What is This?

I read the "What is This?" article in the 9 December 2005 issue of The Citizen Scientist with interest (Scott Vincent, What is This? "Gallery").

It would be very interesting to know the type of plane that produced the undulating contrails in the photographs. Certain types of vehicles tend to shed vortexes while moving, as any motorcyclist can attest to if they've ever followed a large semitrailer truck. I wonder if a particularly boxy kind of aircraft could also shed vortexes at a particular air speed or under certain atmospheric conditions.

I can't tell exactly how many contrails there are in the photographs, which would indicate the number of engines on the plane, but it looks like there may be only one. This would suggest a smaller type of plane or one with the engines spaced very close together.

It would also be interesting to know if the plane was powered by a jet, a turbo-prop, or a piston engine.

It's also, of course, possible that the undulations were caused by atmospheric conditions.

Another possibility is that the plane may have been undulating in it's course. Quite a few aircraft employ electronic control systems, and it's remotely possible that under some circumstances the control system may experience a mild oscillation about a steady state point. Or, it could be due to a mechanical resonance with the rudder system.

Unfortunately, without additional information, it's doubtful if the exact reason can be determined.

David W. Glass

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