Charles C. Ryerson

Design and Fabrication of Teflon-Coated Tungsten Nanorods for Tunable Hydrophobicity

The nature of water interaction with tungsten nanorods (WNRs) fabricated by the glancing-angle deposition technique (GLAD)-using RF magnetron sputtering under various Ar pressures and substrate tilting angles and then subsequent coating with Teflon-has been studied and reported. Such nanostructured surfaces have shown strong water repellency properties with apparent water contact angles (AWCA) of as high as 160°, which were found to depend strongly upon the fabrication conditions. Variations in Ar pressure and the substrate tilting angle resulted in the generation of WNRs with different surface roughness and porosity properties. A theoretical model has been proposed to predict the observed high AWCAs measured at the nanostructure interfaces. The unique pyramidal tip geometry of WNRs generated at low Ar pressure with a high oblique angle reduced the solid fraction at the water interface, explaining the high AWCA measured on such surfaces. It was also found that the top geometrical morphologies controlling the total solid fraction of the WNRs are dependent upon and controlled by both the Ar pressure and substrate tilting angle. The water repellency of the tungsten nanorods with contact angles as high as 160° suggests that these coatings have enormous potential for robust superhydrophobic and anti-icing applications in harsh environments.

Controlled growth of self-organized hexagonal arrays of metallic nanorods using template-assisted glancing angle deposition for superhydrophobic applications.

The fabrication of controlled, self-organized, highly ordered tungsten and aluminum nanorods was accomplished via the aluminum lattice template-assisted glancing angle sputtering technique. The typical growth mechanism of traditional glancing angle deposition technique was biased by self-organized aluminum lattice seeds resulting in superior quality nanorods in terms of size control, distribution, and long range order. The morphology, size, and distribution of the nanorods were highly controlled by the characteristics of the template seeds indicating the ability to obtain metallic nanorods with tunable distributions and morphologies that can be grown to suit a particular application. Water wettability of hexagonally arranged tungsten and aluminum nanorods was studied after modifying their surface with 5 nm of Teflon AF 2400, as an example, to exhibit the significance of such a controlled growth of metallic nanorods. This facile and scalable approach to generate nano seeds to guide GLAD, with nano seeds fabricated by anodic oxidization of aluminum followed by chemical etching, for the growth of highly ordered nanorods could have significant impact in a wide range of applications such as anti-icing coating, sensors, super capacitors, and solar cells.

Superstructure spray and ice accretion on a large U.S. Coast Guard cutter

Abstract Superstructure spray flux and ice accretion were measured on a 115-m Coast Guard cutter in the North Pacific Ocean and the Bering Sea during February and March 1990. This was the first such measurement cruise on a large ship; all previous measurements were on trawlers and patrol boats. Spray event duration averaged 2.73 s, somewhat longer than events measured on a 35-m Soviet trawler. The drop number concentration of most spray clouds was high, ranging from 2.0 × 10 5 to 3.0 × 10 5 drops m −3 . Spray cloud drop sizes ranged from 14 to 7700 μm, with a geometric median of 234 μm. Spray cloud liquid water contents had a very large range with a mean of 64.1 g · m −3 . Ice accretion rates were low, but sufficient for observing greater ice thicknesses on decks than on bulkheads. The ice accretion process was also found to be extremely dynamic, alternately accreting and ablating several times before reaching maximum thickness. No simple relationships were found between time-series of ice thickness during two icing events and controlling environmental parameters.

Visibility Enhancement in Rotorwash Clouds

Enhancing vision in rotorwash dust and snow clouds using remote sensing devices would improve the safety of helicopter operations. Our approach is to simulate remote sensor performance by modeling brownout cloud microphysical conditions. We use computational fluid dynamics techniques to model rotorwash, assuming incompressible and laminar flow, to develop the nearfield and farfield flow around a rotorcraft of given weight and configuration. We are developing two phase flow techniques to incorporate dust particles into the flowfield. Currently, stochastic techniques are being used to simulate particle entrainment in the boundary layer, with ongoing research to model entrainment using more realistic boundary conditions of turbulent flow impinging on a porous, erodible bed. Sensor signal performance is being simulated with MODTRAN, driven by the synthetically created cloud particle size distribution and concentration.

