On Monday, November 21, 2011, Ramy Yanetz wrote: > I haven't tried 6.2.3 yet but I flew with 6.2.2 last saturday (running on > my Streak connected to 302) and something is very wrong with all arrival > altitude calculations in waypoint info and info boxes when combining bug > factor, Headwind and MC >0. Once arrival altitude turned negative it > immediately dropped by 5000 feet or more to something completely wrong. > Sometime it will stuck on zero. If I changed MC to zero it usually fixes > it. I can recreate it anytime I replay my flight. The issue gets worse > the higher the headwind, MC and bug factor. In my example MC=0.5, bug > factor= 67% and head wind = 12 knots. No task set, so next waypoint was > home all the time. Arrival altitude (altitude difference) was correct > until turned negative with the head wind component, then it dropped from > zero to -6000 feet in couple of minutes! I even saw a message that I > will arrive after sunset although the waypoint was only 20 miles away > and there was at least 3 hours to sunset. Please note that the zero MC > calculation was correct in the waypoint info all the time, only the > current MC and safety MC ( if greater than zero) are completely off when > turning negative with polar degradation and significant headwind >10 > knots or so.
You are tuning the parameters in a direction where - if your glider really behaved like that - you would not reach your target. If you 1) degrade pure glide performance significantly 2) use a too low avg. climb rate 3) factor in a strong headwind you will arrive in a situation where no solution exists. For example (I exaggerate, round and use metric values to make calculations easier): Offical L/D 1:40, 50% bugs performance reduction => 1:20. Best glide speed 100 km/h (IAS) Height 1000m + safety height above target Distance to target 20km. With no wind you will just make it to the target without any climbing. Now assume an headwind of 20 km/h => Additional 20% glide performance loss (for simplicity I assume you will still fly the glide with 100km/h IAS). You would need a height of 1200m AT YOUR CURRENT POSITION to reach your target. 200m height gain with a MC of approx. 0.11 m/s => 1800s (1/2 hour) circling time. The drift away from your target during that 1/2 hour because of wind is 10km. But you only made 200m height so you have lost more than you won assuming the L/D of 1:20. There simply exists no solution in this example to reach your target and this will be indicated by xcsoar (e.g. with "---" in WP AltD infobox and the hiding of the final glide bar). Now the above sample was extreme but if you modify the values so that slow progress in direction of your target is just about possible you will see very high but correct estimates given the parameters you provided to xcsoar (both height gain needed and time to reach your target). BTW: Yes, with a MC setting of 0 some of xcsoars calculations are simplified since xcoar assumes you can not gain any height. Thermalling (and it's associated distance to target increase in a headwind) is not considered and arrival height is calculated using a simple glide range calculation which is considering wind (not pure L/D). ------------------------------------------------------------------------------ All the data continuously generated in your IT infrastructure contains a definitive record of customers, application performance, security threats, fraudulent activity, and more. Splunk takes this data and makes sense of it. IT sense. And common sense. http://p.sf.net/sfu/splunk-novd2d _______________________________________________ Xcsoar-user mailing list Xcsoar-user@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/xcsoar-user
