Pirker Final Glide Theory

At 10:14 12 February 2013, Naviter Info wrote:
When you're doing Auto MC please mind the MC
theory:

If you hit sink on the final glide the required MC
value will go down.
Acco=
rding to AutoMC you would be advised to fly slower.
**Slower through
sink**=
??

I don't quite follow this.

Surely the required McCready (McReady?) setting is a
function of height, wind and distance to run.

So if you hit sink and lose altitude of course your
required McCready setting will go down. But your
speed at that setting will still be what is appropriate
for that setting in that amount of sink.

You could of course keep your nerve and leave the
McCready setting where it is- if you expect to go
through lift later this is usually OK- it's a judgement
call. If you do this and don't go through any lift later
you're in a field.

The only way to avoid having to slow down at all is
not to fly through sink.

True. But while you're in sink you need to speed up. At least until you are flying the optimal speed for MC=0 for that sink. The AutoMC suggests you to slow down which is not ok any way you look at it.

Andrej Kolar
--
glider pilots use
http://www.Naviter.com

On Tuesday, February 12, 2013 11:29:03 AM UTC+1, Richard Brisbourne wrote:
At 10:14 12 February 2013, Naviter Info wrote:

When you're doing Auto MC please mind the MC

theory:



If you hit sink on the final glide the required MC

value will go down.

Acco=

rding to AutoMC you would be advised to fly slower.

**Slower through

sink**=

??



I don't quite follow this.



Surely the required McCready (McReady?) setting is a

function of height, wind and distance to run.



So if you hit sink and lose altitude of course your

required McCready setting will go down. But your

speed at that setting will still be what is appropriate

for that setting in that amount of sink.



You could of course keep your nerve and leave the

McCready setting where it is- if you expect to go

through lift later this is usually OK- it's a judgement

call. If you do this and don't go through any lift later

you're in a field.

If you have lost height in a sink zone, your speed will need to be Lower
AFTER the sink zone.

What you do in the sink is up to you (I suppose speed up.)


At 12:09 12 February 2013, Naviter Info wrote:
True. But while you're in sink you need to speed up. At least until you
are
flying the optimal speed for MC=0 for that sink. The AutoMC suggests you
to
slow down which is not ok any way you look at it.

Andrej Kolar
--
glider pilots use
http://www.Naviter.com

At 14:25 12 February 2013, Peter Higgs wrote:
If you have lost height in a sink zone, your speed
will need to be Lowe
AFTER the sink zone.

What you do in the sink is up to you (I suppose
speed up.)


At 12:09 12 February 2013, Naviter Info wrote:
True. But while you're in sink you need to speed
up. At least until yo
are
flying the optimal speed for MC=0 for that sink.
The AutoMC suggests yo
to
slow down which is not ok any way you look at it.

Andrej Kolar
--
glider pilots use
http://www.Naviter.com

Either you're wrong or we have a different
interpretation of what we mean by auto MC.

The theory we are talking about (be it Pirker, Stocker
or whoever), calculates a McCready setting that will
give you the optimum glide path to get in, given
either "dead air" or an averaged amount of lift and
sink to fly through.

Auto MC as I understand the term simply calculates
that notional MC setting for you- it doesn't substitute
for the MC ring, flight director, whatever you use, just
tells you where to set it (or possibly effectively sets it
for you).

If you hit sink, the Auto MC value will go down, as
you've dropped below the predicted glide path.

If you aren't expecting to go through any further lift
to put you back up again, then the correct speed to
fly will be the speed commanded _for the sink rate
you are in_, at the new McCready setting. This may
or may not be faster than you were going before you
hit the sink- either way it's the optimum speed.

The only time you will fly at the MC=0 speed
through the sink will be if the calculation, based on
height and distance, says you can just reach your
goal at MC=0; I'd suggest if that is the case then zero
is indeed the best setting unless you are confident of
finding another thermal and therefore aren't on final
glide any more. It's still the MC speed for the sink
you are in, so may still be fast.

In the extreme case, if the auto MC reading winds
down to zero, but you ignore it and continue to fly on
a high MC setting you will definitely put yourself
below glide path.

Of course if you are still confident of flying through lift
before reaching the goal, by all means keep the
speed on. As I said, it's a judgement call.

