required LD versus required MC to make it home ??

On Aug 23, 12:20*pm, Andy wrote:

Where did the use of L/D (the ratio of lift to drag) to describe a
ground referenced flight path angle originate? *I know it has been
perpetuated by SeeYou, but did they start it?

That goes back to the 50s, very likely. Certainly, it was used on
circular slide rule calculators of the 60s (referenced in Sunship Game
and articles of the era). L/D *is* a little easier to say than "the
inverse of the tangent of the flight path angle", even if it *is*
extremely sloppy shorthand.

-T8

On Aug 23, 9:38*am, T8 wrote:

That goes back to the 50s, very likely. *Certainly, it was used on
circular slide rule calculators of the 60s (referenced in Sunship Game
and articles of the era). *L/D *is* a little easier to say than "the
inverse of the tangent of the flight path angle", even if it *is*
extremely sloppy shorthand.

I've been flying gliders long enough to have used prayer wheels as my
only flight computer. I never used one to compute my required L/D, and
don't know any way to use one to compute achieved L/D. Then, and now,
I considered arrival altitude and computed how high I had to climb to
achieve that arrival altitude.

L over D is no easier to say than FPA. In fact it's one syllable
longer.

Andy (GY)

On Aug 23, 8:17*am, akiley wrote:
On Aug 23, 12:32*am, Darryl Ramm wrote:



On Aug 22, 7:10*pm, akiley wrote:
[snip]
Required L/D to target tells you what you need to achieve. It makes no
sense to fold wind into that, its just the distance divided by the
difference in height. Achieved L/D tells you what you are getting
obviously with wind affects as well, all without any assumptions about
polars, mass, bugs, or wind. That is the beauty of working with L/D
required and achieved.

This is a good point, but since wind isn't factored into required L/D,
you don't know what your achieved L/D is unless you turn around and
head back to the airport. *But it does seem to be safer and more
straight forward. *And I suppose since you are always aware of the
winds, you can make a fairly accurate guess as to what you achieved L/
D is likely to be. *If it's a straight headwind home at 5 knots, I
could just mentally modify what I expect to achieve.

Again the L/D required is a statement of fact (as long as your
altitude and the destination elevation are accurate. It's beautiful
for it's simplicity. It also relates directly to the glide angle (OK
Andy) and you should develop eyeball skill for that over time.

Now its clearer where you are at, I would recommend at this stage of
your flying, where you are just taking steps away from the home
gliderport, to use the PDA calculated arrival height (above a safety
margin, with bugs factored -- in SeeYou Mobile if you want higher bugs
than 30% then you will need to modify the polar parameters). And that
arrival height will give you a safety margin that you can probalby
best relate to.

I suspect what John is talking about with Mc is too much for a new,
pre-XC pilot, it is probalby easier to work with what is likely to be
a more intuitive understanding of arrival height to start with. Then
I'd add the L/D metrics to get a feel for those (esp. as a sanity
check since they don't rely on computations) then maybe move up to
thinking more about the Mc stuff as you worry about XC performance and
develop a feel for what a Mc margin means.

How you are getting the wind calculation? As mentioned by others if
you don't have reliable wind data then worrying about factoring in
wind data may be irrelevant or worse. If you are hand entering wind
data that you trust that is great (all soaring software users knew how
to do that or at least how to reset suspect overly optimistic winds).

What Mc do you actually fly at? And how do you do this? For starting
off I would leave the Mc you actually fly at (i.e. your average
airspeed) low and don't try chasing the speed to fly (STF). Even if
you have a real STF computer that can calculate a reasonable STF there
are technical arguments about why its not as efficient as it might be,
but for a newer XC pilot overly chasing the STF is just a distraction
and especially may make it hard to find lift, estimate whether to take
a thermal, find blue convergence/energy lines etc. And don't try to
closely follow the STF Navbox on SeeYou Mobile, it just cannot
calculate that anything that useful from altitude (GPS or pressure)
data.

---

The PDA software is just a help, like other say, its a moving
sectional chart and a way to reduce calculations you would otherwise
do in your head, with a glide ruler or on a prayer wheel. Often a good
exercise to construct a glide ruler and hand draw some glide circles
on a sectional with different winds factored in. Doing that by hand
for where you fly should gives you a good feel for wind effects -- see
the ruler template at http://www.gliderbooks.com/downloads.html and
instructions in his Glider Pilot's Handbook of Aeronautical Knowledge
book. Just like getting a sectional and marking down landing options
also helps, "flying" to those in Google Earth or visiting them in a
power aircraft really help but there is something beautifully simple
and very tactile about pen and paper that seems to help people really
get a fell for things. GlidePlan (http://www.glideplan.com) can also
do this for you on a Mac or PC but doing by hand at least once is
probably a good idea.

