On 7/31/2011 2:02 PM, Martin Gregorie wrote:
On Sun, 31 Jul 2011 11:30:20 -0600, BobW wrote:


At 17:19 29 July 2011, bish wrote:
Hi

This question has probably been ask many time! My new to me LX 7000
offer the choice of Netto or Relative netto for the vario needle


Snip...

...this may be a good place to define "netto" (as I've
learned/used it...not all soaring descriptions are universal).

To me, "netto" means a vario display indicating the actual vertical air
motion, relative to the earth's surface...i.e. 'net air motion' once the
glider's own speed-dependent sink-rate contribution has been
subtracted/eliminated from the picture. In other words, 'my netto
display' always indicates actual air motion, independent of glider speed
(the 'glider speed' bit being the 'compensation' part). No
interpretation needed - that's the beauty of it, so far as my brain is
concerned. And that's also why the speed ring doesn't require the pilot
to iterate in on the speed to fly...because the glider's increasing sink
rate with increasing speed has already been subtracted out of the
display. Hence the vario needle *always* points to 'absolute air
motion,' and in consequence to the whatever speed to fly your ring
setting calls for.

Yes, I agree, but 'super netto' or 'relative netto' are alternative terms
for something different from either TE vario of 'netto'.

A 'super netto' vario shows what a glider would be doing if it was flying
in the current air mass at its thermalling speed, so as well as the TE
input, it also needs the current IAS and the glider's polar.

I fly with an SDI C4 vario, which is a pure TE vario in climb mode and a
super netto vario in cruise mode. It has several ways of switching
between the two: manual, off the GPS (which is meant to detect circling)
or off airspeed (two separate speeds: cruise-climb and climb-cruise). I
prefer the latter though I needed to tune the C4's switch points to suit
the glider and my flying style. Its noises reflect the mode - climb rate
in climb mode and two other sounds for cruise, when it operates as a
speed director and takes the Macready setting into account.

I really like the way it works and, if forced to replace it, would want a
vario with exactly the same functions. IOW, 'super netto' works well for
me in cruise.

HTH

"Ah so! I think I'm getting a glimmer of 'adjectivized "netto"'."

Cogitating on the statement, "'...super netto' vario shows what a glider would
be doing if it was flying in the current air mass at its thermalling speed, so
as well as the TE input, it also needs the current IAS and the glider's
polar," this - to me - seems to simply be subtracting (roughly) 200 fpm from a
'unadjectivized "Netto"' display, which itself already (as best as is known
and the designer of the instrument can) subtracts out the glider's
speed-dependent, straight-line, polar. It may just be the way my brain works,
but - to me - this definition of 'super netto' merely adds a(n unnecessary)
layer of complexity to a simple concept of crucial interest to every glider
pilot, i.e.: What is the air through which I'm flying, doing?" The answer to
that question - along with the glider pilot's goals of the moment -
determines everything else the glider pilot *might* want to do.

Based on various conversations through the years with fellow glider pilots who
(often, apparently) did not fully grasp the power-inherent-to (concept of?)
'unadjectivized "netto",' and who (also often) 'poo-pooed the concept' by
(correctly) noting the vario would not display actual climb rate when
thermaling (it reads high by the incremental circling sink rate of the glider,
or, the 200 fpm I keep referencing...200 fpm presuming that Joe Glider Pilot
knows how to most effectively thermal his sailplane), I'd guess this is
wherefrom springs the flight-mode-based, mode-switching-vario-based display
apparently known as 'pure TE vario in climb mode' and 'super netto vario in
cruise mode.'

Anything that floats your boat is good, I reckon, but my simplistic brain
can't help but wonder, "Why is any of this necessary, and how is it *better*
than 'unadjectivized "Netto"'? When I first installed my 'unadjectivixed
"Netto"' system (the display replaced an old, sticking, TE-compensated PZL
unit), I left in place - but now vented to cockpit (i.e. non-compensated) - an
electric Ball vario, simply for its audio, which I'd set to squeal above some
daily climb-rate-dependent threshold; else it was silent. A few years later,
when the Ball died, I didn't bother to replace it, going only with the
(silent) 'unadjectivized "Netto"'. Worked just fine for me...though I
occasionally encountered pilots who implied I was 'being dangerous' by soaring
w/o an audio.

A few 'weird Libelle pilots' (and myself) aside, most glider cockpits I've
seen have (at least!) two varios, so I suppose a person might argue that -
when I still had the Ball in place - I was using two varios to do what the C4
(with which I'm 100% ignorant) implements in a single unit...save for the fact
it 'continually subtracts' that aforementioned 200 fpm/2 knots when in cruise
mode.

Anyhow, returning to the O.P.'s O.Q. (original question), my vote would be to
use 'unadjectivized "Netto"' for at least a couple of 'longish soaring
flights' or until such time as what I've tried to describe makes
conceptual/in-flight sense. Once it does, try whatever other display options
the LX-7000 has (all of which likely 'add conceptual complexity to' the basic
'unadjectivized "netto"' concept). Going that route will ensure making 'the
most informed' decision as to 'which is best.'

Have fun!
Bob W.

P.S. Keeping things as simple as possible at the outset will maximize the
likelihood of avoiding 'a mental rathole' quite possibly detectable in
differences between display methodology. What Joe Glider Pilot is (or should
be, dry chuckle) interested in is maximizing effective use of the energy
contained within the air through which he's flying. Anything else is 'somewhat
beside the point' if remaining aloft (or XC) is a given flight's fundamental
goal. Satisfy yourself your instrumentation is - or is not - providing you
'intelligible data' before worrying about 'instrumentation differences.' I
suspect that failure to adhere to this concept is one reason so many pilots
have multiple - competing - varios.