Stanley777 Posted December 15, 2016 Share Posted December 15, 2016 Hi everyone, I think that I know what is going on, but I wanted to check with you knowledgeable people to make sure. Using the autopilot on my default FSX SE Learjet 45, let's say that I have set a heading of due North (that is, obviously, 0 degrees or 360 degrees). But on my GPS it looks like I am going about, oh, 350 degrees once my aircraft has stabilized and is going straight. Or let's say that I have set a heading of due East (thus, 90 degrees). Then my GPS shows approximately 80 degrees. Is this what I think is going on -- that is, a deviation between magnetic direction (using the autopilot) and true direction (using the GPS)? Or do I have some software problem? Thank you, as always. Stanley Intel Core i7-9700K CPU @ 3.60 GHz | NVIDIA GeForce RTX 2070 | Dell U2717D monitor | Thrustmaster T.Flight Stick X Total available graphics memory: 24534 MB; Dedicated video memory: 8192 MB; System video memory: 0 MB; Shared system memory: 16342 MB Link to comment Share on other sites More sharing options...
PhantomTweak Posted December 15, 2016 Share Posted December 15, 2016 You got it right. It's the difference, where you are in the world, between Magnetic and True North. If you were elsewhere in the world, it would be different. Does that answer your question? Pat☺ [sIGPIC][/sIGPIC] Had a thought...then there was the smell of something burning, and sparks, and then a big fire, and then the lights went out! I guess I better not do that again! Sgt, USMC, 10 years proud service, Inactive reserve now :D Link to comment Share on other sites More sharing options...
ponchovilla Posted December 15, 2016 Share Posted December 15, 2016 The GPS shows the MAGNETIC course. Start with your TRUE direction, add or subtract your magnetic VARIATION, and you will get your MAGNETIC direction. I always remember it as "TRUE - VARIATION - MAGNETIC" or "TVM". Or, "This is Very Magnetic." Hope this helps. Fair skies and following winds, -Frank- PROUD FS RTWR Pilot since 2015! Kick the tires and light the fires! We's goin' FLYIN'!:D Link to comment Share on other sites More sharing options...
hovercrafter Posted December 15, 2016 Share Posted December 15, 2016 Compass drift turned on in settings? Ctrl D (I think) will synchronise if drifted off. Gordon Link to comment Share on other sites More sharing options...
Stanley777 Posted December 15, 2016 Author Share Posted December 15, 2016 Hi everyone, Thank you for your responses. But, ponchovilla, your answer confuses me. I thought that the GPS shows true direction and the compass shows magnetic direction. Stanley Intel Core i7-9700K CPU @ 3.60 GHz | NVIDIA GeForce RTX 2070 | Dell U2717D monitor | Thrustmaster T.Flight Stick X Total available graphics memory: 24534 MB; Dedicated video memory: 8192 MB; System video memory: 0 MB; Shared system memory: 16342 MB Link to comment Share on other sites More sharing options...
mallcott Posted December 15, 2016 Share Posted December 15, 2016 Hi everyone, Thank you for your responses. But, ponchovilla, your answer confuses me. I thought that the GPS shows true direction and the compass shows magnetic direction. Stanley Actually you are both right. GPS can show either. Natively it reads rel. true north, but the software can also calculate and display magnetic north, derived from actual measured position and inbuilt data - It calculates the current location and direction of the north magnetic pole and (potentially) any local variations, if the GPS is set to use magnetic compass readings. However your discrepancy is likely a result of not resetting the compass rose to fix gyro drift OR related to course v heading misunderstanding over the effect of crosswind component. Link to comment Share on other sites More sharing options...
