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g-command system is not correct for the FLCS version we had


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Just a minor bug in the CAT I Limiter. The blended AOA feedback bias used in the g-command system is not correct for the FLCS version we had.

According to Figure 3.1 Longitudinal Control Block Diagram from the DTIC paper 'F-16 Simulator for Man-in-the-Loop Testing of Aircraft Control Systems (SIMTACS)' (https://apps.dtic.mil/sti/citations/ADA189675), the AOA bias used for an initial g-command reduction should be 15.8, but not 15.0 as currently is in DCS. This results in a lower AOA limit than expected.

g-command until 15.8.png

The figure is also backed up by the publicly available FLCS flashcard (https://quizlet.com/309832047/flcs-flash-cards/), which states that the G command system decreases available G when AOA > 15.8 (CAT I).

g-command until 15.8 quizlet.png

 

The current 15.0 bias is seems to be used by a very old version of FLCS.

16CM g-command should not be reduced until 15.8 AOA.trk

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  • 7 months later...
Posted (edited)

Hi, in case it's forgotten I'd like to mention that this is not fixed as we're currently at 2.9.7. For other proof check CM-1 manual circa 2007 (not CJ-1), which the FLCS flashcard based its answer on.


Edited by DummyCatz
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10 hours ago, Stroke 3 said:

What does this mean exactly? does it mean its not pulling enough aoa?

As I understand it, it means the jet won't let you pull max G as quickly if it results in AOA exceeding a threshold that is set too low in our F-16. In a very general sense, pulling would initially feel more sluggish at lower speeds with a low AOA bias and more twitchy at higher speeds as AOA bias is increased.  

The FLCS cares about this because stall speed increases in proportion to the square root of load factor.

 


Edited by Yaga
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It would make the jet feel more responsive, so i think it would help in a lot of places. 

Logically, you'd want to set the FLCS threshold and curve for AOA bias so that it keeps the jet just shy of departing. 

 


Edited by Yaga
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Posted (edited)
1 hour ago, Stroke 3 said:

ok thankyou.

Hope this is fixed not sure if it would improve a lot in bfm or general handling.

ITR would get slightly increased at the AOA limit.

Think of a 9.3g pull. As you're bleeding speed, your AOA increases as well. As soon as the AOA exceeds 15.8 (currently 15.0) degrees, the FLCS begins to reduce your g-command (all the way to 1g) as a function of AOA, so you can no longer command 9.3g. This 15.8 acts like a threshold where your stick input starting to get reduced.

 

BTW if you're wondering why CJ-1 manual shows 9.0g limit and 15.0 threshold, because it's the wrong manual for our CM aircraft.


Edited by DummyCatz
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The flashcards @DummyCatz linked are great for demystifying the FLCS, even if our F-16 doesn't agree with them in more than a few spots. 

One such example is our F-16's stick trim being functional (often required, even) with A/P engaged. 


Edited by Yaga
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Yeah. But the Sniper is just an addition to the F16 compared to the FLCS and the flight model thats always present. Also the slow speed handling characteristics which still produce oscillations at some configurations is something that could be related to the FLCS and should be looked at again. Not sure how many efforts to improve the flight model will be done after early access.

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2 hours ago, darkman222 said:

Yeah. But the Sniper is just an addition to the F16 compared to the FLCS and the flight model thats always present. Also the slow speed handling characteristics which still produce oscillations at some configurations is something that could be related to the FLCS and should be looked at again. Not sure how many efforts to improve the flight model will be done after early access.

Yeah you remind me. I'll keep an eye on the slow speed handling.

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