Final glide

wrote on 9/25/2019 11:31 AM:
On Wednesday, September 25, 2019 at 2:14:48 PM UTC-4, Eric Greenwell wrote:
unclhank... wrote on 9/25/2019 5:41 AM:
On Tuesday, September 24, 2019 at 8:14:29 PM UTC-4, wrote:
Truth, and a final glide made at max l/d tells me that the guy already screwed up. The perfect final glide is one that gets you home at the proper altitude and at the max speed. He just screwed up on both counts.

The "perfect" final glide has the pilot crossing the finish at his selected height and at at the same speed as the average for the flight.

You don't really do that, do you? I'll bet you fly the final glide rather slowly
if your final thermal is weak, and rather fast if that thermal is strong, and
don't pay any attention to how fast the flight was before the final thermal.

That depends on the task. The MacCready theory for final glide speed that depends only on the climb rate in the last thermal applies to assigned tasks. AATs (TATs) are different, *if* your decision (last thermal) happens before the last turn, so that you can then choose, e.g., to fly farther into the last turn area but do the whole final glide (from the last thermal to the turn to the finish) slower. In that case, the optimal speed is the MC STF that corresponds to the average climb rate over the whole task. Yeah I know it sounds weird. Reference: the Brigliadoris' book.

That does sound weird, but I stopped flying contests before the turn areas offered
a large range of choices. Does going farther in that situation add more points,
compared to going faster?

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorg...ad-the-guide-1

"Back in the day" I used a homemade cardboard circular-slide-rule-type final glide calculator. It had distance and altitude scales, an airspeed scale, and curves for different winds. You set the distance and altitude and flew the speed according to the estimated wind. As the checkpoints went by, you adjusted the alt/dist to actuals and rapidly homed in on the approximate actual wind (conceptually similar to a pre-GPS LNAV, I believe). The finish margin was whatever you wanted it to be mentally. This was how REAL pilots flew: i.e., using a Sectional chart and compass.

I still keep it tucked away in my cockpit for sanity checks when my moving map shows me multiple altitude margins, including margin to gliding to the home airport, margin over the edge of the finish cylinder at finish height, margin to the center of the finish cylinder at ground level, etc. And then my CN vario shows its own altitude, which, as T8 helpfully explained, is always different, apparently based on total energy conserved in a pull up.

I can trust cardboard. It only offers one version of the truth, although it, too, can be fooled by sink, as happened twice this year on final glides at the CCSC Std. Nats that should have been straightforward but were anything but.

Chip Bearden
JB

On Wednesday, September 25, 2019 at 3:45:29 PM UTC-4, Eric Greenwell wrote:
moshe... wrote on 9/25/2019 11:31 AM:
On Wednesday, September 25, 2019 at 2:14:48 PM UTC-4, Eric Greenwell wrote:
unclhank... wrote on 9/25/2019 5:41 AM:
On Tuesday, September 24, 2019 at 8:14:29 PM UTC-4, wrote:
Truth, and a final glide made at max l/d tells me that the guy already screwed up. The perfect final glide is one that gets you home at the proper altitude and at the max speed. He just screwed up on both counts.

The "perfect" final glide has the pilot crossing the finish at his selected height and at at the same speed as the average for the flight.

You don't really do that, do you? I'll bet you fly the final glide rather slowly
if your final thermal is weak, and rather fast if that thermal is strong, and
don't pay any attention to how fast the flight was before the final thermal.

That depends on the task. The MacCready theory for final glide speed that depends only on the climb rate in the last thermal applies to assigned tasks. AATs (TATs) are different, *if* your decision (last thermal) happens before the last turn, so that you can then choose, e.g., to fly farther into the last turn area but do the whole final glide (from the last thermal to the turn to the finish) slower. In that case, the optimal speed is the MC STF that corresponds to the average climb rate over the whole task. Yeah I know it sounds weird. Reference: the Brigliadoris' book.

That does sound weird, but I stopped flying contests before the turn areas offered
a large range of choices. Does going farther in that situation add more points,
compared to going faster?

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorg...ad-the-guide-1

Assuming you won't finish under-time either way, going farther (up to a point) gives you more points since it increases the overall task speed (total distance divided by total time). The conditions (average climb rate) determine the best XC speed you can get, along with the STF between climbs, and since the distance is flexible you can maintain that speed for the best score.

What is not clear to me is how do you then decide when to leave that last thermal? Perhaps when the climb rate falls below that average climb rate? Assuming you have enough altitude to reach into the last turn area by that point.

On Wednesday, September 25, 2019 at 4:42:56 PM UTC-4, wrote:
On Wednesday, September 25, 2019 at 3:45:29 PM UTC-4, Eric Greenwell wrote:
moshe... wrote on 9/25/2019 11:31 AM:
On Wednesday, September 25, 2019 at 2:14:48 PM UTC-4, Eric Greenwell wrote:
unclhank... wrote on 9/25/2019 5:41 AM:
On Tuesday, September 24, 2019 at 8:14:29 PM UTC-4, wrote:
Truth, and a final glide made at max l/d tells me that the guy already screwed up. The perfect final glide is one that gets you home at the proper altitude and at the max speed. He just screwed up on both counts.

The "perfect" final glide has the pilot crossing the finish at his selected height and at at the same speed as the average for the flight.

You don't really do that, do you? I'll bet you fly the final glide rather slowly
if your final thermal is weak, and rather fast if that thermal is strong, and
don't pay any attention to how fast the flight was before the final thermal.

That depends on the task. The MacCready theory for final glide speed that depends only on the climb rate in the last thermal applies to assigned tasks. AATs (TATs) are different, *if* your decision (last thermal) happens before the last turn, so that you can then choose, e.g., to fly farther into the last turn area but do the whole final glide (from the last thermal to the turn to the finish) slower. In that case, the optimal speed is the MC STF that corresponds to the average climb rate over the whole task. Yeah I know it sounds weird. Reference: the Brigliadoris' book.

That does sound weird, but I stopped flying contests before the turn areas offered
a large range of choices. Does going farther in that situation add more points,
compared to going faster?

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorg...ad-the-guide-1

Assuming you won't finish under-time either way, going farther (up to a point) gives you more points since it increases the overall task speed (total distance divided by total time). The conditions (average climb rate) determine the best XC speed you can get, along with the STF between climbs, and since the distance is flexible you can maintain that speed for the best score.

What is not clear to me is how do you then decide when to leave that last thermal? Perhaps when the climb rate falls below that average climb rate? Assuming you have enough altitude to reach into the last turn area by that point.

For final glide:Based upon current climb rate, with MC set for that, the computer tells you when you are high enough to get back at the selected finish height. One also should adjust for what the sky looks like ahead, what the climb rate trend has been, how tight a margin can be accepted, and then adjusted by a gut factor.
Easy Peasy
UH