My point of view on how AutoMC is actually working on LK.
1. Computer tell you that you can make it to the finish from the current
position and altitude, wind considered, eventually considering also your
current IAS, as an extra altitude if you pull up. This last extra altitude
is optional and by default disabled, to leave some margins.
2. Computer tell you that you shall arrive 0 meters (at worst) over the
desired destination's altitude with a certain MC setting, say 1.2 (I use
m/s).
It considers ballast. And if you dump ballast and it takes 3 minutes to
do it, during those 3 minutes it will shift the polar for wing loading,
adjusting all parameters.
This is the same as in xcsoar .
3. You set the desired MC on your speed to fly instrument, or this value is
sent automatically to it eventually, and you start following the
pullup-pushdown commands seconding the airmass you travel in.
4. If the airmass is equally distributed in sinks and lift, you will be more
or less flying at the desired MC.
5. If unfortunately you meet a large sink area, you will be commanded to
speed up of course, following the STF indicator on the vario, which is still
relative to the desired MC.
6. After some time, your average airspeed will not be anymore the one
relative to the original MC, and of course the glidepath and the arrival
altitude will change, even drastically, to a worst prediction.
7. In LK we use eMC, Equivalent MC , telling you what is the real MC you are
flying it, no matter what you think you are doing.
This eMC (widely used by paragliders, who cannot play with their
instruments too much, not to mention hangglider pilots) can also be assigned
automatically to MC, thus resulting in an accurate prediction based on what
you are actually doing, concentrated on the airmass and not on the
instrument.
In still air, if you fly at MC 2 following the speed to fly indicator on
your vario, the eMC will read 2, precisely.
In sink air, if you try to fly at MC 1.2 but it has been some time since
you have been speeding up to pass a neverending sink area, you may read eMC
3 !

8. You decide what to do. Computer tell you what happen if you start flying
again at the proper STF relative to desired MC 1.2, what happen if you keep
flying like you do, at a real MC 3, and what if you slow down to MC 0.
You want to make it over the finish, not below. Pilot can judge if he can
speed up, slow down, or stop circling as soon as possible.
No computer can estimate an airmass 2 km away, guessing if it is sinking or
raising air.
What we can do, is give clear informations about different scenarios, and
the Equivalent MC helps a lot on this, because otherwise - like it currently
happen on most flight computers, you still keep reading MC set to 1.2, while
your arrival altitude gets lower and lower, and you have no clue on what you
are actually doing.
If you fly using MC, you ought to know what MC you are really flying with,
no matter what you hope to have been using so far.

EqMC stand to MC like CurrentGlide Ratio stand to Required Glide Ratio to
get to a destination.
The difference is that the latter does not consider wind, ballast, extra
speed.

paolo






"Richard Brisbourne" wrote in message
...

At 14:25 12 February 2013, Peter Higgs wrote:
If you have lost height in a sink zone, your speed
will need to be Lowe
AFTER the sink zone.

What you do in the sink is up to you (I suppose
speed up.)


At 12:09 12 February 2013, Naviter Info wrote:
True. But while you're in sink you need to speed
up. At least until yo
are
flying the optimal speed for MC=0 for that sink.
The AutoMC suggests yo
to
slow down which is not ok any way you look at it.

Andrej Kolar
--
glider pilots use
http://www.Naviter.com

Either you're wrong or we have a different
interpretation of what we mean by auto MC.

The theory we are talking about (be it Pirker, Stocker
or whoever), calculates a McCready setting that will
give you the optimum glide path to get in, given
either "dead air" or an averaged amount of lift and
sink to fly through.

Auto MC as I understand the term simply calculates
that notional MC setting for you- it doesn't substitute
for the MC ring, flight director, whatever you use, just
tells you where to set it (or possibly effectively sets it
for you).

If you hit sink, the Auto MC value will go down, as
you've dropped below the predicted glide path.

If you aren't expecting to go through any further lift
to put you back up again, then the correct speed to
fly will be the speed commanded _for the sink rate
you are in_, at the new McCready setting. This may
or may not be faster than you were going before you
hit the sink- either way it's the optimum speed.

The only time you will fly at the MC=0 speed
through the sink will be if the calculation, based on
height and distance, says you can just reach your
goal at MC=0; I'd suggest if that is the case then zero
is indeed the best setting unless you are confident of
finding another thermal and therefore aren't on final
glide any more. It's still the MC speed for the sink
you are in, so may still be fast.

In the extreme case, if the auto MC reading winds
down to zero, but you ignore it and continue to fly on
a high MC setting you will definitely put yourself
below glide path.

