What causes the "smoke trail" at the wing tips of fast flying aircraft?

Question

Is it actually smoke or condensation? What physically causes that?

Answer 1

Condensation. As the air moves over the wings of the plane, the moisture in the air collects on the wing. It is pulled to the wingtips where it then is blown off, and condenses into small lines of "cloud"

Answer 2

Boy, a bit of confusion here. I don't think you are talking about contrails, right? What you mean is the swirling mist seen on the tips of the wings, right? What happens in air, when you change certain physical properties, is that its ability to 'hold' water vapor as a gas increases/decreases. For the wing tips in question, the pressure at certain points in the stream drops below that threshold, and some of the water must become liquid again. This depends on the local humidity and temperature of the air, so it doesn't always happen.

There is a great video of a F14 doing a supersonic flyby of a aircraft carrier. The humidity around the carrier is higher than the surrounding, so when the jet get right next to the ship, a huge halo forms in the otherwise invisible acoustic shock cone around the plane. Same process.

Added:
Sorry, didn't see the contrail misinformation, so I will clear that up too. Contrails are cause by hot humid exhaust gasses from engine combustion, not from aerodynamics. If they were from aerodynamics, they would disappear in a few meters, after the air returned to its original state. The engine exhaust contributes heat and moisture, changing the actual properties of the air for a while.

Answer 3

A lot of people came really close.

The con-trails (condensation trails) you see on planes is caused by the pressure differential of the air over the wing. You have high pressure under the wing, and low pressure over it. As these two pressures meet they create at "High" and a "low" pressure system, like the weather man talks about.

In the Earth's water rich atmosphere this causes the water vapor in the air to condense around “nucleation particles” or specks of dust, to create micro-clouds miles of miles long.

As a matter of fact, the number of con-trail clouds in the atmosphere has caused a phenomenon called “Global Dimming”, in essences because of Contrails and Pollution we have more clouds blocking more of the suns energy. This loss of solar energy has actually cooled the planet by 3 degrees in the past 25 years, even though the effects of “Global Warming” are truly in effect and destroying our environment as we speak.

Answer 4

(for one of the people who answered altready the mach number does not change with air density, but with temperature.) As you climb, the air gets cooler (more dense), but as there is less overall air, the net is the air is less dense. While the less dense air decreases the avaiable power to the engines, the side effect is also that (1) there is less drag and (2) the fuel/ air ratio for combustion is less. So, while there is less power available at high altitudes, less power is required to fly a speed and less drag is there so the fuel burn is significantly less. In terms of speed, the aircraft can fly a "faster speed" the higher it goes as the power it looses it less than the drag it looses with less dense air, but it is so small it most cases that it is not the reason we fly higher. I just ran some numbers for you and between the surface and 18,000ft the speed capabilities are different but above thay the difference in speed is pretty small. For reasons that don't need great explanation for this quesiton, the "indicated airspeed" will have a larger difference to the "ground speed" due to air density, but the ground speed at 35,000ft will closely match the ground speed at 20,000ft. Secondary reasons, as someone else stated is that most weather is located 35,000ft and below so the higher you fly the better chance you can get above a thunderstorm and not have to go around it enroute. In addition, the higher your aircraft can go the less traffic you will encounter so the less potential enroute delays. So... in an way too long answer to your excellent question, aircraft fly higher for better fuel burn and secondarily weather and ATC delays.

Answer 5

It's condensation. The tips are a place of very low air pressure. The boiling temperature for water decreases as the pressure decreases.

Answer 6

Condensation/water vapor.
Indy cars do the same thing. You could see the contrails coming of the rear spoilers (wings) while they were racing at Watkins Glen.

Answer 7

They are called 'contrails' (condensation trails) They form when hot air comes into contact with moist cool air

Answer 8

It's condensation... it can happen with old WWII airplanes as well... the humidity in the air has a lot to do with it... you can research it online.. try going to google.com and type in 'wingtip vorticies' and you will probably find more info there

Answer 9

Vapor as a result of cooling. Cool air can't hold the moisture that warm air can.

Answer 10

Heat baby! Carbon. pure burnt fuel going through the engine. Engine breath, nothing more fierce. mmmmmmmm