alternative McCready theory and variometers

Hi,

The "alternative McCready theory" has been around for decades now. http://www.tbss.us/txfiles/Kai_intro_XC.pdf
It's not opposing McCready, just making a strong case for steadier inter-thermal speeds. But as I'm reading it, it makes the speed command feature superficial.

Is there a variometer manufacturer that doesn't ignore that?

My ideas for features:

* showing equivalentMC http://www.lk8000.it/new-20-features...t-mcready.html
* automatic MC set from equivalent MC

Getting rid of speed command would mean you could have something useful in cruise mode instead. For audio I would probably choose:

* relative netto variometer indication with dead-band.

and more....

Any comments?

Tibor

Correct.



08:43 26 October 2014, wrote:
Hi,

The "alternative McCready theory" has been around for decades now.
http://www.tbss.us/txfiles/Kai_intro_XC.pdf
It's not opposing McCready, just making a strong case for steadier
inter-thermal speeds. But as I'm reading it, it makes the speed command
feature superficial.

Is there a variometer manufacturer that doesn't ignore that?

My ideas for features:

* showing equivalentMC
http://www.lk8000.it/new-20-features...t-mcready.html
* automatic MC set from equivalent MC

Getting rid of speed command would mean you could have something useful
in
cruise mode instead. For audio I would probably choose:

* relative netto variometer indication with dead-band.

and more....

Any comments?

Tibor

Frankly, people who think that "MacCready theory" is wrong and need an "alternative theory" don't understand MacCready theory.

That doesn't mean pushing and pulling and following the vario around. Vario lags make that strategy unproductive. MacCready theory with lags in the vario would say so. However, if you see a beautiful long cloud up ahead with all the signs of strong lift in it that will last several minutes, by all means slow up! If you're stuck in a long lasting river of sink, speed up!

The speed to fly mode remains, in my view, the most useful way to set up a vario for cruising flight. Set it on speed to fly mode with a narrow deadband and a pretty short time constant. So, if you're in zero air flying 80 knots at MacCready 2, it will be silent. If you're flying 60 it will give you a gentle boop boop to remind you that you're cruising too slowly, which your netto would not do. If you had set it on regular TE vario it would be screaming down. What's the point in that?

Then, the speed to fly vairo naturally tells you what the air around you is doing. If it starts rising, you're in better air. That's interesting information. You don't immediately pull back on the stick, as you're flying a basically constant speed. But if the trend is good, the air is smooth, and you see some clouds, then you do gently slow down. And vice versa.

The confusion is in the name. It says "speed to fly" mode, which gives off the air of listening to it and doing huge pulls and pushes. Maybe we should rename it "listen to the air in cruise mode" which is how it works.

This setup works best if the vario units remain in vertical knots, i.e. that the sensitivity of the vario is the same in cruise and climb mode. If you hit 2 knots of lift a previously silent vario should always make the same "2 knots" sound. Of my varios, the 302 and clearnav do that. The LX, while otherwise a very nice vario, is much more sensitive to ups and downs in cruise mode than in climb mode, rendering it pretty useless for this sort of flying.

John Cochrane

On Sunday, October 26, 2014 8:43:45 AM UTC, Tibor Arpas wrote:
My ideas for features:

* showing equivalentMC http://www.lk8000.it/new-20-features...t-mcready.html
* automatic MC set from equivalent MC

As I understand it, 'Equivalent MC' reverses the STF calculation, and produces a figure from your averaged airspeed and the polar for your aircraft.

For example, assume MC theory for a glider states a STF of 150kph for a 2.0m/s estimated climb. 'Equivalent MC' reverses this equation; If you fly this glider at a constant 150kph IAS for the averaging period, the 'Equivalent MC' will be 2.0m/s.

The way I've heard it described, the idea is that you directly compare your 'Equivalent MC' figure with your MC figure and adjust your airspeed accordingly. If 'Equivalent MC' = 2.1m/s and MC = 2.0m/s, slow down. If 'Equivalent MC' = 1.9m/s and MC = 2.0m/s, speed up.

Climb and sink does not directly influence 'Equivalent MC', which is one reason why 'Equivalent MC' might be a poor value to display on a vario.

The way eMC works is quite trivial and straightforward for a pilot and it is
well described (by me) in the mentioned web page.
Most people "wish" to fly at - say - MC 1.0, following their stf indicator
on the variometer.
If they fly in sinking air, being downwind a mountain or in a narrow windy
valley, the STF indicator will tell them to fly faster.
A pilot may not be able to balance sink and lift (negative and positive air
zones) during a long glide, for some reasons:
a) weather condition (rain, for example, but also simply a bad zone with
only sinking air)
b) stress and weakness after many hours of flight
c) ignorance - unable to understand what's going on and recover from bad air

Now here is the problem with flight computers: they keep telling you the
arrival altitude based on the MC you have chosen.
Which is a good choice, if you know what you are doing, but only in such
case.
The Equivalent MC is just an automatic MC set by the calculator by looking
to your real average speed.
The arrival altitude will be coherent with what you are doing, not what you
WISH to have done so far.
Then, I know "my chickens": most people do NOT change MC on the PNA,
expecially in bad situations, but most times they do not use it at all on
the PNA.
So how are we supposed to give estimation of arrival altitudes ? Not using a
random MC of course. So we use equivalent MC.

