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#1
July 14th 16, 03:00 PM
posted to rec.aviation.soaring
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Dick Johnson methodology for measuring glider performance
On Tuesday, July 12, 2016 at 2:45:32 AM UTC-4, Tango Whisky wrote:
The method by Dick Johnson works for gliders with limited performance. Even in "still air conditions", which are typically found in meterological high pressure regions, there are wide-area vertical movements of air. There is no way that the method by DJ can work them out... In addition to airmass movement, there are a couple other serious problems with the methods used: 1) The CG of the plane was not controlled. - what is the effect of forward vs. aft CG on max LD? - what popular plane was measured with a very low LD due to above? Discuss amongst yourselves... 2) The number of (and selection of) datapoints is not adequate Discuss amongst yourselves... ...That's why in Europe, DJ measurements are widely disregarded. Yup. 
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#2
July 14th 16, 04:25 PM
posted to rec.aviation.soaring
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Dick Johnson methodology for measuring glider performance
On Thursday, July 14, 2016 at 9:00:22 AM UTC-5, Dave Nadler wrote:
On Tuesday, July 12, 2016 at 2:45:32 AM UTC-4, Tango Whisky wrote: The method by Dick Johnson works for gliders with limited performance. Even in "still air conditions", which are typically found in meterological high pressure regions, there are wide-area vertical movements of air. There is no way that the method by DJ can work them out... In addition to airmass movement, there are a couple other serious problems with the methods used: 1) The CG of the plane was not controlled. - what is the effect of forward vs. aft CG on max LD? - what popular plane was measured with a very low LD due to above? Discuss amongst yourselves... 2) The number of (and selection of) datapoints is not adequate Discuss amongst yourselves... ...That's why in Europe, DJ measurements are widely disregarded. Yup. For reference see Paul Bikle's "Polars of Eight" in Soaring magazine.
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#3
July 14th 16, 10:35 PM
posted to rec.aviation.soaring
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Dick Johnson methodology for measuring glider performance
Dave Nadler said
1) The CG of the plane was not controlled. - what is the effect of forward vs. aft CG on max LD? - what popular plane was measured with a very low LD due to above? Discuss amongst yourselves... So what is the typical percentage change in L/D from full forward CG to maximum rearward CG? Is it a huge change (10%) or minor change? I have no idea.
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