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.