Undesired ice accumulation leads to severe economic issues and, in some cases, loss of lives. Although research on anti-icing has been carried out for decades, environmentally harmless, economical, and efficient strategies for anti-icing remain to be developed. Recent researches have provided new insights into the icing phenomenon and shed light on some promising bio-inspired anti-icing strategies. The present review critically categorizes and discusses recent developments. Effectively trapping air in surface textures of superhydrophobic surfaces weakens the interaction of the surfaces with liquid water, which enables timely removal of impacting and condensed water droplets before freezing occurs. When ice already forms, ice adhesion can be significantly reduced if liquid is trapped in surface textures as a lubricating layer. As such, ice could be shed off by an action of wind or its gravity. In addition, bio-inspired anti-icing strategies via trapping or introducing other media, such as phase change mate...

Bio-inspired strategies for anti-icing.

Nomenclature Ac = accumulation parameter Cd drag coefficient Ci = lift coefficient Cm = moment coefficient Cp = pressure coefficient c = specific heat at constant pressure, J/(kg-K); airfoil chord, m D = propeller diameter, m; flexural stiffness, N-m D drag force, N d = droplet diameter, m E = total collection efficiency / = freezing fraction g = acceleration caused from gravity, m/s Hi = ice thickness, m Hp = plate thickness, m h = airfoil projected height, m hc = convective heat transfer coefficient, W/(m-K) hfg = heat of vaporization, J/kg hsi = heat of fusion, J/kg / = airfoil drag constant K = thermal conductivity, W/(m-K); inertia parameter K0 = modified inertia parameter k = roughness diameter, m LWC = liquid water content, kg/m M = local Mach number MVD = median volume droplet diameter, m m = mass, kg ra = mass flow rate, kg/s m' = mass flow rate per unit width, kg/(m-s) m" = mass flux, kg/(m-s) n = normal direction P = pressure, Pa p spatial pressure distribution, N/m <2 = heat rate, W q = normal pressure distribution, N/m

Aircraft Anti-Icing and De-Icing Techniques and Modeling

A planar coil construction, especially adapted for use in a force-producing device such as a de-icer, includes first and second sheet-like members, each defined by a continuous electrical conductor having a plurality of turns and first and second ends. The first end of the first conductor defines an electrical input to the coil, while the second end of the second conductor defines an electrical output from the coil. The second end of the first conductor and the first end of the second conductor are electrically connected. The sheet-like members are superimposed such that current flow through adjacent turns of the conductors is in the same direction. Within each sheet-like member, adjacent conductors also have current flow in the same direction. The invention includes a technique for spacing the conductors by means of a dielectric layer, and a technique for encapsulating the sheet-like members. Alternative embodiments are provided wherein different relationships among the sheet-like members are possible as they might be used for force-producing elements in a de-icer.

Method of manufacturing a planar coil construction

Freezing of water droplets on solid surfaces: An experimental and numerical study

The paper summarizes the state of the art in aeronautical drag reduction across the speed range for the conventional drag components of viscous drag, drag due to lift and wave drag. It also describes several emerging drag-reduction approaches that are either active or reactive/interactive and the drag reduction potentially available from synergistic combinations of advanced configuration aerodynamics, viscous drag-reduction approaches, revolutionary structural concepts and propulsion integration.

https://journals.sagepub.com/doi/pdf/10.1243/095441003763031789

Aircraft Drag Reduction-A Review

It is proposed that aircraft can be designed using propellers at the wingtips in such a way that the L/D ratio can be varied by changing the effective aspect ratio in flight. An experimental program testing a wing with propellers mounted at the wingtips is reported. It is shown that the use of a propeller at the wingtip, turning in the direction opposite to that of the wing vortex, shifts the trailing vortex core outboard, decreases the wing drag coefficient, increases the maximum lift coefficient and increases the effective aspect ratio. Rotating the propeller in the opposite direction has the reverse effect. A functional relationship is shown to exist between ACD/CD and Tcd/CLS-

Effects of wingtip-mounted propellers on wing lift and induced drag.

Wind-tunnel tests were conducted on the GA(W)-2 airfoil with 25%-slotted flap at Reynolds number of 2.2x106 and Mach number of 0.13. The tests were made for flap nested and flap deflected cases of 30 and 40 deg with optimum and narrow gaps. Stall characteristics on the airfoil elements were examined through plots of force, moment, and surface pressure data and flow visualisation. Flap deflected configurations indicated a two-stage stall and hysteresis phenomenon. The hysteresis loop appeared to be a function of flap angle, gap geometry, and history of changes in air speed or angle of attack.

Hysteresis Effects on Wind Tunnel Measurements of a Two-Element Airfoil

Electro-Impulse De-Icing (EIDI) is a method of ice removal by sharp blows delivered by a transient electromagnetic field. Detailed results are given for studies of the electrodynamic phenomena. Structural dynamic tests and computations are described. Also reported are ten sets of tests at NASA's Icing Research Tunnel and flight tests by NASA and Cessna Aircraft Company. Fabrication of system components are described and illustrated. Fatigue and electromagnetic interference tests are reported. Here, the necessary information for the design of an EIDI system for aircraft is provided.

Electro-impulse de-icing testing analysis and design

A brief description is given of the theory and history of EIDI (electroimpulse deicing) technology. These descriptions are followed by a summary of the experiments conducted by the authors to investigate the feasibility of deicing electric power lines using EIDI technology. In spite of the features of EIDI technology that make it attractive for power line deicing, the authors were unable to deice a conductor span of any significant length and thus concluded that EIDI technology, in its present form, is not suited for power-line-deicing applications. >

An investigation of power line de-icing by electro-impulse methods

De-icing of aircraft by using the electro-magnetic impulse phenomenon was proposed and demonstrated in several European countries. However, it is not available as a developed system due to lack of research on the basic physical mechanisms and necessary design parameters. The de-icing is accomplished by rapidly discharging high voltage capacitors into a wire coil rigidly supported just inside the aircraft skin. Induced eddy currents in the skin create a repulsive force resulting in a hammer-like force which cracks, de-bonds, and expels ice on the skin surface. The promised advantages are very low energy, high reliability of de-icing, and low maintenance. Three years of Electo-Impulse De-icing (EIDI) research is summarized and the analytical studies and results of testing done in the laboratory, in the NASA Icing Research Tunnel, and in flight are presented. If properly designed, EIDI was demonstrated to be an effective and practical ice protection system for small aircraft, turbojet engine inlets, elements of transport aircraft, and shows promise for use on helicopter rotor blades. Included are practical techniques of fabrication of impulse coils and their mountings. The use of EIDI with nonmetallic surface materials is also described.

Glen W. Zumwalt

Papers

Effects of wingtip-mounted propellers on wing lift and induced drag.

Hysteresis Effects on Wind Tunnel Measurements of a Two-Element Airfoil

Electro-impulse de-icing testing analysis and design

An investigation of power line de-icing by electro-impulse methods

Analyses and tests for design of an electro-impulse de-icing system