Aircraft Structures & Pneumatic Systems PDF

AIR SYSTEM REVIEWER — TOPIC 1-3: AIRCRAFT STRUCTURES & PNEUMATIC SYSTEMS MAJOR AIRCRAFT COMPONENTS TRUSS TYPE (WING) Fuselage Wing Spar - are constructed so that Wing they will absorb the downwards Empennage...

AIR SYSTEM REVIEWER — TOPIC 1-3: AIRCRAFT STRUCTURES & PNEUMATIC SYSTEMS MAJOR AIRCRAFT COMPONENTS TRUSS TYPE (WING) Fuselage Wing Spar - are constructed so that Wing they will absorb the downwards Empennage bending stresses when on the ground Landing Gear and the upwards, rearwards and twisting stresses when in flight. FUSELAGE - The fuselage forms the main body of the aircraft to which the Drag Wire - a wing support of an wings, tailplane, canards, vertical fin airplane for sustaining the backward and engine are attached. reaction due to the drag of the wing. FUSELAGE TYPES Anti-Drag Wire - opposes the drag Truss Type or Framework Type wire. Monocoque Type Semi-Monocoque Type Compression Strut - opposes the compressive loads between the spars TRUSS TYPE - A truss is a rigid arising from the tensile loads framework made up of members, such produced by the drag and anti-drag as beams, struts, and bars to resist wires. deformation by applied loads. SEMI-MONOCOQUE TYPE (WING) MONOCOQUE TYPE - In monocoque Skin – it takes the loads due to structures, the skin takes all the loads differences in air pressures and the placed on the structure and the shape mass and inertia of the fuel (if any) in of the structure provides its strength the wing tanks. and rigidity. Stringers – these are span wise SEMI-MONOCOQUE TYPE - In this members give the wing rigidity by type, the loads imposed on the skin stiffening the skin in compression. are shared by a series of frames, stringers and formers that are Ribs - these maintain the airfoil shape attached to it. of the wings, support the spars, stringers and skin against buckling WINGS - Wings were previously and pass concentrated loads from referred to as main planes. They engines, landing gear and control produce the lift that supports the surfaces into the skin and spars. weight of the aircraft in flight and so must have sufficient strength and Ailerons - extend from about the stiffness to be able to do this. midpoint of each wing outward to the tip and move in opposite directions to WING STRUCTURE create aerodynamic forces that cause Truss Type the airplane to roll. Semi-Monocoque Type AIR SYSTEM REVIEWER — TOPIC 1-3: AIRCRAFT STRUCTURES & PNEUMATIC SYSTEMS Flaps - when extended, the flaps move DIHEDRAL VS. ANHEDRAL simultaneously downward to increase - The dihedral angle is the angle the lifting force of the wing for takeoff between the wing and and landings. horizontal plane when the wing is above the horizontal plane. WINGS (CATEGORIES) - The anhedral angle is the Biplane angle between the wing and Braced Monoplane horizontal plane when the wing Cantilever Monoplane is mounted so that it is below the horizontal plane. BIPLANE - Very few bi-planes fly at more than 200 knots in level flight and WINGS (SHAPES) so the air loads are low which means that the truss type design covered in fabric is satisfactory. BRACED MONOPLANE - Increase in airspeed enabled designers to remove one wing and save the drag it created. CANTILEVER MONOPLANE - In this design, the wing is self-supporting and attached to the fuselage at one end. WINGS (LOCATION) Low wing Mid wing High wing EMPENNAGE - On conventional aircraft, the empennage or tailplane LOW WING - The landing gear legs of normally takes the form of a single a low-wing aircraft are shorter than vertical fin and horizontal surface. those of a high-wing aircraft. MID WING - Mid-wing aircraft have the advantage of improved aerodynamics for high-speed flight but the disadvantage is having spars passing through the middle of the fuselage. HIGH WING - High wing aircraft have the advantages of giving good downward visibility and make cargo loading and unloading easier. AIR SYSTEM REVIEWER — TOPIC 1-3: AIRCRAFT STRUCTURES & PNEUMATIC SYSTEMS LANDING GEAR - The landing gear any other structural members on an supports the aircraft during landing aircraft. Most manufacturers use some and while it is on the ground system of station marking. FUSELAGE STATIONS - These are numbered in inches from a reference point or zero point known as the reference datum The reference datum is an imaginary vertical plane at or near the nose of the aircraft from which all of the fore and aft distances are measured. may call the fuselage station a body station, BS. BUTT LINE (BL) - Buttock line or butt line (BL) is a vertical reference plane down the center of the aircraft from which