Why Do Airplanes Leave Trails in the Sky? By Kristen Dold. March 08,   Contrails are made up mostly of crystalized H2O (water vapor is a byproduct of combustion in jet engines) so you can rest a little easier if you had envisioned plumes of smoke and smog lingering up there at cruising altitude. Whether or not the white lines are visible from the ground depends on the temperature of the atmosphere, as well as something called "vapor pressure" says pilot Patrick Smith, author of Cockpit Confidential. When the air is dry, contrails may evaporate within seconds or minutes, while more humid conditions can leave a contrail cloud lingering in the sky for hour. But why do some planes leave white trails and others do not? White trails from airplanes are often called condensation trails or contrails, but they could also be called clouds. The main reason behind their appearance is the temperature difference between hot humid air around a plane’s engine and low temperatures outside the aircraft. Whether or not condensation trails will form mainly depends on height and composition of the surrounding atmosphere. The atmosphere at high altitude is of much lower vapor pressure and temperature than the exhaust gas from a plane’s working engine. Besides water. Jets leave white trails, or contrails, in their wakes for the same reason you can sometimes see your breath. The hot, humid exhaust from jet engines mixes with the atmosphere, which at high altitude is of much lower vapor pressure and temperature than the exhaust gas. The water vapor contained in the jet exhaust condenses and may freeze, and this mixing process forms a cloud very similar to the one your hot breath makes on a cold day.  Any particles present in the air provide additional sites. Depending on a plane's altitude, and the temperature and humidity of the atmosphere, contrails may vary in their thickness, extent and duration. The nature and persistence of jet contrails can be used to predict the weather.

Some planes in the sky leave trails that persist and spread, het other planes, in the same skyleave short-lived trails, or no trails at all.

Contrails are actually a type of cirrus cloud. When the air is wet and cold enough the trails can stay around for a long time, and sometimes spread out. So you see helpful images like this. But this is wrong. Contrails can fade away, and contrails can persist and spread. It depends on the air they are formed in. Now there jet planes leave trail yours two main reasons why some planes leave trails and some nearby planes do not. The less common reason is that different planes have Jet Planes Leave A White Trail Behind Them Because Word different engines.

Leace engines will jet planes leave trail yours a contrail in the air where another engine will not. Here, for example, are an Airbus A maiden flight: on the left, leaving contrails, and a Boeing maiden flight: not leaving contrails.

You can also get a jet planes leave trail yours effect with engines at different power settings, especially if it affects the exhaust temperature. This can occasionally be seen with high altitude refueling, when the plane being refueled cuts the throttle to near idle in order to separate from the tanker.

The reason that one plane makes contrails or makes contrails that persist, and the other plane does not, is that they are in different regions of the air. Plabes the plane is in wet Jet Planes Leave A White Trail Behind Them Because So air, it makes a contrail. In dry air, it does not. Surely, you might object, they would have to be miles apart? Well, no, and that brings me to another point I fear I must emphasize:.

Look at the bottom of those clouds, see them extend off into the distance. They form a layer at a specific altitude. Above that altitude there are clouds. Below it there are no clouds. The difference between clouds and no clouds is just a few feet. Again they are in a flat layer.

The difference between being in the layer and not in the layer is just a few feet. This layering of the air into wet and dry layers is not limited to clouds. Seemingly clear air also contains exactly the same kind of variation in layers.

This was very neatly illustrated by the recent launch of the Solar Dynamics Observatory. As it ascended it did not leave plannes contrail, until it hit a layer of wet air, when it left a contrail that lasted quite a while, and then it went into dry air again, and planea more contrail. So, if a plane were flying in that middle region then it would probably leave a persisting contrail. If jet planes leave trail yours were above or below oyurs then it would not.

But, you may cry, the planes are at the same altitude. These planes fly at 30, to 40, feet. I took one image of a jet planes leave trail yours nominally at 35, feet.

Then scaled it for 34, If the top plane was flying at 20, feet, then the bottom would be at 18, feet, still nearly 2, feet apart, and looking pretty much the same to the naked eye. And that is with the same model of plane, directly overhead, and right next to each other. A situation that almost never occurs. Just look at this:. They look about the same height, right?

And look at some planes on the ground, where we know they are all peave same distance from the camera. The differences in size are very significant:. The planes leave different trails because the planes are at different altitudes.

