MacCready in the Mountains

[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.

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

[Maule Driver]

"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.

[JJ Sinclair]

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

[Bill Daniels]

"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

[Stewart Kissel]

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
>
>

[JJ Sinclair]

>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

[Tom Seim]

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

[Maule Driver]

"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.

[Martin Hellman]

(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

[Stefan]

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

[Bill Daniels]

"Martin Hellman" > wrote in message

Snip a lot of good stuff________________

> 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.
>

Snip some more good stuff_____________________

The prof is John Cochrane and his articles are here:
http://www-gsb.uchicago.edu/fac/john.cochrane/research/Papers/soaring.html

I like his point that the M value is basically an optimism setting. If you
are optimistic about your situation and the weather ahead, set a high M
value. If you are less optimistic, set a lower M value. That pretty much
takes care of all situations.

Bill Daniels

[Mike Borgelt]

On Mon, 29 Sep 2003 19:51:14 +0200, Stefan >
wrote:

>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

However we will no doubt reinvent the wheel here.
The problem isn't whether to fly Macready speed, it is what to set the
"expected lift strength" to and Reichmann covers this nicely.

Mike Borgelt

[Michael Stringfellow]

A few points that might be worth adding:

1) The application of MacCready theory optimizes your speed over a
cross-country course if you fly at the speed indicated for the expected rate
of climb

2) MacCready flight optimizes time at the expense of height. If you are low
or trying to clear a mountain ridge, it isn't appropriate to fly as fast as
indicated. If you slow down, you will lose less height (often even when in
sink). John Cochrane has given a good description of the trade-off betweeen
speed and height.

3) It probably doesn't pay to follow the guidance of an audio speed-to-fly
vario too aggressively - flying at a more constant speed may often be more
efficient.

and, most important......

4) My experience has shown that people grossly overestimate the achieved
climb rate on a cross-country flight. Here in Arizona, days with memorable
8 to 10 knot thermals rarely produce more than a 5-knot flight average and
2.5 to 4 knot days are more common. If you climb in a rare 10-knot
thermal on a day with a 4-knot average and set your MacCready setting to 10,
you'll be in trouble in a hurry! A good flight computer that will give you
the climb average for a flight will keep you honest!

Mike the Strike

ASW 20 WA

"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.
>
> 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

[Mike Borgelt]

On Mon, 29 Sep 2003 21:18:08 GMT, "Michael Stringfellow"
> wrote:

>A few points that might be worth adding:
>
>1) The application of MacCready theory optimizes your speed over a
>cross-country course if you fly at the speed indicated for the expected rate
>of climb

"expected" rate of climb says a lot. It isn't necessarily the rate of
climb of the whole next thermal.
>
>2) MacCready flight optimizes time at the expense of height. If you are low
>or trying to clear a mountain ridge, it isn't appropriate to fly as fast as
>indicated. If you slow down, you will lose less height (often even when in
>sink). John Cochrane has given a good description of the trade-off betweeen
>speed and height.
>

Speed to fly theory assumes you *will* get the next thermal before you
hit the ground.

>3) It probably doesn't pay to follow the guidance of an audio speed-to-fly
>vario too aggressively - flying at a more constant speed may often be more
>efficient.

Which is why the speed to fly command should be damped considerably
compared to the vario. This is in line with now 20 year old German
research.

It has also been shown that it isn't necessary to fly at the exact
speed to get most of the benefit.

Severe dolphining is detrimental and likely to make you sick.
>
>and, most important......
>
>4) My experience has shown that people grossly overestimate the achieved
>climb rate on a cross-country flight. Here in Arizona, days with memorable
>8 to 10 knot thermals rarely produce more than a 5-knot flight average and
>2.5 to 4 knot days are more common. If you climb in a rare 10-knot
>thermal on a day with a 4-knot average and set your MacCready setting to 10,
>you'll be in trouble in a hurry! A good flight computer that will give you
>the climb average for a flight will keep you honest!
>
>Mike the Strike
>

Anyone who has been around soaring for a while will know that when the
pilot says" it was a ten knot thermal" he means "the vario once
indicated 10 knots during the climb".


This is extended to the day: "there were ten knot thermals that day"
means that "in one thermal that day the vario momentarily read 10
knots"

Maybe we aren't so different from sport fishermen.

The things that John Cochrane mentions in his Macready paper were all
discussed at greater length 30 or more years ago by Anthony Edwards -
the" Armchair Pilot" in Sailplane and Gliding. We are in danger of
reinventing the wheel.

