Dear Mike,
Sorry, I can't remember the source. I was simply intrigued by the idea
of a mile measured in seconds, or in this case microseconds.
Cheers,
Pat Naughtin
Author of the ebook, Metrication Leaders Guide, that you can obtain
from http://metricationmatters.com/MetricationLeadersGuideInfo.html
PO Box 305 Belmont 3216,
Geelong, Australia
Phone: 61 3 5241 2008
Metric system consultant, writer, and speaker, Pat Naughtin, has
helped thousands of people and hundreds of companies upgrade to the
modern metric system smoothly, quickly, and so economically that they
now save thousands each year when buying, processing, or selling for
their businesses. Pat provides services and resources for many
different trades, crafts, and professions for commercial, industrial
and government metrication leaders in Asia, Europe, and in the USA.
Pat's clients include the Australian Government, Google, NASA, NIST,
and the metric associations of Canada, the UK, and the USA. See http://www.metricationmatters.com
for more metrication information, contact Pat at pat.naugh...@metricationmatters.com
or to get the free 'Metrication matters' newsletter go to: http://www.metricationmatters.com/newsletter
to subscribe.
On 2010/04/22, at 22:53 , Michael Payne wrote:
Where on earth did this come from? Radar is just radio and travels
at the speed of light which if memory serves me is 300 000 km/s
(exactly 299 792 458 m/s) regardless of the distance unit used. So
the distance travelled would be (1852 x 2) m or 3704 m for Nautical
miles and 2000 m for Kilometers. I think this is 12,3 µs for
nautical miles and 6,67 µs for kilometers.
Mike
----- Original Message -----
From: Pat Naughtin
To: Michael Payne
Cc: U.S. Metric Association
Sent: Wednesday, 21 April 2010 22:00
Subject: Re: [USMA:47211] Re: Air flight altitudes in meters
Dear Mike,
Can you help me with the places where I have xxxx?
#
Miles of radar in seconds
The time required for a radar signal to travel from the transmitter
a distance of one mile to an object, and then return to the
receiver. Both ordinary (statute) and nautical miles are used: the
radar statute mile is about 10.8 microseconds (µs) and the radar
nautical mile is about xxzx microseconds. An equivalent SI unit
would be the radar kilometre, which is about XXZX microseconds (µs).
#
Cheers,
Pat Naughtin
Author of the ebook, Metrication Leaders Guide, that you can obtain
from http://metricationmatters.com/MetricationLeadersGuideInfo.html
PO Box 305 Belmont 3216,
Geelong, Australia
Phone: 61 3 5241 2008
Metric system consultant, writer, and speaker, Pat Naughtin, has
helped thousands of people and hundreds of companies upgrade to the
modern metric system smoothly, quickly, and so economically that
they now save thousands each year when buying, processing, or
selling for their businesses. Pat provides services and resources
for many different trades, crafts, and professions for commercial,
industrial and government metrication leaders in Asia, Europe, and
in the USA. Pat's clients include the Australian Government, Google,
NASA, NIST, and the metric associations of Canada, the UK, and the
USA. See http://www.metricationmatters.com for more metrication
information, contact Pat at pat.naugh...@metricationmatters.com or
to get the free 'Metrication matters' newsletter go to: http://www.metricationmatters.com/newsletter
to subscribe.
On 2010/04/22, at 00:21 , Michael Payne wrote:
All large modern aircraft built since around 1975 have Inertial
Reference Systems (IRS) for Navigation. Nowadays IRS is a Laser
Ring Gyro with no moving parts. Since around 1995 GPS came on the
scene and the IRS get its initial position from a GPS or pilot
input source, once aligned, the IRS measures motion and
acceleration in 3 axis (plural?) and will determine its own
position. This position information is fed into 3 Flight Management
Computers (FMS) that store the route of flight as Latitude/
Longitude coordinates. The flight management computers receive
input from 3 IRS and 2 GPS receivers and 2 VHF Distance Measuring
Equipment receivers (DME), updating using the distance from 2 or
more known DME sources on the ground to triangulate position using
lateral and altitude information. The FMS will give preference to
GPS position, then FMS position then DME position. Additionally
each FMS compares its position to that of the other two, if one
goes beyond a certain distance from the other two it's voted out of
the computation and the other 2 FMS are used only. The theory is
that if GPS and DME are lost over the oceans the aircraft position
would be known to the FMS based only on IRS information which has a
known drift rate. Before GPS came along IRS was the only source of
position over the oceans until ground stations could be picked up
and the position updated based on DME/DME. It's a very
sophisticated and expensive piece(s) of equipment.
You could say that nowadays GPS is the primary source of navigation
data with IRS as a backup. Large aircraft also use the IRS as the
sole source of attitude information for the pilots (there are 3 of
them), there is no separate attitude or directional gyro, there is
no longer a magnetic compass either, the FMS computes position and
required track based on True North, then adds (or subtracts) the
local magnetic variation to give a magnetic track, all of this from
the database used for navigation.
It is possible to look up the GPS altitude but it's not used for
any purpose. We still use the same pressure level converted to a
Flight Level (1013 hPa) or an altitude MSL based on a local
altimeter setting (QNH). The change from Flight Level to Altitude
varies worldwide by country, in the North America it's 18000 ft,
Mexico 20000 ft. Europe 3-5000 ft above the airport, Australia
15000 ft, Africa 3-5000 ft above the airport.
It's been my experience that GPS is normally accurate to around 5 m
laterally, there are times when there are insufficient satellites
to use for a GPS approach and the pilot is warned. The navigation
is so accurate that ICAO recommends aircraft offset to the right of
track when out of radar contact in case someone is coming the other
way on the same track at the same altitude. This happened in Brazil
about 4 years ago when 2 aircraft coming in opposite
directions collided, the winglet of one apparently sliced the wing
of the other aircraft which crashed, one landed OK.
Mike Payne
----- Original Message ----- From: <mech...@illinois.edu>
To: "U.S. Metric Association" <usma@colostate.edu>
Sent: Monday, 19 April 2010 03:32
Subject: [USMA:47172] Re: Air flight altitudes in meters
What is the contribution of GPS data to the navigation of large
aircraft?
Do GPS data dominate barometric data?
---- Original message ----
Date: Sun, 18 Apr 2010 18:10:10 -0700 (PDT)
From: "John M. Steele" <jmsteele9...@sbcglobal.net>
Subject: [USMA:47170] Re: Air flight altitudes in meters
To: "U.S. Metric Association" <usma@colostate.edu>
Cc: "U.S. Metric Association" <usma@colostate.edu>
Actually, it is nominally based on height above
sea level. Sitting on the runway, with altimeter
correction dialed in, it will read the published
height of the runway above sea level.
At cruise levels, no altimeter correction is used
and reading is called flight level. It is the
height above sea level IF sea level were at 15 °C,
101.325 kPa, and a lapse rate of -6.5 K/km to the
stratosphere (11 km), and zero lapse rate above that
to 20 km. Further it it uses a height variable
called geopotential height, the height that would be
true if gravity were constant with height. There is
a transformation between that and geometric height
in the standard.
------------------------------------------------
From: James R. Frysinger <j...@metricmethods.com>
To: U.S. Metric Association <usma@colostate.edu>
Cc: U.S. Metric Association <usma@colostate.edu>
Sent: Sun, April 18, 2010 8:47:07 PM
Subject: [USMA:47168] Re: Air flight altitudes in
meters
Altimeters work off of atmospheric pressure
readings, Pat. But the readout is in terms of height
above terrain. So assignments and reports are always
in length units. No human pressure to altitude
correlation procedures are used.
Jim