But even better than asking on r.a.s. can you find a local
accomplished XC pilot(s) who can mentor you on all this stuff?

Yes, my club has several and I'm talking to them too. *It's also funny
about gadgets in aircraft. *My feeling is learn to use the autopilot
and whenever you can, learn navigators using simulators. *Half
learning electronics is the most dangerous in my opinion. *I enjoy
navigators, but I'm strict as to when and how to use them.

Compared to power XC flying you are much more dependent on all the
subtleties happening outside the glider, so try to get the PDA into
the background and focus on finding lift, working thermals, finding
energy lines, flying smoothly and efficiently. You can learn a lot
just flying triangles around a local gliderport and just keep stepping
up what you do. There are lots of ways to skin a cat, but if somebody
skilled is willing to mentor you it is worth following the way they do
things so you can more easily learn from them.

If you know of any bugs in SeeYou Mobile, please report then to
Naviter.

Darryl

On Aug 23, 12:54*pm, Andy wrote:
On Aug 23, 9:38*am, T8 wrote:

That goes back to the 50s, very likely. *Certainly, it was used on
circular slide rule calculators of the 60s (referenced in Sunship Game
and articles of the era). *L/D *is* a little easier to say than "the
inverse of the tangent of the flight path angle", even if it *is*
extremely sloppy shorthand.

*I've been flying gliders long enough to have used prayer wheels as my
only flight computer. I never used one to compute my required L/D, and
don't know any way to use one to compute achieved L/D. *Then, and now,
I considered arrival altitude and computed how high I had to climb to
achieve that arrival altitude.

L over D is no easier to say than FPA. *In fact it's one syllable
longer.

Andy (GY)

40:1 seems more intuitive to me than 1.432 degrees, even if it isn't
strictly speaking an angle. I do prefer the term "glide angle" to L/
D.

I've never used a slide rule calculator in the cockpit. I started XC
soaring in the "early electronic" era, but before I could afford such
exotica, I simply used circles on the map, 5 statute miles per 1000'
plus pattern allowance. I always got home. Of course, if the weather
was in any way bizarre, I stayed above my final glide numbers by a
comfortable margin.

IIRC, George Moffatt had a design that incorporated various "glide
angles", expressed as 40:1, 35:1, 30:1 etc. I am uncertain of the
details.

-T8

On Aug 23, 9:00*am, John Cochrane
wrote:
Well, just for a contrary opinion, I disagree with Darryl and Kirk. Mc
setting is the right set of units for everything in soaring.

If you must think about glide angles, the right units are D/L not L/
D. *L/D goes through infinity when you run in to lift. D/L (feet per
mile, meters per kilometer) does not. If you gain 200 feet in lift vs.
lose 200 feet in lift, L/D shows radically different changes, D/L does
not.

The "safety profile" for making it to a goal with constant (say 99%)
probability follows a roughly square root function of distance.
(Square root follows if lift/sink are independent over distance) *Most
of us approximate this with a relatively high Mc setting (3-4) plus a
reserve altitude.

Smoother conditions -- less lift or sink -- means less uncertainty
about your glide. So, paradoxically, you can use more aggressive
safety settings if there is no lift around, because then there is no
sink around. Strong lift mans strong sink; half chance of escaping in
10 knots, half chance of hitting the dirt in 10 knot sink. Therefore,
use a higher Mc setting and higher reserve altitude with stronger lift/
sink or general uncertainty.

To fly a safety glide you want to have the glide computer at a high Mc
setting, but fly slowly and accept weaker lift. Many pilots disconnect
the glide computer from the vario for this reason. Well, I do.
Instrument makers should recognize this difference and make it easier
to have a different Mc for glide than vario.

Wind is irrelevant here, with one exception. As you lower the Mc
setting heading upwind, you will discover a point at which lower Mc
setttings seem to make it worse. This is a featuer not a bug. The best
glide in wind occurs at a higher Mc setting. don't fly slower than
that, don't take weaker thermals than that, or you wont get home

John Cochrane

John, as usual, is correct, but in this case it's a bit of apples and
oranges. Darryl and I use "L/D" as a shorthand for a quick analysis
of the flight path angle required to make a destination. It's totally
Mc independent, and is easy to interpret at a glance on a moving map.
For accurate final glides in competition mode, where more accuracy is
desired, using Mc based on the last climb plus winds is the way to go
(and why I use my SN10 and not SeeYouM for final glides), but I also
crosscheck the two for a sanity check.

