# Other Surface Geometry<no value>

{{< callout context="note" title="NOTE" icon="outline/bulb" >}}

This page is currently WIP.

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### Flaps and spoilers

To define flaps and spoilers, there is both an aerodynamic and a geometric definition. The aerodynamic definition we've already setup in the [previous page](../basic-aerodynamics/), so we need to do the geometric definition, which will be fed into the lift and drag polar curves and will be used to perform the virtual wind tunnel normalization of the aircraft's surfaces.

 

After setting the spoiler and flaps geometry, you should see increased lift forces being applied to the wing over the parts of the wing where the flaps are located:

{{< image-center
    src="images/7_Samples_Tutorials/Tutorials/Define_Flight_Model/geometry/flaps/geometry_20_spoilerflap.png"
    alt="Flaps Applying Extra Forces In The Debug Visualisation" >}}

 

#### Flaps

The flaps really only one essential geometric setting which is the ratio of wing span corresponding to how much the flaps will take up on the wing. This is done by changing the **Span Outboard (%s)** value in the SimObject Editor from the **Flaps** parameter, or by editing the `span-outboard` value in the `flight_model.cfg`:

{{< image-center
    src="images/7_Samples_Tutorials/Tutorials/Define_Flight_Model/geometry/flaps/geometry_19_flaps.png"
    alt="The Flaps Span Parameter in The SimObject Editor" >}}

 

#### Spoilers

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If the aircraft does not have spoilers, you can leave all parameters in this section set to 0.

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The spoiler geometry is defined in the **Geometry** panel of the SimObject Editor, under the **Controls / Properties** section. In the `flight_model.cfg` file, you need to set the following parameters:

[`spoiler_limit`](../../../../content-configuration/cfg-files/flight_model.cfg/#spoiler_limit), [`air_spoiler_limit`](../../../../content-configuration/cfg-files/flight_model.cfg/#air_spoiler_limit), [`spoilerons_available`](../../../../content-configuration/cfg-files/flight_model.cfg/#spoilerons_available), [`aileron_to_spoileron_gain`](../../../../content-configuration/cfg-files/flight_model.cfg/#aileron_to_spoileron_gain), [`min_ailerons_for_spoilerons`](../../../../content-configuration/cfg-files/flight_model.cfg/#min_ailerons_for_spoilerons), [`min_flaps_for_spoilerons`](../../../../content-configuration/cfg-files/flight_model.cfg/#min_flaps_for_spoilerons), [`spoiler_extension_time`](../../../../content-configuration/cfg-files/flight_model.cfg/#spoiler_extension_time), [`spoiler_handle_available`](../../../../content-configuration/cfg-files/flight_model.cfg/#spoiler_handle_available), [`auto_spoiler_available`](../../../../content-configuration/cfg-files/flight_model.cfg/#auto_spoiler_available).

{{< image-center
    src="images/7_Samples_Tutorials/Tutorials/Define_Flight_Model/geometry/flaps/geometry_20_spoilers.png"
    alt="The Spoiler Parameters in The SimObject Editor" >}}

 

 

### Ailerons

Time now to work on the aileron control as it will improve the general stability of the aircraft. Start by defining the **Aileron Area** ({{< glossterm >}}sqft{{< /glossterm >}}), which [`aileron_area`](../../../../content-configuration/cfg-files/flight_model.cfg/#aileron_area) in the `flight_model.cfg` file. If you have this exact data, use it. If you don't have this data, then you can approximate it and try to maintain the same order of magnitude when defining the rudder and elevator surface areas later.

{{< image-center
    src="images/7_Samples_Tutorials/Tutorials/Define_Flight_Model/geometry/ailerons/geometry_21_aileronarea.png"
    alt="The Aileron Area Parameter in The SimObject Editor" >}}

 

Next you'd set the set the **Aileron Up** and **Aileron Down** limit angles (in degrees), corresponding to the in the [`aileron_up_limit`](../../../../content-configuration/cfg-files/flight_model.cfg/#aileron_up_limit) and [`aileron_down_limit`](../../../../content-configuration/cfg-files/flight_model.cfg/#aileron_down_limit) in the CFG file. Again, if you have this exact data, use it, but if you don't then you can usually get away with setting the up limit to 20 and the down limit to 15.

{{< callout context="note" title="NOTE" icon="outline/bulb" >}}

This type of data is rarely found in a {{< glossterm >}}poh{{< /glossterm >}} but can be found on the website of the [FAA](https://www.faa.gov/ "Federal Aviation Administration").

