STF question

On Mar 16, 11:53*pm, Dan G wrote:
So to be clear, when not on final glide, to achieve the best speed-
over-ground the head/tail/cross wind should be ignored when
determining inter-thermal cruise speed?

Dan

I mean, when I think about it, I come to the conclusion that you
always have to (and can only) optimise your speed through the airmass
by flying MC (putting aside what that actually means in reality). If
the resultant XC speed given by MC theory is less than the windspeed,
well, you're stuffed.


Dan

I mean, when I think about it, I come to the conclusion that you
always have to (and can only) optimise your speed through the airmass
by flying MC (putting aside what that actually means in reality). If
the resultant XC speed given by MC theory is less than the windspeed,
well, you're stuffed.

Dan

That's correct. The assumption is that you're flying in thermals, and
thermals drift with the airmass. Actually thermals usually drift a bit
less than airmass, and if you've got ridge or wave, those are
stationary with respect to the ground. But otherwise, by definition
there is no way to fly faster than the optimum speed through the
airmasss -- the fact that the ground is moving around below you is
irrelevant.

John Cochrane

"BB" wrote in message
...
I mean, when I think about it, I come to the conclusion that you
always have to (and can only) optimise your speed through the airmass
by flying MC (putting aside what that actually means in reality). If
the resultant XC speed given by MC theory is less than the windspeed,
well, you're stuffed.

Dan

That's correct. The assumption is that you're flying in thermals, and
thermals drift with the airmass. Actually thermals usually drift a bit
less than airmass, and if you've got ridge or wave, those are
stationary with respect to the ground. But otherwise, by definition
there is no way to fly faster than the optimum speed through the
airmasss -- the fact that the ground is moving around below you is
irrelevant.

John Cochrane

For the ultimate competitor, going fast is their reason for being so the
MacCready formula is very important for them.

For the rest of us, staying in the air and getting home is also on the
priority list. Answering the question, "How far can I go from here?" is
important. That's why I really like the "Glide Amoeba " on the NK glide
computer and the "Glide Footprint" on GPS_LOG WinCE. These simple graphics
take wind and terrain into account as well as the current M setting.

Bill D

On Mar 16, 10:24 pm, "Bill Daniels" bildan@comcast-dot-net wrote:
"BB" wrote in message

...



I mean, when I think about it, I come to the conclusion that you
always have to (and can only) optimise your speed through the airmass
by flying MC (putting aside what that actually means in reality). If
the resultant XC speed given by MC theory is less than the windspeed,
well, you're stuffed.

Dan

That's correct. The assumption is that you're flying in thermals, and
thermals drift with the airmass. Actually thermals usually drift a bit
less than airmass, and if you've got ridge or wave, those are
stationary with respect to the ground. But otherwise, by definition
there is no way to fly faster than the optimum speed through the
airmasss -- the fact that the ground is moving around below you is
irrelevant.

John Cochrane

For the ultimate competitor, going fast is their reason for being so the
MacCready formula is very important for them.

For the rest of us, staying in the air and getting home is also on the
priority list. Answering the question, "How far can I go from here?" is
important. That's why I really like the "Glide Amoeba " on the NK glide
computer and the "Glide Footprint" on GPS_LOG WinCE. These simple graphics
take wind and terrain into account as well as the current M setting.

Bill D

Yes, and all of the glide computers out there take headwind or
tailwind into account when computing the altitude required.

Todd Smith
3S

On Mar 16, 7:07*pm, BB wrote:
I mean, when I think about it, I come to the conclusion that you
always have to (and can only) optimise your speed through the airmass
by flying MC (putting aside what that actually means in reality). If
the resultant XC speed given by MC theory is less than the windspeed,
well, you're stuffed.

Dan

That's correct. The assumption is that you're flying in thermals, and
thermals drift with the airmass. Actually thermals usually drift a bit
less than airmass, and if you've got ridge or wave, those are
stationary with respect to the ground. But otherwise, by definition
there is no way to fly faster than the optimum speed through the
airmasss -- the fact that the ground is moving around below you is
irrelevant.