Always nice to have two opinions in the cockpit - the trick is to
decide which one is right!

Cheers,

Kirk

Thanks Darryl,

How you are getting the wind calculation? As mentioned by others if
you don't have reliable wind data then worrying about factoring in
wind data may be irrelevant or worse. If you are hand entering wind
data that you trust that is great (all soaring software users knew how
to do that or at least how to reset suspect overly optimistic winds).

I don't think SeeYou does very well with winds. This is what I've
experienced and read in other posts. I get winds aloft from several
sources/stations during my home briefing. I enter those directly into
SeeYou and always check them before I do my MC required to target.

What Mc do you actually fly at? And how do you do this? For starting
off I would leave the Mc you actually fly at (i.e. your average
airspeed) low and don't try chasing the speed to fly (STF). Even if
you have a real STF computer that can calculate a reasonable STF there
are technical arguments about why its not as efficient as it might be,
but for a newer XC pilot overly chasing the STF is just a distraction
and especially may make it hard to find lift, estimate whether to take
a thermal, find blue convergence/energy lines etc. And don't try to
closely follow the STF Navbox on SeeYou Mobile, it just cannot
calculate that anything that useful from altitude (GPS or pressure)
data.

My SeeYou is not plugged into anything so it's all GPS. To be honest,
I use it mostly to analyze me flight when I get home. I look at it in
flight to backup a possible creepy feeling because I look a bit low
for my liking. I fly MC zero generally because I'm flying local
working on my thermal technique. If I encounter sink I speed up maybe
10 or 15 knots depending on how large the sink area is. If I have a
headwind I'm trying to penetrate, I will speed up somewhat as well. I
guess what I really want to be sure of is NOT landing out.

The PDA software is just a help, like other say, its a moving
sectional chart and a way to reduce calculations you would otherwise
do in your head, with a glide ruler or on a prayer wheel. Often a good
exercise to construct a glide ruler and hand draw some glide circles
on a sectional with different winds factored in. Doing that by hand
for where you fly should gives you a good feel for wind effects -- see
the ruler template athttp://www.gliderbooks.com/downloads.htmland
instructions in his Glider Pilot's Handbook of Aeronautical Knowledge
book. Just like getting a sectional and marking down landing options
also helps, "flying" to those in Google Earth or visiting them in a
power aircraft really help but there is something beautifully simple
and very tactile about pen and paper that seems to help people really
get a fell for things. GlidePlan (http://www.glideplan.com) can also
do this for you on a Mac or PC but doing by hand at least once is
probably a good idea.

Great ideas. I'm a photographer and made a "Stocker" whizz wheel
using notes from Reichmann's cross country book. Put it together by
scanning a sectional and layering it in Photoshop. That thing turns
heads at the glider club. I've also computed range rings and put
layered them over a sectional offset for winds. That's a time
consuming math project for me anyway, especially if you have a safety
altitude figured in. Anyway, I love the old fashioned approaches and
used them as often as the electronics. I also flew a little Cessna
152 into all the local fields that I might land with gliders.

But even better than asking on r.a.s. can you find a local
accomplished XC pilot(s) who can mentor you on all this stuff?

Yes, my club has several and I'm talking to them too. *It's also funny
about gadgets in aircraft. *My feeling is learn to use the autopilot
and whenever you can, learn navigators using simulators. *Half
learning electronics is the most dangerous in my opinion. *I enjoy
navigators, but I'm strict as to when and how to use them.

Compared to power XC flying you are much more dependent on all the
subtleties happening outside the glider, so try to get the PDA into
the background and focus on finding lift, working thermals, finding
energy lines, flying smoothly and efficiently. You can learn a lot
just flying triangles around a local gliderport and just keep stepping
up what you do. There are lots of ways to skin a cat, but if somebody
skilled is willing to mentor you it is worth following the way they do
things so you can more easily learn from them.

I'm lucky, I have a friend that talked me into soaring last spring.
He has a Ventus 2CX and on any reasonable day, he and his buddies do
250 mile round trips landing at dinner time. Then our club has
several instructors that seem to be very good.

If you know of any bugs in SeeYou Mobile, please report then to
Naviter.

Have done that.


Darryl

On Aug 23, 8:40*am, akiley wrote:
On Aug 23, 10:00*am, John Cochrane
wrote:





Well, just for a contrary opinion, I disagree with Darryl and Kirk. Mc
setting is the right set of units for everything in soaring.

