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AB unavailable with gear down.


DmitriKozlowsky

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Not something I ever experienced in pre latest build. On approach, with gear down, AB is unavailable (to get out trouble). There's a welcome surprise! Finding one self with flaps down, gear down, engine at Mil power, and aircraft is still sinking. Shoving throttle to AB, and.... NO AB. Quickly, as in panic speed, gear UP, flaps to T/O, full AB after gear lights are off. Odd that I have full AB on T/O, with gear down, but not on final.

Is this some new behavior? 

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Went into stable with DCS 2.7.1.7139

  • Fixed SPS landing system causing the afterburner to ignite.
    • Attempting to engage the afterburner with the SPS on, will cause significant thrust decrease due to the open engine nozzle.

 

So with gear down and flaps in landing position and SPS on, there is no after burner ignition available.

Real plane throttle has AB detent, so you won't put throttle that far forward so the nozzle would open, which causes thrust decrease.

Keep throttle below AB detent, fly the pattern/approach as per the book (not to shallow, not too heavy) and there is no need to light the burner on landing. For go-around, flaps to take off position and you can light the burner again.

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The effect triggers specifically at 30 degree flap deflection, which is 5 degrees past the takeoff setting. If you're using a throttle without an AB detent, you can try landing without SPS (just remember to stay fast - the difference in flight characteristics in full landing config without it is significant) or flip the burner cutoff switch, which if I recall right inhibits the nozzle opening behaviour rather than just ignition like the SPS does.

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  • 3 weeks later...

SPS is cut off depending on flap blowback to a certain angle. This blowback happens due to air pressure from motion. Speed at which flaps retract above 30 degree extension I do not remember but it happens.

 

I think 360km/h is figure quoted in flight manual "until warning system signalling is installed to show failure of SPS, approach above this speed such to have safe flight regardless of SPS failure." Flying down slow like we do confident that SPS is working is a potential safety issue in the event SPS fails to deploy.

 

I think it is a crime of design engineers that power lever commanding AB will just schedule nozzle as if AB will work when airplane could easy tell that won't happen. It seems so obvious to route logic for SPS suppression based on landing gear through the SPS disable cockpit switch (which prevents thrust loss on AB command) that I could not believe real airplane did not do this. Some pilot may be killed due to a bonehead oversight. But I am told this bad design is true to the real airplane and DCS module recreates it faithfully. Scandalous!

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To be fair, in the real aircraft, there are detents (including one at min. SPS operating setting, which would solve many threads on Reddit about how supposedly hard the 21 is to land - because people instinctively cut the throttle and immediately lose most of their lift). Likewise, the "danger zone" where the ARU gives you enough control authority to break the plane as you bleed off speed in a hard turn would probably never happen IRL, because the artificial feel should give you the same stick force for the same G and you would feel it.

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