Various people commented on the "wrinkle"...
>I have seen this on other wings of highspeed, subsonic aircraft. I
>believe it is where the airflow over the wing suddenly goes from laminar
>flow to turbulent flow. The sudden change will cause a small difference
>in refraction and produce your "wrinkle in the air."
...and...
>Water in the air, unless it is rain, clouds, or fog, is in the vapor
>form. If it suddenly becomes visible it is due to condensation. If you
>watch high speed aircraft making a sharp turn you can see water
>condesation at the wing tips outlining the wing tip vortices as a kind
>of vapor trail. The phenomenon described sounds more like a sudden
>change in the refractive index of the air over the wing such as might
>occur at a supersonic transition boundry or the place where laminar flow
>changes abruptly to turbulent flow. I believe it is the latter
>phenomenon as it occurs over the top of the wing about a third or more
>back from the leading edge where turbulent flow is expected to begin.
The "wrinkle" that I had seen was not vapor condensation over the wing at
low altitude, but occurred at 35,000 feet and at sustained cruise. This
wrinkle was a true defraction of my vision and when lined up with a
straight line such as the leading edge of the wing would cause a noticable
wiggle in the vision, similar to that of looking through an old window
pane. This anomaly was verticle and extended up above the cabin window.
It was positioned at the CG (center of gravity) point of the plane and
would move forward and back maybe an inch or so as light turbulance was
encountered. When the angle of the sun was perpendicular to the "wrinkles"
(there were several) they would cast shadows on the wing. The wrinkles are
only visible at straight and level cruise.
I thought about the supersonic transition boundry theory for a bit and that
is a possibility. Since the plane is cruising at a speed relatively close
to the speed of sound, the increased airflow speed over the wing can
approach, if not exceed the sonic limit, thereby creating either a caviting
of the atmosphere or a shockwave that is maintained at that point. I do
not believe it to be a separation of the laminar flow as that would occur
near the wing itself.
Ken Norton
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