Use and calibration of Rosemount ice detectors for meteorological research

Abstract Vibrating probe ice detectors made by Rosemount Inc., are used by many researchers for measuring atmospheric icing rates and cloud liquid water contents. The vibration frequency of the probe decreases as ice accretes on it, until the probe is deiced at a factory-set frequency. Rosemount ice detectors are favored because they are readily available, easy to install and simple to operate. They are designed to be used as warning systems for incipient aircraft and antenna icing, and not as precisely calibrated scientific instruments. Calibration cannot be user adjusted, but it can be measured and must be periodically checked if the ice detector is to be used in scientific studies. We briefly describe three models of Rosemount ice detectors that CRREL has used. Methods for collecting and processing the data from these ice detectors are described and evaluated. Procedures developed at CRREL for calibrating Rosemount detectors against a rotating multicylinder in natural icing conditions are presented. Results of calibrations of two model 872B12 Rosemount ice detectors with the rotating multicylinder are presented and discussed. Use of the ice detector record to calculate cloud liquid water content is described.

Overview of Mount Washington Icing Sensors Project

NASA, the FAA, the Department of Defense, the National Center for Atmospheric Research and NOAA are developing techniques for retrieving cloud microphysical properties from a variety of remote sensing technologies. The intent is to predict aircraft icing conditions ahead of aircraft. The Mount Washington Icing Sensors Project MWISP), conducted in April, 1999 at Mt. Washington, NH, was organized to evaluate technologies for the prediction of icing conditions ahead of aircraft in a natural environment, and to characterize icing cloud and drizzle environments. April was selected for operations because the Summit is typically in cloud, generally has frequent freezing precipitation in spring, and the clouds have high liquid water contents. Remote sensing equipment, consisting of radars, radiometers and a lidar, was placed at the base of the mountain, and probes measuring cloud particles, and a radiometer, were operated from the Summit. NASA s Twin Otter research aircraft also conducted six missions over the site. Operations spanned the entire month of April, which was dominated by wrap-around moisture from a low pressure center stalled off the coast of Labrador providing persistent upslope clouds with relatively high liquid water contents and mixed phase conditions. Preliminary assessments indicate excellent results from the lidar, radar polarimetry, radiosondes and summit and aircraft measurements.

