great circle rule

[luckykathryn]

Dear All.

I'm only a private pilot but i'm being ridiculed by my other colleages in the office, therefore I hope you can help me.

We were having an arguement abt if you fly directly from London to Houston that it was quicker (in time and distance) to go in a straight line across the globe. I 100% percent disagree with this. I understand that it is quicker to fly north via greenland etc....

Can someone calculate the distance directly (in time and distance) from London directly to Houston (across the globe) and to go via the north like most normal airliners do.

Thank you !

[qwertyuiop]

I am not very clever and plotting really blew my brain but i think its like this.

Take a globe and place a pin in your start and end point. Attach rubber band to both pins and as long as it is tight (stright line) you have the shortest route.

Problem, or confusion, comes when you draw this on a flat map. The same line will now be curved.

A simplified answer but basically true. (i think!!)

[stargazer02]

Hi there
just get a model globe and show them that it is easier
being a PPL i suggest that it would be good practice for you to figure it out and prove it to your collegues rather that just take someone's word for it.
Perhaps they are just pulling your leg to see the extent of your education in aviation....
Remember never argue with a fool .....people might not know the difference.

[canepa]

HELLO Lucky kathryn,

What you are asking for is a simple problem of spheric trigonometry,

Assuming that :
La and Ga are the coordinates of your departing point. La for latitude and Ga for longitude,
Lb and Gb the coordinates of your arriving point,
D the distance of the circle line between two points,

cos D = sinLasinLb + cosLacosLbcos( Gb-Ga )
cos D = sin51°30sin29°46 + cos51°30cos29°46cos95°22
cos D = 0.340
D=70°12, therefore 4212 NM.

philippe,

[bookworm]

The problem is what you mean by "across the globe". If you turn the globe appropriately you'll see that the great circle is "a straight line across the globe".

[canepa]

hello again,

As I said in my previous message, the distance of the circle line between London and Houston is 4212 NM,

Now if you take the rhumb line, the formula is a bit more complicated and I don't want be rude.
The distance of the rhumb line is 4513 NM.

That should be enough for your colleagues.
4212 NM by the north ( circle line ) and 4513 NM with a constant route ( rhumb line ).

Bye now,

philippe,

[luckykathryn]

Dear Philippe,

Thank you for yr time in doing this for me.

You have mande me very happy that I'm not going stupid and £100 richer. So next time you are in London you are welcome to come out for a few drinks!

[canepa]

I will be delighted to enjoy a beer with you in some cosy pubs in LONDON.

philippe,

[eastern wiseguy]

city to city (http://www.aeroplanner.com/calculators/avcalcdist.cfm)


this might be a bit of fun for your colleagues!;)

[south coast]

phillipe...

are you the same philipe who worked in fort worth a few years back at a small private air school...?

if not, appologies.

[bluue]

LuckyKathryn,

You may care to look at the folowing site. Its very interesting and may help answer your question. [Great circle plotter].

http://gc.kls2.com


bluue:O