What are the Rain Removal Systems Commonly Used for Aircraft?

When operating an aircraft in a storm, rain can present a great obstruction that mitigates a pilot’s ability to fly through visual means. When taxiing on the airway, taking off, or landing, having clear visuals from the cockpit is crucial for safety so as to avoid any collisions. As a result, various rain-removal systems are put in place to remove fluids from the windshield, and each type presents its various advantages and drawbacks. In general, the most commonly used types of rain removal systems include windshield wipers, chemical rain repellent, hydrophobic seal coatings, and pneumatic rain removal systems.

As the most basic type of rain removal system, windshield wipers may be operated either electrically or hydraulically through wiper motors. With a separate wiper system on both the pilot’s and copilot’s windshields, one pilot can always ensure that they have clear vision through the panels even if the other system fails. In a typical windshield wiper system, a wiper blade, wiper arm, and a hydraulic or electrical motor work together in order to force rain pellets off of the windshield as they collect.

Due to their design, the wiper assembly only operates up to a certain airspeed as slipstreams may cause damage to parts. As such, the wiper system is most often used while on the ground, during takeoff, and during the final landing. Windshield wipers are also quite loud during operation due to their mechanical parts, and the shape of the assembly only allows for the wiper blade to remove fluids from a small portion of the windshield. As a result, windshield wipers are typically reserved for heavy rain conditions or as an addition to rain repellent systems.

Beyond mechanical means of rain removal, various rain repellent systems may also be used such as chemical rain repellents. With a chemical rain repellent, a transparent film is applied to the windshield that causes water to behave more similarly to mercury. As water begins to collect on the windshield, it will bead up together in small portions, rather than spread out evenly to reduce visuals. Through beading, removing fluids from the windshield becomes very easy, and beads of water will often naturally fall off the windshield.

To apply chemicals to the windshield, all the pilot has to do is press a button or a switch from within the cockpit, and the amount of repellent is controlled automatically to ensure proper functionality. Despite the ease of use that the system provides, it should only be used during wet situations. If the chemicals are applied to dry windows, the repellent may actually reduce visibility. Additionally, window wipers should not be paired alongside a chemical rain repellent system as it may cause smearing.

Hydrophobic seal coatings serve as an alternative to chemical repellents, also providing the ability to ensure that rain beads up and falls off naturally. Such systems are common to modern aircraft, as their treatment lasts for a long period of time and is quite effective at liquid removal. Despite its longevity, hydrophobic rain repellent systems take more time and effort to restore when their effectiveness begins to decline.

The final major type of rain removal system comes in the form of the pneumatic rain removal system, and they utilize heated air for their functionality. By directing a flow of heated air onto the windshield, rain droplets are broken apart into smaller beads and eventually are cast off of the surface. Additionally, the hot air also benefits visuals as it prevents any moisture from freezing, which can be very hard to remove by mechanical means. To provide hot air for the windshield, air is directed from bleed air or supplied by an electric blower.