On Sat, 2006-04-29 at 08:44 +1000, Robert Hart wrote: > Hi > > I've just come across quite a good tutorial web page that introduces > polar curves and speeds to fly for learning glider pilots. It was > written to prepare people for the FAA glider pilot exam and includes > some quite nice animated graphics to demonstrate what is going on. > > I will certainly be pointing students at this as a learning resource > and I thought others might be interested. > > The link is > http://home.att.net/~jdburch/polar.htm
One interesting point about gliding polars is that over quite a wide speed range (say 2:1) they are all the same shape. That is to say if you stretch (or compress) the horizontal and vertical axes by the appropriate amount they can be made to lie on top of one another. Another way of looking at this is to say that there is a "universal polar" given by: S = (X**3 + 1/X)/2 S is the "normalised rate of sink" i.e. S = Rate_of_sink/Rate_of_sink_at_best_L/D X is the "normalised airspeed" i.e. X = Airspeed/Airspeed_for_best_L/D The first term inside the brackets is X cubed. This polar does not provide a good fit at speeds near the stall or at speeds more than about twice the best L/D speed. As a consequence you could calculate the expected rate of climb required to justify a particular inter thermal cruising speed from: C = X**3 - 1/X where C is the expected rate of climb divided by the rate of sink at best L/D. cheers, Ken _______________________________________________ Aus-soaring mailing list [email protected] To check or change subscription details, visit: http://lists.internode.on.net/mailman/listinfo/aus-soaring
