61
votes
Accepted
Is this contrail from an airplane or a rocket?
I am pretty sure it is an aircraft.
When aircraft fly straight towards you they can appear like rockets. The contrail is distorted by winds in the upper airspace. Yesterday there were a lot of ...
- 83.8k
57
votes
Accepted
Can helicopters create contrails?
If the temperature and conditions are right, yes.
Any aircraft which has a heat engine that burns hydrocarbon fuel, which is pretty much any reciprocating or gas turbine engine used in aviation, will ...
- 74.5k
38
votes
Do commercial flights continue with an engine out?
The image looks like four engines running at the same cruise thrust. The wake vortex is blowing the exhaust of the inboard engines down and the exhaust of the outboard engines out and in the ...
- 56.4k
31
votes
Why are only some aircraft in this formation creating contrails?
From: Forum post - "Trails from the back of Fighter Jets", Metabunk.org
Jets practicing for air-shows (or actually in air-shows) sometimes use smoke to create trails. This is made by injecting ...
- 35.1k
31
votes
Accepted
Were contrails different in the 80s?
There could be a few things:
They are not remembering contrails, they are remembering exhaust. Old jet engines, particularly the early turbo fans and low-bypass turbo jets, as well as early water ...
- 102k
22
votes
Can we see evidence of "crabbing" when viewing contrails?
Yes, you can see evidence, but it isn't the angular misalignment you are picturing...
The aircraft does not crab relative to the airmass, it crabs relative to the earth. So, you will never see the ...
21
votes
How can a two-engine B787 create three contrails?
Contrails are created due to variances in the pressure of the air, coupled with the amount of moisture in that air. When the 2 engines of the B787 blast their exhaust out, the high pressure of the ...
- 227
20
votes
How can a two-engine B787 create three contrails?
Fascinating question. Not being an expert in contrail aerodynamics I'm forced to speculate, but I'm guessing the apparent three trails is caused by the spreading of the trails by wingtip vortexes.
I ...
- 1,063
18
votes
Can we see evidence of "crabbing" when viewing contrails?
Crabbing is the misalignment of the aircraft's longitudinal axis with the direction of travel over ground, caused by crosswind.
The crabbing cannot be seen by looking at the angle at which the ...
- 83.8k
16
votes
Is this contrail from an airplane or a rocket?
That is a contrail from an airplane, not a rocket.
The wideness of the trail at the bottom part of the photo makes it clear that it has been lingering for some amount of time. The distortion is ...
- 23k
15
votes
Accepted
How does contrail formation differ from turbofan to turbojet?
It appears that the higher bypass engines available today increase the contrail occurrence. From Influence of propulsion efficiency on contrail formation by Ulrich Schumann:
The thermodynamic ...
- 100k
12
votes
Can helicopters create contrails?
Contrails off the engine exhausts is unlikely. But in the right conditions, ie damp air, you can get contrails off the "wingtip" vortices, ie off the rotor blade tips.
- 4,624
10
votes
Accepted
Have contrails ever occurred at low altitudes, such as at takeoff?
This is entirely possible if it's cold enough and has also happened. Here's a video of a Tu-204 taking off from Yakutsk at -45°C.
Source
- 9,002
8
votes
Accepted
How do contrails form?
Contrails are formed from the condensation of jet exhaust.
When a hydrocarbon, such as jet fuel, is burned, it produces water vapor and carbon dioxide along with some impurities/unburned fuel. High ...
- 106
7
votes
What causes pulses to appear in some contrails?
This phenomenon--which is not all uncommon-- is 100% meteorological. On a day when conditions favor this, you'll notice this happening in most or all of the contrails visible, or at least in most or ...
- 23k
6
votes
Is this contrail from an airplane or a rocket?
That is just an illusion. The aircraft is flying straight and level and the contrail behind it is being distorted by the winds aloft.
- 37.9k
6
votes
Have contrails ever occurred at low altitudes, such as at takeoff?
Photos of this would be very hard to come by, but yes, in an extremely cold environment, say close to the arctic and antarctic regions of the globe where daylight temperatures can be down around -40°F,...
- 74.5k
5
votes
How do contrails compare between piston-powered aircraft and jet aircraft?
As far as the contrails are considered, there is little difference between the ones formed by different aircraft. Contrails form when the ambient air (which is usually cooler) mixes with the hot, ...
- 100k
5
votes
Accepted
How does engine exhaust temperature affect contrail formation and why?
There are some building-blocks to the answer:
Part 1: Assumption/Simplification
Let's assume for a moment that the only difference between the two planes is the exhaust gas temperature (EGT). A less ...
- 1,547
5
votes
777-300ER venting something from left engine outboard side - what is it?
Well, it's not condensate water from the tail pipe, and it looks to be originating from the main cowl, so it can only be one of the Big Three fluids; fuel, engine oil, or hydraulic oil (for the ...
- 134k
4
votes
How to read the Appleman chart to predict contrail formation?
First of all, the Appleman-chart itself:
Source
Now, let's say we want to know if contrails can form at FL340 at my position, a pretty standard cruise flight level. Because flight levels are ...
- 9,002
4
votes
What causes pulses to appear in some contrails?
In 1992, Aviation Week reported on sightings of unusual contrails which were called "donuts on a rope" because they had evenly spaced puffs along a central line. The article speculated that ...
- 236k
4
votes
What causes pulses to appear in some contrails?
When an object passes through a fluid, it can leave a Kármán vortex street. The vortex street is a common occurrence, but it is only visible when the humidity is just right.
Your picture shows the ...
- 3,461
4
votes
Were contrails different in the 80s?
Years and locations may be relevant here. I have distinct recollections of 1982 where El Nino weather patterns were severe world-wide.
In the eastern U.S., it was the warmest winter in 25 years.
...
- 1,131
3
votes
Why don't the contrails show the curvature of the Earth?
See this link the second answer from the top.
Basically the answer is the curvature of the earth is too small to detect by the naked eye. From a point on the earth, the observed point on the horizon ...
- 5,829
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