On Tuesday, October 23, 2012 4:23:20 PM UTC-7, Martin Gregorie wrote:
On Tue, 23 Oct 2012 00:43:28 -0700, Ramy wrote:



This is an important point which should have been emphasized in the

manual, or I missed it. I bet not many are aware that the bearing to the

target is based on track not heading. The error is relatively small at

lower wind speed, but can be significant in strong cross wind especially

at slow flight.



Surely this is obvious.



As any fule kno[1] a GPS receiver can only know its track vector and

record its track: it doesn't matter whether you carry it forwards,

backwards or sideways, it still correctly records its track without

having the faintest idea of which way its being pointed relative to that

track.



The FLARM depends entirely on GPS for its knowledge of its current track

vector, so it follows that it too knows nothing about its orientation

relative to your gliders fuselage or what the glider's heading might be.





[1] nigel molesworth, the terror of st custards



--

martin@ | Martin Gregorie

gregorie. | Essex, UK

org |

Sure it is obvious when you think about it, but it is not intuitively obvious. I'll admit it did not cross my mind until it was mentioned here, and I would bet that it did not cross most pilots mind. How many pilots you think will intuitively know to look for traffic downwind the first time they get a flarm collision alert when they fly in significant cross wind?

Ramy