White, Grey, and Rainbow Colored CRJ-700 Contrail [Likely Intermixed Engine Configuration]

pseacraft

Active Member
I think if there were any operation or performance differences then the plant manufacturer would not allow them to be mixed, as that would be inviting problems if not worse into an already busy enough situational awareness scenario. Pretty sure the FAA would object too. Maybe a aircraft with a flight engineer but even then I would think not. I also doubt the pilots would know that they had two different model engines unless it was documented in the aircraft gripes/forms (not sure what they would be called in the civilian world).
 

justanairlinepilot

Senior Member.
I think if there were any operation or performance differences then the plant manufacturer would not allow them to be mixed, as that would be inviting problems if not worse into an already busy enough situational awareness scenario. Pretty sure the FAA would object too. Maybe a aircraft with a flight engineer but even then I would think not. I also doubt the pilots would know that they had two different model engines unless it was documented in the aircraft gripes/forms (not sure what they would be called in the civilian world).


I agree.
 

Mick West

Administrator
Staff member
I've been corresponding with someone about the colors in the contrail, and wrote this for them, which I've added to the OP:

.......................................................................................................................................

On that day, March 9th 2014, I took many photos as conditions were great for contrail formation. I did not notice the two-tone colors until later, when I was able to view them on the computer.

There were many clouds, both high cirrus, and some fractus cumulus.

I have uploaded all the photos I took to Flickr in two sets:

http://www.flickr.com/photos/metabunk/sets/72157642297148355/
http://www.flickr.com/photos/metabunk/sets/72157642135454733/

The second set just shows this CRJ700 jet with intermixed engines. The first set is all the other photos, before and after, from that day.

Of note from the CRJ set:
  • A variety of clouds are shown
  • The left trail gets progressively more faint as the plane descends (it's descending towards San Diego Airport, started the descent at the time of the first photo)
  • In 0703 it is descending through the cloud layer. This is the last photo I took that shows the plane.
  • in 0706 the trail shows a transition from distrail to contrail, indicating where it went below the clouds, but still kept on conning.
In the Venice Set:
  • A nice sundog and cirrus fallstreaks in the first few photos
  • The first plane (0662 to 0687) exhibits no coloration, just normal white exhaust contrails
  • In 0673/4 you see distinctive "hybrid" contrails cause by the wake vortices, indicating marginal conditions (i.e. not ice supersaturated)
  • 0709 to 0715 are just low altitude planes on approach to LAX.
  • 0716 to 0734 all show (I think) the same plane
  • 0730 to 0734 show the colors in both sides of a trail
  • 0735 is a wide angle shot I took to gauge the position of the sun
  • 0744 is a calibration shot, showing the camera time 2m20s fast.
Here's 0730:
[Broken External Image]:https://mail.google.com/mail/u/0/?u...p=emb&realattid=ii_144bc32f275b1f73&zw&atsh=1

The distinctive color spectrum is quite noticeable. This would also be a plane flying south to San Diego, and likely descending. Notice the two trails are identical (the small third trail is probably a galley dump - water or beverages from the kitchen)

My theory is:
  1. The air is marginal for contrail growth, around 100% ice supersaturated, so around 60-70% relative humidity with respect to water.
  2. The colored trails indicate a very short period of water condensation, followed by much slower ice crystal size increase by deposition, this progresses though the color spectrum as it increase in size..
  3. The white trails have a longer (but still very short) period in the the liquid phase, and so when it freezes, the ice crystal is already larger than size that creates colors
This implies a difference in the mixing curve as the exhaust goes from its initial temperature and humidity to the ambient. The difference might be from either the start or the end conditions of the mixing, as seen by a white and colored trail visible on A) different planes in different conditions, and B) the same plane with two different engines.

With the CRJ two-tone contrail, the newer engine has cooler exhaust, and so enters the rapid "condensing" portion of the mixing curve earlier than the older hotter engine, and so condenses larger droplet before transitioning through "freezing" to "deposition" and the slow ice crystal growth.
 

Denis DuBay

New Member
Yesterday I was on a Southwest 737 flying from Denver to RDU, just before sunset, heading east, looking out a window on the right side of the plane just behind the wing. Sunlight was hitting the rear of the wing. I noticed odd flickering shadows moving from the fuselage out to the wingtip for maybe five minutes, then stopping as the sun set. I guessed it was shadows from a contrail spooling out from the engines (not visible of course to me in the plane). I asked the pilot upon our arrival at RDU and he confirmed that other aircraft near our altitude headed in the opposite direction were leaving contrails, so he thought I was probably correct.
 
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