M/71 falling short in DYK mode

[Bestandskraft]

Hey guys,

 

I have for the last several hours attempted to attack targets with M/71s in DYK mode. So far, during all my attacks (approximately 20), my bombs have fallen significantly short of the target.

 

My settings:

 

- B1 defined as target (TAKT-IN-9-B1)

- Loadout: 8 M/71 low drag

- DYK attack mode selected

- Target Motion measurement disabled (TAKT-IN-221-LS)

- Radar lock on trigger unsafe (TAKT-IN-252-LS)

- No wind

- QNH 1013

- Temperature 15°C

- Target at sea Level

- QFE set to 1013

- Release with 490 KTAS @ 3331 ft ASL, 27° dive angle

- Airbrakes out

 

It is interesting to note that in Bunyap's DYK tutorial, the exact same problem is visible (note that at 15:50 he is aiming at the center bunker in the farthest row, but both the first bomb and the center of the bomb stick actually impact short of the mark).

 

Edited August 15, 2023 by Bestandskraft

[Rudel_chw]

I cant really tell on the video, but it seems that you pull the trigger when the range line blinks ... you should press it when the "wings" appear on the sides of the aiming point ... this is about two seconds later and that would explain why the bombs fell short.

[Bestandskraft]

Hi Rudel_chw,

 

I have released the bombs one human reaction time after the wings appear, so this cannot be the explanation.

 

Further tests on the same target have revealed the following:

 

With a 36° dive angle and the bombs pickled once the two vertical flashing bars appear (these indicate that I need to break off immediately IAW the manual, i.e. that I have missed my release window), the bombs hit precisely.

 

With a 22° dive angle and the bombs pickled once the two vertical flashing bars appear, the bombs fall significantly long, as one would expect.

 

It might be interesting to note that in my video, the steering cue after bomb release actually appears in the lower part of the HUD (superimposed over the central vertical line), which, IAW the manual, would mean that after bomb release I should push over to bring the aiming cue over the steering cue, thus killing myself.

 

In my test with the 22° dive angle, the steering cue appears at the top of the HUD, which seems logical since following it will result in a normal dive recovery.

[Jediteo]

I have noticed something similar.

 

We'll look into it. Thank you for the thorough bug report.

[Rudel_chw]

I have noticed something similar.

 

We'll look into it. Thank you for the thorough bug report.

 

Thanks to you for caring ... I really love this plane and I'm glad to see it is well mantained.

Best regards

[Nealius]

I've been having issues hitting anything with DYK mode. My procedure is the same as yours, though I have also tried NAV instead of ANF, and occasionally get better results that way. But I still have the HUD suddenly move off target when I press the trigger. My bombs will fall short, fall long, or even off to the side sometimes.

[Bestandskraft]

Please find attached an .acmi recording of the attack and a .kml file for displaying the target. This might help analysing the problem.

 

Place the .kml into C:\ProgramData\Tacview\Data\Static Objects\.

DYK bug.zip

[Bestandskraft]

I have thought about the problem and the available evidence again and I think the issue might be a wrong implementation of the DYK mode itself.

 

Unfortunately the pages describing DYK mode in the declassified Viggen flight Manual (M5800-370011 Del 2) are incomplete and I cannot read Swedish, so what follows is informed conjecture based on the phrase "Bomb are released when the release Parameters are fulfilled on the target marked when the trigger is pulled" on page 301 of the game manual, the phrase "Computer will release bombs on the designated target when the trigger was pulsed" on page 303, the provided HUD pictures and my understanding of conventional bombing in general.

 

I believe that at step 5 on page 302, the radar locks onto the target. At this time, the trigger may be pressed at any time which will cause the target location to be entered into the CK and the HUD picture will jump to step 9, but the bombs will not yet be released. Instead, the pilot needs to follow the steering cue in order to bring the aircraft onto the proper delivery wire. Once the CK determines the required bomb range is reached, bombs will be released automatically provided the trigger is still held.

 

If the pilot does not follow the (upwards) steering command, the aim-off angle will be too small, thus the required bomb range will be reached at an insufficient altitude to clear fragmentation or the ground, in which case HUD step 11 will be shown. Steps 7 and 8 only occur prior to the trigger being pressed, and indicate a diminishing range to the target, which if too low means that regardless of pilot maneuvers, the minimum safe altitude will be undershot and/or the bombs will not arm if released.

Edited December 19, 2017 by Bestandskraft

[Nealius]

I have heard about this steering cue, but I have not seen it, and the time delay between trigger press and bomb release is typically too fast for human reaction time to do any steering anyway.

[microvax]

Yeah DYK is a weird non CCRP mode atm, afaik it should be basically CCRP with steering cues.

[RagnarDa]

Fixes to DYK (precision) mode will be included with next update of the Viggen