John Cochrane

So the conclusion is that the wind has effect only on the final glide,
and requires adjusting the MC setting manually (and keep adjusting as
the wind changes) to optimize the glide over the ground, which in some
cases (long glides into significant head wind) will make the
difference between making it back or landing short. However, while
normally MC values can not be determined by the flight computer since
it doesn't know if,when and how strong the next climb will be, the MC
value for best final glide into the wind CAN be determined by the
flight computer. Wouldn't this be a useful feature, to be able to
select an auto MC for final glides?

Ramy

Bill Daniels wrote:
"BB" wrote in message
...
I mean, when I think about it, I come to the conclusion that you
always have to (and can only) optimise your speed through the airmass
by flying MC (putting aside what that actually means in reality). If
the resultant XC speed given by MC theory is less than the windspeed,
well, you're stuffed.

Dan
That's correct. The assumption is that you're flying in thermals, and
thermals drift with the airmass. Actually thermals usually drift a bit
less than airmass, and if you've got ridge or wave, those are
stationary with respect to the ground. But otherwise, by definition
there is no way to fly faster than the optimum speed through the
airmasss -- the fact that the ground is moving around below you is
irrelevant.

John Cochrane

For the ultimate competitor, going fast is their reason for being so the
MacCready formula is very important for them.

My experience with talking to "ultimate competitors" is that the
MacCready formula isn't even on their radar. It's mainly a topic the
rest of us obsess over, because we think it we just understood it well
enough, we'd go as fast as those other guys. The "ultimate" pilots know
the MC speed isn't important because we rarely fly in pure MC condtions,
and in any case, "risk management" means flying slower to optimize the
chances of finishing the task. John Cochrane's article is a wonderful
exposition of this.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* Updated! "Transponders in Sailplanes" http://tinyurl.com/y739x4
* New Jan '08 - sections on Mode S, TPAS, ADS-B, Flarm, more

* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

On Mar 16, 11:19 pm, Ramy wrote:
On Mar 16, 7:07 pm, BB wrote:



I mean, when I think about it, I come to the conclusion that you
always have to (and can only) optimise your speed through the airmass
by flying MC (putting aside what that actually means in reality). If
the resultant XC speed given by MC theory is less than the windspeed,
well, you're stuffed.

Dan

That's correct. The assumption is that you're flying in thermals, and
thermals drift with the airmass. Actually thermals usually drift a bit
less than airmass, and if you've got ridge or wave, those are
stationary with respect to the ground. But otherwise, by definition
there is no way to fly faster than the optimum speed through the
airmasss -- the fact that the ground is moving around below you is
irrelevant.

John Cochrane

So the conclusion is that the wind has effect only on the final glide,
and requires adjusting the MC setting manually (and keep adjusting as
the wind changes) to optimize the glide over the ground, which in some
cases (long glides into significant head wind) will make the
difference between making it back or landing short. However, while
normally MC values can not be determined by the flight computer since
it doesn't know if,when and how strong the next climb will be, the MC
value for best final glide into the wind CAN be determined by the
flight computer. Wouldn't this be a useful feature, to be able to
select an auto MC for final glides?

Ramy

I think the conclusion is that the wind has effect on the altitude
required for the final glide, but not the speed that you would fly it
at. The speed is determined by the climb rate at the top of the last
thermal.

Some flight computers do an automatic MC setting for a final glide. I
think both Winpilot and Seeyou Mobile do this.

Todd

Ramy wrote:

So the conclusion is that the wind has effect only on the final glide,
and requires adjusting the MC setting manually (and keep adjusting as
the wind changes) to optimize the glide over the ground, which in some
cases (long glides into significant head wind) will make the
difference between making it back or landing short. However, while
normally MC values can not be determined by the flight computer since
it doesn't know if,when and how strong the next climb will be, the MC
value for best final glide into the wind CAN be determined by the
flight computer. Wouldn't this be a useful feature, to be able to
select an auto MC for final glides?


Try GPS_LOG WinCE. It has this feature. At least if I understand you
correctly. One of its displays shows MC and speed to reach destination
from the altitude you are at. all you need is to click it (and
confirm) to transfer MC value. One of "ultimate" competition pilots
asked for it years back.

