Skywriting is the process of using a small aircraft, able to expel special smoke during flight, to fly in certain patterns to create writing readable by someone on the ground. The message can be a frivolous or generally meaningless greeting or phrase, an advertisement aimed at everyone in the vicinity, a general public display of celebration or goodwill, or a personal message such as a marriage proposal or birthday wish.
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The typical smoke generator consists of a pressurized container holding a low viscosity oil such as Chevron/Texaco "Canopus 13" (formerly "Corvus Oil"). The oil is injected into the hot exhaust manifold causing it to vaporize into a huge amount of dense white smoke.
Wind and dispersal of the smoke cause the writing to blur, usually within a few minutes. However special "skytyping" techniques have been developed to write in the sky in a dot-matrix fashion, and are legible for longer despite the inevitable blurring effect caused by wind.
In a 1926 letter to The New York Times one Albert T. Reid wrote:
A technique was developed by Jack Savage, former RAF pilot and writer for Flight magazine, after the First World War and he had a successful skywriting fleet.[2]
Satellite navigation is now used in modern skywriting aircraft, so that the message can be programmed beforehand, resulting in greater accuracy.
The first use of skywriting for advertising purposes was in 1922.[3]
The Wicked Witch of the West skywrites "SURRENDER DOROTHY" in the motion picture version of The Wizard of Oz.