Chapter 3.1 Ice and Rain Protection PDF

ME3531 Aircraft Systems Chapter 3: Ice and Rain Protection For Training Purpose Only  Official (Closed), Non-Sensitive Ice and Rain Protection Ice Control System With aircraft flying under certain altitudes and atm...

ME3531 Aircraft Systems Chapter 3: Ice and Rain Protection For Training Purpose Only  Official (Closed), Non-Sensitive Ice and Rain Protection Ice Control System With aircraft flying under certain altitudes and atmosphere conditions, ice can build up quickly on airfoils and air inlets. Water droplets in the air can be supercooled to below freezing without turning into ice. This unusual occurrence is partly due to the surface tension of the water droplet not allowing the droplet to expand and freeze. However, when the aircraft surface disturb these droplets, they immediately turn to ice and the aircraft surfaces. Icing Effects Ice or Frost forming on aircraft creates two basic hazards: The resulting malformation of the airfoil that could decrease the Temperature drops as aircraft amount of lift. climbs to about 38,000 Feet The additional weight and unequal formation of the ice that could cause unbalancing of the aircraft, making it hard to control. Page  2 For Training Purpose Only  Official (Closed), Non-Sensitive Ice and Rain Protection Types of Ice Clear Ice Formation occurs when the water droplets are large, in condition such as rain and freeze as a smooth sheet of solid ice. Once formed, it is difficult to be removed because it is heavy and hard. Rime Ice Formation occurs when water drops are small, in condition such as Formation of ice on aircraft leading edge light drizzle and freeze in a irregular shape and rough surface. The ice appears in a white appearance because of the air trapped air in the ice and lighter in weight than clear ice. Page  3 For Training Purpose Only  Official (Closed), Non-Sensitive Ice and Rain Protection Ice Detection System Ice can be detected by flight crew visually or ice detector sensors that provides a annunciator light to alert the crew on the icing condition. On some aircraft, the ice detectors will automatically activates ice protection systems. Page  4 For Training Purpose Only  Official (Closed), Non-Sensitive Ice and Rain Protection Ice Prevention The following are some methods to prevent or control ice formation used in aircraft today: Heating surfaces with hot air Heating electrical elements Breaking up ice formation, usually by inflatable boots Chemical application The equipment designed for anti-icing or for de-icing: For anti-icing equipment is turned on before icing conditions and is designed to prevent ice from forming. Deicing equipment is designed to remove ice after it begins to accumulate. Page  5 For Training Purpose Only  Official (Closed), Non-Sensitive Ice and Rain Protection Thermal Pneumatic Anti-Icing Wing Anti-Ice (WAI) System The bleed air is routed to each wing leading edge by an ejector in each wing inboard area. The ejector discharges the bleed air into the tubes for distribution along the leading edge. Fresh ambient air is introduced into wing leading edge by two flush-mounted ram air scoops in each wing leading edge, one at the wing root and one Thermal WAI System near the wingtip. The ejectors entrain ambient air, reduce the temperature of the bleed air and increase the mass airflow in the tubes. The air directed against the leading edge can only escape through the passageway, after which it is vented overboard through a vent in the bottom of the wingtip. Page  6 For Training Purpose Only  Official (Closed), Non-Sensitive Ice and Rain Protection Wing Anti-Ice (WAI) System When the WAI switch is turned on, the pressure regulator allows bleed air from engine compressor at 41 PSI to flow to tubings located at the wing leading edge. The wing leading edge temperature reaches +140 °F, temperature switches turn on the operation light. If the temperature in the wing leading edge exceeds approximately +212 °F (outboard) or +350 °F (inboard), the red Thermal WAI System WING OV HT warning light on the annunciator panel illuminates. Page  7 For Training Purpose Only  Official (Closed), Non-Sensitive Ice and Rain Protection Thermal Electric Anti-Icing For thermal electric anti-ice, current flows through integrated conductive element that produce heat. The temperature of the component is elevated above freezing point of water, so ice cannot form. Electricity is used to heat various components on an aircraft so that ice does not form. Pitot Probe Angle of Attack sensor Engine Pressure and Temperature sensors Windshields Probes with thermal electric anti-icing on one commercial airliner Page  8 For Training Purpose Only  Official (Closed), Non-Sensitive Ice and Rain Protection Chemical Ice and Rain Protection Chemical Anti-Icing This is used in some aircraft to anti-ice the leading edges of the wing, stabilizer, windshield, and propellers. The wing and stabilizers systems are often called weeping wing system or are known as 𝑇𝑇𝑇𝑇𝑇𝑇 𝑇𝑇𝑇𝑇 system. The ice protection is based upon the freezing point depressant concept. An anti-freeze solution is pumped from a reservoir through a mesh screen embedded in the leading edge of the wings and stabilizers. Once the switch is activated by the pilot, the liquid flows over the wing which prevents the formation of ice as it flows. Chemical Anti-icing system The solution mixes with the supercooled water in the cloud, depresses its freezing point and allows the mixture to flow off of the aircraft without freezing. Page  9 For Training Purpose Only  Official (Closed), Non-Sensitive Ice and Rain Protection Chemical Ice and Rain Protection Chemical Deicing When ice has accumulated on the leading edges, the antifreeze solution chemically break downs the bond between the ice and airframe. The aerodynamic forces carry and remove the ice. The system clears the accumulated ice before transitioning to anti-ice protection. Chemical Deicing system Page  10 For Training Purpose Only  Official (Closed), Non-Sensitive Ice and Rain Protection Wing and Stabilizer Deicing Systems The aircraft uses a pneumatic deicing system to break off ice after it has formed on the leading-edge surface. It has inflatable boots and the boots expand when