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On Apr 16, 11:15 am, "Maxwell" wrote:
"Kev" wrote in message It's going to take about 30 seconds to fly a 360 steep turn at 100kts. My wake _should_ descend about 150' during that time (300 fpm). I can't imagine a C172 wake being tall enough to stay in my way unless something else is ocurring (me descending, or the wake staying up). I am certainly no expert on the subject, but I think most of the data on wake turbulence comes from studies held at or very near the ground. My searches on the web show the opposite... or at least that there's studies both at altitude and near the ground. For examples: http://www.nasa.gov/centers/dryden/a...4-14-DFRC.html "NASA research has shown that as large aircraft move through the air, trailing vortices tend to remain spaced less than a wingspan apart while sinking at a rate of several hundred feet per minute. Over time, the sink rate will slow and their strength will taper off. Research has shown, however, that vortices can also rise during conditions of ambient thermal lifting." "Aircraft Accident Reconstruction and Litigation" By M. P. Papadakis, Barnes Warnock MacCormick, states that vortices descend 5-10 fps (30-600 fpm). Based on the numbers I recall, they did indeed teach that the wake from a landing heavy would NORMALLY travel both down and away from the aircraft a 5 kts or so. But they were also quick to mention that a simple 5 kt or so crosswind componet could leave the vortex in the middle of the runway for quite some time. Yes, we were all taught that part. The problem with trying to use this information at altitude is that you don't have the ground to help stablize the vertical movement of the vortex. Here is information taken at altitude: Vortices are 14-36 feet in diameter, approx the wingspan apart, and sink 160 - 1100 fpm. http://www.airpower.maxwell.af.mil/a...ug/carten.html I just think it's an interesting question, because we've all had it happen, but no one here can give a definitive reason for it (beyond "yo stupid of course it does" which is pretty lame even for the usual Mx bashers ;-) I think I've convinced myself that since I don't always hit my wake on a perfect steep turn, and because it mostly seems to happen over areas of rising air, that the explanation is simple. Unless someone can post better research. Thanks, Kev |
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