At 00:18 15 September 2007, Marc Ramsey wrote:
Paul Hanson wrote:
Why do metric variometers read in m/s, instead of
kph
when the metric airspeed is in kph? Would it not make
more sense to use kph on the vario too so quick mental
L/D calculations could be done (for those who do not
use a flight computer etc to think for them)?

Well, altitude is usually measured in meters, and meters/second
is the
preferred SI unit for speed. Which does bring up a
related mystery.
When I was first flying gliders in the northeast US
from the late 60s
through the mid 70s, pretty much all of the ASIs were
in MPH and the
varios were in FPM. When I restarted flying gliders
in California
during the late 80s, pretty much all of the ASIs and
varios were in
knots. Was this a regional thing, or did some sort
of cataclysmic shift
take place while I was off doing other silly things?

Marc

Not too cataclysmic. Somebody was smart enough along
the way to realize that 100fpm was almost exactly 1
knot. Plus, since one degree of latitude was a nautical
mile it only made sense to use knots for vertical and
horizontal motion to reduce cockpit workload in the
days before the electronic flight computer (I learned
some of this from a Derek Pigot book). It was actually
a worse situation than that here in the US, before
the fpm/mph days, when most varios here were expressed
in fps and airspeeds in mph which made for even more
math that was very avoidable (there are still a lot
of archaic instruments used, reading in silly mph and
fpm and even fps; old habits die hard) This is why
I am so baffled at m/s vs kph in a metric cockpit.
To get L/D you need to multiply your m/s vertical speed
by 3.6 to get kph before you can divide it into your
airspeed. The altitude thing is no problem whether
it is expressed in m or km, as that is a mere decimal
place switch with no real math involved, so turning
that into useful range on a map is no problem-once
you have your L/D figured.
Since m/s is the SI for speed, than why kph on the
airspeed? I'm not hung up on m/s vs kph, just the fact
that the ASI and vario should be in the same units
for quick number crunching during X/C. A m/s airspeed
would serve the same purpose with current metric varios
that kph varios would serve with current metric airspeeds.
Altimeters can stay in m without affecting workload.

Paul Hanson
"Do the usual, unusually well"--Len Niemi