If you must think about glide angles, the right units are D/L not L/
D. *L/D goes through infinity when you run in to lift. D/L (feet per
mile, meters per kilometer) does not. If you gain 200 feet in lift vs.
lose 200 feet in lift, L/D shows radically different changes, D/L does
not.

The "safety profile" for making it to a goal with constant (say 99%)
probability follows a roughly square root function of distance.
(Square root follows if lift/sink are independent over distance) *Most
of us approximate this with a relatively high Mc setting (3-4) plus a
reserve altitude.

Smoother conditions -- less lift or sink -- means less uncertainty
about your glide. So, paradoxically, you can use more aggressive
safety settings if there is no lift around, because then there is no
sink around. Strong lift mans strong sink; half chance of escaping in
10 knots, half chance of hitting the dirt in 10 knot sink. Therefore,
use a higher Mc setting and higher reserve altitude with stronger lift/
sink or general uncertainty.

To fly a safety glide you want to have the glide computer at a high Mc
setting, but fly slowly and accept weaker lift. Many pilots disconnect
the glide computer from the vario for this reason. Well, I do.
Instrument makers should recognize this difference and make it easier
to have a different Mc for glide than vario.

Wind is irrelevant here, with one exception. As you lower the Mc
setting heading upwind, you will discover a point at which lower Mc
setttings seem to make it worse. This is a featuer not a bug. The best
glide in wind occurs at a higher Mc setting. don't fly slower than
that, don't take weaker thermals than that, or you wont get home

John Cochrane

I did a little calculation for a standard Cirrus with no wind. *I did
this by using SeeYou mobile in simulator mode. *I did manual math for
angle and feet per NM. *Here are a few numbers. *They might not format
correctly.

Required L/D * * 38, * *28, * 20, * *15, * 10
Required MC * * * 0, * *3.5, *7.4, * 12, * 22
glide angle deg *1.7, * 2.2, *2.9, * *3.8, *5.7
feet per NM * * * *158, *215, 300, *400, *600

Then I added a big headwind. *Required L/D stays the same, but MC
corrects for winds. *... akiley

Okay, for eyeball calculations this makes sense. I normally use miles
per thousand plus 1000' arrival (plus field elevation) to estimate if
I'm high or low. I printed a table that showed how many miles I could
get per 1,000' as a function of Mc (0, 2, 4, 6, 8, 10) and wind (-25
to +25 mph).

If you are just starting to venture out from home and you are in the
US, consider getting a copy of GlidePlan software. It will allow you
to print minimum altitude contours directly onto a sectional chart
(you can even print alternate maps for different wind conditions).
Then all you need to do is figure out where you are on the chart and
it will tell you how high you need to be. Pretty cool. www.glideplan.com

Andy
9B

On Aug 23, 11:56*am, Joseph Kiley wrote:
Thanks Darryl,

How you are getting the wind calculation? As mentioned by others if
you don't have reliable wind data then worrying about factoring in
wind data may be irrelevant or worse. If you are hand entering wind
data that you trust that is great (all soaring software users knew how
to do that or at least how to reset suspect overly optimistic winds).

I don't think SeeYou does very well with winds. *This is what I've
experienced and read in other posts. * I get winds aloft from several
sources/stations during my home briefing. *I enter those directly into
SeeYou and always check them before I do my MC required to target.

SeeYou Mobile does *very* well with wind if it has the data to work
from. With just a GPS input all SeeYou can do is effectively look at
thermal circle drift, that depends on how well you thermal, how long/
far since the last thermal, and lots of other things. When connected
to an external flight computer (like a C302) SeeYou Mobile will use
TAS data from the flight computer and relatively small change in
heading to also calculate winds and it tends to a much better job
overall. This is not just a SeeYou Mobile thing, other devices limited
to just GPS input will often show the same problems. However if you
are in doubt, clobber the wind settings and take a few good clean
circles with any of these devices they should produce a reasonable
idea of the wind. Search r.a.s. on Google for past discussion on
SeeYou Mobile wind calculations by myself and other authors.

What Mc do you actually fly at? And how do you do this? For starting
off I would leave the Mc you actually fly at (i.e. your average
airspeed) low and don't try chasing the speed to fly (STF). Even if
you have a real STF computer that can calculate a reasonable STF there
are technical arguments about why its not as efficient as it might be,
but for a newer XC pilot overly chasing the STF is just a distraction
and especially may make it hard to find lift, estimate whether to take
a thermal, find blue convergence/energy lines etc. And don't try to
closely follow the STF Navbox on SeeYou Mobile, it just cannot
calculate that anything that useful from altitude (GPS or pressure)
data.