measurements left or right can be made. WATER LINE (WL) - This is a ATA CHAPTERS - ATA 100 Chapter measurement of height in inches numbers were a common referencing perpendicular from a horizontal plane standard for all commercial aircraft usually located at the ground, cabin documentation. floor, or some other easily referenced location. Was published by the Air Transport Association on June 1, 1956. ZONING SYSTEM - The aircraft is divided into specified zones and areas LOCATION NUMBERING SYSTEM - by reference planes or coordinates. Various numbering systems are used to facilitate the location of specific wing frames, fuselage bulkheads, or AIR SYSTEM REVIEWER — TOPIC 1-3: AIRCRAFT STRUCTURES & PNEUMATIC SYSTEMS MAJOR ZONES BMC fails, the other BMC takes over 100 - Lower Half of Fuselage most of the monitoring functions of 200 - Upper Half of Fuselage the failed one. 300 - Empennage Assembly 400 - Power Plants and Nacelle Struts CROSS-BLEED VALVE - allows the two 500 - Left Wing sides of the pneumatic system to be 600 - Right Wing isolated or interconnected through the 700 - Landing Gear and Landing Gear cross-bleed duct. Doors (Fixed) 800 - Doors The pneumatic system switches located on the overhead air conditioning panel include the engine 1 and engine 2 bleed push button switches, PNEUMATICS SYSTEMS - the APU bleed push button The aircraft pneumatic systems are switch, and the cross-bleed those that require air to perform their selector switch. function. The switch has three positions, PNEUMATICS SYSTEMS auto, shut, and open. Where is it used? Engine Starting With the cross-bleed selector Hydraulic/Water Reservoir switch in auto, the APU Air-conditioning running, and the APU bleed Cabin Pressurization push-button switch on, the APU Anti-icing bleed valve and cross-bleed valve will open. Both engine PNEUMATICS SYSTEMS bleed valves will close Where does pressurized air come from? If the APU bleed push-button Engine Bleed System switch is selected off, both the APU APU bleed valve and GPU cross-bleed valve will close. BMC 1 & BMC 2 - BMC 1 controls the The engine bleed valves will left side and BMC 2 the right. If one open if the engines are running AIR SYSTEM REVIEWER — TOPIC 1-3: AIRCRAFT STRUCTURES & PNEUMATIC SYSTEMS and the engine bleed push-button switches are on. The ECAM bleed page will Selecting the cross-bleed display the cross-bleed valve in selector switch to the shut green when normally open or position will close the closed. cross-bleed valve. The cross-bleed duct is not Selecting the cross-bleed displayed when the cross-bleed selector switch to open will valve is closed and displayed in open the cross-bleed valve. green when the cross-bleed valve is open. ENGINE BLEED SYSTEM Function: During flight, the aircraft’s engines generate pressurized air as a byproduct of their operation. Mechanism: The engine's compressor section draws in ambient air, The ECAM bleed page can be compresses it, and delivers it at high selected by pressing the bleed pressure to various systems, including pushbutton on the ECAM environmental control and anti-ice control panel or is systems automatically displayed in the Usage: This pressurized air is crucial event of a pneumatic system for maintaining cabin pressure, fault. temperature regulation, and supporting various pneumatic systems The ECAM bleed page displays essential for aircraft performance and information on bleed air valve safety. position, temperature, and pressure of engine bleed air, bleed air sources, and systems supplied. AIR SYSTEM REVIEWER — TOPIC 1-3: AIRCRAFT STRUCTURES & PNEUMATIC SYSTEMS There are two similar engine bleed systems, one for each engine. Each system selects the compressor stage to be used as a source of bleed air and regulates the bleed air temperature and pressure. Acting as a shutoff and pressure regulating valve, the engine bleed valves open pneumatically when engine bleed pressure above 8 psi is detected and the APU bleed valve is closed. Normally, the intermediate pressure stage supplies air to the pneumatic system. When pressure drops, due to low engine speed for example, the high-pressure valve opens to maintain a pressure of 32 to 40 psi. The BMCs 1 and 2 supply information A pre-cooler uses engine fan air to the ECAM bleed page. to cool and limit the When a fault is detected in the temperature of the engine pneumatic system, the bleed bleed air to 200 degrees page is automatically displayed Celsius. The fan air valve is on the lower ECAM display. pneumatically operated. Engine bleed valve position is displayed on the ECAM bleed page. AIR SYSTEM REVIEWER — TOPIC 1-3: AIRCRAFT STRUCTURES & PNEUMATIC SYSTEMS The normal open or closed main engines and can power various positions are displayed in systems within the aircraft. green. Usage: Provides air for air When displayed in amber, it conditioning, engine start procedures, indicates a disagreement and other ground operations, ensuring between the valve position and the aircraft is ready for flight and the BMC commanded position. comfortable for passengers and crew during ground time. The HP valve indication is green when it is in its commanded position and amber when it is not. The engine bleed's pre-cooler inlet pressure is displayed in green if within normal range. If the pressure is below or above the normal range, it is displayed in amber. The engine bleed temperature is measured at the pre-cooler outlet. It is normally green unless the BMC detects low temperature or an overheat condition, then it will be displayed in amber APU (AUXILIARY POWER UNIT) - Function: The APU is a small engine located in the tail of the aircraft, designed to generate power and pressurized air when the aircraft is on the ground. Mechanism: The APU produces pressurized air independently of the AIR SYSTEM REVIEWER — TOPIC 1-3: AIRCRAFT STRUCTURES & PNEUMATIC SYSTEMS The APU bleed valve appears in green on the ECAM bleed page when the APU master switch is on. The cross-line indication means that the valve is closed or not fully open. The in-line indication means that the valve is fully open. The valve is shown cross-line amber when the APU The availability of high pressure air valve is fully closed, with the throughout the bleed air system lends APU master switch is on and the itself readily to the provision of motive APU bleed switch has been on power to crank the engine during the for more than 10 seconds. engine start cycle. The conditions for the APU On the ground, the engines may be bleed valve to open are that the started in a number of ways: APU must be operating at By use of a ground air supply normal speed, there is no leak cart detected, and the APU bleed By using air from the APU – pushbutton switch is on probably the preferred means By using air from another GPU (GROUND POWER UNIT) engine which is already running Function: On the ground, the GPU provides external power to the The supply of air activates a aircraft, including pressurized air. pneumatic starter motor located on Mechanism: Connected to the aircraft the engine accessory gearbox. The via an external hose, the GPU supplies engine start cycle selection enables a pressurized air to power systems while supply of fuel to the engine and the engines are off. provision of electrical power to the Usage: Essential for pre-flight checks, ignition circuits. The pneumatic cabin conditioning, and systems starter cranks the engine to ∼ initialization before the engines are 15–20% of full speed by which time started engine ignition is established and the engine will pick up and stabilize at the ENGINE STARTING ground-idle rpm Function: Delivers high-pressure air to assist in starting the aircraft's engines. HYDRAULIC / WATER RESERVOIR Importance: Engine start-up requires Function: Pressurizes hydraulic significant air pressure to initiate the reservoirs used in various aircraft combustion process. systems. Importance: Hydraulic systems are essential for operating critical AIR SYSTEM REVIEWER — TOPIC 1-3: AIRCRAFT STRUCTURES & PNEUMATIC SYSTEMS components such as landing gear, and controlling humidity levels in the flaps, and brakes. cabin. ANTI-ICING/DE-ICING Function: The system supplies air to the wing anti-icing system to prevent ice accumulation on the wings. Importance: Ice build-up on the wings can significantly impact aerodynamic performance and safety. CABIN PRESSURIZATION FUNCTIONS: 1. Air Supply: The pneumatic system is The figure shows a typical centre responsible for supplying pressurized hydraulic power channel as air to the aircraft cabin. implemented by the Boeing 2. Pressure Control: The system philosophy. The hydraulic reservoir is regulates the cabin pressure by pressurized using regulated bleed air controlling the amount of bleed air from the pneumatic/bleed air system. entering the cabin and the outflow of Supply hydraulic fluid may be air through the outflow valves. pressurized by the two alternate 3.Temperature Regulation: Pneumatic pumps: systems often include components By means of the ACMP powered that help manage the temperature of by three-phase 115 VAC the cabin air. electrical power 4. Safety: The pneumatic system By means of the Air Driven includes safety mechanisms such as Pump (ADP) using pneumatic pressure relief valves and sensors to power as the