On Sat, 2011-11-05 at 21:34 -0700, Ramy Yanetz wrote: > So how do pilots address this? > What I do:
- Check the polar against your glider with long enough final glides to make this a sensible exercise, say 30 - 35 km. Note the predicted arrival height at the start of the FG and check whether you were above or below it on arrival. While you're doing this, there's no need to push the margins - if you're 30 km out and the FG prediction is an 1800 ft arrival, thats good. Fly the FG and see whether you did arrive at 1800ft or not. If the polar is consistently underestimating the glider's performance, fine. If not, consider modifying it and using the modified polar from a file rather than the polar built into XCSoar. In my case (Std Libelle with full span lower surface zigzag turbulators) the Winpilot polar is pessimistic, probably due to the turbs, which add about 1 point to the best glide ratio. - I set safety altitude to 1000 ft By now I've done finals glides under these conditions enough to be confident that the FG prediction is reliable and, if unexpected sink drops me more than 400 ft below my selected safety altitude when heading home after abandoning a task due to weather, to take note and either find a climb pronto, no matter how slow it may be, or to land out. I think the sort of exercise I described above is a good thing to do early in the season when you're getting you eye back in for XC flights, or on days when the good weather slot is predicted to be too short or over too limited an area for an XC. BTW, in my club anyway, 'local soaring' translates as "staying within gliding range of the field". If you go local soaring with a task running in XCSoar whose only TP is your home field, you can easily see if you're in glide range of home by monitoring the FG height infobox. If you fly upwind from the field on a day when there are good thermals to 5500 ft or more and a steady 12-15 kt breeze, you'll find that you can comfortably get 30-35 km away and still be in gliding range of home. Doing this is good preparation if you're checking out XCSoar's FG calculations or if you're an early XC pilot and want to practise FGs. If you're new to XCSoar, this is also a very good way of getting to know how the program works and how to use the information it is showing you. Martin ------------------------------------------------------------------------------ RSA(R) Conference 2012 Save $700 by Nov 18 Register now http://p.sf.net/sfu/rsa-sfdev2dev1 _______________________________________________ Xcsoar-user mailing list Xcsoar-user@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/xcsoar-user
