Wednesday, February 29, 2012

Ice protection - ELECTRICAL SYSTEM

want to read about : Ice protection - HOT AIR SYSTEM
Fig. 13-5 Typical ice protection cyclic sequence
9. The  electrical  system  of  ice  protection  is generally used for turbo-propeller engine installa- tions, as this form of protection is necessary for the propellers.  The  surfaces  that  require  electrical heating are the air intake cowling of the engine, the  propeller blades and spinner and, when applicable,the oil cooler air intake cowling.
10. Electrical heating pads are bonded to the outer skin of the cowlings. They consist of strip conductors sandwiched between layers of neoprene, or glass cloth impregnated with epoxy resin.  To protect the pads against rain erosion, they are coated with a special, polyurethane-based paint. When the de- icing system is operating, some of the areas are con- tinuously heated to prevent an ice cap forming on the leading edges and also to limit the size of the ice that forms on the areas that are intermittently heated (fig.13-4).

11. Electrical power is supplied by a generator and, to keep the size and weight of the generator to a minimum, the de-icing electrical loads are cycled between the engine, propeller and, sometimes, the airframe.
12. When the ice protection system is in operation, the  continuously  heated  areas  prevent  any  ice forming, but the intermittently heated areas allow ice to form, during their 'heat-off period. During the 'heat- on' period, adhesion of the ice is broken and it is then removed by aerodynamic forces.

13. The cycling time of the intermittently heated elements is arranged to ensure that the engine can accept the amount of ice that collects during the 'heat-off' period and yet ensure that the 'heat-on1 period is long enough to give adequate shedding, without causing any run-back icing to occur behind the heated areas.
14. A two-speed cycling system is often used to accommodate the propeller and spinner require- ments; a 'fast' cycle at the high air temperatures when the water concentration is usually greater and a 'slow' cycle in the lower temperature range.  A typical cycling sequence chart is shown in fig, 13-5.

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