MART Vol. II MO/MP - NESA - Civil Air Patrol

typical C172 significantly increase the weight of the aircraft; a quarter-inch coatingof ice can add up to 150 lbs., a half-inch can add ~ 300 lbs., and an inch of clearice can add ~ 600 lbs.From an aerodynamic viewpoint, there is no such thing as "a little ice." Manypilots do not recognize that minute amounts of ice adhering to a wing can result insimilar penalties. Research results have shown that fine particles of frost or ice,the size of a grain of table salt and distributed as sparsely as one per squarecentimeter over an airplane wing's upper surface can destroy enough lift (22% inground effect and 33% in free air) to prevent that airplane from taking off.Many pilots also believe that if they have sufficient engine power available,they can simply "power through" any performance degradation that might resultfrom almost imperceptible amounts of upper wing surface ice accumulation.However, engine power will not prevent a stall and loss of control at lift-off, wherethe highest angles of attack are normally achieved. Further, small patches ofalmost imperceptible ice or frost can result in localized, asymmetrical stalls on thewing, which can result in roll control problems during lift off.Ice accumulation on the wing upper surface is very difficult to detect; it maynot be seen from the cabin because it is clear/white and it is very difficult to seefrom the front or back of the wing. The only way to ensure that a wing is free fromcritical contamination is to touch it!Ice can also accumulate on aircraft during flight, and this icing is a majorproblem in aviation. It is difficult to forecast, because under apparently identicalsituations the icing intensity on the aircraft can vary considerably. The iceaccumulation rate may vary from less than one-half inch per hour to as high asone inch in a minute for brief periods. Experiments have shown that an icedeposit of as little as one-half inch on the leading edge of a wing can reduce lift byabout 50%, increase drag by an equal percentage, and thus greatly increase thestall speed. Obviously, the consequences of ice accumulations can be veryserious.There are only two fundamental requisites for ice formation on an aircraft inflight. First the aircraft must be flying through visible water in the form of rain orcloud droplet, and second, when the liquid water droplets strike, their temperature,or the temperature of the airfoil surface, must be 32º F. or below. Water dropletscooled below 32º F. without freezing are called supercooled water droplets. Theyoften exist in clouds when the temperature within the clouds is below 32º F.Clear ice is a transparent or translucent coating of ice that has a glassysurface appearance. When transparent, it looks like ordinary ice, and is identicalwith the “glaze” which forms on trees and other objects when freezing rain falls tothe earth. It can be smooth or stippled. However, when mixed with snow, sleet,hail, etc., it may be rough, irregular and whitish. It has an appearance differentfrom that of rime ice, due to its different mode of formation and structure. Itadheres very firmly to the surfaces upon which it forms, and is very difficult toremove. Glaze usually forms on the leading edges of wings, antennas, etc., moreor less in the shape of a blunt nose, and spreads back tapering along the wings.When deposited as a result of freezing of super-cooled raindrops or large clouddroplets unmixed with solid precipitation, it can be quite smooth and approximatea streamline form. When mixed with solid precipitation the deposit can becomeespecially blunt-nosed and rough, with heavy protuberances that build out acrossthe normal streamlines of airflow.Rime ice is a white or milky, opaque, granular deposit of ice whichaccumulates on the leading edges of wings, antennas, etc., of an aircraft. Itssurface is ordinarily rough. It has a granulated, crystalline or splintery structure.47