My SeeYou is not plugged into anything so it's all GPS. *To be honest,
I use it mostly to analyze me flight when I get home. *I look at it in
flight to backup a possible creepy feeling because I look a bit low
for my liking. *I fly MC zero generally because I'm flying local
working on my thermal technique. *If I encounter sink I speed up maybe
10 or 15 knots depending on how large the sink area is. *If I have a
headwind I'm trying to penetrate, I will speed up somewhat as well. *I
guess what I really want to be sure of is NOT landing out.

For typical days where there is lift available and as you become more
comfortable with thermaling I would encourage you to try to start with
Mc near 1. Mc == 0 means you really are in desperation mode and don't
really plan to go anywhere. See the discussion in Reichman about this.
Mc=0 quickly becomes a kind of boat anchor dragging on you. If you are
dialing the Mc into a flight computer (or STF ring on a winter vario)
it also starts giving you a feel for how excess Mc helps you if you
run into worse conditions than you expect. You can increase the Mc
setting you fly at up from there as you gain confidence, but dont' go
crazy with it. A rule of thumb often used especially for new XC folks
it to set the Mc conservatively at 1/2 to 1/3 of what you think your
next average climb will be - and even then its just to give you an
idea of average speed to fly, don't go chasing it. Sounds like you
have a good approach as is. The last thermal average climb stats in
SeeYou Mobile can be interesting to check, it will often be much less
than you think, and even then it often misses time wasted mucking
around trying to find lift.

BTW details of wind effects and Mc may not be obvious, search for past
r.a.s. postings by John Cochrane and others on this.

[snip]

Darryl

How I use SeeYou mobile for final glides (when I get a chance to do
them):

With my chosen arrival altitude and my/or the computer's best
estimates of the wind set, then in the likely last thermal I use the
usual McCready/Cochrane considerations plus my personal wimp factor
to decide when to leave the thermal and to judge an appropriate
starting McCready setting. This is just to get in the ballpark of
when to start the glide.

Next, as I start the glide I take note of the required LD (SYM
calculates this to the arrival altitude) and as long as this number
stays the same or gets smaller then I am on glide or can speed up
respectively. If the number gets bigger I have to slow down or
climb. The required LD is wrongly named in SYM - it is actually the
glide angle with respect to the ground. All glide angles converge at
the destination so any glide angle that I can keep constant will
bring me to home at my arrival reserve altitude. This is independent
of any errors in wind/polar/bugs. I never have understood why most
glide calculators seem to work on altitude difference displays
resulting glides vertically parallel to the starting glide angle when
proportionately less altitude difference is required as one gets
closer to the destination.

(I don't find that the method recommended in the SYM manual of
comparing Achieved LD with Required LD is any good because the
Achieved LD varies so much in a much shorter time scale.)

John Galloway

On Aug 22, 8:10*pm, akiley wrote:
Hi All,

I'm aware of and use the math formula to get my rental Cirrus back to
home base, but I like to back it up with SeeYou mobile. *I know it's
recommended to use required LD to target making sure you have entered
a correct polar and safety altitude. *But this doesn't account for
winds does it? *If you are flying away from your target wondering how
far you can safely fly, you can't depend on required LD because big
headwinds can make this number useless. *As an example, I notice I've
got 25LD required to my home base. *I turn around and because of the
headwinds, I can only make 18LC. *Outlanding anyone.

I'm curious about MC required to target. *Wouldn't that be better to
use if you make sure all data is correct such as polar, winds, safety
altitude and make sure the correct target is activated. *This way, I
can wander away from my home field and I know if my MC doesn't fall
below about say 7 (which plays out to about 20 LD in no wind) I am
fairly assured of making it and that this MC will be wind aware. *Of
course it can't know about hitting lots of sink, but it seems a better
way for my type of non task, local soaring.

Before I finish, I would like to note that the MC to target NavBox in
SeeYouM doesn't always update very quickly if you change the winds
aloft manually. *For this problem, I scroll the MC value untill the
little glide slope type indicater on the left side of SeeYou centers,
then compare that MC to the required MC NavBox.

akiley

I look at "altitude required", with either an auto or manually set MC,
depending on the time of day. For a final glide, I climb to the
altitude I feel is appropriate for the glide home and then adjust my
speed, depending on the air mass I am gliding through.