Glider computers - what's important?

Eric Greenwell wrote:

Bill Daniels wrote:

A "glide footprint" shows clearly how to cross a mountain range since it
computes glide distance in all directions. The courseline may happen to
cross the range at a high peak so a list type display will show the goal as
unreachable but the "glide footprint" will show that a slight change in
course will easily clear the terrain.

I can use that feature!

Use GPS_LOG WinCE. It has it.

Henryk Birecki

Hi,

Use GPS_LOG WinCE.

I do.

It has it.

Can you enlighten me on on how the footprint is computed?

Just by looking in a few directions, determining the "points of impact" in
those directions and connecting them? Or is it more complicated?

Would a single mountain on a vast plane look like an island in the glide
footprint?

Ciao, MM
--
Marian Aldenhövel, Rosenhain 23, 53123 Bonn
http://www.marian-aldenhoevel.de
"Success is the happy feeling you get between the time you
do something and the time you tell a woman what you did."

"Marian Aldenhövel" wrote in message
...
Hi,

Use GPS_LOG WinCE.

I do.

It has it.

Can you enlighten me on on how the footprint is computed?

Just by looking in a few directions, determining the "points of impact" in
those directions and connecting them? Or is it more complicated?

It simply looks in 48 directions around the compass and computes the maximum
glide in each direction considering wind, polar, McCready, balast and bugs.
It terminates each glide at the 'safety altitude' you have selected. It
then connects these glide termination points with a line that forms a 48
sided polygon. It does this about once a minute.

Would a single mountain on a vast plane look like an island in the glide
footprint?

A single isolated mountain on a plain would be a "notch" in the polygon, not
an island. If you know the terrain, it's obvious that you can glide around
the mountain and land in the notch on the other side.

Bill Daniels

On Mar 12, 5:08 am, "Bill Daniels" bildan@comcast-dot-net wrote:

It simply looks in 48 directions around the compass and computes the maximum
glide in each direction considering wind, polar, McCready, balast and bugs.

Plase confirm this function uses current MC. I browsed the on-line
manual and I thought it said ZERO MC which is not the implementation I
would want.

Is anyone using the terrain functions on an Aero 1550? If so is
performance adequate?

thanks

Andy

"Andy" wrote:

On Mar 12, 5:08 am, "Bill Daniels" bildan@comcast-dot-net wrote:

It simply looks in 48 directions around the compass and computes the maximum
glide in each direction considering wind, polar, McCready, balast and bugs.


Yes it does. 48 seemed like a good compromise between computation time
and "precision". This could be made a user input parameter in future
editions if there is a general concensus that it would be useful.

Plase confirm this function uses current MC. I browsed the on-line
manual and I thought it said ZERO MC which is not the implementation I
would want.

You are right about documentation. I will need to check in the code.
It may well be ZERO MC as it is a "safety" feature. If you are looking
for a safe place to land you want to fly at best glide angle, not best
time. Anyone would like to comment?


Is anyone using the terrain functions on an Aero 1550? If so is
performance adequate?


I am. I have not seen any problems so far, and I usually do fly in the
mountains.

Henryk Birecki

Henryk Birecki wrote:


Plase confirm this function uses current MC. I browsed the on-line
manual and I thought it said ZERO MC which is not the implementation I
would want.

You are right about documentation. I will need to check in the code.
It may well be ZERO MC as it is a "safety" feature. If you are looking
for a safe place to land you want to fly at best glide angle, not best
time. Anyone would like to comment?

A MC = 0 glide path is very shallow, making it sensitive to small errors
in the assumptions - headwind, bugs, sink, polar. It is very likely to
go wrong. A MC = 4 glide path is much steeper, and by flying it at a MC
= 1 (for example), you have a lot of extra altitude to handle the same
problems. As you point out, if you are trying to get to some place
safely, there's no need to rush!

I would never trust my safety to a MC = 0 glide path, instead, I
routinely use MC = 4. This has proven reliable (but not 100%) over 30
years of soaring in several different gliders.

On days with wave, in the mountains, or gliding over poor landing areas,
I'll use MC = 5, possibly higher, or raise my arrival altitude setting.

It is possible to use an MC = 0 safely if you set a very high "arrival
altitude". To have the same margins I get with MC = 4 and a 1000' AGL
arrival, I estimate it would have to be at least 2000' AGL. Perhaps
someone can comment on the relative merits of a higher MC with a lower
arrival altitude, versus doing the reverse.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly
* "Transponders in Sailplanes" http://tinyurl.com/y739x4
* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

Thanks Eric,

The way I read your post is that you are using MC setting as a safety
margin thing to avoid false hopes. GPS_LOG uses pattern altitude to
accomplish that. On the other hand it just says that different people
have different preferences. Since philosophy behind GPS_LOG is to
allow users to configure it as much as possible to their preferences
rather than me telling them what they should use, I will add a YABO
(Yet Another Bloody Option) in next release of the program.

