Directional Gyro drift

[johnhinson]

I was wondering what decides whether an aircraft suffers gyro drift in FS9. I know you can configure FS to self-correct all aircraft but if that option is not ticked it is necessary to manually correct it in most "classic" aircraft, e.g. DC-3s, DC-7Cs etc etc but modern jets do not (which I assume is accurate).

My puzzle is that the Curtis Commando doesn't seem to suffer drift and whilst I hold my hands up and admit I'm not using the full v2 package "as supplied" I don't think that would make any difference. I assumed that specific gauges do or don't suffer from drift but tests now suggest this is not the case. So, if not, is this configured in the aircraft.cfg, the .air file or the model? I'm not averse to a bit of meddling to get the results I want but I'm not quite sure where to start.

John

[stansdds]

Good question, same goes for FSX. Some aircraft feature gyro drift, some do not.

[Tom/CalClassic]

Good question - I have absolutely no idea...

A quick search of the DC-6B and C-46 aircraft.cfg files turns up that the DC-6B has the following section:

[direction_indicators]
direction_indicator.0=1,0

While the C-46 has:

[direction_indicators]
direction_indicator.0=3,0


The Aircraft Container SDK says that the indicator types are:

0 - None
1 - Vacuum Gyro
2 - Electric Gyro
3 - Electro-Mag Slaved Compass
4 - Slaved to another indicator

So perhaps a Vacuum Gyro is subject to gyro drift while an Electro-Mag Slaved Compass is not?

[sunny9850]

That seems to be the case. We ran into this question with the L-049, specifically with the small DG built I to the old AP we used in that model vs the main DG.
One drifts and the other one doesn't

Cheers
Stefan

[Johan Dees]

www.flightsimworld.com/forums/index.php?showtopic=108038

It is not necessarry correct in the Curtiss, the addon maker might have done it on purpose ?

[falcon]

In real life, Tom is correct. Vacum gyro's are subject to drift. Since the sim life is trying to duplicate FDE's as close to the real, than I assume they wrote it that way.
Falcon

[Tom/CalClassic]

To be honest I don't know which is correct for propliners - the flight manuals I've read don't seem to mention it.

The C-46 FD was one of the last ones that FSAviator updated and I know he doesn't think that FS gyro drift is very realistic (too fast?), so maybe he set it that way to get rid of it?

[sunny9850]

Technically it does not matter if you spin the gyros by air movement or electrically. It's the slaving that does make the newer ones more accurate and far less prone to drift.
www.pilotfriend.com/training/flight_training/fxd_wing/di.htm

The reason why some do more and some less within FS is IMHO strictly a case of MS coding not being quite as real as it gets. Basically treating all electrically driven gyros as slaved units and those vacuum driven ones as the unslaved variety.

Cheers
Stefan

[johnhinson]

Many thanks to everybody for the answers - I shall try changing the entries.

Best wishes,

John

[capflyer]

Stefan, I'm not quite sure that's true. I have several addon aircraft with type "2" Electric gyros and they drift just like the others. Electric gyros tend to drift less (as in real life), but only type "3" Slaved gyros don't drift. Electric gyros tend to drift less as they are usually spun faster than vacuum and vacuum isn't exactly "constant", leading to more variation in speed and lag during acceleration than with an electrical gyro.

Also, I may be wrong, but I'm pretty sure the DC-6 and DC-7 were delivered with slaved gyros. I know my Convairliner book shows they were delivered with flux-gate compasses (which is a type of slaving), but the FS model does not reflect this. I think what confuses many is that most of the early slaved direction indicators still had a drift knob. This was intentional as these still had gyros and could be operated without the flux gate as they failed quite a bit early on.

[Tom/CalClassic]

Hi,

I have seen references to flux gate compasses in the manuals, but didn't make the connection that these were relatively immune to drift. I have reread some of these, and other than the "caging" process you are supposed to do when stopped and level (I assume this is a form of calibration), there are no further adjustments required. This caging process must be performed each time you apply power to the compass, after warming up for 3 minutes. It says that the flux gate compass drives the azimuth wheels in the RMI, determines the VOR radials, and drives similar instruments. It also says the heading reading may vary from the magnetic compass by as much as 5 or 6 degrees, but if off by 10 degrees there is probably something wrong. There are typically two compasses installed in most propliners, one driving the captains' instruments, and the other the copilots'.

So I guess I should change those to type 3.

Thanks,

[Johan Dees]

en.wikipedia.org/wiki/Heading_indicator

"Some more expensive heading indicators are 'slaved' to a sensor (called a 'flux gate'). The flux gate continuously senses the earth's magnetic field, and a servo mechanism constantly corrects the heading indicator.[1] These 'slaved gyros' reduce pilot workload by eliminating the need for manual realignment every ten to fifteen minutes."

[Tom/CalClassic]

Thanks for the confirmation.

I've made the change to all my flyable aircraft, and they will become available as they get updated for other reasons. Of course, you all can make the edit right now.

I didn't know if the B377's should get the change, since they were built so early?

[sunny9850]

Hi Cap,

That's entirely possible, it has been a while since we did that. And it was that one specific gauge that reacted that way....it may have been coded internally to act as if it was slaved.
I guess a single exception does not a rule make

In the real world you are certainly correct that electric gyros would generally be a lot more resistant to the precession effects because of their higher rpm.
Vacuum or pressure driven gyros should reach their minimum required speed well below the usual 5" of system pressure. But of course they do have many more ways to get "sloppy" because of contamination, filter issues etc.

Having a slaved HSI was one of the major priorities for out Saratoga for those very reasons. And of course even better are the new mini glass panels from Aspen.

Cheers
Stefan

[capflyer]

Tom, the B377 was also equipped with such compasses. Boeing actually called them "Slaved Gyros" and the instruments were so labelled on the panel. I just double checked my B-377 manual to be sure.