Of course if you are still confident of flying through lift
before reaching the goal, by all means keep the
speed on. As I said, it's a judgement call.

On Tuesday, February 12, 2013 11:19:06 AM UTC-5, Richard Brisbourne wrote:
At 14:25 12 February 2013, Peter Higgs wrote:

If you have lost height in a sink zone, your speed

will need to be Lowe

AFTER the sink zone.



What you do in the sink is up to you (I suppose

speed up.)





At 12:09 12 February 2013, Naviter Info wrote:

True. But while you're in sink you need to speed

up. At least until yo

are

flying the optimal speed for MC=0 for that sink.

The AutoMC suggests yo

to

slow down which is not ok any way you look at it.



Andrej Kolar

--

glider pilots use

http://www.Naviter.com



Either you're wrong or we have a different

interpretation of what we mean by auto MC.



The theory we are talking about (be it Pirker, Stocker

or whoever), calculates a McCready setting that will

give you the optimum glide path to get in, given

either "dead air" or an averaged amount of lift and

sink to fly through.



Auto MC as I understand the term simply calculates

that notional MC setting for you- it doesn't substitute

for the MC ring, flight director, whatever you use, just

tells you where to set it (or possibly effectively sets it

for you).



If you hit sink, the Auto MC value will go down, as

you've dropped below the predicted glide path.



If you aren't expecting to go through any further lift

to put you back up again, then the correct speed to

fly will be the speed commanded _for the sink rate

you are in_, at the new McCready setting. This may

or may not be faster than you were going before you

hit the sink- either way it's the optimum speed.



The only time you will fly at the MC=0 speed

through the sink will be if the calculation, based on

height and distance, says you can just reach your

goal at MC=0; I'd suggest if that is the case then zero

is indeed the best setting unless you are confident of

finding another thermal and therefore aren't on final

glide any more. It's still the MC speed for the sink

you are in, so may still be fast.



In the extreme case, if the auto MC reading winds

down to zero, but you ignore it and continue to fly on

a high MC setting you will definitely put yourself

below glide path.



Of course if you are still confident of flying through lift

before reaching the goal, by all means keep the

speed on. As I said, it's a judgement call.

Agree 100%. You can fly yourself into the ground before reaching your goal.. If you are really on final glide, you, by definition, are not going to stop and thermal. That, is final glide, by definition. If you are flying a MC value of four and fall below glide path, auto MC may tell you to slow down just enough to make your goal, at a lesser MC value. Auto MC continues to give you the speed to fly in sink. Auto MC really just resets the equation such that you can make it to goal without stopping to thermal.
To make a point in argument, it is often helpful to push the situation to extremes to test the validity of arguments.
If, for example, you are flying a MC value of 10 and you hit sink, your computer will tell you to speed up. Better judgement would be to reset MC value to a value of 3. Doing so gives you the added altitude for computations for making the final glide home. The computer will still give you speed to fly signals while flying through sink as well as through lift. If you are already flying a McCready of 0, then you are no longer on final glide if you hit sink and fall below glide path to make the goal home.

On Tuesday, February 12, 2013 12:09:20 PM UTC, Naviter Info wrote:
True. But while you're in sink you need to speed up. At least until you are flying the optimal speed for MC=0 for that sink. The AutoMC suggests you to slow down which is not ok any way you look at it.



Andrej Kolar

--

glider pilots use

http://www.Naviter.com

I have been looking at it differently. For an area of strong sink the appropriate airspeed at the optimum MC0 setting for prioritising getting through sink with minimum height loss (rather than maximising XC speed) may well be higher than the optimum speed for cruising in still air at a positive MC setting. For example if, when cruising at MC3kts in still air, one encounters sink of anything greater than 3kts then MC0 will command a higher speed.

So, if I encounter strong sink at an altitude low enough that I am concerned about dropping below a sensible operating band, I wind the MC back to zero (or small positive if final gliding into a headwind) temporarily. That is the one situation that I actually pay close attention to the speed command which will be telling me to speed up rather than slow down.

In the case of a Required MC advisory reading, the calculation will presumably be related to optimising a final glide and it would be dropping the advised MC gradually as the reserve is eaten up, rather than winding straight back to zero as I do, so it is even more likely that the speed command would call for an increase in airspeed in strong sink rather than a decrease.

John Galloway