And yes, code says program is currently using zero MC.

Henryk Birecki

Eric Greenwell wrote:

Henryk Birecki wrote:


Plase confirm this function uses current MC. I browsed the on-line
manual and I thought it said ZERO MC which is not the implementation I
would want.

You are right about documentation. I will need to check in the code.
It may well be ZERO MC as it is a "safety" feature. If you are looking
for a safe place to land you want to fly at best glide angle, not best
time. Anyone would like to comment?

A MC = 0 glide path is very shallow, making it sensitive to small errors
in the assumptions - headwind, bugs, sink, polar. It is very likely to
go wrong. A MC = 4 glide path is much steeper, and by flying it at a MC
= 1 (for example), you have a lot of extra altitude to handle the same
problems. As you point out, if you are trying to get to some place
safely, there's no need to rush!

I would never trust my safety to a MC = 0 glide path, instead, I
routinely use MC = 4. This has proven reliable (but not 100%) over 30
years of soaring in several different gliders.

On days with wave, in the mountains, or gliding over poor landing areas,
I'll use MC = 5, possibly higher, or raise my arrival altitude setting.

It is possible to use an MC = 0 safely if you set a very high "arrival
altitude". To have the same margins I get with MC = 4 and a 1000' AGL
arrival, I estimate it would have to be at least 2000' AGL. Perhaps
someone can comment on the relative merits of a higher MC with a lower
arrival altitude, versus doing the reverse.

Hi Eric,

I agree that higher MacCready settings are safer. I have found that many
glider pilot find that point difficult to get their heads around - probably
because using a higher MC causes your glide computer to show that you need
more altitude, and because you will be flying faster (which seems less
conservative) if you follow the speed director.

But you are correct that it gives you a less shallow glide with more
options. Also, if you slow down and fly at best L/D you should do much
better than the glider computer thinks you can do.

I never fly with my MacCready ring or speed director set to zero. I think
that is unsafe.

Here in Minnesota I don't use a MacCready of 4 though. I use about 1/2 to
3/4 of the value of my actual measure climb rates in thermals.

I suppose that higher arrival altitudes can be used to do the same thing -
increase safety.

Good Soaring,

Paul Remde

"Eric Greenwell" wrote in message
news:sYoJh.9072$S06.356@trndny08...
Henryk Birecki wrote:


Plase confirm this function uses current MC. I browsed the on-line
manual and I thought it said ZERO MC which is not the implementation I
would want.

You are right about documentation. I will need to check in the code.
It may well be ZERO MC as it is a "safety" feature. If you are looking
for a safe place to land you want to fly at best glide angle, not best
time. Anyone would like to comment?

A MC = 0 glide path is very shallow, making it sensitive to small errors
in the assumptions - headwind, bugs, sink, polar. It is very likely to go
wrong. A MC = 4 glide path is much steeper, and by flying it at a MC = 1
(for example), you have a lot of extra altitude to handle the same
problems. As you point out, if you are trying to get to some place safely,
there's no need to rush!

I would never trust my safety to a MC = 0 glide path, instead, I routinely
use MC = 4. This has proven reliable (but not 100%) over 30 years of
soaring in several different gliders.

On days with wave, in the mountains, or gliding over poor landing areas,
I'll use MC = 5, possibly higher, or raise my arrival altitude setting.

It is possible to use an MC = 0 safely if you set a very high "arrival
altitude". To have the same margins I get with MC = 4 and a 1000' AGL
arrival, I estimate it would have to be at least 2000' AGL. Perhaps
someone can comment on the relative merits of a higher MC with a lower
arrival altitude, versus doing the reverse.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly
* "Transponders in Sailplanes" http://tinyurl.com/y739x4
* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

"Andy" wrote:

On Mar 12, 5:08 am, "Bill Daniels" bildan@comcast-dot-net wrote:

Plase confirm this function uses current MC. I browsed the on-line
manual and I thought it said ZERO MC which is not the implementation I
would want.

I forgot to add in my previous post: If you really want to have "real
time" feedback in GPS_LOG for whether you can clear a mountain range
on course, you would not be looking at the GLIDE footprint, but at
forward looking terrain plot. This gives you glide path at your
current speed, wind... plotted with the ground profile. Got me through
several passes that I would have never attempted without that
information.

Henryk Birecki