On May 3, 5:50*pm, Ramy wrote:

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-


Ramy, I think you will find that your mountain clearance example is
really a "final glide" computation. You have a fixed point on the
ground you must reach at or above a certain altitude. So, this is
really a final glide, and not a basic speed to fly to achieve a
maximum speed over the ground for the soaring conditions computation.
Whether the thermals are drifting at the same speed as the free air
mass or not is really relevant. And John Cochrane has published an
analysis on this. As I recall, he said you need to be more picky
about taking only climbs that meet your MC setting when going upwind
(especially when getting close to a turnpoint) and can be a bit less
picky when going downwind towards a turnpoint.

Now, I have seen an instance when the computer said I could not get
home when I had MC 0 dialed in but could with a higher MC setting
entered. This was because I had about 50 knots wind on the nose, and
best L/D was at about 50 knots. I was 10 miles out at about 11000
above field elevation, in my 604. I dialed MC up to 4, it said to fly
about 80 knots, so now I had a ground speed and all of the sudden, I
had 6000+ feet of extra altitude. Again, this was really a final
glide case, and not a best speed over the ground case, assuming you
wil lclimb again. It showed that when you have MC set to zero, it does
not give you the coreect speed to fly to maximize your range if there
is wind.

So, speed to fly is only affected by a headwind when you are
approaching a set point you must reach or clear. This may be an area
with no lift downwind of it that you cannot clear because of wind if
you fly a true anticipated MC speed but could if you flew a higher MC
speed (see above example). Again, this is really a final glide issue,
as you have a set place you have to get to from the altitude you have
on hand. Sit down sometime with your polar and a calcualtor. I will
be very surprised if you can prove to me that flying faster than MC
optimum speed (using simple climb and glide theory, no bumps in
between) into a headwind will result in a faster speed over the ground
in getting from A to B than the optimum speed as defined by your polar
for a given MC setting.

Do any of the computers out there now have a mode that will give you
your speed to fly for maximum range if you are flying into the wind?
Or downwind? Or, is it up to us to know our polar, and have
determined best L/D speeds for different amounts of wind?

Steve