Netto

On 7/29/2011 11:19 AM, 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.
Why should I choose one or the other?
Or which is most usefull?
Thank you
S6

Uh oh...one of those 'religious questions' on RAS. Everyone tighten your
seatbelts!

Disclaimer: I have absolutely Zero Experience/Exposure to an LX 7000. The rest
of this comes from a pilot having flown only w. a(n excellent) mechanical
netto display since 1981.

Further - displaying additional ignorance here - I'll admit to being uncertain
what 'relative netto' actually is or means. That noted, after being exposed to
*netto* 'way back when' and pondering on it briefly, my brain asked itself the
question, "What more do I need or want to know than what the air is actually
doing?" From that single piece of information, everything else I - as Joe
Glider Pilot - might *want* to do becomes immediately obvious.

Assuming your ship has decent speed compensation, a netto display instantly:
1) lets you accurately conclude if the air through which you're flying is
'climbworthy,' and 2) (when combined with a good, old-fashioned, speed-to-fly
ring, set as desired for the day in question, and, flying in descending air)
instantly/continuously points to the correct speed to fly, in a non-iterative
manner. Non-netto mechanical displays with which I'm familiar, achieve these
two things only via indirect/iterative means, IMHO. Joe Pilot has to do
considerably more mental work/instrument-gazing with a non-netto display.

All bets may be off with electronic?microprocessor-based indicators...though
just because something is electronic is no guarantee of 'new-&-improved' or
'simpler' or 'better' information display, in my experience.

To my way of thinking (being a simple kind of guy), an analog-displayed netto
(whether achieved mechanically or electronically), combined with a speed ring,
is simple and intuitive, and not obviously improved upon. (I'm aware of how
useful a well-implemented audio can be...)

Downsides?
1) You'll get 'somewhat bogus' information on tow, due to the influence of the
towplane's added energy...truly a minor deal to me. Certainly it never
hampered/bothered my "OK to release?" decision, since the first few moments of
towed flight - regardless of towplane or situation - quickly allows
determination of that particular tow combination's steady state netto
indication, hence anything above that is lift, of immediately known strength.
2) Some don't like not 'knowing' the actual climb rate when climbing, since
the needle displays air vertical motion, not glider vertical motion. Never
having had difficulty subtracting 200 from a needle indication, it never
bothered me. Besides, having begun soaring in the days before electronics, I
quickly developed the habit of timing my actual rate of climb (sweep second
hand and altimeter) anyway, from which I concluded most people were hopeless
optimists when it came to reporting *their* climb rates.

Use what works best for how your mind works, and go have fun!

Regards,
Bob W.

P.S. Kinda-sorta related, don't lose sleep over errors inherent in 'polar
uncertainties' (e.g. ballast or not, circling or not). From Joe Average
Pilot's perspective. this sort of 'stuff' is in the noise level compared to
the lift/sink strengths on which you'll be basing your 'thermic day' flight
decisions.