Why are headings still magnetic?

Mxsmanic wrote:
The SR-71 navigated by finding stars in the sky
[...]
(although it could not see them through cloud cover).

I thought the SR-71 flew above all the clouds.

Roy Smith writes:

I thought the SR-71 flew above all the clouds.

It did, but the aircraft's ANS would take a preliminary fix even as it
taxied out to the runway, if the sky was clear.

--
Transpose mxsmanic and gmail to reach me by e-mail.

Mxsmanic,

However, if it is designated 22 (it can be 22 or 23 if the real
heading is 225), an increase of only one degree in its true magnetic
heading would require a change to 23.


Hence my use of the words "up to".

--
Thomas Borchert (EDDH)

On Sat, 02 Sep 2006 21:09:00 +0200, Mxsmanic
wrote:

I was wondering about that. Seems like the airports around me have
had the same runway numbers for quite a while, but maybe my memory is
poor, or maybe I'm in a lucky position with respect to the magnetic
pole.

Since the markings are to the nearest degree, how often would they
have changed in your neighborhood?

"Roy Smith" wrote in message
...
I thought the SR-71 flew above all the clouds.

And high enough that the sky was dark even when the sun was out -- at least
from the photos that I've seen published...

And it was VERY fast. Look up the records they set and then
do some algebra. KC 135 tankers can do about 500 knots and
the SR 71 refueled twice on the record trip California to
London. Just figure out the maximum speed of the SR if it
spent a total of 30 minutes in the refueling process on a 2
hours flight...dash speed of 6,000 maybe.



"Grumman-581" wrote
in message
...
| "Roy Smith" wrote in message
| ...
| I thought the SR-71 flew above all the clouds.
|
| And high enough that the sky was dark even when the sun
was out -- at least
| from the photos that I've seen published...
|
|

And then there is DFW where parallel runways are 17L, 17C, 17R, 18L and
18R.
--
Gene Seibel
Gene & Sue's Aeroplanes - http://pad39a.com/gene/planes.html
Because we fly, we envy no one.




Mxsmanic wrote:
Thomas Borchert writes:

Let's assume Runway23. It's designated when the real direction is 225.
Now, how much has the real direction to change upwards for it to be
designated 24?

Eleven degrees.

However, if it is designated 22 (it can be 22 or 23 if the real
heading is 225), an increase of only one degree in its true magnetic
heading would require a change to 23.

The rule is to round the true magnetic heading to the nearest multiple
of ten and then drop the last digit. If the true heading ends in 5,
you can round up or down (there is no preference).

--
Transpose mxsmanic and gmail to reach me by e-mail.

A Blackbird would use less fuel if it didn't leak prior to take-off.


Jim Macklin wrote:
And it was VERY fast. Look up the records they set and then
do some algebra. KC 135 tankers can do about 500 knots and
the SR 71 refueled twice on the record trip California to
London. Just figure out the maximum speed of the SR if it
spent a total of 30 minutes in the refueling process on a 2
hours flight...dash speed of 6,000 maybe.



"Grumman-581" wrote
in message
...
| "Roy Smith" wrote in message
| ...
| I thought the SR-71 flew above all the clouds.
|
| And high enough that the sky was dark even when the sun
was out -- at least
| from the photos that I've seen published...
|
|

Mxsmanic wrote:
Like AM radio, magnetic headings are still with us, even though
navigation in general has advanced by leaps and bounds. When will
true headings be used? The magnetic poles are in continuous motion;
the rotational poles are stable.

Eventually, the magnetic poles will move so far that every station and
aircraft everywhere will have to be recalibrated to account for it,
and all charts will have to be changed. And the poles occasionally
reverse, which would also be somewhat of a disaster for
magnetically-based aviation.


So what instrument would you suggest we use for true headings? GPS does
not give you true heading; it can only give a true course. You can't
reliably use a GPS for verifying your runway heading. GPS headings only
work when you are in motion. Remember the Comair accident? I suspect
such accidents will increase if we switch to GPS based true headings.

Your suggestion will only work if we install gigantic beacons at the
true poles which everyone can navigate by. At present mother nature has
given us such a beacon, albeit a less than perfect one.

Because that's the way it's always been done?