It is important to state that in our software it is possible with a few
clicks to change from manual to automatic MC and there is always an overlay
indicator telling the pilot if the MC is stuck by him or it is dynamically
changing automatically.

Personally I change to manual MC only to understand the possible choices
available, and then back to eMC.
Now it may be worth saying that all the pilots in my area use LK with a
database of mountains, passes, ridges etc.
And in practice we all fly with at least two or three simultaneous
destination - we call them multitargets in the software -: one or more
landing places (in the alps you need to know if you have a place to land
reachable, it is not like in flat lands where you can land anywhere. ), the
task next turnpoint, and the next ridge , next mountain peak, or mountain
pass. So we do constantly look at the arrival altitude over the next ridge
and we can speed up and slow down and look instantly to the estimation.
Then we have a dedicated page to tell us how far we can go and how fast,
making a choice of peaks and ridges around in our direction. But that's not
related to eMC although quite innovative concept .

by the way the flight season this year in the alps has been.. a disaster.
Someone has stolen us the summer.
paolo




wrote in message
...

On Sunday, October 26, 2014 8:43:45 AM UTC, Tibor Arpas wrote:
My ideas for features:

* showing equivalentMC
http://www.lk8000.it/new-20-features...t-mcready.html
* automatic MC set from equivalent MC

As I understand it, 'Equivalent MC' reverses the STF calculation, and
produces a figure from your averaged airspeed and the polar for your
aircraft.

For example, assume MC theory for a glider states a STF of 150kph for a
2.0m/s estimated climb. 'Equivalent MC' reverses this equation; If you fly
this glider at a constant 150kph IAS for the averaging period, the
'Equivalent MC' will be 2.0m/s.

The way I've heard it described, the idea is that you directly compare your
'Equivalent MC' figure with your MC figure and adjust your airspeed
accordingly. If 'Equivalent MC' = 2.1m/s and MC = 2.0m/s, slow down. If
'Equivalent MC' = 1.9m/s and MC = 2.0m/s, speed up.

Climb and sink does not directly influence 'Equivalent MC', which is one
reason why 'Equivalent MC' might be a poor value to display on a vario.

On Sunday, October 26, 2014 5:04:49 PM UTC+1, wrote:


As I understand it, 'Equivalent MC' reverses the STF calculation, and produces a figure from your averaged airspeed and the polar for your aircraft.

For example, assume MC theory for a glider states a STF of 150kph for a 2..0m/s estimated climb. 'Equivalent MC' reverses this equation; If you fly this glider at a constant 150kph IAS for the averaging period, the 'Equivalent MC' will be 2.0m/s.

The way I've heard it described, the idea is that you directly compare your 'Equivalent MC' figure with your MC figure and adjust your airspeed accordingly. If 'Equivalent MC' = 2.1m/s and MC = 2.0m/s, slow down. If 'Equivalent MC' = 1.9m/s and MC = 2.0m/s, speed up.

Yes.
Little clarification: for basic function you don't need to set the MC into the variometer, just keep it in mind.
Little modification: If 'Equivalent MC' shows 2.1 and you expect 2.0 in front of you don't bother slowing down. 0.1 m/s difference is negligible.

I think it's totaly intiuitive to fly fast into good weather and fly slowly into bad weather. This would be just little guidance to learn and later confirm the numbers.


Climb and sink does not directly influence 'Equivalent MC', which is one reason why 'Equivalent MC' might be a poor value to display on a vario.

No, I totally would want it to be adjusted for sink and climb.

LK8000 doesn't adjust for that, so it's probably not a good example/definition. What I meant is "flown MC". Its reversing the STF calculation and producing a figure from averaged airspeed, the polar and the rise/sink.

Also as a precaution against a common mistake of flying so slowly in sink that you're actually achieving smaller then maximal achievable L/D I would like to have immediate warning for that (spead up!).

Doesn't take long for the boffins to start once macready is mentioned.

Macready works.

What doesn't work so well is the push/pull speed to fly modes of
"smart"varios (and the way Pilots interpret them)

I like Netto in cruise so I can adjust my speed and track accordingly.

I don't require any "speed to fly" function from the electronics. (I seem
to do
OK ignoring them)

Difficult for me to find any instrument that caters for this.

