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Indiafoxtecho avatar image
Indiafoxtecho asked CodenameJack447 answered

FCS PARAMETERS

We are trying to develop a proper FCS flight model for our F-35, but using the default FCS features the response at high speed seem very sluggish.
Is it possible to have an explaination of the FCS logic in MSFS and what are the parameters we need to tinker with to affect its behavior?


aircraftflightmodel
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FlyingRaccoon avatar image
FlyingRaccoon answered

Hello @Indiafoxtecho

Apart from stall protection, only these parameters are exposed:
1649688930483.png


Are you sure you're not hitting the load limit defined with these parameters when flying in these high speed conditions?

Regards,
Sylvain


1649688930483.png (170.2 KiB)
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Indiafoxtecho avatar image
Indiafoxtecho answered

Hello @FlyingRaccoon

Thanks for your reply, but I think my question was not clear enough - so I will elaborate it a little.

First thing, however, I believe there is a mistake in the entries you mentioned from the SDK documentation you mentioned - as the description says ft per second^2 while these entries typically are in "g"s and they seem to be so in MSFS (e.g. from Asob F/A-18 E)

positive_g_limit_flaps_up = 9.9

positive_g_limit_flaps_down = 9.9

negative_g_limit_flaps_up = -3

negative_g_limit_flaps_down = -3

load_safety_factor = 2

load_g_limiter_g = 7.5


Back to the question, I was looking for more details like:

- Autotrim logic (if any) or target AoA or G-load (some military FBW-FCS system aim to a specific AoA with the stick at rest, or will bring the aircraft to 1G -although the latter seems to have been abandoned by modern aircrafts).

- PID entries (are they the same as the A/P? or are they separate but not exposed)

- Surfaces actually controlled by the AP

Reason for asking is that we have been trying to implement it in our F-35, but the planes becomes practically not controllable above M0.8 - it is not a g-limiter problem as the plane does not seem to react even to minimal controls... things seem to get a little better by increasing the trim authority, but that should not be a factor... or should it?




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FlyingRaccoon avatar image
FlyingRaccoon answered

Hello @Indiafoxtecho

The unit error in the documentation will be fixed with SU10.

As for the control at high speed, some other parameters you can check are FBWPitchTrimScalar and FBWHighSpeedRollSpeedScalar in systems.cfg AUTOPILOT section.
They will be documented with SU10 but are already available in SU9. Check the F/A-18 for reference.

AP is controlling aileron for roll and elevator for pitch unless you use the aileron_to_elevator_gain parameter in the flight_model.cfg AIRPLANE_GEOMETRY section (will also be documented for SU10).

You can also check your elasticity tables and use the Debug Aircraft Tracking window to check how your control surfaces are moving.

Regards,
Sylvain

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CodenameJack447 avatar image
CodenameJack447 answered FlyingRaccoon commented

Hi! Could you please extend what this means?

AP is controlling aileron for roll and elevator for pitch unless you use the aileron_to_elevator_gain parameter in the flight_model.cfg AIRPLANE_GEOMETRY section (will also be documented for SU10).


I thought this was used for Elevons... Hence my surprise.






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Yes, that's for elevons. We use this parameter on the F/A-18.

I'm just saying that the surfaces controlled by the AP depends on the geometry configuration basically.

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CodenameJack447 avatar image
CodenameJack447 answered

Understood, Thanks!

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