Evaluation of three helicopter preflight deicing techniques

Procedures for preflight deicing of helicopters have not been refined nor standardized. Parked helicopters are often exposed to weather, allowing freezing precipitation and snow to accumulate on airframe and blade surfaces. Unless removed, snow and ice may linger after precipitation ends, grounding aircraft for hours to days, depending upon temperature. Newer helicopters with comlposite blades and fuselage components are susceptible to damage corn deicing operations because thermal and mechanical damage can cause delamination. In addition, glycol-based deicing fluids may cause corrosion of critical rotor head components. Therefore, there is a need to develop different ground deicing techniques for helicopters. This paper describes an experimental evaluation of the use of infrared radiation, hot water and hot air to deice helicopters before flight. The purpose of the experiment was to evaluate the effectiveness of each deicing method, and to assess the potential themial effects of each on rotor blade composites. Our greatest interest was the potential for using infrared radiation as a deicing agent, a technique that has been used to deice fixed-wing aircraft, but not helicopters. Introduction and Problem Hangared helicopters are protected from weather. However, helicopters exposed to ,weather during military, search and rescue, medevac, anld oil rig supply operations allow freezing precipitation and snow to accumulate on airhame and blade surfaces when parked. Adhering snow and ice may linger after a storm passes, grounding aircraft for hours to days, unless frozen precipitation is manually removed. Reports that manual deicing methods can require up to four hours to prepare a single aircraft for flight, and the inefficiency of manual methods, justifies the need for finding better methods. Modem helicopters are mor’e likely to be damaged by ice and snow removal techniques than are fixed-wing aircraft because large portions of rotor blades and fuselage surfaces are constructed of composites. Composites are susceptible to damage from physical impact, scraping, high temperatures, and rapid thermal cycling. In addition, glycol deicing fluids may corrode helicopter rotor heads and wash lubricants from bearings. This paper is declared a work of the U.S. Government and is not subject to copyright protection in the IJnited States. Boots and covers are occasionally used to protect helicopter components from ice and snow on the ground. For example, covers for blades, rotor heads, wind screens, tail rotors, engine inlets and, as on fixed-wing aircraft, pitot covers, are often used. However, reports of freezing of covers to aircraft surfaces make them less practical than desired. In addition, their use requires knowledge that freezing or frozen precipitation may occur when the aircraft is parked. Unless forecasts of freezing precipitation are very reliable and precipitation probabilities are high, aircraft are unlikely to be covered prior to a storm resulting in snow or ice-covered aircraft requiring deicing. This paper describes an experimental evaluation of the use of in&red radiation, hot liquid, and hot air to deice Army Blackhawk helicopters before flight. It also describes the utility of a portable ice imager system for use in deicing procedures. The purpose of the experiment was to identify deicing techniques available for helicopters, to select and evaluate the effectiveness of several methods, and to assess the potential thermal effects of each on rotor blade composites.

UAV Icing Flight Simulation

Unmanned Aerial Vehicles (UAVs) are necessary tactical tools for Army field commanders requiring surveillance, targeting aids, and communication links. Icing and freezing precipitation can create serious problems for Army UAVs. Though the Army UAVs were not initially flown in Kosovo between October and April because of icing, and flights were not launched when icing was forecast, 25% of UAV flights encountered icing. The Armys present icing avoidance approach is to not fly when icing is forecast. While this solves, in part, the problem of aircraft icing, it negatively impacts mission success. To explore the impact of icing on UAVs and the potential use of low weight, low-power remote sensing systems to allow UAVs and other aircraft to avoid or minimize icing conditions during flight, we have looked at the environmental conditions conducive to icing potential, sources of field measurements and models for characterizing natural icing conditions, and models that predict ice accretion on airfoils. Techniques have been developed to simulate ice accretion rates, type, and shape on airfoils for flights in natural icing conditions. This paper discusses our approach and simulation techniques and presents some preliminary results.

Thermal Deicing of Polymer Composite Helicopter Blades

This paper presents the results of an investigation to determine if thermal deicing methods (hot air, hot water, hot glycol, or radiative heat) would damage the composite materials in helicopter blades. Samples made from Blackhawk helicopter blades were thermally cycled in the regime of the temperatures of thermal deicing methods and then mechanically load tested. The strength reduction was compared with the number of thermal cycling and the temperatures of thermal cycling. The strength results and the modes of failure indicate that damages indeed do develop in the composites, especially along the bond line of the composite skin and the nomex core of the blade structure, and mechanical strength is reduced.

Evaluation Of Environmentally Friendly, Glycol-Free Mobile Aircraft Deicing System

The U.S. military is evaluating environmentally friendly alternatives for aircraft deicing operations. Our goal is to prevent water and ground contamination while meeting mission flight requirements and enhancing safety. To address this goal a demonstration was performed in April 2002 at Eglin AFB, McKinley Climatic Chamber of a simulated integrated portable infrared and forced air/fluid assisted deicing with an ice imager. Such an integrated system may meet environmental standards, enhance safety, satisfy most military deicing requirements, and have commercial application. We plan to integrate these technologies, including an environmentally friendly deicing fluid, into a single unit for field testing during the winters of 2002-03 and 2003-04 at operational airfields. We compare deicing rates and environmental impacts using the simulated integrated deicing system versus a more traditional forced air/glycol deicing truck.