I've always wondered how skywriting is done. And yes, even though I think google is over-rated, I've even checked there and cannot find my answer.

I've asked people and read books, but never got a satisfactory answer.

So, how is it done? I've heard "they use some kind of oil" and "it's just smoke" but how exactly does the pilot or his offsider create the writing?

Looking foward to finally finding the answer... :)

Its just avtur (as used in jet engines, which is a pure parafin) which is squirted into the hot exhaust manifold of the engine. The smoke comes out the engine exhaust pipe.

Edited to change avgas to avtur (Avgas is leaded 100octane fuel, like the old 5 star fuel, used in piston powered aircraft avtur is a pure parafin used in jet engines

Antifreeze, ethylene-glycol, would give the same effect, mixed with water would make larger clouds.

"but how exactly does the pilot or his offsider create the writing?"

good flying skills and push the button at the right time.

Thanks, Geoff and phfitz, for the info. Any further details on exactly how this is done would be appreciated. Do they have a tank with the avtur ready all the time, or is it set up specially for skywriting planes? Etc???? Thanks. :)

I see these guys around New York fairly often--

http://www.echonyc.com/~goldfarb/photo/david.jpg

They seem to have five planes in formation printing dot matrix text in the sky. I'm guessing it must be computer controlled.

I know, I know, "take it to hybrid"...

That is quite cool, David. Nice that they spelled your name. :) It certainly does look computer controlled.

I think the whole thing was an ad for something like the "David F. Scheinbaum Insurance Agency." I don't recall the exact name, but I took the liberty of cropping out the rest of it in camera.

One of the best ones I've seen was about five years ago, I think during the Australian Formula One Grand Prix. It just said "AGFA FILM". :)

They definately use Avtur. Its cheap, and very easily available at airfields.

The aircraft must be fitted with an extra tank, and must be clearly marked as avtur only, and is pumped inside the aircrafts hot exhaust.

It is similar for jet aircraft, the avtur is pumped into the hot jet eflux, but obviously doesnt need a different tank, and just comes from the main fuel tank.

The UK hawk T1 has clearly visible pipes for smoke, in the smoke equiped models, such as those in use by the red arrows.

Thanks, Geoff. That's the best explanation I've ever been given. :)