On Thursday, May 3, 2012 12:48:50 PM UTC-7, Mike the Strike wrote:
On Thursday, May 3, 2012 11:48:50 AM UTC-7, Brad wrote:
I am using an oldeer Ilec SB-8 STF vario system, am very happy with it
and absolutely love the vario function (been an Ilec user for many
years) but in my Tetra-15 I am finally using a STF system, and have a
few questions.

Since this unit does not use GPS info , when I am in a headwind or
tailwind the P/S info is all the unit has available for speed
info...............yesterday I was in an area of extended strong sink,
along with a strong headwind............with no GS reference (per
GPS), what kind of accuracy does the SB-8 STF info have? And what can
I do to remedy this.

Another issue on that flight was a battery that dropped below
10volts............the STF needle was behaving rather badly!

Brad

Assuming that you are flying in accordance with standard MacCready theory, your speed-to-fly does not depend on the windspeed. The only time headwinds become important is on final glide and the adjustment is not large and can usually be safely ignored.

Mike

I dare to challenge this common claim that STF does not depend on windspeed unless on final glide. The above claim may only be true when flying over flatland. It is not true when flying over mountain terrain, which is the type of flying most of us do in western US. When flying over mountain terrain, the lift tends to remain in the same spots and don't drift with the wind. It may be tilted at most. Also the wind is significant for terrain clearance, so you certainly need to fly faster in head wind if terrain clearance is an issue. And finally, thermals do not always drift as fast as the wind. As such, you should almost always add speed when flying up wind, the stronger the headwind the faster you should fly. How faster is another question, I believe most flight computers don't take wind in account, especially when not in final glide. Adding half the wind speed sounds about right, I usually bump up my MC setting by 0.5 for head wind of up to 10 knots, by 1 for 10-20 knots and so forth.
I'll be happy to hear other opinions.

Ramy