# skywriting **URL:** \ **Category:** Factual Questions\ **Created:** [March 13, 2000, 7:43pm UTC](https://boards.straightdope.com/t/skywriting/8495 "2000-03-13T19:43:00Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![Red\_2](https://avatars.discourse-cdn.com/v4/letter/r/a5b964/32.png) [@Red\_2](https://boards.straightdope.com/u/Red_2)\ **Post date:** [March 14, 2000, 6:08am UTC](https://boards.straightdope.com/t/skywriting/8495/1 "2000-03-14T06:08:00Z")
What is that stuff that planes spit out when skywriting AND why do (what I assume are) passenger jets leave those long white trails up at cruising level? Is this the same stuff? ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [March 14, 2000, 6:44am UTC](https://boards.straightdope.com/t/skywriting/8495/2 "2000-03-14T06:44:00Z")
yes it is the same stuff and it is water vapor, the product of the combustion of hydrocarbon compounds. Jets produce masive amounts which condenses immediately as they fly so high where the temperature is so low. smaller planes at lower altitudes would produce some on frigid days but they can add water (and coloring) to produce more than would naturally be produced. That way they can turn it on and off at will. If you look at the exhaust of your car on a freezing day you will observe the same thing ---
**Author:** ![Fear\_Itself](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/fear_itself/32/19637_2.png) [@Fear\_Itself](https://boards.straightdope.com/u/Fear_Itself)\ **Post date:** [March 13, 2000, 7:43pm UTC](https://boards.straightdope.com/t/skywriting/8495/3 "2000-03-13T19:43:00Z")
You know, **sailor** , it really makes you look foolish when you post your WAG’s as though they are facts; next time do a little research before you do your Cecil impersonation. From the site of [The Pepsi Cola Aerial Entertainers](http://www.wanews.com/airpro/acts/Pepsi.html): > [@](#): > > Amount and Type of Smoke Oil Used Per Performance: > > Skydancer - 15 gallons - Texaco Canapus #13. > Skywriter - 25 gallons - Texaco Canapus #13. > Sky Magic - 25 gallons - Texaco Canapus #13. For more information on skywriting, try [SkyTypers](http://www.skytypers.com/) (SkyWriting/What is SkyWriting?), which identifies the smoke as a “bio-degradable trail of vapor”, which if I were to **guess** is also Texaco Canapus #13. It certainly isn’t water vapor. * * * TT “It is better to know some of the questions than all of the answers.” –James Thurber ---
**Author:** ![Red\_2](https://avatars.discourse-cdn.com/v4/letter/r/a5b964/32.png) [@Red\_2](https://boards.straightdope.com/u/Red_2)\ **Post date:** [March 13, 2000, 8:01pm UTC](https://boards.straightdope.com/t/skywriting/8495/4 "2000-03-13T20:01:00Z")
Well…I had already accepted sailor’s answer but you, Thuccotash, through a wrench into the whole works! If skywriters use special oils to make skywriting, then what, in the name of (insert diety here), is the stuff that jets spew out in those long, straight trails? Is sailor still correct about the water vapor? ---
**Author:** ![labradorian](https://avatars.discourse-cdn.com/v4/letter/l/3ec8ea/32.png) [@labradorian](https://boards.straightdope.com/u/labradorian)\ **Post date:** [March 13, 2000, 8:08pm UTC](https://boards.straightdope.com/t/skywriting/8495/5 "2000-03-13T20:08:00Z")
The stuff the jets (and other types of aircraft) spew out at high altitudes is exhaust. What you _SEE_ is the water vapour condensation trails when little bits of exhaust “seed” the vapour in the air. * * * **Dee da dee da dee dee do do / Dee ba ditty doh / Deedle dooby doo ba dee um bee ooby / Be doodle oodle doodle dee doh** [http://members.xoom.com/labradorian/](http://members.xoom.com/labradorian/) ---
