What Makes Airplane Visual Trails
I like to watch clouds change into shapes of animals and other creations of our Lord. Contrails are equally fascinating aviation science. Some misinformed people want to call them “chemtrails” to encourage their ideological concepts. These trails are made of nothing devious, just engine exhaust materials, ice crystals from the air vapors, and the trailing vortices that begin at the wing tips of the airplane. The airplane will not fly if vortices are not created. That brings up some questions.
Why do you only see these trails at high altitudes of 25000 to 50000 feet? Some days you don’t see the trails at any altitude even on clear days. Why is that? The airplanes are still flying! The scientific question is, what makes the trails visible only at high altitudes? Even more amazing, on some days you may see these trails extending behind the airplane for many miles. How can that happen? Unfortunately, some miss-informed people like the climate-change crowd see these trails polluting the air with carbon emissions. They are making one of God’s magnificent creations an enemy. We’ll show you there is no more carbon created by these vortices than what was already there to start with. The effect of the engine exhaust is another story.
Some facts about the vortices and some about the atmosphere must be understood to explain the formation of the visual vortices at high altitudes. Let’s start with the atmosphere. Our dry air is made up of nitrogen, oxygen, argon, carbon dioxide, and small amounts of other gases. Air also has variable amounts of water vapor. Air composition, temperature, and atmospheric pressure vary with altitude. Vapor pressure is more complicated. Vapor pressure is the pressure that air and other substances must reach before creating vapors (like boiling water). How does that happen?
When we examine the effect of increasing altitude on these two terms, we find air pressure goes down rapidly, but so does the vapor pressure, even more than the air itself because it is highly a function of temperature. Not until the altitude gets into the 25000-to-50000-foot level do these two pressures begin to approach each other. Then the airplane’s jet exhaust reduces the air pressure to its vapor pressure. If the humidity is high enough, we get ice crystals. These ice crystals get entrained into both the jet exhaust and the wing tip vortices. Note, we said “humidity” is already in the air to be turned into ice crystals. The air pressure must reach its vapor pressure to release the water vapor, which at once turns to ice crystals due to very low temperature. Some scientists say there must be particles of carbon dioxide in the water vapors. If so, the air already has carbon dioxide. We don’t need carbon dioxide from the engine exhaust to get visual vortices. Vortices can create their own ice crystals.
We have answers to two of the questions: (1) The altitude for visual vortices, and (2) Visual vortices occur when the humidity is high enough. The other question is: How can the visual vortices extend so far downstream. This is one of the amazing effects of the wing tip vortices. Another amazing effect is creating their own Ice crystals.
Wing tip vortices can become very powerful whirlwinds. The larger the airplane, the more powerful they get. I have experienced that personally. This is discussed in the beginning of my book “Chasing A Whirlwind”. I nearly lost my life in a small airplane caught in the wing tip vortex of a large cargo airplane. This vortex was hovering in a very dangerous position just above the runway. That is why I have learned a lot about vortices. Most of the airplane trails you see in the high altitudes are from very large airplanes.
As the vortex leaves the wing tip it only has a small part of the vortex. More vorticity leaves the training edge of all lifting parts of the airplane, and it is entrained into the wing tip vortex downstream to create the ultimate vortex strength. You can’t see this vorticity, but it is there. That is a very important effect of a vortex. This entertainment is lowering the atmospheric pressure in the core of the vortex, and this is exactly what is needed for the air pressure to reach the vapor pressure. This sets the conditions for ice crystals at these high altitudes. Now you can see the vortex. See the attached photograph (Figure 1). While climbing to the visual height, we saw several Vortex trails (High Humidity). Air Traffic Control” (ATC) makes sure the airplanes are at different heights.
I like to see a single vortex trail that is extremely long. Sometimes you can see details of the dynamic vortex. See Figure 2. Look carefully and you can see both trailing vortices from the airplane. These trails are approximately 100 miles long. How can a dynamic vortex trail extend so far without breaking up? First, it is the power or linear momentum of these vortices, which was discussed previously. This keeps it moving downstream. Second, it is the angular momentum which comes from the rotation. Eventually these forces and moments are overcome, and the vortex will begin to break up. Occasionally you can see this happening. I have zoomed into figure 2 and seen some of this action. One of the two vortices has begun to breakdown. The whole vortex core is swirling, but still very strong and you can see the periodic effect.
This concludes the discussion of the visual vortices. Frieda and I plan to continue the blog, “Faith, Aviation and Science,” periodically with articles related to our books. If you have not read our books, they are thoroughly described in our website Chasingawhirlwind.com
You can also buy the author-signed books at https://whirlwinds-together.square.site . Future blogs will include flight tests of methods of using vortices to reduce drag and improving flight control to save lives. These methods are discussed in the book, “Chasing a Whirlwind”.
Figure 1 Multiple Vortices
Figure 2 Very Long Vortex Trail
