Great Circle

Sorry for the above insouciant response.
The shortest distance would be a straight line I believe!
Probably you mean the shortest distance an airplane could travel over the surface of a sphere, in which case the Great Circle Route would indeed win I think.
http://www.gis.psu.edu/projection/chapter9.html
 
maximus said:
Is the closest distance between two points the great circle distance?
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No, but travelling through the earth is pretty much not gonna happen unless the Vulcans land sometime soon. So, we settle for second best and travel great circle routes when travelling over great distances. On short hauls, rhumb lines are used most oft unless your autopilot is tied into your GPS and you have it set to navigate by GC routing. Otherwise it's not worth the hassel.
 
Max, check:

http://www.aopa.org/members/ftmag/article.cfm?article=4633

A great circle course, if extended, will cut the Earth in equal halves. It's the shortest distance between any two points on the line. When flying along the equator, or along any north-south meridian, the course flown will be a great circle, and also represents a Rhumb line course. (A Rhumb line is a line upon the surface of the Earth that makes the same angle with all meridians, or imaginary circles.)

Jim
 
Those who really want to get into this subject can enjoy AFPAM11-216 Air Navigation, the official training handbook for Air Force navigators.
 
Stretch a string or thread between any two points on a globe. The path of the thread between the two points is the great circle route between those two points.

Regarding great, or not so great, circles, from what locations on the globe can you walk a mile south, then a mile west, then a mile north and be back where you started.
 
Bobby Day said:
Stretch a string or thread between any two points on a globe. The path of the thread between the two points is the great circle route between those two points.

Regarding great, or not so great, circles, from what locations on the globe can you walk a mile south, then a mile west, then a mile north and be back where you started.
Click to expand...

North Pole
 
maximus said:
Is the closest distance between two points the great circle distance?
Click to expand...
Max, spherical geometry is a blast, that is the geometry of the surface of a sphere.

Any two straight lines (on the surface of a sphere) intersect.
Two lines determine not one point, but two.
On and on it goes....
 
The Great circle is the most direct and Henning said it so well for we cannot fly through the earth to get to our destination. I remember so well and thanks to Bruce, two lines determine our position and destination. First learning to navigate as a deck hand on boats with a sextant shooting sun sights and working the sextant at night with star charts. Yes getting the heavenly body on the "horizon" at night was a real challenge but wow I do appreciate those early navigators. I was 14 working on delievering boats from New England to the Mid and South East Atlantic as a deck hand. Charts, Chronometers, DF, Sextants, Taffrail Logs and a real good Whisky Compass,are a navigators best friend.

John J
 
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Hmmmn. This is prompting me to go dig up my old cNAV textbooks....now that'll be a challenge...
 
Bobby Day asked:

Regarding great, or not so great, circles, from what locations on the globe can you walk a mile south, then a mile west, then a mile north and be back where you started.

Henning said:
North Pole
Click to expand...

North Pole is one correct answer. There is another. Actually, if you want to be exact, there are an infinite number of additional correct answers.

This is thread creep but another Nav. riddle. What US state is surrounded by six other states and it is possible to fly due south out of that state into each of the adjacent states?
 
bbchien said:
Max, spherical geometry is a blast, that is the geometry of the surface of a sphere.

Any two straight lines (on the surface of a sphere) intersect.
Two lines determine not one point, but two.
On and on it goes....
Click to expand...

How do to straight lines intersect if they are parallel of each other?
 
maximus said:
How do to straight lines intersect if they are parallel of each other?
Click to expand...

On the surface of a sphere, straight lines can only be parallel to each other at two points, on the opposite sides of the sphere.

Take a globe and look at the equator and at the arctic circle for example. Put a straight edge along the arctic circle and you will see that it isn't straight. Flying along the arctic circle, you would need a slow turn toward the pole to remain on the circle.

spherical geo is fun but not very intuitive until you get into it. We tend to think of things in two dimensions. After all, the world is flat. Well at least we (mankind) thought so for many years....

-Skip
 
maximus said:
How do to straight lines intersect if they are parallel of each other?
Click to expand...