**Author:** ![tanstaafl](https://avatars.discourse-cdn.com/v4/letter/t/ba8739/32.png) [@tanstaafl](https://boards.straightdope.com/u/tanstaafl)\ **Post date:** [March 13, 2000, 8:20pm UTC](https://boards.straightdope.com/t/skywriting/8495/6 "2000-03-13T20:20:00Z")
Actually a large portion of the exhaust _is_ water vapor. The primary results of burning a hydrocarbon fuel in air are carbon dioxide and water (and small amounts of a host of other things). The same can be said of the exhaust coming out the back of your car. The water vapor in the exhaust condenses almost immediately, most of it on small particles which are also part of the exhaust as labradorian said. Contrails can also be formed because of low-pressure vortices which are produced behind the wingtips of an aircraft. If conditions are right the pressure drop is enough to cause some moisture to condense out of the air. * * * “It turns out it isn’t so much a law of physics as it is a local ordinance.” ---
**Author:** ![tanstaafl](https://avatars.discourse-cdn.com/v4/letter/t/ba8739/32.png) [@tanstaafl](https://boards.straightdope.com/u/tanstaafl)\ **Post date:** [March 13, 2000, 8:23pm UTC](https://boards.straightdope.com/t/skywriting/8495/7 "2000-03-13T20:23:00Z")
Actually a large portion of the exhaust _is_ water vapor. The primary results of burning a hydrocarbon fuel in air are carbon dioxide and water (and small amounts of a host of other things). The same can be said of the exhaust coming out the back of your car. The water vapor in the exhaust condenses almost immediately, most of it on small particles which are also part of the exhaust as labradorian said. Contrails can also be formed because of low-pressure vortices which are produced behind the wingtips of an aircraft. If conditions are right the pressure drop is enough to cause some moisture to condense out of the air. * * * “It turns out it isn’t so much a law of physics as it is a local ordinance.” ---
**Author:** ![Fear\_Itself](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/fear_itself/32/19637_2.png) [@Fear\_Itself](https://boards.straightdope.com/u/Fear_Itself)\ **Post date:** [March 13, 2000, 8:39pm UTC](https://boards.straightdope.com/t/skywriting/8495/8 "2000-03-13T20:39:00Z")
From [: > [@](#): > > **vapour trail** > > also called CONDENSATION TRAIL, OR CONTRAIL, streamer of cloud sometimes observed behind an airplane flying in clear, cold, humid air. It forms upon condensation of the water vapour produced by the combustion of fuel in the airplane engines. When the ambient relative humidity is high, the resulting ice-crystal plume may last for several hours. The trail may be distorted by the winds, and sometimes it spreads outwards to form a layer of cirrus cloud. On rare occasions, when the air is nearly saturated with water vapour, air circulation at the wing tips of an airplane may cause sufficient pressure and temperature reductions to cause cloud streamers to form. BTW, here’s [url=“[http://orbital.nethelpnow.com/unlimited/roadtripamerica/people/skytype.htm](http://orbital.nethelpnow.com/unlimited/roadtripamerica/people/skytype.htm)”]another site](][Brittannica.com](http://Brittannica.com)[/url) about skywriting that identifies the smoke oil used by SkyTypers as “paraffin based”. * * * TT “It is better to know some of the questions than all of the answers.” –James Thurber ---
**Author:** ![Fear\_Itself](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/fear_itself/32/19637_2.png) [@Fear\_Itself](https://boards.straightdope.com/u/Fear_Itself)\ **Post date:** [March 13, 2000, 8:41pm UTC](https://boards.straightdope.com/t/skywriting/8495/9 "2000-03-13T20:41:00Z")
Oops. Try [Brittannica.com](http://www.britannica.com/bcom/eb/article/0/0,5716,76790+1,00.html) * * * TT “It is better to know some of the questions than all of the answers.” –James Thurber ---
**Author:** ![Red\_2](https://avatars.discourse-cdn.com/v4/letter/r/a5b964/32.png) [@Red\_2](https://boards.straightdope.com/u/Red_2)\ **Post date:** [March 13, 2000, 8:44pm UTC](https://boards.straightdope.com/t/skywriting/8495/10 "2000-03-13T20:44:00Z")
OK. Got it. Nuff said