a double-swept shape to change the BVI to attenuate this problem by as much as 3–4 dB. The new blade shape is combined with another technology, called Blue Pulse, which adds 3 flaps to the trailing edge of the rotor blades. These flaps move up and down at 15–40 times per second, using piezoelectric motors to further reduce BVI by a total of 5 dB (66%).

Sandblaster enables the pilot to "see" through the cloud and guide the helicopter to a preset landing point. The pilot is able to interact with the system to avoid obstacles in the landing zone.

Sikorsky, when flying its S97 Raider (X2) high-speed compound helicopter in helicopter mode, stops the propeller and operates with reduced rotor rpm, sharply reducing noise. MD Helicopters uses NOTAR technology to eliminate tail rotor and associated noise.

Bell is devoting much work on the civil side at reducing gearbox and tail rotor noise and is developing a new blade tip shape. And Boeing is investigating the application of what it calls smart material actuated rotor technology (SMART) using piezoelectric actuators to drive trailing-edge flaps. Under test conditions, main rotor noise was reduced by half (3 dB). Final configuration could use materials which flex when subjected to electrical fields.

• Vibration. Under a DARPA contract, Sikorsky is researching use of the nanotech mission adaptive rotor (MAR), which morphs to reduce vibration, improve performance and extend range.

• Degraded visual environment. BAE Systems' BLAST (for brownout landing aid system technology), Sikorsky Sandblaster and Elbit Systems Dust-Off all use similar strategies in coping with this perennial threat—a millimeter-wave radar seeker to scan a landing zone in real time in combination with digital terrain elevation data and situational information and warnings via a brownout symbology set that uses a cockpit, head-up or helmet-mounted display.

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