Is my CDI weird? (trk attached)

[Spirit X]

So I feel like I'm just starting to get a grip on the nav systems on A10 after a week or so of reading and playing, mostly reading. I'm still a little confused about the CDI though.

 

My main question is: does the CDI ever rotate by itself or do you always have to manually set the course? Is there no way to just slave it to the heading needle? It just seems weird that it still shows deviation correctly but does not show the correct heading.

 

While I've been experimenting with it, I've noticed some odd behaviours. Mostly after I program an in-flight fligh plan. It seems that once I've programmed and activated my plan, the CDI does not function at all until I've got close to my second waypoint. Then it suddenly kicks in.

 

Have attached a trk to demonstrate. These times are all according to the stopwatch in the pit which I start at the beginning of the mission (I assume that's how you guys do this?):

• Take off isn't until about 10 mins (still learning the manual start-up sequence)
  
• After take off I fly a couple of waypoints from the pre-flight flight plan. Showing the CDI functioning correctly (although not rotating).
  
• 15:00 - I start orbitting in autopilot while I'm creating new marks and waypoints for my flight plan.
  
• 18:55 - I start programming the flight plan using my new waypoints.
  
• 21:00 (ish) - I'm done with the plan and start flying it. You can see that the CDI is not functioning and I fly across the flight path a couple of times to demonstrate.
  
• 31:50 - I'm getting close to the second waypoint and suddenly the CDI starts working.
  
• 33:40 - I turn on the ILS and from there on in everything is pretty normal as far as I can tell.
  

Any help with this would be great as I haven't found any threads mentioning these issues.

 

Thanks.

NavTest01.trk

[Sven2157]

So I feel like I'm just starting to get a grip on the nav systems on A10 after a week or so of reading and playing, mostly reading. I'm still a little confused about the CDI though.

 

My main question is: does the CDI ever rotate by itself or do you always have to manually set the course? Is there no way to just slave it to the heading needle? It just seems weird that it still shows deviation correctly but does not show the correct heading.

 

The Course needle direction( what the "course" is turned to on the HSI ) is irrelevant when using GPS. The Course Deviation Indicator( CDI ) will center when you are on course and "deviate" left/right when you are off course. The GPS system is constantly updating your Lat Lon, and receiving information from a Satellite.

 

However, the Course Needle direction is important when using INS and straight VOR navigation. Inertial Navigation System( INS ) uses a system of sensors to record your movement. Much like being blind folded in a car and trying to feel where you are going. Very High Frequency Omnidirectional Range( VOR ) broadcasts a frequency out in a directional( 0-359° in increments of 1° ) range. Much like the spokes on your Bicycle tire. When you set the Course Needle to a specific degree and have your NAV radio tuned to a specific frequency, you are telling the system that you want to fly on a specific "spoke". The CDI will tell you if you are on that "spoke" or not. Because the INS relies on VORs and other navigation systems like this( ADF, NDB, etc, etc ), you should set your course.

 

Hope that helps!

[Rongor]

Because the INS relies on VORs and other navigation systems like this( ADF, NDB, etc, etc ), you should set your course

No, it doesnt. The INS is not a FMC and also doesnt interact with some sort of Nav-database. INS determines your position by accelleration sensors and gyros. This is the reason we have to wait some time for alignment after starting up the CDU.

Also there is no VOR inside DCS world. At least we have no VOR receiver in the A-10C. Only the TACAN. TACAN works like secondary radar, your TACAN radio interrogates the TACAN station and receives distance and bearing values. So again, no setting of course is necessary.;)

 

Bytheway, ADF and NDB refer to the same technique. NDB is the ground installed radio beacon, ADF is your airborne receiver to work with NDBs..

[Rongor]

To answer the OPs question, your CDI is working fine, from your description (dont have DCS here at the moment so couldnt watch your track).

You will have to switch on STR PT on the NMSP. Then the bearing pointer 2 in the HSI will point to the active waypoint. If you want to fly directly inbound on the present bearing, you can now turn the course knob until the course is equal to the direction of the bearing pointer 2. From now on the CDI needle will wander out of the center if you deviate from the track.