Compass swing on an RV6

[Airmutt]

Yes, GPS in its pure sense does not know or provide heading.

Hand held units take advantage of MEMS and contain devices such as accelerometers, magnetometers or GNSS antennas all of which provide heading information. Almost every Garmin handheld has a compass page and the user can define the format - True, Magnetic, Grid. Hence their ability to display a compass rose.

Fixed units take advantage of similar devices (typically standalone) or receive heading info for other units such as an INS/INUs. The communication with these units is prioritized.

We did inflight alignments but we were equipped with dual GPS and INU units. In reality it’s a blended solution. Perhaps it was a bad use of terminology on my part but as an Atlanta native I call any soda a Coke.

I understand there are methods to determine heading by GPS lone but it involves using two units or two antennas. Unfortunately the science is beyond me. If I remember correctly it’s based on two points establish a line. By tracking the movement of the line the heading can be established? Someone way smarter than me can confirm or deny.

[Sam Buchanan]

Yes, GPS in its pure sense does not know or provide heading.

At the risk of beating a horse that may be drawing its last breaths.....

Yes, in its purest sense GPS doesn't know or provide heading. Matter of fact....in any sense it doesn't know or provide heading. It can only provide ground track.

Perhaps this can be an informational thread for aviators who may not fully understand the function and limitations of GPS; the poorly written AC could be misleading. Maybe this will help.....and I hope this hasn't sounded snarky.

[Dana]

How does an INS work in practice? I know how it works, in theory, but there has to be some way to initialize at startup it so that it knows its initial heading, no? Or does it have an internal magnetic sensor? Otherwise it seems like a DG, you'd have to set it to match the mag compass before takeoff, but if it's the mag compass you're trying to calibrate...

[Airmutt]

Here is a brief excerpt from Honeywell….

An inertial navigation system (INS) calculates the location, orientation and velocity of a moving object without the need of GPS technology.
An INS device typically uses accelerometers and gyroscopes, meaning motion and rotation sensors, that communicate with a computer unit which then translates the data into actionable controls. This is your basic inertial navigation system, to which other features can be added. For example, inertial navigation systems can be upgraded with magnetic sensors and barometric altimeters.
INS devices operate on a dead reckoning system, which means that the initial position, velocity and orientation of the vehicle are provided by an external source, which can be a GPS satellite receiver or an operator. Equipped with this data, the INS can begin calculating position, velocity and other movement elements. As the vehicle continues to move, the INS device will keep calculating and updating, on its own, all motion elements via the information received from motion sensors.