HSI drifting error

[simurqq]

No doubt, skills come with experience... After years of flying found myself in a situation when I don't know how to compensate for heading indicator's drifting error without pressing on D. This is bugging indeed, especially in the nothern latitudes (BC, Alaska, Siberia) where magnetic variance changes significantly.

Any advice from real-world experience is highly appreciated!

Thank you!



Sent from my Galaxy S4 using Tapatalk

[Oracle427]

I don't understand what question you are asking.

Friction forces that cause the heading indicator to slowly drift out of alignment has nothing to do with magnetic variance. It sounds like that you are seeing the need to adjust the indicator more often to match what the compass is reading thanks to the relatively rapid change in variance.

Normally, one should check if the indicator needs adjustment to match the compass once every 15 minutes.

[simurqq]

I was wondering how real pilots adjust heading indicator. In FSX, particularly in the northern latitudes, I usually notice that drifting reaches 5-10 degrees, hence my claim about variance.

So, thank you for a tip on comparing heading indicator's reading to compass!


Sent from my Galaxy S4 using Tapatalk

[AKar]

Victor,

Directional gyro may show erroneously because of friction and other instrument imperfections, but main reason for gyro drift we see here in sim is Earth's rotation. While it has nothing to do with magnetic variance (declination), it does dependent on your latitude (and is simulated in FSX). You can calculate the effect simply by ±15*sin(latitude) degrees per hour, negative sign for northern hemisphere and positive for southern. Note that your westerly/easterly movement also causes similar effect, called transportation wander, that adds up to that.

You can understand the root cause by parking an imaginary airplane to North Pole and noting that its directional gyro wants to point to fixed direction in space while the airplane rotates with Earth. As Earth rotates about 15 degrees an hour (counter-clockwise seen above in this setup), the indicated heading will decrease at that rate.

In many actual units, I understand that drift effect can be compensated for by knowing the approximate latitude at which the airplane is operated, and adjusting the gyro to automatically counteract the drift at given rate, therefore requiring less adjustment by pilot, but other than that there is not much else you can do but to compare with magnetic compass, and correct a few degrees every fifteen minutes or so. Note that instrument errors of several degrees are easily tolerable in most real world flying, and nowhere near as annoying as it is in the sim to have your instruments just a bit off.

-Esa

[simurqq]

Thank you very much for comprehensive answer, Esa! That will do the trick I'm sure...


Sent from my Galaxy S4 using Tapatalk

[n421nj]

Get level and set DG to compass heading or get rich and install an HSI that is slaved to compass