source. monitor and maintain the correct pressure. The pneumatic pressure driving the ADP is controlled by means of a 28 IMPORTANCE: VDC powered solenoid controlled Passenger Comfort Modulating Shut-Off Valve (MSOV) Crew Efficiency upstream of the ADP. Safety Operational Range AIR CONDITIONING Function: The pneumatic system AIR CONDITIONING - An aircraft provides high-pressure air to the air air-conditioning system falls under conditioning system to regulate the ATA Chapter 21 (AIR CONDITIONING cabin environment. AND PRESSURIZATION). Importance: Proper air conditioning ensures passenger comfort by Hot, high pressure air is supplied to maintaining an optimal temperature two packs. The packs are responsible AIR SYSTEM REVIEWER — TOPIC 1-3: AIRCRAFT STRUCTURES & PNEUMATIC SYSTEMS for basic temperature regulation. From The packs supply dry air to the cabin the packs the air is distributed for air conditioning, ventilation and throughout the aircraft. pressurization. The main component of each pack assembly is the air cycle The pressurization system controls the machine. Hot air from the pneumatic airflow overboard to maintain the system is supplied to the pack through cabin pressurization within safe limits. the pack Flow Control Valve (FCV). The FCV adjusts the flow rate through the pack and is the pack Shut-Off Valve (SOV). Air Conditioning System Controllers ACSC 1 - sends the pack outlet temperature demand to pack 1 ACSC 2 - sends the pack outlet temperature demand to pack 2. To control the pack outlet temperature, the ACSC modulates the Bypass Valve and the Ram-Air Inlet doors. From the mixer unit, the air is distributed to the cockpit and the forward and aft cabin zones. Some of The packs supply the mixer unit. Three the air from the pneumatic system is separate aircraft zones are supplied used for the optimized temperature from the mixer unit: regulation system. This hot air is mixed cockpit with the air from the mixer unit to forward cabin adjust the temperature in each zone aft cabin independently. The trim air Pressure Regulating The air is distributed throughout the Valve (PRV) and the trim air valves cabin and finally, discharged are controlled by the ACSCs. overboard through the outflow valve to maintain pressurization AIR SYSTEM REVIEWER — TOPIC 1-3: AIRCRAFT STRUCTURES & PNEUMATIC SYSTEMS AIR CON. SYSTEM REQUIREMENTS air is introduced to the cabin through Provision of fresh air - Fresh forward facing air intakes air must be provided at a rate of 1 pound per seat per minute A typical system for a light aircraft is in normal circumstances, or at shown in the figure above which also not less than 0.5 pound features hot windscreen demisters and following a failure of any part a fresh air blower for use on the of the duplicated ground when there is no ram air. air-conditioning system. Temperature - Cabin air temperature should be maintained within the range 65°F to 75°F, (18°C to 24°C). Relative humidity - The relative humidity of the cabin air must be maintained at approximately 30% (at 40,000 feet the relative humidity is only 1 to 2%) Contamination - Carbon monoxide contamination of the cabin air must not exceed 1 part in 20,000. Ventilation - Adequate ventilation must be provided on the ground and during unpressurized phases of flight. Duplication - The air COMBUSTION HEATER - The fuel conditioning system must be used in the heater is normally that duplicated to the extent that no which is used in the aircraft's engines single component failure will and the heater works by burning a cause the provision of fresh air fuel/air mixture within the combustion to fall to rate which is lower chamber. than 0.5 pound per seat per minute. RAM AIR SYSTEM - In these systems, which are used in unpressurized piston engine aircraft, ambient atmospheric AIR SYSTEM REVIEWER — TOPIC 1-3: AIRCRAFT STRUCTURES & PNEUMATIC SYSTEMS ENGINE DRIVEN CABIN The point to note is the pressure rise SUPERCHARGER (BLOWER) across the compressor which allows SYSTEMS - When a supply of air from the use of much lower initial tapping the compressor of a gas turbine pressures while still being able to engine for air conditioning or achieve a sufficiently high pressure pressurization is not available, cabin drop across the turbine air supply may be provided by blowers driven through the accessory gearbox or by turbo compressors driven by bleed air. The blower must be capable of supplying the required mass flow of air under all operating conditions which means that at sea level with the engine running at high speed too high a mass flow will be delivered, therefore in order to prevent over pressurization AIR