Aircraft Ice and Rain Protection | Aircraft Systems

Aircraft Ice and Rain Protection

Rain, snow, and ice are transportation’s longtime enemies. Flying has added a new dimension, particularly with respect to ice. Under certain atmospheric conditions, ice can build rapidly on airfoils and air inlets. On days when there is visible moisture in the air, ice can form on aircraft leading-edge surfaces at altitudes where freezing temperatures start.

Water droplets in the air can be supercooled to below freezing without actually turning into ice unless they are disturbed in some manner. This unusual occurrence is partly due to the surface tension of the water droplet not allowing the droplet to expand and freeze. However, when aircraft surfaces disturb these droplets, they immediately turn to ice on the aircraft surfaces.

Aircraft icing refers to ice accretion on surfaces of an aircraft flying in icing conditions. According to analyses of the causes for the aircraft accidents in recent years, aircraft icing is a major external cause. The number of flight accidents and events caused by aircraft icing. Most of the accidents were fatal, originating from the general aviation.

Aircraft icing influences the flight safety in many ways:
  1. Under icing conditions, the aircraft’s maximum lift coefficient and the slope of lift curve decrease, the drag and the critical stall speed increases.
  2. Wing icing can lead to a decrease in the airfoil stall angle of attack, while tailplane icing may cause a tailplane stall, especially in flap downwash flows. Both situations may cause pitch instability and further lead to a crash.
  3. Additional rolling moment can be caused by asymmetric icing, one side anti-icing system break-down, and formation of the ice ridge by water droplets beyond the ice protection system.
  4. The control efficiency reduces. Icing on tailplane may produce increased stick force that may reach hundreds of pounds in weight and increase difficulty in the manipulation. Icing on rudder movable structure may cause the rudder surfaces stuck and the aircraft uncontrollable. Icing on flap leading edge will cause the air separation in advance on the flap surfaces and slump in the flap efficiency.