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.


Fuels

Boeing DiscRotor takes off vertically with rotor blades extended and retracts them for fixed-wing forward flight.

Power beaming is the wireless transfer of energy over distances using laser light to create an endless source of power to the aircraft. Biofuels are the product of catalyzing renewable jet fuel (biofuels) from sources such as alcohols, sugars, biomass and organic materials known as pyrolysis oils.

From a technical standpoint, liquid hydrogen (LH2) could be an alternative future fuel. Finally, present sources of energy include batteries, ultracapacitors and solar power. Ultracapacitors charge and discharge much faster than batteries, and, because capacitors don't suffer the wear and tear of chemical reactions, they last longer.

• Power beaming. LaserMotive (US) previously set the world record for the longest-duration laser-powered helicopter flight when it flew a tethered remote-controlled helicopter up to 6 hrs at a time for 4 days at the Association for Unmanned Vehicle Systems Intl (AUVSI) conference in Denver CO.

LaserMotive foresees 3 possible applications—stationary platforms, extended-endurance aircraft operating away from the beaming station (and returning to recharge when the batteries run low), and laser-powered UAVs that would stay on patrol within line-of-sight of the beaming station, which could be mobile.

• Biofuels. FAA recently awarded 8 grants to catalyze renewable jet fuel. In addition, the contracts call for research into alternative jet fuel quality control and for examination of how jet biofuels affect engine durability. They also provide guidance to jet biofuel users about factors that affect sustainability.

• Hydrogen. NATO Research and Technology Organization (RTO) believes that, because of high hydrogen production costs and the missing infrastructure, LH2 remains unattractive for operation at this time. However, the direct operating cost (DOC) crossover cost between kerosene and LH2 could be reached by 2040.

• Electric/solar. In addition to the OEMs mentioned previously with interests in electric propulsion, EADS has a project based on speculation about how aviation's next-generation batteries will "exceed energy densities of 1000 Wh/kg within the next 2 decades," and power superconducting electric motors to drive counter-rotating shrouded propellers.

EADS predicts, "Combined with a radical approach to airframe design, the expected promising developments in electric propulsion technologies could pave the way toward ultraquiet and emission-free flight."

Rotor systems

Wieland Helicopter Technologies (WHT) CoaX 415T 5-seat helicopter is one of several models the company is developing.

Slowed rotor/compound (SR/C) aircraft are a hybrid between an airplane and a rotorcraft in which the rotor is slowed and unloaded to reduce drag in high-speed flight, while using a wing to provide lift in that condition.

The mono tiltrotor (MTR) combines an advanced coaxial rotor system with sophisticated kinematics that morph the aircraft topology for efficient flight over the entire operational envelope.

The variable diameter tiltrotor (VDTR) uses a telescopic blade that extends in the hover to reduce disk loading and retracts in forward flight to reduce tip speed. Coaxial designs feature 2 rotors turning in different directions on a common mast, thereby eliminating the need for a tail rotor.

The mission adaptive rotor (see above) uses piezoelectric materials that flex when subjected to electrical fields to change and adapt the rotor blade while in motion. Finally, the objective of the compound helicopter is to achieve high-efficiency hover, high-speed flight, and seamless transition between these flight states.

• SR/C. Although Carter Aero­space Technologies currently uses the SR/C concept on an autogiro, it could be applied to a helicopter.

• MTR. Baldwin Technology proposes an innovative cargo rotorcraft architecture. The rotorcraft integrates a coaxial prop/rotor, a folding lifting wing system, a lightweight airframe and what the manufacturer calls an efficient cargo handling system capable of transporting a variety of mission tailored payloads rapidly and economically.

• VDTR. Sikorsky revisited this concept for a Joint Heavy Lift (JHL) study. With JHL funding, NASA awarded Sikorsky a contract to answer questions on the viability, performance and risk areas associated with a VDTR configuration.

Sikorsky studied the VDTR but shelved the concept around 2000. VDTR tries to balance the power requirements for vertical and forward flight in a tiltrotor by varying the diameter of the rotor in helicopter and airplane mode. Sikorsky's design uses a jackscrew-actuated mechanism.

• Coaxial rotors. Coaxial designs are more stable, quieter and more maneuverable, have a better power-to-weight ratio than traditional helicopters, produce greater lift and are more efficient.

Sikorsky used its X2 demonstrator as a "flying wind tunnel" to determine main rotor to propulsor aerodynamic interaction, shaft angle optimization for performance, and blade tip clearance for a range of maneuvers. Wieland Helicopter Technologies (WHT) is an Australian company currently developing a range of 2 to 5-place manned helicopters and UAVs.

• MAR. Sikorsky is researching the use of active rotors with on-blade control to eliminate need for the rotor swashplate.

• Compound helicopter. The Boeing CSAR DiscRotor takes off vertically like a helicopter, with telescoping rotor blades extended, then converts to fixed-wing forward flight by retreating the blades into the disc, which is then stopped.

The aircraft is then able to cruise long distances at high speeds on its swept wing and dual ducted propellers. Eurocopter's X3 is built around a Dauphin helicopter frame and is aimed at a wide range of applications, including long-distance search-and-rescue (SAR) missions, coast guard and border patrol missions, passenger transportation and intercity shuttle services.

Eurocopter says it could also be well tailored for military missions in special forces operations, troop transportation, combat SAR and medevac.

Conclusion

Alan Kay, the father of the personal computer and modern multi-windowed interfaces, declared, "The best way to predict the future is to invent it." The objective of innovation is to improve a product with respect to its characteristics, intended use or value. Strong innovators do consistently well.

It is clear that ingrained corporate cultures make it difficult to foster dialogue and open collaboration across the industry.

It is equally clear, given the usual 10–15 years from initial concept to fielding, that the market will not be satisfied with an unending stream of derivative products. Large-scale prototyping of advanced configurations will be necessary and these demands will best be served by sharing both the benefits and the burdens of a consortium established to take on such projects.

Gutenberg created the printing press by adapting a mature technology—the winemaking press—from an entirely different field. His open access to a broad range of technologies enabled a whole new era in data dissemination.

The rotorcraft industry will gain similar insights, breakthroughs and commercial viability by innovating and devising new ways to collaborate and share.

Don Van Dyke is an 18,000-hr TT pilot and instructor with extensive experience in charter, business and airline operations. A former IATA ops director, he has served on several ICAO expert panels and is a Fellow of the Royal Aeronautical Society.

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