DISTRIBUTION - Most of the supply ducts, a mass flow passenger transport aircraft supply controller signals spill valves to vent warm air to the cabin walls by means the excess air flow to atmosphere. This of floor and wall passages which method is wasteful and is avoided maintains the interior surfaces at where possible by using variable cabin temperature, reducing draughts, speed drives. direct heat losses which in turn allows the entering air temperature to be closer to the cabin temperature. The ducting is in two distinct sections to provide for separate flows of cold and heated air. The cold (conditioned) air is supplied to the passengers through the gasper air system. TURBO-COMPRESSOR (BOOTSTRAP) - This is the most popular air cycle system in current use being used where high pressure bleed air is not available or its use is undesirable as in the case of aircraft using high bypass ratio or small turbo propeller engines. AIR SYSTEM REVIEWER — TOPIC 1-3: AIRCRAFT STRUCTURES & PNEUMATIC SYSTEMS avoid the worst of the weather VAPOR CYCLE (REFRIGERATION conditions whilst maintaining SYSTEM) - A refrigerant is used to cabin pressure at a comfortable absorb heat from the charge air by level. changing its state from liquid to gas. Aircraft can achieve high rates The refrigerant is a liquid which boils of climb and descent with small at approximately 3.5°C (38°F) at sea corresponding rates of cabin level atmospheric pressure. pressure changes. The airframe structure must, therefore, be strong enough to withstand the differential pressures generated without being too heavy and therefore uneconomic in operation. SYSTEM CONTROL - Cabin pressurization is controlled by having The condenser is positioned so that a constant mass flow of air entering cold ram air passes over it and the the cabin and then varying the rate at refrigerant changes back to its liquid which it is discharged to the state giving up latent heat to the ram atmosphere. air. Closing the valve reduces the outflow CABIN PRESSURIZATION - Modern and increases the pressure, opening aircraft operate more efficiently at the valve increases the outflow and high altitudes and have high rates of reduces the pressure. climb and descent. OUTFLOW VALVE - Allows for air to Modern aircraft are pressurized for exit the cabin at a controlled rate the following reasons: which results in the cabin becoming The aircraft can fly at an pressurized. altitude where it can operate efficiently, economically and AIR SYSTEM REVIEWER — TOPIC 1-3: AIRCRAFT STRUCTURES & PNEUMATIC SYSTEMS SYSTEM INSTRUMENTATION The minimum indications required for a pressurization system are: Cabin Altimeter - This gauge reads cabin pressure but is calibrated to read this in terms of the equivalent altitude of the cabin. Cabin Vertical Speed Indicator - This indicates the rate at which the aircraft SAFETY VALVE - A simple mechanical cabin is climbing or descending. outwards pressure relief valve fitted to relieve positive pressure in the cabin Cabin Differential Pressure Gauge - when the maximum pressure This indicates the difference in the differential allowed for the aircraft absolute pressure between the inside type is exceeded that prevents the and outside of the aircraft cabin and is structural maximum difference being generally calibrated in psi. exceeded. INWARDS RELIEF VALVE - A simple mechanical inwards relief valve is fitted to prevent excessive negative differential pressure which will open if the pressure outside the aircraft exceeds that inside the aircraft by 0.5 to 1.0 psi. DUMP VALVE - A manually operated component, the Dump Valve, will enable the crew to reduce the cabin pressure to zero for emergency depressurization. ANTI-ICING / DE-ICING - Without exception, the formation of ice or frost on the surfaces of an aircraft will cause a detrimental effect on aerodynamic performance. AIR SYSTEM REVIEWER — TOPIC 1-3: AIRCRAFT STRUCTURES & PNEUMATIC SYSTEMS MAJOR AREAS AFFECTED BY ICING Two different approaches are Wing Leading Edge generally used: Engine Intake De-icing – where ice is allowed to Pitot-Static System accumulate prior to being removed. Windscreen Anti-icing – where the object is to Propeller prevent any ice accumulation. ALTITUDE AND CHANCE OF ICING - There are a number of avenues which Icing on aircraft in flight is caused need exploring and these include primarily by the presence of detection and warning systems and super-cooled water droplets in the the methods used to protect the atmosphere. aircraft, which can be any or all of the The actual amount and shape following: of the ice buildup depends on Pneumatic – Expanding rubber boots