Tom





01:24 27 October 2014, Tibor Arpas wrote:
On Sunday, October 26, 2014 5:04:49 PM UTC+1,
wrote:

=20
As I understand it, 'Equivalent MC' reverses the STF calculation, and
pro=
duces a figure from your averaged airspeed and the polar for your
aircraft.
=20
For example, assume MC theory for a glider states a STF of 150kph for a
2=
..0m/s estimated climb. 'Equivalent MC' reverses this equation; If you
fly
t=
his glider at a constant 150kph IAS for the averaging period, the
'Equivale=
nt MC' will be 2.0m/s.
=20
The way I've heard it described, the idea is that you directly compare
yo=
ur 'Equivalent MC' figure with your MC figure and adjust your airspeed
acco=
rdingly. If 'Equivalent MC' =3D 2.1m/s and MC =3D 2.0m/s, slow down. If
'Eq=
uivalent MC' =3D 1.9m/s and MC =3D 2.0m/s, speed up.

Yes.=20
Little clarification: for basic function you don't need to set the MC
into
=
the variometer, just keep it in mind.
Little modification: If 'Equivalent MC' shows 2.1 and you expect 2.0 in
fro=
nt of you don't bother slowing down. 0.1 m/s difference is negligible.

I think it's totaly intiuitive to fly fast into good weather and fly
slowly=
into bad weather. This would be just little guidance to learn and later
co=
nfirm the numbers.

=20
Climb and sink does not directly influence 'Equivalent MC', which is
one
=
reason why 'Equivalent MC' might be a poor value to display on a vario.

No, I totally would want it to be adjusted for sink and climb.=20

LK8000 doesn't adjust for that, so it's probably not a good
example/definit=
ion. What I meant is "flown MC". Its reversing the STF calculation and
prod=
ucing a figure from averaged airspeed, the polar and the rise/sink.

Also as a precaution against a common mistake of flying so slowly in sink
t=
hat you're actually achieving smaller then maximal achievable L/D I would
l=
ike to have immediate warning for that (spead up!).

Then it would be called MC, not equivalent MC. You would set up the real MC
you are following on the vario which is obtainable on many instruments that
send to the PNA this setting every time you change it (LX V7 for example).
And for the purpose of giving you some information you dont already know
(the MC you did set manually) it would be useless: you would never know what
you are really doing.
Despite you have set MC to 1ms, you are flying much faster because you are
in sink since some time.
Some people think that after a long sink we can expect a "long" lift, but
generally they outland if they dont do a 90 degrees turn and run away the
sink area. The loss of altitude has to be accounted as a pure loss with no
gain expected for sure.
The precaution you mention is the STF audio that since decades already does
what you say.





"Tibor Arpas" wrote in message
...

No, I totally would want it to be adjusted for sink and climb.

LK8000 doesn't adjust for that, so it's probably not a good
example/definition. What I meant is "flown MC". Its reversing the STF
calculation and producing a figure from averaged airspeed, the polar and the
rise/sink.

Also as a precaution against a common mistake of flying so slowly in sink
that you're actually achieving smaller then maximal achievable L/D I would
like to have immediate warning for that (spead up!).

On Sunday, October 26, 2014 1:54:55 PM UTC+1, John Cochrane wrote:


The confusion is in the name. It says "speed to fly" mode, which gives off the air of listening to it and doing huge pulls and pushes. Maybe we should rename it "listen to the air in cruise mode" which is how it works.

This setup works best if the vario units remain in vertical knots, i.e. that the sensitivity of the vario is the same in cruise and climb mode. If you hit 2 knots of lift a previously silent vario should always make the same "2 knots" sound. Of my varios, the 302 and clearnav do that. The LX, while otherwise a very nice vario, is much more sensitive to ups and downs in cruise mode than in climb mode, rendering it pretty useless for this sort of flying.


Exactly! I would love to be able to listen to the air in cruise but the LX and ILEC sounds make little sense to me, I agree they are useless.

And If I understand you correctly the 302 and ClearNav then have what I called "relative netto" audio. (relative netto indicates the vertical speed the glider would achieve IF it flies at thermalling speed)
But how much is it skewed with MC settings?

On a given thay after a couple of thermals I have THE SOUND I want to hear in the next thermal in my mind. If in cruise I hear something ressembling that , or better, I'd pull up into the thermal - perfect.

On Mon, 27 Oct 2014 00:55:20 -0700, Tibor Arpas wrote:

And If I understand you correctly the 302 and ClearNav then have what I
called "relative netto" audio. (relative netto indicates the vertical
speed the glider would achieve IF it flies at thermalling speed)
But how much is it skewed with MC settings?

Not quite. 'Netto' mode tells you what the air mass is doing by
subtracting the glider's polar from the vario indication. When My SDI C4
vario is in cruise mode it bases its STF indication (both display and
sounds) on what it thinks the air mass is doing. I imagine that the 302
and Clearnav do much the same.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
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