Aim-7 Flies Straight for 1.5-2s (no 'English Bias')

[Smyth]

Based on a forum search this has been mentioned before but apparently not reported as a bug specifically, so I wanted to raise the issue again.

The Aim-7 family in DCS appears to fly straight for 1.5s (-F/M) or 2.0s (-E2) after launch before trying to turn toward the target, which is not correct behavior. More specifically, DCS Aim-7 wings unlock at ~0.5s (this is correct) and the autopilot rolls 45deg (also correct), but then flies straight until the seeker locks on at 1.5s or 2.0s (not correct).

To illustrate, I have attached short .trk files for an -E2 and -M launched from the F15C at 15 degrees pitch-up and co-altitude with a target at 15kft. Misalignment between the launching aircraft and the target should trigger an immediate 'English Bias' turn, but the missile does not attempt to correct.

For reference the IRL guidance timeline of an Aim-7E is:

• 0s
  • Start of ejector stroke
  • Motor ignition voltage applied
• 0.5s
  • Electronic wing unlock
  • Starts roll 45deg (from '+' to 'x' orientation)
  • Starts 'English Bias' turn
  • Antenna pointed toward target
• 0.5s - 1.5s
  • Normal target lock window
• 1.5s
  • Proximity fuse armed (DF mode)
• 2.9s
  • Motor burnout

While I think developers probably know this, I want to mention for the sake of the general forum population that 'English Bias' is jargon for the maneuver commanded at launch to correct misalignment between the launching aircraft and the intercept course computed by the fire control radar. The Aim-7's own SARH seeker attempts to lock on during the bias turn, and takes over steering commands whenever it succeeds.

The short delay before electronic wing unlock is supposed to be just enough for the missile to clear the nose of the aircraft, un-mask its seeker, and maneuver safely. Unlike in-game, the pilot of the launching aircraft should not see a Sparrow flying straight for any time before suddenly turning toward its target. It will already be starting to turn by the time it is visible.

This leads to my question for ED: is English Bias supposed to be included in the missile API but not working currently/yet, or is flying straight until seeker lock-on intended behavior?

If 'English Bias' logic is not planned in the near future, can you please consider adjusting the existing delay time to approximate the IRL behavior more closely? A delay of 0.5s or 0.6s would be correct under most conditions, to represent when the missile really starts turning. The seeker will be fully locked before the 1.5s proximity fuse delay regardless, and fusing is what sets the practical minimum range of a Sparrow.

 

SparrowNoBiasE2.trk SparrowNoBiasM.trk

[GGTharos]

First, wrong missile (the sequence you've posted here is for an E of some sort, not F/M/P).

Second, in DCS the motor doesn't ignite on ejection anyway, so that needs to be taken care of as well, and third 'english bias' has no bearing on things in-game since the missile does not behave in a way that requires it (ie. seeker is locked at launch).

Unlocking maneuvering at 0.5 seconds would be the thing to do, vs. keeping it locked up for the amount of time you've mentioned, but the F/M/P may be doing this dynamically based on distance to target or FLOOD (dogfight and FLOOD are the same thing and the missile would launch unconstrained, an MRM launch defined as exceeding a certain flight time to target would be more restricted)

[Smyth]

8 hours ago, GGTharos said:

First, wrong missile (the sequence you've posted here is for an E of some sort, not F/M/P).

That is for -E or Skyflash, yes. One of my attached tracks is the -E2 though. It is available on the player-controlled F-15C for some reason.

In the end I'm only hoping for ED to acknowledge that Sparrows of any species shouldn't be flying straight after launch. Whether they choose to fix this the easy way (just unlock wings at 0.6s) or the hard way (re-write missile API) is not something I have a strong opinion on.

[GGTharos]

I agree it should be corrected, this has been mentioned a long while ago.   Also because rocket motor thrust is 'instant', the rocket motor isn't ignited when the cable separates during missile ejection.