Debunked: High Bypass Turbofans do not make Contrails [actually they make more] — A more detailed look at why modern engines make contrails in a wider range of conditions. The key difference is jet planes leave trail yours exhaust gas temperature, as explained in the more recent Metabunk article. This is an excellent addition! Same aircraft, same altitude- different engines, different contrails. I have a little addition to your information.

Sometimes an extra trail is caused by pplanes dumping of wastewater via vents on jet planes leave trail yours underside of the fuselage.

When looking at the Tu we llanes that the water dump point is at the same location as the origin trail in the video. Here is a picture shot of 2 airliners including the corresponding radar image. I mostly say: Different engines of different age with different powersettings on different locations create different contrails. Though jet planes leave trail yours will vary with plane. Some APUs auto shut-off at altitude. I think APU trails are pretty rare. Some of the supposed photos might be mast drains, or even a third tail mounted engine not visible from the ground.

We rarely use the APU in flight, the most common reason to keep the APU running during takeoff is to have more power on the engines, although this is different for each traik of aircraft.

On takeoff the APU provides bleed air, preventing a power reduction on the engines. In flight it backs up both electrical and bleed air system.

We can use the APU bleed for 2 packs up to We can use the APU for power up to I am not a rocket scientist, I am only a layman, but would like to point out that rocket exhaust from an Atlas V rocket or whatever types this may be is not the same as engine exhaust from a commercial airliner engine.

They are made up of different types of gasses and therefore cannot be used to jet planes leave trail yours anything in this argument. What if rocket exhaust due to its composition exhibits different effects as it jet planes leave trail yours throught different layers of humidity.

Do you have observations of other rocket launches? Is rocketry another of your hobbies? Rocket fuel has additives like oxydisers. Maybe that explains this white looking trail that we see. Rocket launching can be very technical.

Sometimes different types of fuels and mixtures are used at different times during a lauch to achieve higher buring rates to gain velocity. Maybe that is what we are seeing there.

Sometimes they vent of stuff during the course of a rocket launch. Do rockets go straight up jst your arrow indicates. Did this rocket go straight up? Where is your proof that this rocket went straingt up? What is the frail temperature of rocket exhaust during the various stages of assent? What are the differences in temperature and humidy that enable you yougs lable the photo as a wet or dry zone.

Do you have the met data from this location for the different layers of atmoshpere? You have left me with way more question than you have answered. Can you please help me understand? Your photo of the fifth contrail above could actually also be from another jet that is flying at a higher altitude than the jet we see. We cannot see this second jet because it is higher and smaller than this big jet and is being obscured by the big jet.

Is this not possible? This is a bad photo. Without a good photo this is a bad argument. Which is what this post is about — that there are some regions of air that are different from other regions of air. Contrails form in those regions. Both produce lots of water. I label the regions as wet and dry based on where the contrail shows up, the description from the rocket scientist.

Since the rocket was jet planes leave trail yours into orbit it would not be going exactly straight up all the way, but not too far off.

It certainly started straight up. It does not change the argument that some planes operate the APU in flight, and this creates an additional contrail. Using this argument, and looking at the second photo from the top, are those two planes at exactly the same altitude?

Perhaps the plane on the right is flying in a different layer an that is why we planess re not seeing the formation of a contrail. Do you have the actual measured flight altitudes of these jet planes leave trail yours aircraft?

Is one aircraft ahead of jet planes leave trail yours other? Without a line of reference or actual flight altitude data, this is a bad photo should jet planes leave trail yours be used in this aurgument. The photo shows two planes that were part of a study into the formation of contrails.

They were deliberately flown together at the same altitude.

Mar 21,  · The trails in the wake of jets are mostly condensation, caused by the engine emitting hot, humid air into a cold atmosphere. That’s why they are called “contrails,” short for “condensation. If you look at the sky on a clear day, you can see one or more of the planes moving, leaving white lines (Contrails) behind. Sometimes you can’t see the plane, but you guess that a plane passed a short time before the tracks in the sky. These white lines can be intriguing to those who . Aug 30,  · Much like a car might make a little white cloud near its exhaust on a cold morning, a plane will often leave a trail if the conditions are right. Exhaust from jet engines is pretty much all water vapor, although there can be trace content of sulfur oxides, carbon dioxide, nitrogen, unburnt fuel, soot and small particles of metal.

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