MacCready in the Mountains

I fly a lot in the mountains and find MacCready speed-to-fly information,
completely worthless. Let me explain; Before crossing a ridge, I will fly
slower (below MC), so that I'm assured of making the next ridge. After crossing
the ridge, I may fly faster than MacCready. If I set the proper MC setting in
my computer. I am constantly bombarded with WRONG information coming from the
computer audio.

For the last few flights, I have tried something new. I turned OFF the computer
audio (B-100) and turned on the back-up vario (B-40), Now I have audio only
when going UP and nothing when going down. I locked the computer in cruse mode
and if I need to know what MacCready thinks about the speed I should be flying,
all I have to do is look at the speed-to-fly needle.

One more tid-bit, I had radio interference (breaking squelch) when I installed
the B-100 in my Genesis. I found that the cable to the LCD display was real
sensitive to triggering the interference. When I would bring the radio antenna
cable close to the LCD cable, It would break squelch. I completely solved the
problem by keeping these two cables 6 inches apart. I also found the NMEA cable
from the Cambridge GPS would trigger the radio squelch, if it was closer than
6 inches to the LCD cable.
Cheers,
JJ Sinclair

"JJ Sinclair"
I fly a lot in the mountains and find MacCready speed-to-fly information,
completely worthless. Let me explain; Before crossing a ridge, I will fly
slower (below MC), so that I'm assured of making the next ridge. After
crossing
the ridge, I may fly faster than MacCready. If I set the proper MC setting
in
my computer. I am constantly bombarded with WRONG information coming from
the
computer audio.

Interesting. Why wouldn't you treat crossing a ridge as a final glide
condition and set the appropriate MC to make it? Then why wouldn't you go
back to normal MC setting after crossing, i.e. forecast you next climb? I
would think that both of these approaches would result in highest speed over
distance.

Haven't done this stuff in awhile but that's what I recall from the theory.

Hi there, Mauel Driver.
Thats just why I no longer have cruise audio information. It was always telling
me something I had decided NOT to do (speed up or slow down) So, I found myself
changing the MacCready setting, just to get the audio to shut-up.

I guess what I am saying is; MacCready is a flat-land soaring aid and doesn't
work in the mountains. Anyway, I sure like the back-up audio ONLY telling me
when we are going UP and NOTHING when I'm cruising.
JJ Sinclair

"JJ Sinclair" wrote in message
...

Does that make sense relative to your practice of turning off the MC
audio?

Yeah, I have the B-40 audio on all the time set for up only, so it is
telling
me to slow down or thermal in lift. Just isn't constantly giving me input
about
the cruise speed I have chosen. Works for me.
JJ Sinclair

Makes sense to me too. McCready requires an estimate of the NEXT thermals
strength. In the big mountains thermal strengths vary widely so there's no
way to be sure what to set.

On the good side, thermal strengths are likely to be so strong that the
McCready speed-to-fly computation will ask for speeds that far exceed
"reasonable and safe". The maximum turbulence penetration speed (Vb) then
becomes the best speed to fly. Makes me wish the designers would spend some
time raising the Vb speeds instead of the L/D.

Bill Daniels

I was just contemplating such issues as I was bouncing
around today in the Colorado high country. My scenario
was this-FL140 and real strong/turbulent rotor-thermal-ridge
lift, which happened to be best in close to the rocks
which I was still looking up at. MC said to slow down
while running through this strong stuff, NO WAY JOSE!
I wanted a lot of airspeed regardless of the lift
and what the computer was telling me. And I also had
to deal with the same ridge crossing issues as JJ.



At 03:12 28 September 2003, Bill Daniels wrote:

'JJ Sinclair' wrote in message
...

Does that make sense relative to your practice of
turning off the MC
audio?

Yeah, I have the B-40 audio on all the time set for
up only, so it is
telling
me to slow down or thermal in lift. Just isn't constantly
giving me input
about
the cruise speed I have chosen. Works for me.
JJ Sinclair

Makes sense to me too. McCready requires an estimate
of the NEXT thermals
strength. In the big mountains thermal strengths vary
widely so there's no
way to be sure what to set.

On the good side, thermal strengths are likely to be
so strong that the
McCready speed-to-fly computation will ask for speeds
that far exceed
'reasonable and safe'. The maximum turbulence penetration
speed (Vb) then
becomes the best speed to fly. Makes me wish the designers
would spend some
time raising the Vb speeds instead of the L/D.

