CHEMICAL RAIN REPELLANT

Chemical Rain Repellant

Many of the jet transport aircraft have a chemical rain repellent system that uses a liquid chemical sprayed on the windshield to prevent the water reaching the surface of the glass. Since it cannot wet the surface and spread out, the water will fore beads and the wind can easily carry it away and leave the glass free of water so the pilot's visibility will not be distorted.

The repellent is a syrupy liquid that is carried in pressurized cans connected into the rain repellent system. When the aircraft is flying in rain so heavy that the windshield wipers cannot keep the windshield clear, the pilot can depress the Rain Repellent button and a single timed application of the liquid will then be sprayed out onto the windshield. The windshield wipers will then spread the liquid out evenly over the wiped sur­face.

The liquid should never be sprayed onto the windshield unless the rain is sufficiently heavy, because too much repellent can smear on the windshield and be difficult to see through. The repellent is difficult to remove if it is sprayed onto a dry windshield.

The operating system shown in Figure 7.4 con­sists of two pressurized containers of repellent and two DC solenoid valves that, once actuated, are held open by a time-delay relay. When the Rain Repellent push-button switch is depressed, the fluid flows for the required period of time, which is less than a second, and then the valve closes until the push button is again depressed. The number of times the button is depressed is determined by the intensity of the rain.

3. Pneumatic Rain Removal Systems High-pressure compressed air may be ducted from the engine bleed air system into a plenum chamber and then up against the outside of the windshield in the form of a high-velocity sheet of air. This air blast effectively prevents the rain hitting the windshield surface and adhering to it.