Mike Borgelt

[Mike Borgelt]

On Mon, 29 Sep 2003 16:40:28 -0700, "Greg Arnold"
> wrote:

>Further, I believe that you want to use the average climb rate at the point
>where you leave the thermal, not the average climb rate for the entire
>thermal.
>
>
Only because that should be the same as the expected average at the
bottom of the *next* thermal.

The only time you don't base Speed to fly settings on the *next*
thermal is when leaving the final glide thermal - then you should use
the rate of climb in the last circle or so.

Mike Borgelt

[Greg Arnold]

"Mike Borgelt" > wrote in message
...
> On Mon, 29 Sep 2003 16:40:28 -0700, "Greg Arnold"
> > wrote:
>
> >Further, I believe that you want to use the average climb rate at the
point
> >where you leave the thermal, not the average climb rate for the entire
> >thermal.
> >
> >
> Only because that should be the same as the expected average at the
> bottom of the *next* thermal.


Right, the point being that the climb rate in the middle of a thermal is
irrelevant.


>
> The only time you don't base Speed to fly settings on the *next*
> thermal is when leaving the final glide thermal - then you should use
> the rate of climb in the last circle or so.
>
> Mike Borgelt

[Stewart Kissel]

Here is another fly to throw into the ointment. It
is not uncommon in the Rocky Mountains to be forced
to leave strong thermals due to FL180. So how would
you set a MC when you are departing thermals before
they weaken?



At 01:42 30 September 2003, Greg Arnold wrote:
>
>'Mike Borgelt' wrote in message
...
>> On Mon, 29 Sep 2003 16:40:28 -0700, 'Greg Arnold'
>> wrote:
>>
>> >Further, I believe that you want to use the average
>>>climb rate at the
>point
>> >where you leave the thermal, not the average climb
>>>rate for the entire
>> >thermal.
>> >
>> >
>> Only because that should be the same as the expected
>>average at the
>> bottom of the *next* thermal.
>
>
>Right, the point being that the climb rate in the middle
>of a thermal is
>irrelevant.
>
>
>>
>> The only time you don't base Speed to fly settings
>>on the *next*
>> thermal is when leaving the final glide thermal -
>>then you should use
>> the rate of climb in the last circle or so.
>>
>> Mike Borgelt
>
>
>

[Robert Ehrlich]

JJ Sinclair wrote:
>
> >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.
>

There is nothing wrong with the theory. It says you set MC to the strength of
the next thermal you *can* reach. If there is a mountain between you and the
thermal that you can't pass with this setting, you can't reach it. So the
optimal strategy in this case, as someone mentionned before, is to fly to
the mountain as in a final glide, i.e. climb in the last thermal before
it (if possible) up to the height allowing to pass it (with any suitable
margin) at MC setting equal to the strength of this last thermal.

[Greg Arnold]

Don't you want your climb rate at the top of the current thermal to equal
your expected climb rate at the bottom of the next thermal, and won't those
climb rates determine your speed between the thermals?


"Todd Pattist" > wrote in message
...
> "Greg Arnold" > wrote:
>
> >the point being that the climb rate in the middle of a thermal is
> >irrelevant.
>
> Except for the final glide thermal, the climb rate in your
> current thermal is always irrelevant to your cruise after
> that thermal (except to the extent that you think the next
> thermal will be similar).
>
> Todd Pattist - "WH" Ventus C
> (Remove DONTSPAMME from address to email reply.)

[Maule Driver]

"Michael Stringfellow" > wrote in message
ink.net...
> 2) MacCready flight optimizes time at the expense of height. If you are
low
> or trying to clear a mountain ridge, it isn't appropriate to fly as fast
as
> indicated. If you slow down, you will lose less height (often even when
in
> sink). John Cochrane has given a good description of the trade-off
betweeen
> speed and height.
>
Clearing a mountain ridge is simply a final glide exercise. You should fly
as fast as indicated assuming you have set yourself up for a proper final
glide with appropriate risk factors applied. And if the air is lively, MC
speed to fly works quite nicely.

I was always amazed at how many pilots in competitions could not or would
not perform a reasonable final glide calculation, and then fly it. I
started doing it with a homemade whiz wheel and found I could beat 50% of
regional competitors on *any* final glide (not to say the same the 50%
wouldn't beat me during almost any other contest task element).

When the GPS computers came online, I could consistently hit the airport on
a final glide flying strict MC and GPS calc'd final glide by just giving
myself a 500' cushion at the airport. That seemed to beyond the capability
of at least 80% of regional competitors and a shocking number of national's
competitors. Amazing!