Bill Daniels

McCready speed-to-fly computation will ask for speeds that far exceed
"reasonable and safe".

I find the same thing, Bill, and as a consequence, almost never set MacCready
any higher than 3. For a long time now, I have had serious questions about the
theory that MacCready is based on. I'm sure it's fine in Uvalde, but it SUX in
Minden.

Note, SUX is an Air Force term meaning, This peace of equipment isn't operating
properly.


JJ Sinclair

I stopped using McCready some years ago. It proved more of a
distraction than anything else. I now fly a slow, medium or fast glide
(and sometimes a very fast glide).

Mountains are different because they generate their own weather,
minimizes the knowledge that you gained during the previous part of
your flight. And this is dramatically different depending upon
direction. The sink on the lee side can be heart stopping. I recall
clearing a mountain range in Montana by 200 feet (at the lowest point
into the wind), saving a late night retrieve.

If you haven't flown western mountains you've got to try it. It is
soaring at its ultimate. We are talking about big mountains and big
sky; 15 kt thermals to 18K. And you Nevada guys: you haven't lived
until you have ridge soared Mt. Ranier! Eat your hearts out!

Tom

"Tom Seim"
If you haven't flown western mountains you've got to try it. It is
soaring at its ultimate. We are talking about big mountains and big
sky; 15 kt thermals to 18K. And you Nevada guys: you haven't lived
until you have ridge soared Mt. Ranier! Eat your hearts out!

I agree. Glad I had a chance to fly some comps at Minden and Livingston MT.
I've always thought that competitive soaring is the most *efficient* way to
experience different sites. The schedule and tasking drives you to fly to
places and on days you might otherwise opt for a beer.

Of course, a part of your life is yet to be lived unless you've ridge soared
the appalachians. Post frontal 30 knot wind out of the northwest can give
you the choice on a single cc flight of a good pounding 20' from the trees,
10+ knot thermals about a wingspan wide, and wave. You never get as high or
as strong as out west but redlining a wingspan from the ridge and less than
1,000 feet over the tree covered valley can curl the hairs on your neck just
the same.

Of course there is a certain joy in waking up in Uvalde to a cool overcast
morning that turns into the 10th straight day of horizon to horizon cloud
streets. Boring? Nah.

(JJ Sinclair) wrote in message ...
I fly a lot in the mountains and find MacCready speed-to-fly information,
completely worthless. Let me explain; Before crossing a ridge, I will fly
slower (below MC), so that I'm assured of making the next ridge. After crossing
the ridge, I may fly faster than MacCready. If I set the proper MC setting in
my computer. I am constantly bombarded with WRONG information coming from the
computer audio.

Something that is rarely said when MacCready speed to fly is discussed
(including texts on soaring!) is that there is a major assumption in
the math behind it: that you can stop at any point and immediately
find a thermal of the strength indicated in the MacCready window.
Wouldn't that make soaring easy -- and probably a bit boring.

There was an interesting article in Soaring Magazine about a year ago
which talked about related issues. Sorry I don't have the date, but if
memory serves me it's by a Biz School prof from Chicago. He argued
that you should use a lower setting when close to the ground because
you have less time to find a thermal and will almost surely have to
settle for a weaker one. Once you're high, you have more time to be
picky and can use a setting close to or even equal to the maximal
thermal strength of the day.

An earlier posting got close to these ideas when it pointed out that
the setting should be the expected strength of the next thermal --
which will clearly depend on how much time you have to be picky.

There is another point that needs to be mentioned: Maximizing speed
over a task is only one goal, so the MacCready math leaves out other
factors as well. How much emphasis should be placed on not landing
out? not landing out in a bad field and damaging the ship? not landing
out in hostile terrain and maybe getting killed? And so on. An
optimization that took all these factors into account is impossible,
which is where common sense (like JJ's not above) comes in.

Martin

Martin Hellman wrote:

Something that is rarely said when MacCready speed to fly is discussed
(including texts on soaring!) is that there is a major assumption in
the math behind it: that you can stop at any point and immediately
find a thermal of the strength indicated in the MacCready window.
Wouldn't that make soaring easy -- and probably a bit boring.

There was an interesting article in Soaring Magazine about a year ago
which talked about related issues.


The best and most complete discussion of this issue is still Helut
Reichmann's Book "Cross Country Soaring".

Stefan