Cheers,
Henryk Birecki

What we're really talking about here is; How high should I climb in
the last thermal? I think you should take it to the altitude where
your computer shows you have final glide at your last MC setting. Lets
say its 3, but your last thermal is pumbing out a solid 4 knots. Do
you stay longer (climb higher) or leave when you have final glide into
the current wind? The rule I use is; Climb higher, if the average
thermal strength is above 3 knots and then adjust my MC setting to
come home faster. If my final thermal is only 2 knots, I leave as soon
as I have final glide + pattern altitude ( I use 500 feet).
Other thoughts?
JJ

Ramy wrote:
On Mar 16, 7:07�pm, BB wrote:
I mean, when I think about it, I come to the conclusion that you
always have to (and can only) optimise your speed through the airmass
by flying MC (putting aside what that actually means in reality). If
the resultant XC speed given by MC theory is less than the windspeed,
well, you're stuffed.

Dan

That's correct. The assumption is that you're flying in thermals, and
thermals drift with the airmass. Actually thermals usually drift a bit
less than airmass, and if you've got ridge or wave, those are
stationary with respect to the ground. But otherwise, by definition
there is no way to fly faster than the optimum speed through the
airmasss -- the fact that the ground is moving around below you is
irrelevant.

John Cochrane

So the conclusion is that the wind has effect only on the final glide,
and requires adjusting the MC setting manually (and keep adjusting as
the wind changes) to optimize the glide over the ground, which in some
cases (long glides into significant head wind) will make the
difference between making it back or landing short. However, while
normally MC values can not be determined by the flight computer since
it doesn't know if,when and how strong the next climb will be, the MC
value for best final glide into the wind CAN be determined by the
flight computer. Wouldn't this be a useful feature, to be able to
select an auto MC for final glides?

Ramy

On Mar 17, 6:03Â*am, JJ Sinclair wrote:
What we're really talking about here is; How high should I climb in
the last thermal? I think you should take it to the altitude where
your computer shows you have final glide at your last MC setting. Lets
say its 3, but your last thermal is pumbing out a solid 4 knots. Do
you stay longer (climb higher) or leave when you have final glide into
the current wind? The rule I use is; Climb higher, if the average
thermal strength is above 3 knots and then adjust my MC setting to
come home faster. If my final thermal is only 2 knots, I leave as soon
as I have final glide + pattern altitude ( I use 500 feet).
Other thoughts?
JJ



Ramy wrote:
On Mar 16, 7:07�pm, BB wrote:
I mean, when I think about it, I come to the conclusion that you
always have to (and can only) optimise your speed through the airmass
by flying MC (putting aside what that actually means in reality). If
the resultant XC speed given by MC theory is less than the windspeed,
well, you're stuffed.

Dan

That's correct. The assumption is that you're flying in thermals, and
thermals drift with the airmass. Actually thermals usually drift a bit
less than airmass, and if you've got ridge or wave, those are
stationary with respect to the ground. But otherwise, by definition
there is no way to fly faster than the optimum speed through the
airmasss -- the fact that the ground is moving around below you is
irrelevant.

John Cochrane

So the conclusion is that the wind has effect only on the final glide,
and requires adjusting the MC setting manually (and keep adjusting as
the wind changes) to optimize the glide over the ground, which in some
cases (long glides into significant head wind) Â*will make the
difference between making it back or landing short. However, while
normally MC values can not be determined by the flight computer since
it doesn't know if,when and how strong the next climb will be, the MC
value for best final glide into the wind CAN be determined by the
flight computer. Wouldn't this be a useful feature, to be able to
select an auto MC for final glides?

Ramy- Hide quoted text -

- Show quoted text -

This is all correct when you have enough altitude that all you need to
decide is how much higher you should climb to fly faster, a typical
contets scenario. I was thinking more of final glide at the end of the
day when you trying to stretch a marginal glide to try to make it home
against significant head wind (think final glide to Truckee from the
north end of the Pine Nuts or Airsailing). Normally you would put MC=0
when you want to maximize your glide, but if you have 20 knots head
wind a setting MC=1 will be better. Sounds like GPS-LOG is doing this.

Ramy