Why don't flight computers adjust STF for wind?

My understanding is that modern flight computers (which seem to have 10X more features than anyone could possibly use) don't make adjustment to STF calculations for the wind. From my reading of recent "authoritative" sources (Brigliodori, Kawa) it is optimal to increase speed into the wind and decrease speed downwind, relative to non-adjusted McCready. Also of critical importance to me would be a final glide optimizer. Currently when making a final glide I "move the dial" up and down in McCready speeds as I get close to final glide. Often changing the McCready value up into the wind and down with the wind leads to lower required altitude.

Am I missing anything?

2C

On Friday, January 10, 2014 1:10:45 PM UTC-6, Kevin Christner wrote:
My understanding is that modern flight computers (which seem to have 10X more features than anyone could possibly use) don't make adjustment to STF calculations for the wind.

They do make very good adjustments for the wind in the sense that if you dial in MacCready 3 into the wind they will tell you you need a lot more altitude than if you dial in MacCready 3 going downwind.

The speed to fly calculation is not affected by wind, as long as thermals drift with the wind. You still fly MacCready 3 airspeed in MacCready 3 lift. The final glide calculation is also not affected by wind. You still leave a 3knot thermal when you hit the MacCready 3 altitude, corrected for wind.

There are second order effects -- thermals don't drift exactly with the wind, you may be able to bump more or less effectively depending on wind, etc. But it would take a whole new generation of theory and software to begin to quantify these effects.

The optimal MacCready setting is affected by wind, when you're going in to a turnpoint. You want to both fly faster and be choosier about thermals going to an upwind turnpoint, and fly slower and take weaker lift going to a downwind turnpoint. This is currently handled by just increasing or decreasing the MacCready setting, which is what Brigliadori and Kawa are advocating..

The setting choice can be done quantitatively, see "upwind and downwind" here

http://faculty.chicagobooth.edu/john...ring/index.htm

The only thing a flight computer can productively add is this calculation. I've been bugging the CN folks do implement this for a while. All it takes is to present the equivalent after-turnpoint mac cready setting for the current value. But they answer (correctly, from a business standpoint) "we're not putting in a number that only you care about!"

John Cochrane

The only thing a flight computer can productively add is this calculation.. I've been bugging the CN folks do implement this for a while. All it takes is to present the equivalent after-turnpoint mac cready setting for the current value. But they answer (correctly, from a business standpoint) "we're not putting in a number that only you care about!"

If Brigliadori and Kawa care, it might be worth adding!

2C

I think I would modify John's statements just slightly. He says "You want to both fly faster and be choosier about thermals going to an upwind turnpoint, and fly slower and take weaker lift going to a downwind turnpoint."

I would say, you want to fly faster 'after the last climb going into an upwind turnpoint' and be choosier about thermals (particularly the last one before the turnpoint) when going to an upwind turnpoint and 'be more willing' to fly a little slower, or take a weaker climb (particularly the last one before the turn) when going to a downwind turnpoint.

Key is that theory is different when trying to maximize altitude over the ground at a fixed point some distance away then it is to maximize achieved cross country speed through the air.

Sound about right, John?

George Moffat:
"Always go into an upwind turnpoint low"

Anonymous:
"Yep, Ol' George sure landed out a lot of his competitors with that one!"

See ya, Dave "YO electric"

On Friday, January 10, 2014 3:10:57 PM UTC-6, Dave Nadler wrote:
George Moffat:

"Always go into an upwind turnpoint low"



Anonymous:

"Yep, Ol' George sure landed out a lot of his competitors with that one!"



See ya, Dave "YO electric"

no matter downwind or upwind ... use the horseshoe theory cheers S9

On Friday, 10 January 2014 22:01:28 UTC+2, wrote:

There are second order effects -- thermals don't drift exactly with the wind, you may be able to bump more or less effectively depending on wind, etc. But it would take a whole new generation of theory and software to begin to quantify these effects.


John Cochrane

Yes, theoretically *if* thermals would drift perfectly with wind, there wouldn't be any windshear across thermals, resulting that they would be completely symmetrical (round). Or they would ascend at impossible angles (2 m/s thermal drifting in 20 m/s wind would result 1:10 angle).

Flying under clouds with real-time wind information is quite revealing.

krasw

On Monday, January 13, 2014 2:34:40 AM UTC-6, krasw wrote:
Yes, theoretically *if* thermals would drift perfectly with wind...

Uh oh. Next problem. If thermals don't drift at the same speed as the wind, how accurate is that wind speed your computer derrives from drift while you are thermalling?

Steve

On Monday, January 13, 2014 11:17:35 AM UTC-5, Steve Leonard wrote:
On Monday, January 13, 2014 2:34:40 AM UTC-6, krasw wrote:
Yes, theoretically *if* thermals would drift perfectly with wind...

Uh oh. Next problem. If thermals don't drift at the same speed
as the wind, how accurate is that wind speed your computer derrives
from drift while you are thermalling?

Steve

It is well known that thermals do not exactly drift with the wind.
Consider the inertia of the heated parcel of air as it rises through
increasing wind aloft...
Hang-glider pilots have known for decades to fly upwind in thermal
wind shadows.

Not all flight computers use drift while thermalling to estimate
wind! For example, the ILEC SN10 does not...

Hope that helps,
Best Regards, Dave "YO electric"

PS: Steve, how's the first SN10 ever delivered to a customer treating you?

Steve Leonard wrote, On 1/13/2014 8:17 AM:
On Monday, January 13, 2014 2:34:40 AM UTC-6, krasw wrote:
Yes, theoretically *if* thermals would drift perfectly with
wind...

Uh oh. Next problem. If thermals don't drift at the same speed as
the wind, how accurate is that wind speed your computer derrives from
drift while you are thermalling?

My experience with a 302 and SeeYou Mobile was the differences were
small compared to other variations due to time, location, and altitude,
and small enough that I usually didn't notice any difference. But, there
may be places that do have bigger differences, and I just didn't fly there.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)