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tml asked Nocturne answered

rudder_lift_coef and elevator_lift_coef documented twice (and differently)

In the SDK documentation, the parameters rudder_lift_coef and elevator_lift_coef in the [AERODYNAMICS] section of flight_model.cfg are documented twice, differently:

elevator_lift_coef

Define the slope of the lift curve of the elevator surface of the aircraft. Default is 5.0. This can be scaled with the elevator_effectivenessparameter in the [FLIGHT_TUNING] section.

vs

elevator_lift_coef

This defines elevator lift vs elevator AoA. This should be aspect ratio dependent and fall between 3 and 5 for most planes (5 is very twitchy and stable). The theoretical maximum is 2Pi.

And ditto for rudder_lift_coef.

Which one is correct? In the first one, what does the slope of a curve even mean when you don't tell what the units of the axes are? And if the default is 5, that is then said to be "very twitchy and stable". How can something be twitchy and stable at the same time?

Also related, as these are single numbers, why does the [FLIGHT_TUNING] section then need to have the elevator_effectiveness and rudder_effectiveness parameters that just scale them? If one wants to scale elevator_lift_coef, one could simply specify a different value for it?

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Looks like someone was a little overly zealous in adding this new .cfg parameter to the SDK. Both descriptions are correct; imo they should be combined. There appears to be a typo in the parenthetical in the 2nd description. I think it should say, "5 is very twitchy and 3 is very stable."

As for your comment regarding the coordination with the effectiveness parameters in the [Flight Tuning] section, I wonder the same thing except from the opposite direction. If we already had the capability to scale the default lift curve slope for the rudder and elevator controls, why do we need new variables to accomplish the same function?

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Nocturne answered

SU6 saw an update to all the documentation relating to the flight model and engines, and as such the issue of the duplicate parameters was resolved with that update, an the explanation greatly expanded too.

https://docs.flightsimulator.com/html/Content_Configuration/SimObjects/Aircraft_SimO/Flight_Model_Definition.htm?#elevator_lift_coef

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