the surface temperature. (mechanical). Kinetic air heating. Thermal – Electrically heated, oil Kinetic heating by water heated, air heated. droplets. Liquid – Freezing point depressant Latent heat of fusion, (caused fluids. (FPD) by the water droplets changing Ice detection – is provided from liquid to solid upon automatically by the provision of ice impact). detectors which relay a warning to the Evaporation. flight crew. Convection. Anti-Icing – is the application of continuous heat or fluid. STANDARDS OF PROTECTION - The De-Icing – is the intermittent aircraft must be cleared of ice, frost application of fluid, heat or and snow prior to dispatch and the mechanical effort. regulation requires that public transport aircraft shall be provided ICE DETECTOR HEADS with certain protective equipment for Teddington Ice Detector – this flights in which the weather reports detector consists of an airfoil shaped available at the time of departure mast protruding into the airflow and indicate the probability that conditions visible from the cockpit. predisposing to ice formation will be encountered. The requirements cover such considerations as the stability and control balance characteristics, jamming of controls and the ability of the engine to continue to function in icing conditions. AIR SYSTEM REVIEWER — TOPIC 1-3: AIRCRAFT STRUCTURES & PNEUMATIC SYSTEMS Smiths Ice Detector - consists of a hollow tube, attached to the aircraft by one end and has holes drilled in the leading and trailing faces; there are four holes in the leading edge and two in the trailing edge. ELEMENT ICE SENSING UNIT Sangamo Weston Ice Detector - ice can only be formed when there is a combination of moisture and freezing temperatures. MECHANICAL ICE DETECTOR HEADS English Electric (Napier) Ice Detector - in the Napier ice detector a serrated rotor shaft is continuously driven by an electric motor. Beta Particle Ice Detection Probe - two probes, mounted perpendicularly from the forward fuselage, plus a relay and the flight deck warning constitute the basic system. Rosemount Ice Detector - this detector consists of a short cylindrical probe mounted on a vibrator housing which vibrates the probe axially at about 35 kHz. AIR SYSTEM REVIEWER — TOPIC 1-3: AIRCRAFT STRUCTURES & PNEUMATIC SYSTEMS MECHANICAL DE-ICING - The de-icer boots, or overshoes, consist of layers of natural rubber and rubberized fabric between which are FLUID SYSTEMS - This system disposed flat inflatable tubes closed at prevents the adhesion of ice on the ends. surfaces by pumping de-icing fluid to panels in the leading edge of the THERMAL DE-ICING - In systems of airfoil, and allowing the fluid to be this type, the leading edge sections of carried over the surface by air wings including leading edge slats but movement. not leading edge flaps, and tail units are usually provided with a second, inner skin positioned to form a small gap between it and the inside of the leading edge section. WINDSCREEN WIPERS - Independent two speed wipers are usually provided for both pilots. ELECTRICAL DE-ICING - In an WINDSCREEN WASHERS - This electrical heating system, heating system sprays washer fluid into the elements either of resistance wire or windscreen panels, and is used in sprayed metal, are bonded to the air conjunction with the wipers to clean intake structure. the windscreens, a typical control panel is shown in the figure below, where a single washer control button controls the fluid for both screens. AIR SYSTEM REVIEWER — TOPIC 1-3: AIRCRAFT STRUCTURES & PNEUMATIC SYSTEMS WINDSCREEN RAIN REPELLENT PROPELLER PROTECTION SYSTEMS SYSTEM - The rain repellent system FLUID SYSTEM - The fluid system consists of four valve/timer nozzles, provides a film of de-icing fluid to the two for each screen and a manifold propeller blade surfaces during flight which stores and distributes the fluid which mixes with the water or ice and to the nozzles reduces the freezing point of the mixture ELECTRICAL HEATING SYSTEM - In electrical systems, the basis for effective de-icing is formed by resistance wire heating elements bonded to the leading edges of the propeller blades; in the case of turbine engine propellers, wire woven or sprayed elements are also bonded to the front shell of the spinner. FLUID DE-ICING SYSTEM - The method employed in this system is to spray the windscreen panel with a methylalcohol based fluid. ELECTRICAL ANTI-ICING SYSTEM - This system employs a windscreen of special laminated construction heated electrically to prevent, not only the formation of ice and mist, but also to improve the impact resistance of the windscreen at low temperatures.