Are sectional paths correct across "long" distances?

wrote in message . com...
Kyler Laird wrote in message ...
Awhile ago I pointed out in rec.aviation.piloting that one of my
tools will generate a map using stitched sectionals for a given
route.
http://groups.google.com/groups?hl=e....edu.au#link10
Ben Jackson mentioned that it didn't look correct to just draw a
straight line between two points so far away (across multiple
sectionals). I have looked into it a few times but I haven't
come up with a definitive answer.

So...anyone know the answer? Pilots are certainly accustomed to
drawing straight lines on a sectional to find the shortest path
between two points, and I've never been taught to do anything
other than align sectionals by sight to plan multi-sectional
flights. Does this not work over long distances?

One path I know fairly well is LAF-MER. The Great Circle path
happens to go right near Denver (where I usually stop). If that
path is plotted as a straight line on the sectionals
https://aviationtoolbox.org/Members/...selected.x=411
it appears to follow the path I'd expect.
https://aviationtoolbox.org/Members/...selected.x=427

Also, there's an easily-identified area on that path where Iowa,
Illinois, and Missouri meet. Take a look at the Great Circle
route.
http://gc.kls2.com/cgi-bin/gcmap?PAT....380N+120.568W
Again, this seems to match the area on the straight-line path
drawn on the sectional.
https://aviationtoolbox.org/members/...selected.y=324

Anyone know for sure whether or not this is an accurate way of
depicting Great Circle paths in the conUS?

Thank you.

--kyler

As a rule of thumb:

Use this equation to draw the bow. It gives the distance offset from
a straight line for the circle route.

A: Lat
A: Longitude

B: Lat
B: Longitude

A and B are the two locations.

C: km of rhumb line.


Nathanial Bowdich has an equation there for this method and is
forgotten, but available from his Navigation Book.

Except his method is to find the equation that fits the geometer's
rhumb line, meaning Bowdich only has a method of navigation and not
the true rhumbline solution.

Making my equation a constant for the earth sphere type, where only
the geometry of all spheres allows the applied line!! That is geometer
talk btw.

C*1.3 seconds= Alat

C*1.3 seconds= Blat

Two simulatanous equations to solve for C, the rhumbline. Longitude is
the reason for the 1.3 seconds of time arc, as a constant.

Meaning just take the time of the trip and lengthen until the A and
the B are equal latitudes!

That is it.

Douglas Eagleson
Gaithersburg, MD USA

Aslo note that to solve, the definition of seconds is a distance for
the place. A place on the map selected for the rhumbline. And here,
the 1/2, the distance of the straight route line is the selected
point.

This makes the time to go one half the route a time for the least
pleasent route to navigate. Does a new rhumbline for the half the
original route have to be mathematically converging??? Ha ha!

Never, because another system of equations would be encountered. A
short trip!!

So, the reason for the clarification is to cause the time to equal the
rhumbline. A simple rule of thumb. Time will equal distance
navigationally.
A nonphysics solution because it is caused by the relation of location
to the definer of location, as the time of rotation. The lattitude
and longitude are time locations!

Douglas Eagleson
Gaitherbsurg, MD USA

"Kyler Laird" wrote in message
...
"Peter Duniho" writes:

There is absolutely no basis for Center ever asking you to justify your
choice in flight planning.

My use of "explain" was apparently ambiguous. I've not been asked to
justify my route (that I recall), but I have been asked to elaborate on
how
I'm going to deal with airspace barriers. I got the feeling that they
wanted more than "I'm going to avoid them."

But frankly, that's just a red herring anyway. There's no way in hell
that
any controller would want to know why you flew a sectional straight line
instead of a great-circle route or vice a versa. The difference is just
noise to them.

Again, that's off the subject. I don't know that I'm capable of providing
further clarification on my preference to have all of my maps (and paths)
be aligned.

That's my own laziness though. I'm perfectly happy justifying the use of
Great Circle paths for the tools I build solely because it's The Right
Thing to do.

--kyler

When flying VFR, I've been asking about my planned route of flight before.
The controller is just doing his/her job and wants to get the heads up.

"Roy Smith" wrote in message
...
In article ,
(Paul Tomblin) wrote:
snip
You've got to go pretty big distances before GC errors start to become
significant. For example, to go from 38N/77W to 38N/122W (roughly
Washington, DC to San Francisco, CA), the rhumbline is 270 and the GC is
284. 14 degrees on a coast to coast trip. If you're flying it nonstop
in a jet, it makes sense to take that into account. For most of us
flying spam cans, we just can't fly long enough legs for it to become
significant.


And it is all moot anyhow, since you'd be IFR and not using VFR charts...

"F1" wrote in message
...
When flying VFR, I've been asking about my planned route of flight before.
The controller is just doing his/her job and wants to get the heads up.

Did the controller ask you to explain why you chose one route versus
another? I doubt they did. That is the issue here, not a controller's
general interest in which way you're going.

In article ,
"Peter Duniho" wrote:

"F1" wrote in message
...
When flying VFR, I've been asking about my planned route of flight before.
The controller is just doing his/her job and wants to get the heads up.

Did the controller ask you to explain why you chose one route versus
another? I doubt they did. That is the issue here, not a controller's
general interest in which way you're going.



I've had controllers ask me "how I'm navigating" while VFR. But I
believe the intent of the question has generally been, "Can you give me
a heads-up where you're heading so I can anticipate your flight path
better?" Sometimes I think it's been, "Based on where you said you were
going, I'm wondering if you're lost; do you need some help?"

In all cases, if I've come back with something like, "We're going to be
maneuvering in the area of X for a while", or "We're going to be
following X, Y, and Z", (no matter how absurd or circuitous that path
might have been), that's seem to satisfy the controller.

"Roy Smith" wrote in message
...
[...]
In all cases, if I've come back with something like, "We're going to be
maneuvering in the area of X for a while", or "We're going to be
following X, Y, and Z", (no matter how absurd or circuitous that path
might have been), that's seem to satisfy the controller.

Exactly. That was my point. The controller doesn't care, and has no reason
to care, why you pick a particular route. They just want to know what the
route is (and much of time, they aren't too terribly concerned about that
either, if you're VFR).

Pete

The controller doesn't care, and has no reason
to care, why you pick a particular route. They just want to know what the
route is (and much of time, they aren't too terribly concerned about that
either, if you're VFR).

An amusing incident: 20 or 30 years ago, I left central PA for
Rochester, NY, and asked for flight following. (Pretty wild country
much of the way.)

Since thre ae no VORs along that route, Center asked me for my route.
I said "Direct Rochester." A pause. Then he asked, "Do you have
RNAV?"

I said, "No, I have a line on a chart."

There was a long period of silence. I guess it was a young controller
who had never heard that before.

vince norris