RV8Squaz

RV8Squaz

Well Known Member
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
 
keep in mind. Roads and fences were laid out by farmers and Civil engineers, accuracy may not have been considered.
 
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.
 
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!
 
It depends

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.

Andrews.jpg
 
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Ah yes, that would be the Exxon Fullerton oil field in the photo. Current supplier of a good chunk of my flying budget!:D
 
At our end of Arizona..

...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....:D

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.
 
az_gila said:
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.
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Gil, there's no wind in Kansas (unless your name is Dorothy, I guess)! :D

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

Cheers,
Bob
 
n5lp said:
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.
Click to expand...
That's funny. Maybe the Texas School Board changed the state's geography standards or something. :D
 
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az_gila said:
..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....
Click to expand...

rvmills said:
Gil, there's no wind in Kansas (unless your name is Dorothy, I guess)! :D...
Click to expand...

I don't know how the Cessna guys did it but when I used the roads it was back in the days of yore when airplanes, including my RV, had directional gyros. I would momentarily align the airplane with the line while setting the gyro. I would use the road direction most closely aligned with the wind.

The actual compass swinging would be with reference to the gyro with frequent gyro resets.
 
I had to replace the compass in my C-152 and put in a SIRS Navigator. The AP on the field told me to swing the compass as follows since we do not have a compass rose on the field. With the engine running and the DG stabilized, put the airplane on a known heading such as the taxiway that ran parallel to the runway. Adjust the DG accordingly. Then taxi out to the ramp and put it (the DG) on the 360* heading and adjust compass, then the 180* and adjust, then the 270*, then the 090*. Do that a couple times and you get it as close as can be. Worked very well and I love that SIRS!
 
Surveying : RVer's today using the hard work our founding fathers

Historically, the laying out of our country was extremely important as settlers were often on the heels of the surveyors. Look at the number of founding fathers who were surveyors...it's impressive and their role in our country was extremely important. By the way, the US Congress vote was one shy of founding our national standards on the metric system way back when. Now here we are hundreds of years later commenting on the work of those folks who drug chains over mountains and swamps!

The accuracy of most of them is very impressive considering what they had to work with. However, a few really botched it: like the north Georgia/Tennessee boundary.
 
A minor error...

n5lp said:
..... 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.
....
Click to expand...

Since the magnetic deviation is around 9 degrees in this part of TX, I wonder if they got the sign wrong when they corrected the Magnetic North for True North.

One little mistake at the beginning of the day, and at the end of the day, "screw it, no-one will notice"...:D

Or perhaps the Spanish laid it out before the Texans got there....:)
 
Using GPS - a better way

The GPS (my 496, anyhow) uses the magnetic data from a given year. It happens that it is not the same year as FAA uses on charts (at least on IFR charts, likely on VFR, too). As you know, the magnetic pole is moving so different years give different results. For that reason, I suggest using the GPS another way.

Side note: you can fly from VOR to VOR with GPS perfectly accurately, but your magnetic path will not necessarily be exactly what is shown on the IFR chart. It is only a problem, if at all, when you have to fly a bearing from a VOR without knowing the end point. This would also apply when intercepting a radial without a known intersection.

If I remember correctly you can set your GPS to display true direction. It has to know this to use lat-long accurately. It shows magnetic only as calculated and derived from true north and based on your position.

Decide what kind of magnetic reference you want to use and apply it yourself while flying a given ground track using GPS true direction.

If you know a given road is accurate then by all means fly it, but that is not as easy as it sounds unless you are down fairly low.
 
az_gila said:
Since the magnetic deviation is around 9 degrees in this part of TX, I wonder if they got the sign wrong when they corrected the Magnetic North for True North.

One little mistake at the beginning of the day, and at the end of the day, "screw it, no-one will notice"...:D

Or perhaps the Spanish laid it out before the Texans got there....:)
Click to expand...