Yes, a lot of reinventing the wheel going on. Just read Reichmann for a
good foundation.

[Greg Arnold]

You have proved my point by having to use an example of a climb that is cut
off due to cloudbase, and by assuming that the next thermal is in an
entirely different airmass with very weak lift.

In the more general case (the one we normally talk about), you are going to
try to match the climb rate at the top of the current thermal with the climb
rate at the bottom of the next one. That matching exercise will depend on
the nature of both the current thermal and the next one. So the cruise
speed depends on the nature of both thermals. Neither is more important
than the other in determining cruise speed.



"Todd Pattist" > wrote in message
...
> "Greg Arnold" > wrote:
>
> >Don't you want your climb rate at the top of the current thermal to equal
> >your expected climb rate at the bottom of the next thermal, and won't
those
> >climb rates determine your speed between the thermals?
>
> Yes, but the climb rate in this thermal only affects when
> you leave it, not how fast you cruise, while the climb rate
> in the next thermal controls how fast you cruise. If you
> hit cloudbase while climbing at 10 knots, but can only get
> to the bottom of a 2 knot thermal, then you fly M=2 to that
> 2-knotter, not M=10.
>
> Todd Pattist - "WH" Ventus C
> (Remove DONTSPAMME from address to email reply.)

[Greg Arnold]

>
> > Neither is more important
> >than the other in determining cruise speed.
>
> Unless they are different, in which case the next one
> controls cruise speed. Of course if they are the same, I
> might as well say the next one controls instead of the
> current one. If you want to assign some control over cruise
> speed to the current thermal provided it's the same as the
> next one, I don't see any reason to argue, as we agree on
> what the pilot does, but it seems odd to me to put it that
> way. I think of it as leaving the current thermal when I
> can get to something as good or better, and cruising at the
> M-speed that matches the climb rate of the next one. If
> it's stronger, I run faster.


In that case, haven't you stayed in the current thermal too long?


If I think it will be weaker,
> I run slower.


In that case, shouldn't you stay in the current thermal longer?



> Todd Pattist - "WH" Ventus C
> (Remove DONTSPAMME from address to email reply.)

[Andy Blackburn]

Obviously I'm not as good as some people here at knowing
exactly how strong the next thermal's going to be...

;-)

At 21:06 02 October 2003, Greg Arnold wrote:
>
>
>>
>> > Neither is more important
>> >than the other in determining cruise speed.
>>
>> Unless they are different, in which case the next
>>one
>> controls cruise speed. Of course if they are the
>>same, I
>> might as well say the next one controls instead of
>>the
>> current one. If you want to assign some control over
>>cruise
>> speed to the current thermal provided it's the same
>>as the
>> next one, I don't see any reason to argue, as we agree
>>on
>> what the pilot does, but it seems odd to me to put
>>it that
>> way. I think of it as leaving the current thermal
>>when I
>> can get to something as good or better, and cruising
>>at the
>> M-speed that matches the climb rate of the next one.
>> If
>> it's stronger, I run faster.
>
>
>In that case, haven't you stayed in the current thermal
>too long?
>
>
>If I think it will be weaker,
>> I run slower.
>
>
>In that case, shouldn't you stay in the current thermal
>longer?
>
>
>
>> Todd Pattist - 'WH' Ventus C
>> (Remove DONTSPAMME from address to email reply.)
>
>
>

[Greg Arnold]

Todd:

My final comment on this matter -- you are talking about exceptions to the
general rule, not about the general rule. Exceptions to the general rule
don't disprove the general rule.

Greg


"Todd Pattist" > wrote in message
...
> "Greg Arnold" > wrote:
>
> >> I think of it as leaving the current thermal when I
> >> can get to something as good or better, and cruising at the
> >> M-speed that matches the climb rate of the next one. If
> >> it's stronger, I run faster.
> >In that case, haven't you stayed in the current thermal too long?
> >
> >If I think it will be weaker,
> >> I run slower.
> >In that case, shouldn't you stay in the current thermal longer?
>
> You don't always have the option to stay longer or leave
> earlier. Cloudbase can cut the top off. If all you can get
> to from cloudbase is a weak thermal, then you go slow, even
> if you would have preferred to climb longer. A ridge you
> need to cross could require you to climb higher in a weak
> thermal, even if would have preferred to leave earlier and
> even if you can get to the strong thermal at high speed once
> you are high enough to cross. Moreover, sometimes you just
> change your mind about how strong the next one will be. The
> bottom line is it's the next thermal I can get to that
> controls the speed I fly to get there.
>
> Todd Pattist - "WH" Ventus C
> (Remove DONTSPAMME from address to email reply.)

