reported F-16 HUD tadpole

[Grindle]

Since the most recent 2.7 update I've noticed flying even in auto pilot that the hud tadpole will not line up with the steerpoint. Is it me or what's going on? Also, it's very hard to get the CCRP fall line to match the target steerpoint. I'll practice some more but I hope someone confirms this or correct me.

 

Thanks 

 

 

[Vakarian]

I don't know if my eyes are failing me, but on the first pic, you are not lined up with the steerpoint, that's why tadpole is not aligned with your FPW

[Grindle]

It was on auto pilot for a very long time and wouldn't line up and it was on a straight coarse, this was on the Syria free flight quick start mission. Lining up the tadpole with the flight path marker is what I'm wanting but auto pilot wouldn't keep it straight like it's supposed to. I'm sure there's something I'm not understanding and I definitely don't want to look stupid or dumb but I'm just learning. Thanks for the feed back.

 

Salute!  

[WHOGX5]

44 minutes ago, Grindle said:

It was on auto pilot for a very long time and wouldn't line up and it was on a straight coarse, this was on the Syria free flight quick start mission. Lining up the tadpole with the flight path marker is what I'm wanting but auto pilot wouldn't keep it straight like it's supposed to. I'm sure there's something I'm not understanding and I definitely don't want to look stupid or dumb but I'm just learning. Thanks for the feed back.

 

Salute!  

A word of advice as I see you don't have a lot of posts: Don't ever mention that other F-16 sim or post pictures from it or anything like that on this forum. The moderators will remove your posts if you do and you'll probably receive warnings/strikes too.

 

Regarding the issue at hand, pretty much all the moving HUD symbology in the DCS F-16 is broken to some degree. It's most likely going to stay that way for the foreseeable future judging from the patch history for the DCS F-16 over the last year.

[snipy]

Although, maybe that should be re-thought.  Because seeing those two side by side... there ain't no comparison between the two graphically.  At all.  The other is comically bad, by comparison, graphically speaking. 

[Florence201]

You also make no reference to wind at altitude. The auto pilot will be flying the jet to meet the SP, but pictorially it will look offset in the HUD. 

Edited June 19, 2021 by Florence201

[TobiasA]

F-16_autopilot_crosswind.trk

 

This is a track with a simple autopilot engagement during crosswind. The autopilot does not compensate for crosswind, and I think this is wrong since the vertical axis depends on the FPM but the horizontal does not, instead it points the nose to where the waypoint is.
The tadpole does not show to the waypoint but to a point somewhere else which is affected by wind, which is wrong, and then the autopilot follows the wrong tadpole.

 

Edited June 19, 2021 by TobiasA

[Frederf]

Short story: By the track posted above DCS behavior is currently not correct. It is seen that when the current heading is equal to the bearing to destination the GCSC is positioned to indicate zero steering error (i.e. gun cross at diamond). This is wrong.

 

Long story: The GCSC "tadpole" mechanization is based on the following logic:

• INS calculates a ground track value. This is the azimuth component of the velocity vector. Visually to the pilot this is the direction of the FPM. A
• INS calculates a great circle steering solution. This is the current direction of the great circle path from current position to given destination. B
• MMC subtracts B from A to get steering error. C
• MMC look at FPM symbol on HUD wherever it is.
• MMC picks a position that is displaced laterally (in azimuth) relative to FPM symbol to place GCSC symbol based on the magnitude of error C.

When FPM* is pointed at the steerpoint diamond (or above/below) the steering error C is zero and the FPM and GCSC will be overlayed. *If drift cutout is enabled then FPM is displaced from it's true position in which case its positioning relative to the steerpoint diamond is meaningless. The GCSC positioning relative to FPM is still and is always a valid indication of steering error.

 

The result is that in normal operation (no drift cutout) FPM at the diamond means that tadpole is on FPM. It doesn't matter where your nose is. You can be pulling 6Gs with 20 degrees AOA and your gun cross is way off in the rhubarb. For the instant that FPM azimuth is pointing at destination tadpole will show all is well. In crosswind your nose will be pointed upwind, your FPM will be downwind of nose and pointed at the destination. Then steering error is zero, tadpole positioned on top of FPM.

 

One detail about the tadpole positioning is that the displacement is not linear with error or rather it's about 1:1 in a small window around alignment I think about +-3°.  In this range the tadpole will seem to be placed "in the real world". But between about 3° to 20° steering error the positioning of the tadpole is not 1:1 but reduced.  So at say 10° error the tadpole won't be displaced 10° to the side but less. As you turn to destination you'll see the tadpole move toward the FPM slowly until you're nearly aligned then the sensitivity increases.

