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donstim avatar image
donstim asked GrimPhoenix9349 edited

Flap/aileron span values

It is unclear to me exactly how to determine the values to use for aileron_span_outboard and the flaps span-outboard. The description for the aileron span says, "

The outboard aileron span, expressed as a .

This is the ratio of wing length from the tip to the end of the aileron surface. A larger aileron will increase the roll moment of aileron deflection, but it will also increase the local drag generated by aileron deflection."

A ratio is a comparison of two lengths. What are the two lengths this variable is a ratio of? For the following example, is the numerator A, B, or C (or some other length)? Is the denominator the wing span, half the wing span, or half the wing span minus half the fuselage diameter (or some other length)?

screenshot-1322-li.jpgThe description for the flaps span-outboard variable says, "Outboard span area, as a This is how far out from the middle the flaps stretch. On most planes this will be 1.0 - aileron_span_outboard. This value needs to be matching the lift and drag added by flaps. Small flap systems should add small amounts of lift."

How far out from the middle of what? The middle of the airplane? Or should this be the percentage of the half wing span - half fuselage diameter (i.e. distance from the fuselage to the tip of one wing). Eyeballing the example picture, this would be around 0.6 or so?


Also, what are the default values for these parameters if there is no value specified in the flight_model.cfg file?

aircraftflightmodel
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FlyingRaccoon avatar image
FlyingRaccoon answered GrimPhoenix9349 edited

@donstim My bad.

We'll have the doc updated on this.
These are expressed as percentage of the total wing span, from root to tip.
Aileron starts from the tip and flaps start from wing root.

Some important info that is missing from the doc at the moment is that, despite flaps span being defined in each flap section, the span is common to all and can't be less than 40%.
Basically, it will take the maximum span value defined in flap sections and clamp it between 0.4 and 1.0

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Thanks, that is exactly the answer I was looking for. If possible, could you identify that as the answer?
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I have to ask why you would put an arbitrary limit on this? Minimum of 40% is going to mess up the F4 Phantom which we have long-term plans for, the span of the flap is (off the top of my head) somewhere between. 25% and 30%.


I do not see the need for limits to be imposed by the core flight model which do not exist in real life?

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OzWookiee avatar image
OzWookiee answered donstim commented

AFAIK It it the percent of half-wingspan

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That would make the most sense to me (or half span minus half fuselage diameter, so half the span from the fuselage outward), but I can't understand the description that was given.
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No I don't think you need to remove the half fuse width. Simply length_of_flap / halfspan_wing.


So if you wing span is 30', halfspan is 15, and your flaps are 6' then the ratio is 6/15 or 0.4


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Depends on how they coded it. I'd like to get an answer from Asobo.
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OzWookiee avatar image
OzWookiee answered tml commented

OK So digging into this a little more it seems like it is (half-wingspan - half-fuselage) if we go back to the original FSX SDK: https://docs.microsoft.com/en-us/previous-versions/microsoft-esp/cc526949(v=msdn.10)

span-outboard The percentage of half-wing span the flap extends to (from the wing-fuselage intersection).


So reading that it indicates "from the wing-fuselage intersection". Looking at the P-51 it has a wingspan of 37 ft. Each flap has a span of 112.94" and the fuselage is described as having a frontal area of 11.54 ft2 which we could estimate as being ~3.4ft in diameter.

(112.94/12) / (37/2)-(3.4/2)

9.41 / (18.5 - 1.7)

9.41/16.8

0.56



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Yes, but I was wondering if they had maybe changed that.
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Would be nice if there was some way to specifically tell where the "wing-fuselage intersection" is then, too. Or if it at least was documented how that is estimated. I guess it is the fuselage_diameter parameter, which is assumed to be constant along the whole length?


(So much of this would be much simpler if the sim would just look at the 3D model for measurements. This would then require that you put some dummy objects in the 3D model that would follow some certain naming convention. But that would be trivial to do.)

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FlyingRaccoon avatar image
FlyingRaccoon answered FlyingRaccoon converted comment to answer

Hello.

The span goes from the wing tip to the wing root.
You can use the AircraftEditor "sim forces" debug panel to see if it matches.

Regards,
Sylvain


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This may be the accepted answer, but it doesn't actually answer the questions that were asked. How does one determine the `aileron_span_outboard` and the `flaps_span_outboard`?

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OzWookiee answered

Ok cool so my original assumption was correct.

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