jpspencer(at)cableone.net
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 Posted: Wed Jul 22, 2009 7:04 pm Post subject: Aluminum paired VGs |
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Somebody in the VG thread asked about installing the paired aluminum vgs on the wing...first of all let me say that I don't care whose vgs anybody buys, or if they don't buy any at all.
I have had a set of the aluminum paired vgs on my Legal Eagle for some time. They are carefully homemade, by me. They helped the lowspeed handling considerably and lowered the stall speed several mph, as expected.(I never tested the cruise, I don't care how fast it goes) Before installing JGs vgs on my 701, I made and installed(taped) a set of the aluminum ones on my slatless wing and did some testing. The handling improved,as compared to with slats, but the cruise speed decreased as compared to the clean(no slats or vgs) wing. I went back and dug for a while but didn't come up with the numbers. I have them here somewhere, I know, as I have just about everything that I have touched since birth. Anyway, I can tell you that in my case anyway that the drag went up with that set positioned at 8% MAC, the same position as my Stolspeed vgs. I abandoned them early on in the testing, in favor of the individually mounted ones, due to the drag increase. My clean wing flew 90.25 mph, with Stolspeed vgs, also 90.25. If I remember correctly, with the aluminum vgs mine did 88.(round struts at that time)Under the tail, in the elevator slot where they are hidden from cruise airflow, there shouldn't be any increase in cruise drag, I wouldn't think.
As an aside, I would say that precise, definitive testing on a plane as slow as ours is more difficult that on faster ones cause the differences in speed after a change are often so small as to be difficult to see and accurately measure(what did we ever do w/o GPS?)...it takes a lot of dedication and effort, a casual approach will give flawed results. On our planes a 2 or 3 mph change in airspeed is hard to see, but is a huge percentage change, relatively speaking. Small atmospheric variations on a 90 mph airplane have a huge effect, and often mask the result, or magnify it. I did over 40 hours of testing on vgs before I was satisfied with my results. And that is nothing compared to what JG has done. I was able to match his claims.
FWIW
Joe
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