[777coletrain]

I've noticed this recently also

[Frederf]

Track included

F16 tadpole heading v track.trk

[[ED]Ben]

Hi - I may be totally misunderstanding this report, but as i understand it, you fly the FPM to the tadpole for steering to steerpoint. The tadpole would be offset to show any correction for wind. If no wind tadpole aligned with steerpoint marker. 

If you think it should operate differnetly, please could you supply some evidence? 

Thanks

[TobiasA]

vor 6 Stunden schrieb [ED]Obi:

Hi - I may be totally misunderstanding this report, but as i understand it, you fly the FPM to the tadpole for steering to steerpoint. The tadpole would be offset to show any correction for wind. If no wind tadpole aligned with steerpoint marker. 

If you think it should operate differnetly, please could you supply some evidence? 

Thanks

Hi,

the FPM already shows the wind compensated flightpath. The tadpole should point at the steerpoint.

See the video at 10:59. You can clearly see the crosswind component, but the tadpole is on the steerpoint, FPM, tadpole and steerpoint align and you are flying towards the steerpoint.

If you recreate this in DCS, it looks different.
Video:

DCS:

I think you can see what I mean- where the tadpole is in the HUD video and where it is in DCS.

Apart from that, it is a pretty close representation, and the amount of work that has gone into that is outstanding.

Thanks a lot!

[Frederf]

7 hours ago, [ED]Obi said:

Hi - I may be totally misunderstanding this report, but as i understand it, you fly the FPM to the tadpole for steering to steerpoint. The tadpole would be offset to show any correction for wind. If no wind tadpole aligned with steerpoint marker. 

If you think it should operate differnetly, please could you supply some evidence? 

Thanks

The tadpole is not located in exterior coordinate system like TD box or steerpoint diamond. Tadpole placement on the HUD is solely relative to the FPM and depends solely on the MMC INS steering error value. The tadpole is only guaranteed to be over the steerpoint diamond at zero error.** With steering error the tadpole displacement is not exactly 1:1 on HUD. During a turn the GCSC will be clamped to edge of the allowable GCSC position until steering error is some rather large value (10~20 degrees?) and then slowly slide toward FPM until about 3 degrees at which point the sensitivity is higher (about 1:1).*

**Because drift cutout moves FPM from true VV position then GCSC may not be over steerpoint diamond in this case as GCSC position is relative to FPM symbol and not actual VV position.

Steering error is the difference between INS ground track and calculated great circle true course to destination. The airplane's heading has no input into the equation. It is only the airplane's motion that matters. The steering error value also drives the "W" symbol on the MFDs in the same way. When airplane velocity vector (azimuth component) is pointed at destination then steering error is zero and GCSC and "W" vertical bar are both centered. This is why drift cutout has no effect on the GCSC function since its placement is relative to FPM symbol (even when FPM is not placed at actual VV).

The consequence is that when VV is in the same vertical plane as the steerpoint diamond then steering error must be zero.

Reference -34 (any F-16C/D they all work the same) section 2 inflight procedures, section steering. Notice the figure at the end of the section which has the various directions and angles. "True ground track (058)" and the line through steerpoint determine the value of "G/C steering error" which in the example is 6°.

*I've looked at various HUD tapes and the exact relationship of GCSC placement output to steering error input is not identical. One I saw had a two-stage equation with a high sensitivity region (0~3°), low sensitivity region (3~20°), and a clamped region (>~20°). Another HUD type had only one-stage behavior and the clamp limit was lower (~10°). If this particular variant has one-stage or two-stage behavior and what the steering error value limit of being unclamped from the max displacement I don't know. But in no case was GCSC placed in "world coordinate system."

Edited November 22, 2021 by Frederf

[[ED]Ben]

Thanks Both - i will take another look. Appreciate the detailed responses

[[ED]Ben]

reported - Thank you for the detailed report - helps alot

[777coletrain]

The tadpole in the HUD seems to just sit directly above the waypoint when the waypoint is within its range of motion. I'm linking a closed thread where Frederf went into the movement of the tadpole in way more detail than I would be able to. He has pictures of what it does in the real jet, I'm going to include one of the pictures here and one from the track I'm including as an example.

 

F16 Tadpole 6 06 22.trk

Edited June 6, 2022 by 777coletrain

[BIGNEWY]

Posts merged, this is reported 

thanks