inflated by pneumatic pressure which breaks away ice accumulated on the boot and deflated by vacuum suction. The vacuum is continuously applied to hold boots tightly against the aircraft structure while the boot is not in use. Cross-section of a pneumatic deicing boot uninflated (top) and inflated (bottom) Page  11 For Training Purpose Only  Official (Closed), Non-Sensitive Ice and Rain Protection Pneumatic Deice Boot System During a normal flight, all of the components are de-energized in the deicing system. The discharge air from the dry air pumps is dumped overboard through the deice control valves. The deflate valve is open connecting the deice boots to the suction side of the pump through the check valve manifold and the vacuum regulator. The vacuum regulator is set to supply the optimum suction to hold the boots tightly against Pneumatic deicing system for a twin engine aircraft with the airfoil surfaces. reciprocating engines Page  12 For Training Purpose Only  Official (Closed), Non-Sensitive Ice and Rain Protection Pneumatic Deice Boot System When the wing switch is pushed ON, the solenoid- operated deice control valves in each nacelle open and the deflate valve energizes and closes. Pressurized air from the discharge side of the pumps is routed through the control valves to the deice boot. When the system reaches 17 psi, pressure switches located on the deflate valve de-energize the deice control valve solenoids. The valves close and route pump air output overboard. The deflate valve opens and the boots are again connected to vacuum. Pneumatic deicing system for a twin engine aircraft with reciprocating engines Wing deice switch. Page  13 For Training Purpose Only  Official (Closed), Non-Sensitive Ice and Rain Protection Deice Boot Maintenance The life of the deicers can be greatly extended by storing them when they are not needed and by observing these rules when they are in service. 1. Do not drag gasoline hoses over the deicers. 2. Keep deicers free of gasoline, oil, grease, dirt, and other deteriorating substances. 3. Do not lay tools on or lean maintenance equipment against the deicers. 4. Wrap deice boots in paper or canvas when it is in storage. 5. Use mild soap and water solution to clean the deicers. 6. Cleaning agent, Naptha can be used to remove grease and oil. Page  14 For Training Purpose Only  Official (Closed), Non-Sensitive Ice and Rain Protection Propeller Deice System The formation of ice on the propeller leading edges, cuffs, and spinner reduces the efficiency of the powerplant system. Electrothermal Propeller Device System Many propellers are deiced by an electrically heated boot on each blade. The boot, firmly cemented in place, receives current from a slip ring and brush assembly on the spinner bulkhead. The slip ring transmits current to the deice boot. Many propellers are deiced by an electrically heated boot on each blade. The boot, firmly cemented in place, receives current from a slip ring and brush assembly on Electro thermal propeller deice system components. the spinner bulkhead. The slip ring transmits current to the deice boot. Page  15 For Training Purpose Only  Official (Closed), Non-Sensitive Ice and Rain Protection Rain Control System There are several different ways to remove the rain from the aircraft windshield. Windshield Wipers Chemical Rain Repellent Windshields treated with hydrophobic surface seal coating Windshield wipers The electrical windshield wiper system consists of the wiper blades that are driven an electric motors which ensure that clear vision for the pilots when operating the aircraft. Windshield wiper Page  16 For Training Purpose Only  Official (Closed), Non-Sensitive Ice and Rain Protection Rain Control System Chemical Rain Repellent The windshield glass is treated with chemicals, a transparent film is formed that causes the water to behave very much like mercury on glass. The water draws up into beads that cover only a portion of the glass and the area between beads is dry. The water is readily removed from the glass. A rain repellent system permits application of the chemical repellent by a switch or push button in the cockpit. The Cockpit rain repellant system proper amount of repellent is applied regardless of how long the switch is held. This system should only be used in very wet conditions. The rain repellent system should not be operated on dry windows because heavy undiluted repellent restricts window visibility. Page  17 For Training Purpose Only  Official (Closed), Non-Sensitive Ice and Rain Protection Rain Control System Windshield Surface Seal Coating Some aircraft model use a surface seal coating, called hydrophobic coating that is on the outside of the external surface of the windshields. The water draws up into beads that cover only a portion of the glass and the area between beads is dry. The water is readily removed from the glass. The coatings cause raindrops to bead up and roll off, allowing the flight crew to see through the windshield with very little distortion. Hydrophobic coating on windshield The hydrophobic windshield coating reduces the need for wipers and gives the flight crew better visibility during heavy rain. Page  18 For Training Purpose Only  Official (Closed), Non-Sensitive Ice and Rain Protection Windshield Frost, Fog, and Ice Control System Electric Transport category aircraft windshields are typically made of laminated glass, polycarbonate, or similar ply material. Typically, clear vinyl plies are also included to improve performance characteristics. The laminations create the strength and impact resistance of the windshield assembly. The laminated construction facilitates the inclusion of electric Cross-section of a transport category windshield heating elements into the glass layers, which are used to keep the windshield clear of ice, frost, and fog. The elements can be in the form of resistance wires or a transparent conductive material may be used as one of the window plies. To ensure enough heating is applied to the outside of the windshield, heating elements are placed on the inside of the outer glass ply. Windshields are typically bonded together by the application of pressure and heat without the use of cement. Page  19 For Training Purpose Only