skywriting

skywriting, advertising medium in which aircraft spell out trade names and sales slogans in the sky by means of the controlled emission of thick smoke. The technique was first developed (1922) by J. C. Savage, a pioneer English aviator. Letters a mile high and a mile wide can be formed by the movements of specially built planes equipped with the smoke-emitting apparatus. Engine heat is used to turn specially treated paraffin oil into white smoke, which is discharged under pressure. The "writing" is done at heights of 10,000 to 17,000 ft (3,048–5,182 m) and is feasible only in cloudless skies in which there is no more than a moderate wind. Contracts are commonly made for skywriting over a designated place, e.g., a racetrack, fair, bathing beach, or carnival, and for a specified day and time. Skytyping, the name given to a more modern form of skywriting, involves the use of five to seven planes. They fly rigidly parallel and equidistant courses as nearly in perfect unison as possible. The message to be written is arranged on a master control panel, and as the planes fly abreast electronic signals cause the smoke-emission mechanism in each plane to release puffs of smoke accordingly.