Nautical Miles vs Statute Miles ?

[Robert Eilers]

Sorry guys, I have arrived at the "who gives a &%$!" level.

[Indopilot]

George,

I have taken off from Gallup headed west on a hot day with a full load in the 171. After a slight deviation to miss the tv antenna's of the trailer park and checking for loose screws as we went past all the street light heads at the truck stop. I figured I had it made as it was all down hill Statute Miles to Winslow and the Knots in my stomach were starting to ease up.

[N4064V]

I always use statue miles so that I go faster!

[170C]

Well as I tell most everyone, Ole Pokey doesn't fly in knots. There isn't anything in the instrument panel marked in those nautical terms. If I were sailing, it'd be in knots, but I'm flying and my antiquated, glow in the dark airspeed indicator is in statute miles and a plane of this vintage never saw an ap indicator in knots. (Now before someone jumps on me and tells me a 1928 whatever had an as indicator in knots, I mean a C-120, 140, 150, 170, 172 180 up until years after ours were produced.) Ocassionally I will put one gps on knots & one on statute so I can tell how far in knots I am from some place to tell center or the tower. Also on rare occasions if I am flying with someone who insists on using knots I'll do the dual thing also. Most of the time if I am approaching an apt I'll just tell them I am X miles out and let them figure our whether its statute or knots. If I am in a good mood I may tell them X statute miles. Getting contrary in my advanced age aren't I 1

[cessna170bdriver]

Also a nautical mile is shorter at the Equator than at the poles, so your unit of measurement is not consistent. This could equate to about 60'.

Not really.

A nautical mile is only historically defined as a minute of arc. There was a time in history when the earth was considered to be round for all practical purposes, and navigators felt lucky to hit the correct country. In those days defining a nautical mile to be a minute of arc was more than adequate.

Since the earth is roughly 25 miles shorter than it is wide, the length a great circle minute of arc does vary as you move from the equator to the poles. When it became important for navigators to hit targets smaller than countries, a more precise definition of the nautical mile became necessary. The National Institute of Standards currently defines the international nautical mile as 1852 meters. Exactly. Wikipediaagrees.

The bottom line is that these days a nautical mile is a nautical mile is a nautical mile whether it's on the north pole or equator or on the moon. It's a VERY consistent unit of measurement.

I differentiate between navigating and flying the airplane. I navigate (how far is it, and how long will it take me to get there?) with knots because that is the default for all of my nav gear. It's easy to change the GPS to statute miles, but leaving it alone is even easier. If my loran has an option, I don't know about it. My DME doesn't give me a choice.

I fly the airplane (deploy flaps, set approach speeds, etc) in miles per hour simply because my original airspeed indicator and all of the published performance data for the airplane uses that unit. I see no reason to replace a perfectly good instrument or convert the data. I'd feel the same way if it had been done in pounds per square foot or furlongs per fortnight.

To each his own, Miles

[GAHorn]

Also a nautical mile is shorter at the Equator than at the poles, so your unit of measurement is not consistent. This could equate to about 60'.

From Wikipedia:
The historical definition differs from the length-based standard in that a minute of arc, and hence a nautical mile, is not a constant length at the surface of the Earth but gradually lengthens with increasing distance from the equator, as a corollary of the Earth's oblateness, whence the need for "mean" in the preceding sentence. This length equals about 1,861 metres at the poles and 1,843 metres at the Equator, a variation of one percent

The nautical mile is not "shorter" at the equator. It's the same all over the world. It's just that it's longer than a minute-of-arc with increasing distance from the equator. (Although Paul Wood sometimes gets his drawers in a knot.)

[Harold Holiman]

I started flying with statute miles, all my planes have had the airspeed indicator marked primmarly in statute miles, and my brain works more naturally in statute mile (when it works). I mainly used knots when flying a newer aircraft marked primarly in knots (which I did not often do) or when flying IFR (which has been a long time ago). I figured mph worked good for me in 45 years of flying so why change.

Harold

[flat country pilot]

Can the Garmin 296, 396 or 496 show mph and statue miles at the same time?

Bill

[jrenwick]

Can the Garmin 296, 396 or 496 show mph and statue miles at the same time?

Bill

I don't think so. There's a global "units" setting page, where you can set distance units to statute, nautical, or metric. All speed and distance displays respond accordingly.

[flat country pilot]

That's what I thought. It's just a little computer, Garmin could program them to show both.

However that could get confusing if the pilot read the wrong number.

Bill

[3958v]

With my anywhere map you just touch the groundspeed with the stylus and it will switch between the two. I use statue miles when talking to non aviation people and nautical miles while talking to aviation people. Bill K

[GAHorn]

... and inches, when talking to women.

[blueldr]

Re the above:

Go metric! Centimeters !

[GAHorn]

Re the above:

Go metric! Centimeters !

I think you meant kilograms.

[blueldr]

OK, George. You win.