HSI bug - Bearing Pointer vs. Course Indicator

[VTJS17_Fire]

Hi,

 

maybe I'm doing something wrong or overlook something, but IMO the Course Indicator on the HSI (upper, right corner) doesn't show the correct bearing/ course to the selected waypoint.

 

I attached a simple mission. If you look at the HSI (already on the runway) and switch trough the different waypoints, you'll see a deviation between the Bearing Pointer and the Course Indicator.

 

The Bearing Pointer's shows the correct course to reach the selected waypoint, the Course Indicator is wrong.

 

If that's a bug, please confirm.

 

 

Gruß Fire

 

 

EDIT: Ok, attachment is now online.

f15c_nav.miz

Edited July 1, 2014 by VTJG17_Fire

[Magician]

Hi,

 

maybe I'm doing something wrong or overlook something, but IMO the Course Indicator on the HSI (upper, right corner) doesn't show the correct bearing/ course to the selected waypoint.

 

I attached a simple mission. If you look at the HSI (already on the runway) and switch trough the different waypoints, you'll see a deviation between the Bearing Pointer and the Course Indicator.

 

The Bearing Pointer's shows the correct course to reach the selected waypoint, the Course Indicator is wrong.

 

If that's a bug, please confirm.

 

 

Gruß Fire

 

 

EDIT: Ok, attachment is now online.

 

Not a bug, the course indicator shows the course to fly along the line from the previous waypoint. The Course deviation indicator in the HSI shows how far off that line you are. The marker in the HUD shows the bearing from wherever you are, there is also a little arrow outside the compass rose in the HSI which indicates the bearing to the waypoint from wherever you are.

 

ETA: "Flying the course line" can be pretty important for mission timing and threat avoidance, assuming the flight plan was created with those things in mind.

Edited July 1, 2014 by Magician

[Magician]

Additionally, if you bank the F-15C to center the director bar (short vertical line) over the VVI in the HUD, it will direct you onto and along the course line in the most expeditious way (supposedly).

[VTJS17_Fire]

Not a bug, the course indicator shows the course to fly along the line from the previous waypoint.

Source? In the DCS F-15C Flight Manual is nothing about that.

 

... there is also a little arrow outside the compass rose in the HSI which indicates the bearing to the waypoint from wherever you are.

Yep, the Bearing Pointer. But, what you say, didn't work. Fly my mission and at WP1 turn to WP2. According to your explanation, the Bearing Pointer (little arrow outside the compass rose) should match with the Course Indicator (upper, right corner in the HSI) ... but it don't.

 

 

regards,

Fire

[Magician]

Source? In the DCS F-15C Flight Manual is nothing about that.

Source is general knowledge about aircraft Navigation instruments, gained from many sources. The manual doesn't spell it out the way I did buit it does say this:

 

In the center of the display is the course deviation indicator. The course deviation dots show the deviation of the current aircraft position from the required course line. Each dot represents a 5- degree deviation from the set course. During an Instrumented Landing System (ILS) landing, the bars show the aircraft deviation from the landing course. In this situation it is identical to the ADI ILS bar indicator. Bear it in mind that these bars will move in opposite directions.

 

In the right upper corner of the instrument, the set course numerical indicator is shown. In the upper left corner, the range to the selected waypoint is indicated in nautical miles.

 

If the CDI is off by one dot, the bearing should be different than the course by 5 degrees. (according to the manual, YMMV)

 

 

Yep, the Bearing Pointer. But, what you say, didn't work. Fly my mission and at WP1 turn to WP2. According to your explanation, the Bearing Pointer (little arrow outside the compass rose) should match with the Course Indicator (upper, right corner in the HSI) ... but it don't.

 

 

regards,

Fire

 

It takes time and distance to turn a plane, if you wait till you overfly the waypoint to start your turn to the next one, you can expect it to be off the course line when you finish the turn. Especially so if the turn is particularly sharp and/or the distance to the next WP is particularly short.

 

ETA: Unfortunately the director bar doesn't anticipate the next WP to direct a smooth transition, unless you time a manual WP switch in advance of reaching it.

Edited July 1, 2014 by Magician

[Magician]

I do recall the A-10A training video on navigation goes into some detail about the HSI functions, anticipating turns etc... Don't know about the F-15 video though. But the HSI works the same in both.

[Magician]

Just for further edification, the "Set Course" is something that is done manually on most real mechanical HSI's (and on the DCS: A-10C). In the case of the FC3 American aircraft, it is done automatically according to the flight plan, on a WP to WP basis (or runway heading in ILSN mode).

 

If you were able to manually adjust it, it would agree with (or be 180 degrees off) the bearing when the CDI is centered.

Edited July 2, 2014 by Magician

[Magician]

I just had a look at and flew your mission;

 

Especially so if the turn is particularly sharp and/or the distance to the next WP is particularly short.

 

No and/or about it, that flight plan has both.

 

That being said, when I got the CDI centered on each leg, the course and bearing agreed.

[VTJS17_Fire]

If the CDI is off by one dot, the bearing should be different than the course by 5 degrees. (according to the manual, YMMV)

But it doesn't.

 

 

It takes time and distance to turn a plane, if you wait till you overfly the waypoint to start your turn to the next one, you can expect it to be off the course line when you finish the turn. Especially so if the turn is particularly sharp and/or the distance to the next WP is particularly short.

Thanks for that, but I've about 5.000 flight hours in the F-15 since LOMAC. ;)

 

 

In the case of the FC3 American aircraft, it is done automatically according to the flight plan, on a WP to WP basis (or runway heading in ILSN mode).

