Metric Soaring

Clearly metric is a superior system for most expressions
of measurement, but it seems surprisingly inefficient
for flying (especially soaring) in it's current form,
which brings me to my question(s).
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)?
After doing a little homework, I figured out a 5 m/s
is 18kph (1m/s is 3.6 kph). If I used metric to fly
(I'm just plane knots) I would much rather have a vario
that went up/down to 20kph, and was hash marked on
single kilometers with numbers every 5th hash mark
for the main vario.
For a weak lift unit it would be hash marked for 1/5
kilometers but numbered every whole kilometer up/down
to 5kph.
Strong lift versions would be up/down to 30 or 40kph,
hashed every second kilometer and numbered every 5th
hash mark...Just a thought, but makes me curious.

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

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

Because 1 or 2 km/hour is really slow, but 1 or 2 meters per second is
not. (Imagine the ASI in meters/second.)

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

Actually, I think it's one minute of latitude equals a nautical mile - works
great at a chart table with dividers but not much use in a glider cockpit.

I don't think vario units make much difference - up is good, more up is
better on any vario. Most varios aren't all that accurate anyway. Airspeed
units are more critical but most pilots just use the colored arcs and the
STF audio from the vario.

I've never used a vario in knots and an airspeed in knots to figure the d/h
ratio. The electronic gadgets do that if you are interested.

Now altimeters in meters are a pain. With 3200' per rev on the big hand how
do you know it isn't stuck?

BD


"Paul Hanson" wrote in message
...
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

Paul Hanson wrote:

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)

I don't dispute the abstract benefits of having the vario and airspeed
in the same units. As a practical matter, it isn't much use. Having
the airspeed in knots does help with manual navigation using sectionals.
I have never, however, done any L/D calculations based on vario
readings, and I don't know of anyone else who does. In fact, flight
computers and software do not use instantaneous (or average) vario
readings for navigation or final glide calculations, the vario is only
used to determine speed to fly.

So, the question still remains, why did the US gliding community make a
relatively quick shift from MPH and FPM to knots, when just about
everything else happens so slowly?

Marc

On Sep 14, 10:42 pm, Marc Ramsey wrote:
....
So, the question still remains, why did the US gliding community make a
relatively quick shift from MPH and FPM to knots, when just about
everything else happens so slowly?

Marc

The entire US light plane community did it, not just gliding. And the
only real difference was the airspeed indicator. A vario marked in
100's of feet/min can be read as knots, they could have been changed
just by re-painting the face plate :-)

Why it was done is something that I am not sure about, but probably
the FAA pushed aircraft manufacturers to standardize on knots. FAA
regulations all reference knots, not mph.

Todd Smith
3S

On Sep 14, 8:27 pm, "Bill Daniels" bildan@comcast-dot-net wrote:
Actually, I think it's one minute of latitude equals a nautical mile - works
great at a chart table with dividers but not much use in a glider cockpit.

I would use my thumb and index finger on a sectional chart to measure
distance all the time. Good enough considering the uncertainty of the
airmass we fly in.

Using NM and feet altitude also makes the E-6B wizz wheel into an
instant glide computer. Just put altitude vs. distance and the arrow
points to the glide ratio. Do this every few miles and you can see a
trend - constant or decreasing and you can probably make it.

Also, 20:1 and 30:1 are useful numbers for most sailplanes. An ASK-21
will most likely do 20:1 and an ASW-20 will do 30:1 (though I used to
do 20:1 when over rough terrain or expecting strong sink). So, take
the distance in NM and multiply by 200 and you have 30:1. Multiply by
300 and you have 20:1. Granted, this would be just as easy in metric
units, but not the map measurements.

Someday, I just might have a complete electrical failure... and it's
nice to have a few mental tricks available.

-Tom

toad wrote:
On Sep 14, 10:42 pm, Marc Ramsey wrote:
...
So, the question still remains, why did the US gliding community make a
relatively quick shift from MPH and FPM to knots, when just about
everything else happens so slowly?

Marc

The entire US light plane community did it, not just gliding. And the
only real difference was the airspeed indicator. A vario marked in
100's of feet/min can be read as knots, they could have been changed
just by re-painting the face plate :-)

All the airplanes I've flown use MPH, but the youngest one was built in
the 70s. I need to experience something newer, one of these days...

Why it was done is something that I am not sure about, but probably
the FAA pushed aircraft manufacturers to standardize on knots. FAA
regulations all reference knots, not mph.

That does explain the change in airspeed units, the change to knots on
the vario still seems a bit "radical" for glider pilots to pull it off
that quickly...

Marc

Does this have something to do with US pilots' copying
the panels of the Europeans, who were winning big time?

At 03:30 15 September 2007, Marc Ramsey wrote:
snip

That does explain the change in airspeed units, the
change to knots on
the vario still seems a bit 'radical' for glider pilots
to pull it off
that quickly...

Marc