Hi Chris,
I think you are correct. Directly behind the aircraft, the contrails
definitely line up with the engine pods. The third line seems to drift
from the left to the right, and I can't offer a reason for that.
My impression is that is was a wide-body twin-jet. At six miles away, I
was just surprised that I got this much detail.
Jim Nichols
Tullahoma, TN USA
On 12/30/2013 3:37 PM, Chris Barker wrote:
> I wouldn't have thought that it would be vortices, Jim, not at cruise
> speeds;I should have said that contrails always came from the engines.
>
> The other sort of "trail" is merely condensation because of the reduced
> pressure in vortices – traditionally from the wingtips at high angles of
> attack, but increasingly from further inboard as wings and fuselages become
> more aerodynamically efficient
>
> Your photo shows 2 contrails, it's just that one is distorted, making it look
> like a total of 3.
>
> Chris
>
> On 30 Dec 13, at 20:41, Jim Nichols <jhnichols@xxxxxxxxxxxxx> wrote:
>
>> Things get complicated, Bill. Yes, contrails can be formed as a result
>> of moisture content in the engine exhaust. But they can also be formed
>> by the pressure and temperature gradients in tip vortices. This can be
>> affected by the presence or absence of "winglets". And the tail
>> surfaces can also shed vortices.
>>
>> I would not count trailing condensation lines and equate that to the
>> number of engines. From the sun's reflection off the large nacelles, I
>> would associate the shape with that of a large twin-jet.
--
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