Duke - whiskey compass grossly incorrect
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I was flying the Grand Duke and although rarely refer to the whiskey compass, I did note yesterday how grossly incorrect it was.
The whisky compass was reading 290, and my electric/gyro compass was reading 265. I also checked the magnetic heading in the GTN750 readout to confirm my suspicion, and it also read 265 magnetic.
I also checked that no windshield heating was active.
I just wanted to pass this info. back in case it's something that slipped through, or got spoiled in one of the SimUpdates.
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I was flying the Grand Duke and although rarely refer to the whiskey compass, I did note yesterday how grossly incorrect it was.
The whisky compass was reading 290, and my electric/gyro compass was reading 265. I also checked the magnetic heading in the GTN750 readout to confirm my suspicion, and it also read 265 magnetic.
I also checked that no windshield heating was active.
I just wanted to pass this info. back in case it's something that slipped through, or got spoiled in one of the SimUpdates.
@Captain_J Many other high current electrical systems can effect the magnetic compass, but it should not be as much as 25°. I just tested this, and I don't see any discrepancy, so please grab a screenshot of the entire cockpit next time you see the issue.
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I haven't had a chance to dive back in and obtain screenshots, however I had a thought. Is it possible the whisky compass was showoing the physical / actual heading, but the DG and the GTN750 was giving physical track data instead heading data?
I suggest this because on the day, I was heading west, and there was an 80 to 100 knot northwesterly wind. There was therefore probably a 20 to 30 degree tack / clockwise heading correction to correct for the high cross-track wind from the right. Would that explain the coincidental 25 degree difference???
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I haven't had a chance to dive back in and obtain screenshots, however I had a thought. Is it possible the whisky compass was showoing the physical / actual heading, but the DG and the GTN750 was giving physical track data instead heading data?
I suggest this because on the day, I was heading west, and there was an 80 to 100 knot northwesterly wind. There was therefore probably a 20 to 30 degree tack / clockwise heading correction to correct for the high cross-track wind from the right. Would that explain the coincidental 25 degree difference???
@Captain_J The GTN 750 should give your track, since that's all a GPS knows, but your HSI is slaved to a flux-gate magnetometer, and will always show magnetic heading, unless the magnetometer coupling fails.
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@Captain_J On the Map page, I believe it is Menu → Map Settings → Map → Heading Up. I believe the option is there, although I'm not entirely brushed up on how it works since I've never used it IRL.
Garmin says Heading Up is available when a suitable heading source is connected, such as ARINC 429, RS-232, or an approved synchro heading source, such as the Bendix/King KI-525A HSI. The Century NSD-360A HSI itself is not listed as a compatible heading source.
That said, the Collins RMI-30 requires a synchro-format heading input to function and the Century IV also uses heading information from the NSD-360A/Century compass system, which could plausibly include a bootstrap synchro output. So it is plausible that the same synchro heading source is also providing heading information to the GTN 750.
Another interesting point is that the GTN requires a heading input, along with electronic TAS data (typically from an ADC) to calculate the Wind Speed and Direction Field. (A flight school I rent from found that out when they tried to equip an old 172n with a 650).
Though none of this appears to be simulated by TDS/PMS, and the Heading Up option and Wind Field will simply work regardless of the aircraft.
