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
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