A Tale of Two Takeoffs

On Sat, 17 Jun 2017 19:57:22 -0700, Echo wrote:

I must admit the downwash discussion is one I'm not fluent on. I've been
around a while, but it's certainly an interesting concept I don't know
much about. Makes you wonder how high a position you'd have to be for it
not to matter...especially when you consider actual climb gradient,
compared to AoA and angular fluid dynamics from the tug wing back to a
glider 200' back. I haven't seen it in any book, but the books have been
updated a few times and it doesn't mean it doesn't exist.

Its even a bit worse than has been described: your outer wings and
ailerons are in the tow plane's wingtip vortex, which adds a still
further to the AOA difference due to the upward flaw in that part of the
vortex.

Low tow may be a better answer simply because it puts the whole glider
below the tugs downwash and tip vortices. It certainly feels smoother,
but doesn't sort out takeoff and initial climbout problems.

Side comment: the issue of wingtips extending beyond the tug's wing
downwash in pretty much unique to our sailplanes: all of the Allied troop
carrying gliders during WW2 had lower spans than their tugs (a Waco CG4
is smaller than a C47 - look it up if you don't believe me). The only
exceptions were the British Hamilcar (about 6 feet bigger span than the
Halifax tow plane and one or two of the German and Russian troop carriers
when towed by single engine aircraft and, of, course the Me 321 Gigant.


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