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Technical Paper

Laboratory Testing of Aircraft Anti-Icing Fluid Rehydrated Gel Residues

Gel residues occur as the result of repeated anti-icing fluid application that leaves a powdery film upon dryout that, when rehydrated, can swell up to over 600 times its weight. When these gels collect on aircraft flight control surfaces in aerodynamically quiet areas and freeze, they give rise to reduced performance, increased stick force, slowed rotation and have caused jammed flight controls. Laboratory tests have been developed to simulate the gel formation by drying out fluids and rehydrating them. However, by their complex nature, much variation is seen between test results from different laboratories and the results are not yet considered by fluid users. Testing carried out at AMIL on different fluids with different test methods has led to a more reproducible results and a potential classification of fluids based on their gel formation potential (GFP).
Technical Paper

Issues and Testing of Non-Glycol Aircraft Ground Deicing Fluids

Deicing fluids are used to remove and prevent ice formation on aircraft before takeoff. These fluids are essentially composed of water, a freeze point depressant (FPD) usually glycol, a surfactant or wetting agent and a corrosion inhibitor. All commercial fluids are qualified to SAE (Society of Automotive Engineers) specifications, which test for aerodynamic acceptance, anti-icing endurance, corrosion inhibition, material compatibility, fluid stability and environment. However, these tests have been built around a fluid with a glycol FPD. More recently, with environmental pressure, fluids with other FPDs have been developed and qualified. The other FPDs include: acetates and formate salts, sorbitol, and other undisclosed FPDs. The acetates and formates, which came out in the early 1990s led to suspected corrosion problems. This led to the additional requirement for corrosion tests for non-glycol deicing fluids in paragraph 3.1.1 of AMS1424.
Technical Paper

Experimental Study of Snow Precipitation Over a Generic Deicing Fluid without Fluid Flow

Deicing and anti-icing fluids are used to remove and prevent ice formation on aircraft before takeoff. Holdover times (HOT) published by the FAA are used by pilots as guidelines indicating the amount of effective time of a fluid under certain freezing precipitation types. However, the times on these tables are based on endurance time tests involving a visual estimate of failure on a flat plate [1]: when 30% of the fluid is covered with white snow under snow precipitation, although the times have been correlated to aircraft wing tests [2] they do not address the mechanism of fluid failure. To measure and understand the fluid mechanisms conducting to failure, the Anti-icing Materials International Laboratory (AMIL) developed a simplified test with a generic deicing propylene glycol-based fluid. The test consisted of pouring 400 mL of the generic deicing fluid on a 5 dm by 3 dm level flat plate where the plate edges were rimmed with insolated walls to make a waterproof open box.
Technical Paper

Endurance and Aerodynamic Performance Certification of Aircraft De/Anti-icing Fluids

Three performance certification tests are required for the assessment of aircraft de/anti-icing fluids. The two first, measuring anti-icing endurance, consists of the Water Spray (WSET) and the High Humidity Endurance Tests (HHET). The third, for aerodynamic performance, consists of the Flat Plate Elimination Test (FPET). The three performance tests, used for both deicing and anti-icing fluids, are described in the annexes of AMS1424 and AMS1428. Since February, 2003 they are covered by aerospace standards AS5900 for aerodynamic, and AS5901 for anti-icing endurance performance. The WSET anti-icing endurance test measures the time that a fluid protects a plate, inclined at a 10° angle, subjected to freezing precipitation, from a specified amount of icing. This WSET time then defines the fluid type: it must exceed 3 minutes for a Type I, 30 minutes for a Type II and 80 minutes for a Type IV fluid.