Netto

On Sun, 31 Jul 2011 11:30:20 -0600, BobW wrote:

On 7/31/2011 9:43 AM, John Sinclair 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

During cruise with pure Netto selected the needle will be down most of
the time. When you go through a 3 knot thermal your display will go
from 600 down to 300 down, hard to realize you are in a 3 knotter. If
you select relative Netto, the display will show the climb rate you
will get if you slow down to thermal speed, or 300 up! Much easier to
read and understand. I never use anything but relative netto. JJ


Because JJ's description of "netto" apparently conflicts with what I
posted earlier, 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



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martin@ | Martin Gregorie
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