I just figured it was the old "I just won the nats and didn't even know what speed to fly" routine!
Cheers Ben On 25 Oct 2016 5:53 PM, "Mike Borgelt" <[email protected]> wrote: > If you go to our website there's a nice little polar coefficient > calculator. You need the polar at any weight (and know what that weight > is) Any other desired weight such as the minimum flying weight and it just > calculates the coefficients for you. It includes the speeds for min sink > and best L/D and the performance at those speeds for a sanity check on the > numbers. The 3 coefficient approximation isn't necessarily very good a very > low speeds but if you get it right from best L/D to the maximum useful > speed (usually about 4 knots sink at that speed) you will be doing well. > There's a small text file that explains how to use the tool. > It also calculates what I call the D coefficient which is the relative > netto offset which is the CIRCLING sink rate of the glider. Around 1.6 > times the min sink rate at that weight is good. It does vary with bank > angle of course. Some people have been "educating" others with the wrong > definition of relative netto which just shows they didn't understand it. > > The numbers the program gives are actually for our instruments. Left out > is that the A coeff is multiplied by 10^-4, the B coefficient by 10^-2 and > B is ALWAYS a negative number. > > Also note that this approximation is not based on physics. It is a curve > fitting exercise. In reality the polar sink is closer to sink = A*V^3 + > (B/V) > > Also see the Basic Sailplane instruments article on the website. > > So once again the lack of proper theoretical training rears its head. The > effect of weight on the polar should just be a normal part of every glider > pilot's training. > > Congratulations on your win, Adam! > > Mike > > > > > > > > > > > > At 04:01 PM 10/25/2016, you wrote: > > Content-Language: en-AU > Content-Type: multipart/alternative; > boundary="_000_HK2PR04MB08979EBE201C68E51AD6F > 9A3A2A80HK2PR04MB0897apcp_" > > G’day All, > > Just wondering whether anyone knows the formula for converting a baseline > empty polar curve (speeds/sink rates) to a ballasted polar curve? I’ve > read it somewhere in the past, but cant find it easily now. > > > Cheers, > WPP > _______________________________________________ > Aus-soaring mailing list > [email protected] > http://lists.base64.com.au/listinfo/aus-soaring > > *Borgelt Instruments* - > *design & manufacture of quality soaring instrumentation since 1978 * > www.borgeltinstruments.com > tel: 07 4635 5784 overseas: int+61-7-4635 5784 > mob: 042835 5784 : int+61-42835 5784 > P O Box 4607, Toowoomba East, QLD 4350, Australia > > _______________________________________________ > Aus-soaring mailing list > [email protected] > http://lists.base64.com.au/listinfo/aus-soaring > >
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