rotorcraig
20th Apr 2004, 19:45
Have just been asked a GPS question by a friend which actually related to snowboarding, but translates well onto aviation thus someone reading may know the answer (I didn't!)
I take my GPS with me on a flight from A to B which happens to be exactly 20nm. Time happens to be exactly 20 minutes (let's keep the maths simple!)
Of course, I need to climb to a reasonable altitude and subsequently descend to land. Loads of satellites visible, thus good 3D fix throughout.
So, does the GPS record 20nm over 20 minutes thus 60kt average?
Or does it record 20.5nm (or whatever) due to the climb and descent over 20minutes thus 61.5kt average speed?
I guess the question in a nutshell is "does a 3D fix mean 3D actuals for time and distance calculation, or are these 2D calculations regardless of 3D fix?"
RC
I take my GPS with me on a flight from A to B which happens to be exactly 20nm. Time happens to be exactly 20 minutes (let's keep the maths simple!)
Of course, I need to climb to a reasonable altitude and subsequently descend to land. Loads of satellites visible, thus good 3D fix throughout.
So, does the GPS record 20nm over 20 minutes thus 60kt average?
Or does it record 20.5nm (or whatever) due to the climb and descent over 20minutes thus 61.5kt average speed?
I guess the question in a nutshell is "does a 3D fix mean 3D actuals for time and distance calculation, or are these 2D calculations regardless of 3D fix?"
RC