[FIXED INTERNALLY] Tadpole not giving steering que to intercept steerpoint

[Evovcui]

Your description is just what I feel... Following the cue I can hardly get the right heading when I level out.

[razo+r]

Labelled "Not a bug", but at the same time it's labelled as "Investigating". GG

 

https://forums.eagle.ru/showthread.php?t=251170&highlight=steerpoint+cue

[JTFF - Raph]

+1

[Tomsk]

Here's another illustration of the problem: I am keeping the tadpole centred as I turn away from the steerpoint faster and faster:

 

chYbNLgnigY

 

The problem is the tadpole is currently showing how far the steerpoint deviates from the vertical plane of the aircraft. So if the steerpoint is directly underneath the belly of the aircraft it shows as being "centred". As the above video shows, this means you can be going nowhere near the steerpoint and it'll still show as "centered" if you bank the plane steep enough so that the steerpoint is directly underneath the belly of the plane. This error is also what makes it crazy hard to follow the tadpole: in order to turn towards where the tadpole is indicating you have to bank the plane towards the tadpole, but that extra bank means the steerpoint is even less "underneath" the plane's vertical axis .. and so it moves the tadpole further away from you.

 

This isn't right, the tadpole should instead be showing things in terms of headings only. If your heading is directly towards the steerpoint it should be centred, irrespective of bank angle. It should show guidance of where to turn so that your heading will point directly towards the steerpoint. Note that your heading towards the steerpoint does not change just because you bank the aircraft, it only changes if you actually turn and change heading.

 

You can see the contrast with the HUD tapes that were posted earlier in the thread: in real life just banking the plane doesn't move the position of the tadpole. That is because the real life tadpole is showing to what degree your plane's heading is pointing towards steerpoint, which does not change just by banking the plane.

Edited October 19, 2019 by Tomsk

[Frederf]

That should be double checked if steering error is comparison of heading to heading to steer or velocity azimuth to desired track. I'm almost positive that it's the latter which means FPM matters and gun cross doesn't. I.e. if you're 90 AOB and pulling 20 AOA across the horizon the steering error will be zero when FPM is on the diamond and heading shows 20 degrees past the wings-level wind corrected heading to steer.

 

Looking more closely the following aspects of GCSC positioning can be summized:

 

• GCSC vertical positioned same pitch as FPM (unsure nadir, zenith)
  
• GCSC lateral position relative to FPM displays steering error
  
• GCSC lateral position is approximately 5:3 ratio to steering error
  
• GCSC is directly above steerpoint diamond at zero steering error (drift norm)
  

Looks like the total lateral displacement is about +-3 degrees on the HUD but represents about +-5 degrees of steering error. When the FPM is dragged through the desired direction you'll see the GCSC come unclamped from the lateral limit when steering error is about 5 and then the diamond will move toward the FPM by 5 degrees at the same time as the GCSC slides about 3 degrees to line up. There's a parallax effect as the GCSC moves through ~6 degrees of HUD space to represent 10 degrees of steering error.

[Tomsk]

Yes, good clarification, I would also very strongly suspect that the tadpole shows relative bearing between the ground track (I.e relative to the FPM) and the steerpoint rather than simply where the nose is pointing (I.e. relative to the gun cross). This of course would give wind corrected directions to fly to the steerpoint.

Edited October 20, 2019 by Tomsk

[VampireNZ]

Perfect example below of how it should work - tadpole should not be related to bank angle - it stays where it is and you bank over to place the FPM on the tadpole and level out.

Note in this vid how you can bank left and right over the tadpole and it stays 'still' relative to the desired direction, not shooting left and right across the HUD with bank angle changes.

 

[Deano87]

Glad to see this thread re-opened. Currently its not really usable.

[Hamilton]

The movement does seem janky - like it is linked to the horizon bars on the HUD, so when you bank it scoots over to the side.

 

In my experience with the tadpole it stayed pretty neutral horizontally and you could bank over to it and place the FPM on it, not bank over and have to try and guess where it will centralise again when you level out.

 

 

Exactly, certanly it´s not OK the way it is now.

[P3CFE]

The Tadpole is very bugged..it should not react on roll !!!

Note: Maybe a little, because of INS inaccuracy during movement about the Ptch roll and Yaw axis.

 

It should only react on heading change..Not roll Change.

 

Seems like It is programmed more as a flight director with command steering..... that is wrong !

It should behave like a needle pointing to the steerpoint at all times.

 

 

Glad it is being investigated, but I hope it doesn't take to long..it is a clear mistake !

[Swift.]

This looks like exactly the same issue razbam had with their harrier ccrp bombing line. It moves the wrong way when you roll.

[P3CFE]

I also remember that that was unworkable in the Harrier.

 

I have checked that out a moment ago....and luckily that fault seems to be fixed.

It was the same kind of error.

 

Greetz

[txmtb]

This looks like exactly the same issue razbam had with their harrier ccrp bombing line. It moves the wrong way when you roll.

 

 

Weird you say that, was running F16 ccrp practice last night and was thinking that the tadpole should act more like the ccrp line.

[Dispatch]

I just ignore it till fixed.

[Frederf]

I think GCSC placement can be solved with brief mathematical understanding. GCSC has three aspects to its display:

 

• Cue vertical position
  
• Cue horizontal position
  
• Cue line direction
  

Display of these three aspects are controlled by only thee variables:

 

• Flight path angle
  
• Great circle steering error
  
• Bank angle
  

Cue vertical position is simply equal to FPM vertical position referenced to the pitch ladder (FPA). Perhaps the FPM is 6 degrees above the horizon. Then cue is placed 6 degrees above the horizon. It doesn't matter bank or gun cross location.

 

Cue lateral position is based on great circle steering error value. When steering error is >10° left or >10° right, cue is clamped to left or right edge of pitch ladder respectively. When steering error is zero then FPM and cue are laterally aligned. Positions between full deflection and zero steering error are proportional in placement (e.g. 4° error is 40% from FPM to lateral limit).

 

Great circle steering error is the calculated great circle track to destination minus the azimuth component of the velocity vector. For example the airplane turning right, pulling 10° AOA 90° bank and currently heading 160°. The heading is 160° but the azimuth of the velocity vector is 150°. If the calculated great circle track to destination is 213° then steering error is 213-150=+63°. The steering error is not the difference between desired track and heading nor is it the difference between a calculated heading to steer and heading.

 

Drawing of the cue line is up from 180 left to 180 right based on steering error. When steering error is zero cue line is vertical (toward zenith). Bank angle is subtracted to ensure that cue line points up relative to vertical and not HUD orientation.

[Evovcui]

The navigation symbols of f15 su27 behave exactly the same as f16. All of these nav symbols link to the roll in a wrong way. So this is a long existing mistake. I wonder when this [investigation] will finish.

Edited November 1, 2019 by Evovcui