PhantomTweak Posted December 15, 2016 Share Posted December 15, 2016 Compass drift turned on in settings? Ctrl D (I think) will synchronise if drifted off. Gordon Actually, it's just "D", not Ctrl-D. Like the local altimeter reset, to get the proper setting in the Kholsman (sp?) Window is simply "B". This is by default, BTW. You can change the key assignment like any other. I've gotten into the habit, personally, of hitting "D" "B" about every 15 min or so. Just as a precaution. Whether I am travelling straight to someplace, or just puttering around an area for fun. Whether I have the real world (where IS that place, anyway??) weather on or not. Just a habit. Have fun flights no matter what :D Pat☺ [sIGPIC][/sIGPIC] Had a thought...then there was the smell of something burning, and sparks, and then a big fire, and then the lights went out! I guess I better not do that again! Sgt, USMC, 10 years proud service, Inactive reserve now :D Link to comment Share on other sites More sharing options...
Stanley777 Posted December 15, 2016 Author Share Posted December 15, 2016 Hi everyone, I also press 'd' and 'b' every once in a while. But even without doing that, what is the setting to prevent gyro drift? I thought it was the following: Settings > Realism > do not check "Enable gyro drift" Is that correct? Stanley Intel Core i7-9700K CPU @ 3.60 GHz | NVIDIA GeForce RTX 2070 | Dell U2717D monitor | Thrustmaster T.Flight Stick X Total available graphics memory: 24534 MB; Dedicated video memory: 8192 MB; System video memory: 0 MB; Shared system memory: 16342 MB Link to comment Share on other sites More sharing options...
mallcott Posted December 15, 2016 Share Posted December 15, 2016 Hi everyone, I also press 'd' and 'b' every once in a while. But even without doing that, what is the setting to prevent gyro drift? I thought it was the following: Settings > Realism > do not check "Enable gyro drift" Is that correct? Stanley Yes Link to comment Share on other sites More sharing options...
lnuss Posted December 15, 2016 Share Posted December 15, 2016 That's correct Larry N. As Skylab would say: Remember: Aviation is NOT an exact Science! Link to comment Share on other sites More sharing options...
pcwildman Posted December 16, 2016 Share Posted December 16, 2016 My two cents- the GPS only knows the direction you are traveling in, usually expressed as Magnetic. The compass indicates which way the nose is pointing. After accounting for MagDev and Wind you could be facing 20 degrees off the course you are actually flying. So your compass may say 340 (the direction you're facing- heading) and the GPS says 360 (the direction you are flying- course). I've been wrestling with this for years doing spreadsheet navigation and it's still confusing with the terminology- course, heading, bearing (which is used to indicate either heading or course). Hope this helps. And I hope I have it right! Phil And why turn off gyro drift? It is a real world phenomena. Link to comment Share on other sites More sharing options...
TseTse Posted December 17, 2016 Share Posted December 17, 2016 The GPS displays your aircraft's magnetic TRACK. The compass displays your aircraft's magnetic heading. Variation doesn't play a huge role here, but the winds aloft that causes the aircraft to crab into the wind does play a role. http://i.imgur.com/iMDlMAv.jpg TseTse i5-9600K @ 3.7~4.5GHz | RTX2060 Super 8GB | 32GB DDR4-3200 | 1TB Samsung 840EVO | Z390 Chipset | Windows 10 x64 Link to comment Share on other sites More sharing options...
ponchovilla Posted December 17, 2016 Share Posted December 17, 2016 Another thing to consider is which map window you have showing in the GPS. The window with the compass rose will show your magnetic course - you'll always be moving toward the top of the window. The other map window is oriented toward true north. This window will have true north at the top of the window no matter which direction you fly. Fair skies and following winds, -Frank- PROUD FS RTWR Pilot since 2015! Kick the tires and light the fires! We's goin' FLYIN'!:D Link to comment Share on other sites More sharing options...
Stanley777 Posted December 17, 2016 Author Share Posted December 17, 2016 Hi ponchovilla, Your last comment was quite instructive. I always use the second window, the one with the map window oriented toward true north. Stanley Intel Core i7-9700K CPU @ 3.60 GHz | NVIDIA GeForce RTX 2070 | Dell U2717D monitor | Thrustmaster T.Flight Stick X Total available graphics memory: 24534 MB; Dedicated video memory: 8192 MB; System video memory: 0 MB; Shared system memory: 16342 MB Link to comment Share on other sites More sharing options...
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