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Sikorsky Aircraft Corporation flew the S-92A® helicopter into natural and tanker artificial icing conditions as part of the certification program for the rotor ice protection system (RIPS). Icing tanker tests were conducted during the late winter of 2004, and natural icing flights were made during the spring of 2004, winter of 2004-05, and early fall of 2005. One goal of the natural icing flight program was to obtain water-dominated icing encounters at temperatures between -15 and -23.33°C. Past studies have shown that mixed-phase icing is often found in this temperature range, and that most icing occurs at temperatures warmer than -15°C. Tanker tests were conducted at specific temperatures at altitudes below about 3 km (10,000 ft), and under prolonged weather conditions meeting visual flight rules (VFR). This represents a challenging combination of conditions to find within a small radius of operation from a given airport.

Sikorsky Aircraft Corporation designed, tested, and certificated a rotor ice protection system (RIPS) for the S-92A® helicopter, using a combination of analytical methods, simulated ice and artificial icing, dry air tests, and tests in natural icing conditions. The S-92A RIPS is a dual-redundant ice protection system, with the necessary reliability to meet the certification requirements of the US Code of Federal Regulations. Certification for the S-92A to fly in icing conditions was granted by the Federal Aviation Administration (FAA) in October 2005 and Transport Canada validated this certification soon thereafter. A Technical Visa was issued by the European Aviation Safety Agency (EASA) in April 2006. The S-92A is now in operation throughout the world, with several operators regularly experiencing icing conditions during their winter operations. With the icing certification of the S-92A a reality, Sikorsky has committed to the design of a RIPS for the S-76D™ helicopter.

The Sikorsky DELICE empirical icing code that calculates the effects of inflight icing on 2D lift, drag, and pitching moment increments has been adapted for use in Sikorsky's General Helicopter (GenHel) simulator code. DELICE was integrated into the GenHel main rotor, tail rotor, and horizontal and vertical stabilizer calculations, which allows GenHel to predict the effect of ice accretion on these surfaces on aircraft flight dynamics in trimmed and maneuvering flight. Deicing algorithms have also been included in the icing code to predict both the effect of a deicing system on aircraft flight dynamics in icing conditions and the effect of a failure in the deicing system. The GenHel icing code has been correlated with other icing predictions. It is believed that this is the first application of an icing code to a flight simulator, either for fixed-wing or rotary-wing applications.

A team from the USA rotorcraft industry, NASA, and academia was established to create a validated high-fidelity computational fluid dynamics (CFD) icing tool for rotorcraft. Previous work showed that an oscillating blade with a periodic variation in angle of attack causes changes in the accreted ice shape and this makes a significant change in the airfoil drag. Although there is extensive data for ice accumulation on a stationary airfoil section, high-quality icing-tunnel data on an oscillating airfoil is scarce for validating the rotorcraft icing problem. In response to this need, a two-dimensional (2D) oscillating airfoil icing test was recently performed in the Icing Research Tunnel at the NASA Glenn Research Center. Three leading-edge specimens for an existing 15-inch chord test apparatus were designed and instrumented to provide the necessary data for the CFD code validation.

Sikorsky Aircraft certificated the Model S-92A™ helicopter for flight in icing conditions in 2005. Since that time, the aircraft has flown in icing conditions throughout the world and the approval to launch a flight when icing conditions are forecast or reported has been valuable to operators. However, when the rotor ice protection system was inoperative due to a system failure, use of the aircraft on days of forecast icing was prohibited. Sikorsky Aircraft, therefore, elected to obtain certification of the S-92A helicopter to an EASA limited icing Special Condition so that UK and Norwegian operators in the North Sea sector could complete a mission when icing conditions were forecast, should the RIPS be inoperative on that day. A review of previously available icing data indicated that the S-92A helicopter could meet the requirements of the EASA Special Condition, but that additional flights were required to demonstrate full compliance.

An integrated approach for modeling the ice accretion and shedding of ice on helicopter rotors is presented. A modular framework is used that includes state of the art computational fluid dynamics, computational structural dynamics, rotor trim, ice accretion, and shedding tools. Results are presented for performance degradation due to icing, collection efficiency, surface temperature and water film properties associated with runback-refreeze phenomena, and shedding. Comparisons with other published simulations and test data are given.

In 2014 PZL Mielec obtained an EASA Type Certificate extension for the PZL M28 05 airplane for flight into icing conditions and this has been validated by the FAA. Thus, a project that lasted four years was finished successfully. During this period, activities consisted of icing analyses, wind tunnel tests in the NASA Glenn Research Center Icing Research Tunnel, and natural icing flight tests, artificial icing flight tests, flight tests with simulated ice shapes, and calibration tests. Flights in measured natural icing conditions began during the spring of 2009 and certification flight tests were performed in 2012. The natural icing test flights, apart one flight in the USA, were performed in Poland in the Mielec area. The final test campaign can be divided into two phases: (1) March -April flight tests campaign; and (2) November - December flight test campaign, the latter after introducing some design changes in airframe ice protection system.

Sikorsky Aircraft Corporation designed a new advanced technology composite main rotor blade for a growth BLACK HAWK helicopter, now designated the UH-60M. The UH-60M main rotor blade has new airfoils, a larger blade chord, and a swept, tapered, anhedral tip, with a rotor ice protection system (RIPS) similar to that of the UH-60A/L helicopter. The UH-60A/L RIPS control system was retained and the new blades were fitted with heater elements similar in geometry to those of the UH-60A/L main rotor blades, but with the outboard extent of the heater mat 10 inches more inboard than that of the UH-60A/L and the woven wire heater resistance was changed to maintain the same power density as the UH-60A/L. Analyses and S-92A® helicopter artificial and natural icing flight test data show that the increased blade chord, improved airfoils, and advanced blade geometry result a minimal change in BLACK HAWK icing flight characteristics.

Modern rotorcraft must have the capability to operate in all-weather conditions. Sikorsky Aircraft has conducted icing research and ice protection system development for helicopters over the past 58 years and the pace of that work has accelerated during the past two decades. Sikorsky participated in several helicopter icing flight tests, conducted wind tunnel tests of scale models and full-scale components, tested simulated ice shapes, and developed analytical tools for use in the design, certification, and qualification for flight in icing conditions. Engine inlets, airspeed systems, main rotor droop stops, and windshields are generally protected by thermal anti-icing systems. When rotor ice protection is required, rotors are protected with electrothermal deice systems. The UH-60A BLACK HAWK electrothermal rotor ice protection system, developed in the late 1970s, has been installed in 2400 H-60 helicopters and it remains one of the most effective rotor ice protection systems.

The effects of inflight atmospheric icing can be devastating to aircraft. Universities and industry have been hard at work to respond to the challenge of maintaining flight safety in all weather conditions. Proposed changes in the regulations for operation in icing conditions are sure to keep this type of research and development at its highest level. This is especially true for the effects of ice crystals in the atmosphere, and for the threat associated with supercooled large drop (SLD) icing. This collection of ten SAE International technical papers brings together vital contributions to the subject. Icing on aircraft surfaces would not be a problem if a material were discovered that prevented the freezing and accretion of supercooled drops. Many options that appeared to have promising icephobic properties have had serious shortfalls in durability.