[Robert Ehrlich]

Todd Pattist wrote:
>
> "Greg Arnold" > wrote:
>
> >My final comment on this matter -- you are talking about exceptions to the
> >general rule, not about the general rule. Exceptions to the general rule
> >don't disprove the general rule.
>
> OK, but the general rule is that the rate of climb in the
> next thermal has to equal the rate of climb in the current
> thermal for the current thermal to affect your cruise speed
> to the next thermal. As soon as that's not true, the next
> thermal and it's an "exception." Thus we agree on
> what the pilot does, even if we don't agree on how to
> describe it :-)
>

And anyway, even if both are equivalent, it is simpler to
state "the next thermal controls (with no exception)", than
"the climb rate at the top of the last thermal, which should
be the same at the bottom of the next one, controls, with
some exceptions"

[Bill Daniels]

I still don't think you guys get it. Yesterday, while flying over the Rocky
Mountains in my Nimbus 2C I was seeing 5 M/S on the averager, yet if I set
the M number to 5, the speed command would ask for 200+ MPH. Given the level
of turbulence associated with 5 M/S lift and the fact that I was flying dry,
I stayed in the green arc.

The other thing that no one has mentioned is that, at the high altitudes
required over mountains, the True Airspeed calculation has a larger effect
on average XC speed than the McCready calculation so flying slow and staying
high gets you a higher real speed.

In the mountains, structural limits, safe landing areas and terrain
clearance set maximum speed. McCready numbers are academic.

Bill Daniels



"Robert Ehrlich" > wrote in message
...
> Todd Pattist wrote:
> >
> > "Greg Arnold" > wrote:
> >
> > >My final comment on this matter -- you are talking about exceptions to
the
> > >general rule, not about the general rule. Exceptions to the general
rule
> > >don't disprove the general rule.
> >
> > OK, but the general rule is that the rate of climb in the
> > next thermal has to equal the rate of climb in the current
> > thermal for the current thermal to affect your cruise speed
> > to the next thermal. As soon as that's not true, the next
> > thermal and it's an "exception." Thus we agree on
> > what the pilot does, even if we don't agree on how to
> > describe it :-)
> >
>
> And anyway, even if both are equivalent, it is simpler to
> state "the next thermal controls (with no exception)", than
> "the climb rate at the top of the last thermal, which should
> be the same at the bottom of the next one, controls, with
> some exceptions"

[Bill Daniels]

"Marc Ramsey" > wrote in message
m...
> "Bill Daniels" > wrote...
> > I still don't think you guys get it. Yesterday, while flying over the
Rocky
> > Mountains in my Nimbus 2C I was seeing 5 M/S on the averager, yet if I
set
> > the M number to 5, the speed command would ask for 200+ MPH. Given the
level
> > of turbulence associated with 5 M/S lift and the fact that I was flying
dry,
> > I stayed in the green arc.
>
> I would look carefully at the polar you are using and/or the instrument,
it's
> calling for a lot more speed than I would expect. On the other hand, I
almost
> always set my MC to half of what I'm expecting the next climb to be, and
it
> seems to work pretty well.
>
> > The other thing that no one has mentioned is that, at the high altitudes
> > required over mountains, the True Airspeed calculation has a larger
effect
> > on average XC speed than the McCready calculation so flying slow and
staying
> > high gets you a higher real speed.
>
> Be careful, though, polars are based on "indicated" speeds. Most modern
> electronic variometers show something approximating a "true" climb rate.
Some,
> but not all, glide computers assume you are setting the MC to a "true"
climb
> rate, and actually convert it to an "indicated" (lower) equivalent climb
rate
> before applying the speed to fly calculation.
>
> > In the mountains, structural limits, safe landing areas and terrain
> > clearance set maximum speed. McCready numbers are academic.
>
> Perhaps, but I think the main problem is that many pilots fly far too fast
for a
> given climb rate, due to instrumentation problems, incorrect polars, and
> incorrect understanding of what the MC numbers actually mean.
>
> I 've carefully verified the speed to fly calculations and corrections in
the
> software I use in my LAK-17, and at 15K+ feet with full water and MC 5
(knots),
> cruise speed to fly is normally less than 120 knots.
>
> Marc
>
5 meter/second = 9.7 knots. I was setting M in meters per second. The
speed command just says push or pull. I think my computer is pretty well
set up. I think we agree on this: Most pilots fly too fast.