If you look at a map of that part of Texas, you'll see that the section lines are just parallel and perpendicular to the highway through there. Just a few miles north of the part in Larry's photo, the highway takes a slight bend, and the section lines on either side follow right along.:confused:
 
Again... does not account...

hevansrv7a said:
.....Decide what kind of magnetic reference you want to use and apply it yourself while flying a given ground track using GPS true direction.

If you know a given road is accurate then by all means fly it, but that is not as easy as it sounds unless you are down fairly low.
Click to expand...

...for any offset to counteract cross winds... GPS gives an accurate Ground Track.

As I mentioned before... do it while you taxi and the cross wind should not come into play...:)
 
Part right part maybe

az_gila said:
...for any offset to counteract cross winds... GPS gives an accurate Ground Track.

As I mentioned before... do it while you taxi and the cross wind should not come into play...:)
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Yes, I did ignore XW and that is a problem, just as it would be with flying a road. I like the taxi idea. And you can check the airport diagram or other data for the actual 3-digit heading of the runway.

GPS ground track is accurate, but how do we define accuracy?
  • For true, it is easy to define: agrees with Lat-Long.
  • For magnetic, it is not easy because you need to incorporate the magnetic variation (or is it deviation - I always get those mixed up) and there are multiple references for that. GPS will be accurate within its own frame of reference, but not necessarily agree with FAA nor be accurate for today.
 
If only that were possible in Vermont where most roads are shaded by maple trees and are as bent as a dog's hind leg :)
 
WI Grid North

In Wisconsin the section lines are based on State Plane Coordinates and aligned to grid north. Each section line has a slightly different bearing because they are based on physical monuments buried in the ground or under pavement. In one quarter section near my home, the bearings for 4 sides of the box are N 87-45-35 E, N 02-05-22 W, N 89-29-26 E and N 01-27-45 W. Adjacent quarter section lines (1/2 mile apart) can differ by almost 2 degrees.
 
jsharkey said:
If only that were possible in Vermont where most roads are shaded by maple trees and are as bent as a dog's hind leg :)
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Many years ago, at a fly-in in a part of Tennessee with very few straight roads, I overheard a participant from Ohio make the comment that if one could hold a heading by ground reference over Tennessee, they could do it over open water...
 
Should not be a problem....

hevansrv7a said:
......GPS ground track is accurate, but how do we define accuracy?
  • For true, it is easy to define: agrees with Lat-Long.
  • For magnetic, it is not easy because you need to incorporate the magnetic variation (or is it deviation - I always get those mixed up) and there are multiple references for that. GPS will be accurate within its own frame of reference, but not necessarily agree with FAA nor be accurate for today.
Click to expand...

The magnetic variation is in the FAA database for all of the sectionals, and is updated regularly - check your sectional chart legend for the Isogonic Lines, and the year the FAA references them to for that chart edition.
This database is in your aviation GPS.

There are not multiple references to that.

Perhaps you are thinking of the GPS data coordinate references, which would have an insignificant affect on displayed Ground Track over the short distances we are using to taxi....:)

I say the taxi method referencing to your aviation GPS with an up-to-date database is in the +/- 1 degree range - probably better than most other methods...:cool:
 
Thanks guys and particulary Joe for the links. There's a whole world about land surveying I didn't know anything about before this thread.

I have swung my compass on a compass rose in the past. I also have SIRS compass and seems to be very reliable and accurate. I regularly use the taxi method with the GPS to set the DG and crosscheck it with the compass which seems the best way to set the DG. However, my DG drifts a little and I thought using the section lines would be a great way to cross check the compass and DG in-flight. I realize that mag heading will be off in wind. But you can do this when there is little or no wind or just simply forget about the wind correction for a few seconds and keep the fuselage aligned with the section lines. Now that I know section lines are generally referenced to True North I can add/sub the variation and check my DG and compass. The compass seems pretty accurate. I had tried it on my way back from SNF. I followed a north bound section line and the compass was reading 005 which is about dead on for central FL. I assumed the lines were referenced to True, but now I know for sure. Thanks!

Jerry
RV-8 N84JE
 
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