Different airplane trails?

Question

What factors contribute to different airplane trails?
Some times the trails criss-cross across the sky and seem to last forever, other times I can watch the trail fade shortly behind the plane as it passes.. and still other times I see planes with no trails at all.
I'm guessing either differences in the atmosphere or differences in engine cycles... can anybody educate me, please?

Answer 1

There are 2 kinds of common contrails, aerodynamic and exhaust. There is only ONE thing necessary for them to form: moisture in the air. They can be formed by moisture that is already there, or moisture that is put there as the result of burning fuel.
When the air becomes saturated, the moisture turns to ice crystals. How long they last is dependant on the amout of moisture and the amount of wind at that altitude.

Answer 2

It has everything to do with the temp and wind at the altitude of the contrails... They cross because airplanes cross over the same navigation points in different directions... As for the length of the contrails, if the wind is pretty calm, contitions are favorable for the contrails, if it is windy, they can be broken up... the biggest variable in the equation is the temp. Because they are made up of such tiny crystals, they must be well below zero to freeze... below 32 degrees farenheit will cause most water to freeze but not when the droplets are that small... the reason that you only see a short contrail is that the air moving over the wing creates an area of such low pressure that the temp. drops well below zero in that area, (as the pressure of any gas drops, so does the temp) and that will crystalize any water vapor in the air, then when the air heats back up, the trails will evaporate... The final and least important variable is the wing area, the bigger the wing the bigger the air disturbance and the larger the contrail but since you didnt ask about size of the trails thats unimportant... hope that helped

Answer 3

There are 3 main factors - atmospheric conditions, wing design, and fuselage/tail shape. Engines have little effect, as contrails are caused by the air being compressed and swirled as it passes over the wing tips.

If the air at that altitude is fairly dry, the moisture in the contrail will be absorbed fairly quickly. Winds at that altitude also influence whether they are dispersed or not.

Wing design is also important - the shape of the vortices determines whether they will blend together, or remain as 2 distinct trails. Separate trails will usually dissipate faster than blended trails, since they have a greater surface area.

Finally, the shape of the aircraft, especially at the rear, will make a difference, as some cause more turbulence behind them, which will help the contrails dissipate (military aircraft are usually more aerodynamic than civilian, which is why they usually leave the longest-lasting trails. They also travel faster, which makes for denser contrails)

Hope this helps.

Answer 4

When you see no plane trails at all, that means that plane is not at the altitude cold enough for the exhaust to be seen. It is opposite when you see the trails.

When you see trails fade shortly away, there may be lots of wind blowing it away. As it blows away, the exhaust dissipates. When you see trails stay in the sky for a long time, there may be very calm winds up there.

Answer 5

Most of it has to do with the winds that are present at the airplane's altitude. The contrails can be blown apart, or will stay a long time with no wind at all.