The point is that in mountain flying, total reliance on McCready speeds is
misleading and possibly dangerous if it induces a pilot to fly too fast.
Certainly, you don't want to base your strategic or possibly even your
tactical decisions on the McCready speed to fly. Be aware of it and factor
it in, but don't be a slave to it.

In a wide area of homogeneous airmass characteristics where thermals are
uniform in strength, diameter and spacing, the McCready speed to fly is a
major determinator of flying technique.

Flying in high mountain country is just the opposite. You had better be
ready for a complete weather change every few minutes. Thermic conditions
will cycle very fast and you may see blue sky, towering cumulus,
overdevelopment and back to blue in a single interthermal glide.

Bill Daniels

[Marc Ramsey]

"Bill Daniels" > wrote...
> 5 meter/second = 9.7 knots. I was setting M in meters per second. The
> speed command just says push or pull. I think my computer is pretty well
> set up. I think we agree on this: Most pilots fly too fast.

I was aware that you were talking in m/sec. Here's what you said:

> I still don't think you guys get it. Yesterday, while flying over the Rocky
> Mountains in my Nimbus 2C I was seeing 5 M/S on the averager, yet if I set
> the M number to 5, the speed command would ask for 200+ MPH. Given the
> level of turbulence associated with 5 M/S lift and the fact that I was flying
dry,
> I stayed in the green arc.

If I plug MC 10 knots into my speed to fly spreadsheet for my LAK-17A 18M dry
(which is likely to have a higher STF than your IIC for the same MC setting), I
get 148 mph (130 knots) for 0 airmass movement. In order to get an STF of 200
mph, I would need to be in 10 knots of sink.

Your computer may be well set up, but it appears to be giving bogus STF...

> The point is that in mountain flying, total reliance on McCready speeds is
> misleading and possibly dangerous if it induces a pilot to fly too fast.
> Certainly, you don't want to base your strategic or possibly even your
> tactical decisions on the McCready speed to fly. Be aware of it and factor
> it in, but don't be a slave to it.
>
> In a wide area of homogeneous airmass characteristics where thermals are
> uniform in strength, diameter and spacing, the McCready speed to fly is a
> major determinator of flying technique.
>
> Flying in high mountain country is just the opposite. You had better be
> ready for a complete weather change every few minutes. Thermic conditions
> will cycle very fast and you may see blue sky, towering cumulus,
> overdevelopment and back to blue in a single interthermal glide.

I fly in high mountain country, just like you. I also spend a lot of time
cruising. For those times when I have a decent idea of what the next climb
rate is going to be, I'd want a computer which isn't telling me to fly 50+ MPH
faster than I should be...

Marc

[Bruce Hoult]

In article >,
"Marc Ramsey" > wrote:

> If I plug MC 10 knots into my speed to fly spreadsheet for my LAK-17A
> 18M dry (which is likely to have a higher STF than your IIC for the
> same MC setting), I get 148 mph (130 knots) for 0 airmass movement.
> In order to get an STF of 200 mph, I would need to be in 10 knots of
> sink.

Which is not at all impossible in the mountains!

-- Bruce

[Marc Ramsey]

"Bruce Hoult" > wrote...
> In article >,
> "Marc Ramsey" > wrote:
>
> > If I plug MC 10 knots into my speed to fly spreadsheet for my LAK-17A
> > 18M dry (which is likely to have a higher STF than your IIC for the
> > same MC setting), I get 148 mph (130 knots) for 0 airmass movement.
> > In order to get an STF of 200 mph, I would need to be in 10 knots of
> > sink.
>
> Which is not at all impossible in the mountains!

He didn't say he was in 10 knots of sink. The implication was that STF called
for a "cruise" speed of 200+ MPH. It does not.

Marc

[Fat Albert]

As opposed to speed to fly the decision on when to leave a thermal is easy

'Climb only high enough in the current thermal to reach a better one or the
finish line'

Works in or out of the Mountains

"Todd Pattist" > wrote in message
...
> Andy Blackburn > wrote:
>
> >I looked at several flight traces from ASA contest
> >days in Arizona this year and found that the pilots
> >who flew farther between taking thermals (and used
> >broader altitude bands as a result) had higher average
> >climb rates and better achieved X-C speeds than those
> >who stayed higher. That is, they kept pushing farther
> >(and lower) to get the better thermals.
>
> Even if they weren't pushing on for a better thermal (and
> they probably were), there is often some time lost centering
> each thermal, and that's pure lost time. Working a narrower
> band means more thermals and more of those centering losses.
> I just wish I could convince myself to work the broader band
> more :-)
>
> Todd Pattist - "WH" Ventus C
> (Remove DONTSPAMME from address to email reply.)