then either the message is never seen together in its entirely

The movie The Wizard of Oz, a smash hit when it came out in 1939, had a scene where the wicked witch wrote SURRENDER DOROTHY OR DIE in the sky with her broom. Ever since sky writing has fascinated people. (The witch's message was actually just special effects, produced in a 6 foot by 6 foot glass tank.) But sky writing goes back further than that. It was first tried in1922 in England. Advertisers began using skywriting at the same time but Pepsi-Cola made it famous, using skywriting from 1931 to 1953.

How is the smoke made? Skywriting smoke is produced by injecting paraffin oil into the exhaust of the plane. As it heats in the exhaust, the oil produces an environmentally friendly white smoke that forms the letters as it lingers in the air. Of course, the pilot must select when to inject the oil so that part of a letter is formed.

The letters are about a mile tall and the message may be as long as fifteen miles. The drifting smoke only retains a letter for at most 20 minutes so the message must be written quickly and without mistakes. There is no such thing as a smoke eater to erase mistakes! The success of the mission is determined by several factors. First the skill of the pilot. He must be both skilled and artistic. Second, the plane must have sufficient maneuverability and power. The power is partly needed to produce sufficient heat (1500 degrees) to vaporize the paraffin oil. Some recommend planes with at least 450 horsepower engines because they are six times hotter than small plane engines.

Besides these factors, there is the weather. The wind cannot exceed three to five miles per hour. The sky must be nearly clear for the white letters to be visible against the blue sky. Since wind speed may vary at different heights, the planes will fly anywhere from 7000 and 17000 feet. At these heights, the message is visible for thirty miles on either side. Cooler air temperature makes more smoke, but the air temperature cannot exceed 95 degrees. The best months for these conditions are September and October.

The message usually contains four to six letters and it takes one to two minutes to form each letter. A shorter message is more likely to be visible at once. When a message is longer than this, then either the message is never seen together in its entirely, or multiple planes get involved. The two or three pilots coordinate their maneuvers so that their work together will produce the message visible in its entirety for a few minutes before it drifts away.

How large is the message? It is usually four to six letters and it takes one to two minutes to form each letter. A shorter message is more likely to be visible at once. Why not make it longer? When a message is longer than this, it will take too long to form so that it is seen all at once. One remedy is to hire multiple pilots. The two or three pilots coordinate their maneuvers so that, as they work together, they will produce the message visible for the minutes before it drifts away.

This method of advertising is so novel that it almost demands to be read all the time the letters are forming. So what kind of people would benefit from hiring skywriting to get their message across? Skywriting has been used to advertise soft drinks, motion pictures, websites, political candidates, products, and so forth. One company says they skywrite fifty marriage proposals each year.

What is the cost for skywriting? This depends on the company, and availability. If you must fly a skilled pilot from some distance, the cost of transportation could be greater than the message writing itself. Generally for local skywriting, prices start around $1000 and multiple messages are discounted.