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The entire process from ice accretion to ice impact with ice shedding in between still needs refinement. This paper presents key points illustrating the need for improvements in understanding the mechanical properties of ice accretion on helicopter rotor systems.

Helicopter rotor systems are increasingly using flexible composite structures to provide the required control movement for the rotor blades. These structures such as rotor head flex beams can experience very high surface strains, which can be in the order of 15,000 με. This makes it difficult for them to be monitored using conventional surface bonded strain sensors. Helicopter rotor hubs incorporating thick composite flexures are subjected to delamination failures with correlate to bending excursions. Measurement of this deflection could be used to predict remaining useful life of the flexure and other hub components. Previous efforts to measure surface strains using fiber optic sensors led to mixed results and prompted an effort to explore embedded sensors. As part of a Vertical Lift Consortium project, the authors tested proof of concept manufacturing specimens to establish the ability of the sensors to survive the cure process in a closed cavity mold tool.

As part of icing certification flight test programs, artificial ice shapes are typically installed onto aircraft fixed leading edges in order to quantify changes to the handling qualities and performance characteristics of the aircraft in icing conditions. Artificial ice shapes allow a test team to evaluate what are generally the worst combinations of flight conditions for different ice protection system configurations. The goal of this paper is to discuss the details behind the design, development, construction, and installation of artificial ice shapes as they pertained to the evaluation of the need for horizontal stabilizer ice protection on the BA609 Tiltrotor with a focus on the extrapolation methods used to design the shapes.

As the technology in rotor deicing matures, more programs are willing to engage in the certification of their helicopters for flight into icing conditions. The S-92A™ helicopter, AW139, V-22, and EC225 aircraft have been certified/qualified recently and are illustrative examples of such engagement. The state-of-the-art configuration definition of rotor ice protection systems that have been introduced into the western rotorcraft manufacturer's production line has been limited to electro-thermal deicing systems. System configurations may use either chordwise or spanwise shedding schemes and could differ in design and operation. Regardless of the selected design configuration, an analysis of the required extent of protection coverage must be performed unless one has access to data offering sufficient similitude in terms of airfoil geometry and flight conditions.

This paper reviews some previous and current helicopters designed for heavy lift. Technology status is also reviewed and the problem of arrested development is shown to be in part due to the economics of insufficient utilization. Nevertheless, both military and civil needs are discussed and are projected to grow. A possible resolution of this utilization dilemma is suggested via tri rotor and quad rotor variants of the tilt rotor family of V/STOL aircraft. Multi (greater than two) rotor dynamic systems are projected to weigh less than twin rotor systems and are therefore a way of avoiding rapid design disc loading increases in an attempt to maintain productive vehicle weights. In addition, development risk, investment, and logistic costs are minimized if dynamic components are planned or in use on a smaller aircraft with high production potential. The current paper compares three and four rotor, tilt rotor V/STOL aircraft with an advanced tandem helicopter. All have four engines.

This paper describes the design objectives, features and performance of the recently developed Bell Model 222. The Model 222 was designed to meet the needs of the worldwide commercial market. Primary design objectives were safety, efficiency, reduced cost of ownership, and superior handling qualities. From the test results, the Model 222 is a fuel conservative, productive aircraft with excellent flying qualities. Federal Aviation Administration Air-worthiness Standards, Transport Category Rotorcraft (FAR Part 29 - Category A) provides the basis for civil certification; however, the 222 far exceeds the FAA requirements for fail-safe design and crashworthiness. Redundancy, 8g seats, crash resistant fuel tanks, and real twin-engine safety are examples. The latter refers to the fact that for any altitude at which the helicopter can hover OGE, it can continue to cruise if one engine fails. The first flight was in August 1976 and development is essentially complete.