[RESOLVED] Tomcat heading drift - ED Forums
 


Notices

Reply
 
Thread Tools Display Modes
Old 04-08-2019, 11:16 AM   #1
=BJM=
Member
 
Join Date: Nov 2015
Posts: 750
Default [RESOLVED] Tomcat heading drift

I have been having difficulty achieving the correct heading and abeam distance downwind and I noticed something...

My heading as indicated on the HUD and VDI will slowly drift left as I progress on the downwind.

I have a carrier setup on the Caucasus map heading 090 (084 magnetic). On the downwind, I attempt to head 264 magnetic, however; I slowly see my heading drift left to the point where when I am abeam the LSO platform, my heading in cockpit is 260 and on the F10 map it's 275 (which would be 269 magnetic). That is a 9 degree error and would explain why I cannot line up correctly on the downwind and struggle with getting the correct abeam distance.

There is no wind.

I flew a Case I at Nellis to test this further and saw that there was no heading drift here and all compass heading matched up. This issue seems to be when landing on the carrier only.

Is this an intended "feature" of the Tomcat or is it a bug?
__________________
i5 7600K @4.6GHz | 1080 Ti | 32GB 3200MHz | SSD | 27" 2560x1440p | X-55 HOTAS and Pro Flight Rudder | TrackIR 5

Last edited by IronMike; 04-14-2019 at 04:14 AM.
=BJM= is offline   Reply With Quote
Old 04-08-2019, 02:50 PM   #2
Moafuleum
Member
 
Join Date: Jun 2016
Posts: 203
Default

HB said that the carrier influences the local magnetic field. Hence i guess it is intended
Moafuleum is offline   Reply With Quote
Old 04-08-2019, 02:53 PM   #3
=BJM=
Member
 
Join Date: Nov 2015
Posts: 750
Default

Quote:
Originally Posted by Moafuleum View Post
HB said that the carrier influences the local magnetic field. Hence i guess it is intended
I understand that, but I thought that was just while on the carrier deck. Are you saying that the carrier's influence extends out some distance as well?
__________________
i5 7600K @4.6GHz | 1080 Ti | 32GB 3200MHz | SSD | 27" 2560x1440p | X-55 HOTAS and Pro Flight Rudder | TrackIR 5
=BJM= is offline   Reply With Quote
Old 04-08-2019, 03:33 PM   #4
Moafuleum
Member
 
Join Date: Jun 2016
Posts: 203
Default

Quote:
Originally Posted by =BJM= View Post
I understand that, but I thought that was just while on the carrier deck. Are you saying that the carrier's influence extends out some distance as well?
Magnetic fields don't decay according to a step function but continuously. Don't quote me on that but I believe I read somewhere that it can be one or two miles (or more?). The nearer to the source the more distinct the effect will be.
Moafuleum is offline   Reply With Quote
Old 04-08-2019, 03:36 PM   #5
Cobra847
3rd Party Developer
 
Cobra847's Avatar
 
Join Date: Sep 2012
Location: Helsingborg, Sweden
Posts: 3,009
Default

Quote:
Originally Posted by =BJM= View Post
I understand that, but I thought that was just while on the carrier deck. Are you saying that the carrier's influence extends out some distance as well?
Yes

But it decays quite fast.
__________________
Nicholas Dackard

Founder & Lead Artist
Heatblur Simulations

https://www.facebook.com/heatblur/
Cobra847 is offline   Reply With Quote
Old 04-08-2019, 03:55 PM   #6
=BJM=
Member
 
Join Date: Nov 2015
Posts: 750
Default

Quote:
Originally Posted by Cobra847 View Post
Yes

But it decays quite fast.
Holy moly! Phenomenal level of detail indeed!!

Well, they say the HUD is useless in landing mode and now this added on top of that...can the Tomcat get anymore difficult to land?!


What is the correct procedure to account for this? How do we fly the correct headings? Is it just all visual?
__________________
i5 7600K @4.6GHz | 1080 Ti | 32GB 3200MHz | SSD | 27" 2560x1440p | X-55 HOTAS and Pro Flight Rudder | TrackIR 5
=BJM= is offline   Reply With Quote
Old 04-08-2019, 04:05 PM   #7
Moafuleum
Member
 
Join Date: Jun 2016
Posts: 203
Default

Quote:
Originally Posted by =BJM= View Post
What is the correct procedure to account for this? How do we fly the correct headings? Is it just all visual?
Tacan needle should always point towards the ship's direction. The question is, does the tuned course line also drift? Since it is set to a specific bearing. If not, then this is your solution.
Moafuleum is offline   Reply With Quote
Old 04-08-2019, 03:09 PM   #8
ivo
Member
 
ivo's Avatar
 
Join Date: Dec 2010
Location: Fighter town
Posts: 659
Default

For my cent I believe 9 degrees are the difference between boat and the deck carrier...
__________________
cpu:I7-6700k Z170 16GB Ram DDR4 Gtx 1080 8Gb DDR5 11GBs SSD 500 Gb 2 HDD 1Tb Evga supernova G2 850w Case Bequiet series 800 Silent base Win 10 pro 64 bit

My wishlist: F16C/F-35/B-17G/F4U Corsair/Yak-3/P-40C Tomawhak

ivo is offline   Reply With Quote
Old 04-08-2019, 03:46 PM   #9
Biggus
Junior Member
 
Join Date: Aug 2011
Posts: 77
Default

That's a phenomenal level of detail.
Biggus is offline   Reply With Quote
Old 04-08-2019, 07:17 PM   #10
Super Grover
Member
 
Super Grover's Avatar
 
Join Date: Nov 2010
Posts: 111
Default

It's quite complicated. There are a few reasons why your magnetic heading could have been that wrong. Did you take off from a carrier? If yes, then probably you got some initial error on the AHRS directional gyro -> error in the magnetic heading in SLAVED mode after launch. Even if you do nothing, it should return to normal after a while (much longer while), but you have to fly level and constant speed (and flying constant low speed in the F-14 is a challenge).
The magnetic field from the carrier decays really fast with distance from the ship, so I don't think it could cause that. Plus the magnetic heading is gyro stabilized (in SLAVED), so even when you do a really close fly-by, it shouldn't impact your magnetic heading.

Then, there's the magnetic flux valve (Magnetic Azimuth Detector - MAD) in the vertical tail. It's fixed. It feeds the AHRS with the relative direction of the magnetic North. When you roll or pitch, it becomes sensitive to the vertical component of Earth's magnetic field. This means - it becomes erroneous. That's why the directional gyro slaves to the MAD only in horizontal flight. At least in theory. In practice - you fly constant speed in a nose up attitude or with some hardly noticed bank for long enough, your directional gyro will slave to a slightly erroneous magnetic North.

That's why it's important to observe the HSD and the TID for the MV acronym (magnetic variation). It is displayed alternately with the IN or IM when the difference between the computed magnetic variation (MC) and the manual magnetic variation (VM) is greater than 5°.

If your directional gyro/synchro is shifted, it may result in erroneous interpretation of the TACAN direction on all instruments. You might have the carrier straight in front of your nose, but the BDHI will show the TACAN a few degrees to your left or right. However, the radial (bearing) reading would be correct; it would be just your magnetic heading wrong.

And there's much more...
__________________
Krzysztof Sobczak

Heatblur Simulations
https://www.facebook.com/heatblur/
Super Grover is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

All times are GMT. The time now is 12:19 AM. vBulletin Skin by ForumMonkeys. Powered by vBulletin®.
Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.