Nope, for the Nav mode this isn't true. I measured the direct course (WP to WP) in the mission editor and the Course Indicator in the HSI is always 10 degress off.

 

For Example (from my mission):

Mission Editor WP1 to WP2: 210°

HSI WP1 to WP2: 200 (already with the corrected course)

 

Mission Editor WP1 to WP2: 170°

HSI WP1 to WP2: 160 (already with the corrected course)

 

Screenshots attached.

 

 

I just had a look at and flew your mission;

That being said, when I got the CDI centered on each leg, the course and bearing agreed.

I tested it over 10 times and it doesn't work for me. Give us a Track, or it didn't happen ...

 

My track with the bugged HSI course indicator is attached. Also two screenshots, which confirm the deviation (with CDI centered) between Bearing Pointer (HSi and HUD) and Course Indicator.

 

 

regards,

Fire

 

 

PS: I also attached the direct course from the Mission Editor, so you can see what you have to fly from WP to WP. ;)

HSI_bug.trk

Edited July 2, 2014 by VTJG17_Fire

[104th_Maverick]

Source? In the DCS F-15C Flight Manual is nothing about that.

 

Yeah although you wont find much in the manual about it, it has been this way for years since FC1.

 

If you select a waypoint, the needle will 'point' to that waypoint... but the coarse as already mentioned will line up with the previous waypoint.

 

So the only way you can line them up properly .... is if you fly overhead waypoint 1... then start flying straight towards wp2 ;)

 

Thanks for that, but I've about 5.000 flight hours in the F-15 since LOMAC.

 

 

Then you really should have known this already sir :P

 

My track with the bugged HSI course indicator is attached. Also two screenshots, which confirm the deviation (with CDI centered) between Bearing Pointer (HSi and HUD) and Course Indicator.

 

I see your pictures and the numbers 'should' line up sir, do you have any wind in your mission? I'll do a quick flight later on just to verify this!

Edited July 2, 2014 by [Maverick]

[VTJS17_Fire]

;2106687']

I see your pictures and the numbers 'should' line up sir, do you have any wind in your mission? I'll do a quick flight later on just to verify this!

No wind. ;)

I know, they "should" ... :music_whistling:... that's why, I'm posted this. :smartass:

[Magician]

Okay, I see the issue now. It has nothing at all to do with the bearing pointer, or the course needle, it's that the 10's column of the set course window doesn't roll, it snaps to the next number after the 1's column fully reaches "0".

 

So it looks like it says 200 on WP 2, but if you look closely, the bottom of the 9 is still showing, and the 10's column just hasn't snapped to 1 yet. Another clue is if you look at the course needle, it is pointing at 210 (ETA: btw, the CDI in the picture for that wypoint ain't centered).

 

The exact same thing with WP 3 looking like 160, but the 9 is still showing at the top. And the course needle is showing 170.

 

But there is no problem at all with WP 4, it looks like 40 and it is 40.

Edited July 2, 2014 by Magician

[Magician]

As for the course needle and bearing pointer lining up vertically when the CDI is centered and the plane is on course with no wind, I dare anyone to show otherwise.

 

Turns out the director bar will cause an overshoot back and forth if you don't stay on it diligently enough, or don't switch waypoints soon enough. But eventually it will get you on course on the course line.

 

Unfortunately it seems to want to put your nose on course rather than your flight path in a crosswind situation. A problem both ameliorated and exacerbated by the CAS Yaw channel bug. If you use the CAS Yaw channel, the nose is aligned with the flight path, but you will be slipping pretty seriously in a crosswind.

[Magician]

On the A-10C, the 10's and 100's columns both roll along with the 1's column as the 1's column rolls between 9 and 0.

[VTJS17_Fire]

The exact same thing with WP 3 looking like 160, but the 9 is still showing at the top. And the course needle is showing 170.

Ok, but there's something buggy, right?

[Magician]

Ok, but there's something buggy, right?

 

Only that perhaps the coding should go ahead and round up and snap the 10's column up one when the course ends with a 9.7 or so or greater. Other than that it would take a major coding change to either make the 1's column round and snap, or make the 10's and 100's columns roll. But in that second case it would just make it even harder to read in situations like this (Found that out when I was doing it with the A-10C, trying to read the course when all the numbers are "in between" is a genuine PITA)

 

ETA: Overall I think they made a decent compromise between realism and making it legible the way they did it. It's not a bug, just what they decided to do it to minimize confusion... how often does the course actually end with 9.7 or greater?... ok, so twice in that flight plan LOL.. but that seems to be a fluke (or intentional). Seriously even with the proposed rounding up, that'll just make some people confused about whether it was between 209 and 210, or between 219 and 220 (the answer is in where the needle points).

 

Personally, I only find that window useful for making a precise setting of the course when doing it by hand, which makes it irrelevant to me in FC3 aircraft. I "fly the needles", and they are accurate, right down to some fraction of a degree.

Edited July 3, 2014 by Magician

[Magician]

I was recently flying the A-10A and happened to notice the set course window on that plane is completely borked. It seems to bear no relation at all with the course to fly. Now that one is either a bug, or not implemented at all.

 

On a side note, the director bar on that plane also wants to line up the nose with the bearing to the WP, rather than the flight path. At least it has the SPI/WP box in the HUD that you can line up the VVI with, and an EAS yaw channel that doesn't center the VVI.