Section lines/roads on the ground

RV8Squaz · #1 04-22-2010, 07:27 AM

Anyone know if the section lines and or roads are oriented generally to True North or Mag North? I think True North but I am not sure. I thought it would be an easy (read lazy) way to do a quick compass swing or check. I have an RV-8, so it would be an easy way to have the airplane in a level attitude with the engine and electronics running.

Jerry
RV-8 N84JE

hydroguy2 · #2 04-22-2010, 07:42 AM

keep in mind. Roads and fences were laid out by farmers and Civil engineers, accuracy may not have been considered.

jnorris · #3 04-22-2010, 07:45 AM

IIRC they are aligned with true north. For what it's worth, here's what Wikipedia has to say:

http://en.wikipedia.org/wiki/Section...land_surveying)

Here's some more info:

http://www.topodepot.com/USGS_PLSS_BACKGROUND.aspx

Ron Lee · #4 04-22-2010, 07:45 AM

Around here (Colorado) I assume true north. Apply magnetic variation (deviation?) and they are around 350, 80, 170 and 260 degrees magnetic. Close enough for my flying.

Ironflight · #5 04-22-2010, 07:57 AM

I remember reading an article many years ago in Flying magazine that followed a Cessna Skyhawk through it's production test flight and on through the process of customer delivery. What stuck with me was that the pilot had a specific checklist he had to go through for each airplane, and one of the items was to swing the compass - in flight - using the vast array of straight lines available in central Kansas. Hard to beat those section lines!

n5lp · #6 04-22-2010, 08:10 AM

Where I live the lines are very reliably true cardinal directions and I have used them to help swing compasses. I have flown some places in West Texas where they are not. I don't know what they are but it seems like they are off more than if they were magnetic directions. Maybe about 20?. I find it very disorienting.

edit:

I found one of the areas I was thinking about. The photo below is from an area west of Andrews, Texas. The lines are about 15? off in the direction away from magnetic north.

airguy · #7 04-22-2010, 09:25 AM

Ah yes, that would be the Exxon Fullerton oil field in the photo. Current supplier of a good chunk of my flying budget!

az_gila · #8 04-22-2010, 09:50 AM

...they are set on the True cardinal directions.

A check of the County GIS surveys can even show the accuracies involved.
For the square mile section I live in, the E/W lines are off by 6 minutes and 4 minutes of a degree.
The N/S lines are off by 2 minutes and 1 minute.

Certainly good enough to fly by....

Probably somewhere near you is a road called "Baseline Road" - that should be the most accurate in your area...

With reference to the Cessna guys flying section lines to check their compass, it seems to me that that does not take into account any wind drift correction angles.

I have checked my compass while moving on long, straight taxiways, using the GPS ground track as a master reference. The GPS display will have already corrected for magnetic deviation. Go to enough airports and you can get enough data to make a Compass Correction Card.

rvmills · #9 04-22-2010, 10:13 AM

Quote:

Originally Posted by az_gila

With reference to the Cessna guys flying section lines to check their compass, it seems to me that that does not take into account any wind drift correction angles.

Gil, there's no wind in Kansas (unless your name is Dorothy, I guess)!

Gonna have to find Baseline Road here...neat idea!

Cheers,
Bob

alpinelakespilot2000 · #10 04-22-2010, 10:19 AM

Quote:

Originally Posted by n5lp

I have flown some places in West Texas where they are not. I don't know what they are but it seems like they are off more than if they were magnetic directions. Maybe about 20º. I find it very disorienting.

edit:

I found one of the areas I was thinking about. The photo below is from an area west of Andrews, Texas. The lines are about 15º off in the direction away from magnetic north.

That's funny. Maybe the Texas School Board changed the state's geography standards or something.