There's really no such thing as a straight line on the surface of a sphere. Such a line can appear straight on a projection from the sphere, but then it depends on the projection.
 
bbchien said:
Hmmmn. This is prompting me to go dig up my old cNAV textbooks....now that'll be a challenge...
Click to expand...

The nice thing about the aerial sextant is that it's a bubble sextant so you can get a horizon (the height of eye correction at 12000' would just be way out of hand, plus you could be over clouds) even at night.
 
John J said:
The Great circle is the most direct and Henning said it so well for we cannot fly through the earth to get to our destination. I remember so well and thanks to Bruce, two lines determine our position and destination. First learning to navigate as a deck hand on boats with a sextant shooting sun sights and working the sextant at night with star charts. Yes getting the heavenly body on the "horizon" at night was a real challenge but wow I do appreciate those early navigators. I was 14 working on delievering boats from New England to the Mid and South East Atlantic as a deck hand. Charts, Chronometers, DF, Sextants, Taffrail Logs and a real good Whisky Compass,are a navigators best friend.

John J
Click to expand...

Many miles with an Admiral Full View sextant, a Walker Log and a Casio G-Shock watch. As for doing star sights, I've got two tips for you. Unaugmented, shoot your 3 star running fix shots at dusk and dawn, that way you can see the horizon easily. If you need to shoot at night, every sextant I know of has for available a Practice Horizon Bubble, if it doesnt come equiped with a light (some do some don't) you can rig one. Use the bubble sight for the horizon.
 
Henning said:
Many miles with an Admiral Full View sextant, a Walker Log and a Casio G-Shock watch. As for doing star sights, I've got two tips for you. Unaugmented, shoot your 3 star running fix shots at dusk and dawn, that way you can see the horizon easily. If you need to shoot at night, every sextant I know of has for available a Practice Horizon Bubble, if it doesnt come equiped with a light (some do some don't) you can rig one. Use the bubble sight for the horizon.
Click to expand...


Henning;


Thank you very much for the note ; :redface:

I was always a fumble fingers with the controll knobs on that sextant. I did work on the practice bubble and that really helped. Yes I do remember the Walker log. I use to use an old Army red light to "see the horizon". Wow this is great. I worked on the 3 star and that was so much fun and what a great education. I still go out at night and site stars for it keeps me aware. I still have the old Bendix Portable DF unit. It is 40 years old but it still works great.

Thank you agan for I do love to work the old stuff for who knows we may need it same day :redface:

John J
 
John J said:
Henning;


Thank you very much for the note ; :redface:

I was always a fumble fingers with the controll knobs on that sextant. I did work on the practice bubble and that really helped. Yes I do remember the Walker log. I use to use an old Army red light to "see the horizon". Wow this is great. I worked on the 3 star and that was so much fun and what a great education. I still go out at night and site stars for it keeps me aware. I still have the old Bendix Portable DF unit. It is 40 years old but it still works great.

Thank you agan for I do love to work the old stuff for who knows we may need it same day :redface:

John J
Click to expand...


Sometimes my mates will look at me funny when I break out the sextant and the H.O.s., then I make them do it. I do at least one or two fixes a week when underway just to stay in practice.
 
Bobby Day asked:

Regarding great, or not so great, circles, from what locations on the globe can you walk a mile south, then a mile west, then a mile north and be back where you started.

Quote:
Originally Posted by Henning
North Pole



North Pole is one correct answer. There is another. Actually, if you want to be exact, there are an infinite number of additional correct answers.

This is thread creep but another Nav. riddle. What US state is surrounded by six other states and it is possible to fly due south out of that state into each of the adjacent states?

Answers to the above riddles:

The infinite number of locations is any point ~1+(1 over 2Pi) miles north of the south pole. The circumference of the earth at 1 over 2 Pi miles north of the south pole is 1 mile.

The state is Arkansas. The western boundary of the Missouri boot heel slants to the southwest so it is possible to fly due south from Arkansas into Missouri. Similar situation with the Arkansas/Oklahoma border north of Ft. Smith. The rest are obvious.
 
Henning said:
Sometimes my mates will look at me funny when I break out the sextant and the H.O.s., then I make them do it. I do at least one or two fixes a week when underway just to stay in practice.
Click to expand...
Every P3 skipper is qual'd to do this.... :)
 
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