Metric Soaring

On Sep 16, 2:08 am, Ralph Jones wrote:
snip

Well, to get all pedantic, there have been several definitions of the
nautical mile, one of which was one minute of longitude at the
equator -- which has the advantage of being unambiguous since the
equator is a circle to very high precision. If you define it as a
minute of latitude you still have to specify the latitude where you
make the measurement, because the earth is not exactly spherical;
England defined it for a time as one minute of latitude measured at
the latitude of London.

Today it's simply defined as exactly 1852 meters, but "the arc length
subtended by one minute of latitude" is just peachy for navigational
purposes.

We got around to 'the arc length subtended by one minute of a great
circle' when I did a maritime navigation class back in the mid-90s.
It's a definition which is not quite correct, but resolves the
differences between lines of latitude & longitutude for this purpose.

I recalled a one-page article in Soaring magazine that promoted the
idea of using knots for vertical speed on the variometer. I finally
found it in the Soaring magazine index: June 1963. The author used a
pseudonym ("Sinbad"). I assume the soaring world was moving in that
direction anyway but this was the first our little group in the
midwest had heard of this idea. Within a few years, certainly by 1970,
everyone seemed to be switching over to knots both in conversation as
well as what they ordered on new instrument dials. It was a change for
me from feet per second (on a Cosim pellet vario--anyone remember
those?), meters per second (what the Winters of that era used), and
feet per minute (various varios of that day plus all of the light
aircraft rate-of-climbs we stuck into our glider panels as backups,
the most famous of which was the "Memphis" ROC that came out of Beech
Bonanzas from a decade or two earlier).

Chip Bearden
ASW 24 "JB"
USA

I have been really distressed since returning to Alaska from St.
Auban a few years ago when I had to give up my very easy metric 20/1
glide calculator system for 1/250,000 maps, i.e., my right hand with
four fingers, and a metric altimeter.

Life should be so easy here. Here's why:

A hand's width, just above the knuckles, is 20k on my marked up French
road map commonly used for soaring in the Sud Alpes. So at 20/1, you
need 1,000 meters to glide your hand's width across the map. Two
fingers on the map to a safety field requires 500 meters plus pattern
entry height which I had already marked on my map. All I had to do
was to count my fingers to the landing field, multiply by 250, and
add the pattern entry height to know whether I had to buy a new glider
or not.

It doesn't get much simpler than that which is fortunate for me
because I can't do much more complicated calculations in my head,
especially when I am stressing because I am low and lost in the
mountains in a foreign country where the only people who speak worse
French than I do are my fellow Alaskans Jeff Banks and Ed Kornfield
who also flew from St. Auban. No GPS, PDAs, or complicated glide
calculators (formerly known as prayer wheels in the old days of
circular slide rules), just lay your hand on the map, count your
fingers, and add.

One note on French altimeters: In addition to being marked in meters,
the French, rather sensibly when you think about it, have the -0- mark
on the altimeter on the bottom of the dial and you go up from there.

Pete Brown
Anchorage


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

Well, actually, it is!

I was taught this trick years ago----glad to see it works in "metricland"
also.

One finger width on a USA Sectional Chart 1:500,000 is (approximately) 5 NM
One Nautical Mile is (approximately) 6000 ft

So--at 30:1 (200 ft/mi), one finger is about 1000 ft required.
At 20:1(300 ft/mi), one finger is about 1500 ft required.

Add in pattern altitude, and there you are!

Hartley Falbaum
USA "KF"


wrote in message
ups.com...
I have been really distressed since returning to Alaska from St.
Auban a few years ago when I had to give up my very easy metric 20/1
glide calculator system for 1/250,000 maps, i.e., my right hand with
four fingers, and a metric altimeter.

Life should be so easy here. Here's why: