What is with the Tadpole line

[777coletrain]

I recently noticed something strange with the tadpole in the F-16. In HUD tapes the line coming from the tadpole seems to direct the FPM to the selected steer point while in DCS it directs the nose of the aircraft. The manuals state that the line indicates the bearing to the point. So the tadpole in DCS would be indicating exactly what the manual says where the real aircraft doesn't. Is this something that changed with block numbers or is the manual saying bearing in relation to the FPM? It could also just be me not understanding something, either way I'm including some pictures to show what I'm talking about.

Edited January 19, 2022 by 777coletrain
Phrasing

[razo+r]

https://forums.eagle.ru/topic/274534-f-16-hud-tadpole/#comment-4831785

[777coletrain]

That thread is about the lateral displacement of the tadpole, I'm talking about the direction the line is pointing from the tadpole. 

[Antiguedad]

The great circle steering cue (tadpole) consists of a 12 mr line extending outward from a 6 mr circle. The location on the HUD of the roll-stabilized steering cue is relative in azimuth to the flightpath marker; steering is accomplished by flying the flightpath marker to the steering cue. The orientation of the steering cue line on the HUD indicates bearing to the steerpoint. At the 12 o'clock position relative to the horizon, the steering cue line indicates that bearing to the steerpoint is zero degrees; at the 3 o'clock position, the steering cue line indicates that bearing to the steerpoint is 90 degrees right.

So, in the upper picture the steer point is to the right and the steering cue line points to the right. And in the bottom picture you're going straight to the steerpoint, so the steering cue line points to the top. If you were going away from the steerpoint, the steering cue line would point to the bottom.

[777coletrain]

19 minutes ago, Antiguedad said:

So, in the upper picture the steer point is to the right and the steering cue line points to the right. And in the bottom picture you're going straight to the steerpoint, so the steering cue line points to the top. If you were going away from the steerpoint, the steering cue line would point to the bottom.

Sort of, the steering cue seems to be pointing relative to different points though. In the top picture it is pointing right because the steerpoint is to the right of the nose of the aircraft (like stated in the manual) while in the bottom picture it is slightly left because steerpoint is slightly left of the flight path marker.

Edited January 19, 2022 by 777coletrain

[Antiguedad]

So, you mean that in the upper pic the tadpole should be pointing to the top/right up, too? Now think I understand what you're saying.

The upper seems to have a heavy crosswind, maybe it's related. MAybe a no-wind situation could help..

Edited January 19, 2022 by Antiguedad

[777coletrain]

6 minutes ago, Antiguedad said:

The upper seems to have a heavy crosswind, maybe it's related. MAybe a no-wind situation could help..

Yeah the wind is what is causing this to happen. My confusion is from the top and bottom pictures being different. The top (DCS) is doing exactly what the manual says it should do, but the bottom (actual F-16) is not following what the manual says. It appears that in the actual airplane the "bearing" is based off of the flight path marker instead of the actual bearing of the aircraft. 

[Frederf]

According to the literal text it would be bearing and in a crosswind with nose left of track the tick mark would be rotated CW. However it could easily be inexact wording as so much of nav steering is track based.

HUD tapes showing the tick orientation while FPM and GC are on opposite sides of the steerpoint should determine which.

[777coletrain]

The bottom picture is set up like that although I can try to find another instance of it

[Frederf]

I didn't look. Certainly in that picture the heading is left of destination, track is right of destination and GCSC tic shows a correction to the left which suggests tic is track-based and not heading-based.

[Machalot]

Is there a clear definition of bearing as used in the manual? Couldn't it be refering to the relative bearing between the track and the destination? That would agree with the HUD tape. 

[777coletrain]

I haven't seen anything however the term 'bearing' is used correctly in other parts of the manual. I wouldn't be surprised if they do mean it in that way, however I think ED would need more evidence to change this to match the HUD tapes.