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{{< image-center
    src="images/7_Samples_Tutorials/Tutorials/Define_Flight_Model/geometry/ailerons/geometry_21_aileronlimit.png"
    alt="The Aileron Limit Parameters in The SimObject Editor" >}}

 

Now you need to define what percentage of length of the wing is covered by the ailerons. Usually, this distance plus the percentage of the length of the wing covered by flaps, is equal to approximately 100% of the total wing length. This can't currently be set in the editor so you need to edit the [`aileron_span_outboard`](../../../../content-configuration/cfg-files/flight_model.cfg/#aileron_span_outboard) parameter in the `flight_model.cfg` file directly.

 

Next you can define how much control you want to be applied to the ailerons, depending on the speed of the aircraft. This is a table that defines the ratio of aileron control depending on the amount of dynamic air pressure, and can be set by scrolling to the bottom of the Geometry panel in the SimObject Editor to the section on **Elasticity Tables** and selecting the **Aileron** tab. If you are editing the `flight_model.cfg` file, you'd use the [`aileron_elasticity_table`](../../../../content-configuration/cfg-files/flight_model.cfg/#aileron_elasticity_table) parameter.

{{< image-center
    src="images/7_Samples_Tutorials/Tutorials/Define_Flight_Model/geometry/ailerons/geometry_21_ailerontable.png"
    alt="The Aileron Elasticity Table in The SimObject Editor" >}}

 

The current dynamic air pressure is displayed on the debug [Speed](../../../../devmode/editors/simobject-editor/debug_info/simobject-debug-menu/#speed) window to help adjust the aileron control depending on the current speed:

{{< image-center
    src="images/7_Samples_Tutorials/Tutorials/Define_Flight_Model/geometry/ailerons/geometry_22_pressure.png"
    alt="The Dynamic Pressure Value In The Debug Aircraft Speed Window" >}}

 

At lower speeds, up to climb speed, this ratio is usually 100% and it starts decreasing at cruise speed and can reach values close to zero when the plane is flying over speed, above the red bar (complete loss of authority).

 

Another adjustment that needs to be made is to define the maximum authority of the ailerons. This will be done to achieve the maximum roll speed that is possible with the aircraft at a given speed, and is set from the **Aileron Effectiveness** setting in the Flight Tuning section, or using the [`aileron_effectiveness`](../../../../content-configuration/cfg-files/flight_model.cfg/#aileron_effectiveness) parameter in the `flight_model.cfg` file.

{{< image-center
    src="images/7_Samples_Tutorials/Tutorials/Define_Flight_Model/geometry/ailerons/geometry_21_aileroneffect.png"
    alt="The Aileron Effectiveness Parameter in The SimObject Editor" >}}

 

If you have this value, then you should use it. Otherwise, most aircraft can achieve maximum roll speeds of more than 30 degrees per second. For a {{< glossterm >}}ga{{< /glossterm >}} aircraft 30 to 60 degrees per second is a good start. The above parameter allows you to scale the aileron authority up or down depending on your needs.

 

When testing, you can find the current roll speed in the SimObject Editor [Tracking](../../../../devmode/editors/simobject-editor/debug_info/simobject-debug-menu/#tracking) debug window, and in the image below you can see an example of the forces that are being applied as a result of the aileron angles when the aileron angles are maximal:

{{< image-center
    src="images/7_Samples_Tutorials/Tutorials/Define_Flight_Model/geometry/ailerons/geometry_21_aileronforce.png"
    alt="Illustration Of Maximal Aileron Forces" >}}

 

 

### Stability

Finally, it is time to set the aircraft **Stability**. Based on the dimensions and geometric definition of the aircraft, the surface based aerodynamics simulation automatically calculates the minimum rotational air friction, but because a real airplane is not made of perfect surfaces with a perfect shape, real rotational friction is always going to be higher. So, to adjust the rotational friction you can go to the Flight Tuning panel and edit the **Pitch**, **Roll**, and **Yaw Stability** settings, or edit the `flight_model.cfg` file [`pitch_stability`](../../../../content-configuration/cfg-files/flight_model.cfg/#pitch_stability), [`roll_stability`](../../../../content-configuration/cfg-files/flight_model.cfg/#roll_stability), and [`yaw_stability`](../../../../content-configuration/cfg-files/flight_model.cfg/#yaw_stability) parameters.

{{< image-center
    src="images/7_Samples_Tutorials/Tutorials/Define_Flight_Model/geometry/geometry_23_roll.png"
    alt="The Roll Stability Parameter in The SimObject Editor" >}}

 

Note that here you need to enter values that are greater than zero to maintain backwards compatibility with the legacy flight model - however, you can enter 0.01, for example, if you want only the minimum rotational friction. If the plane has more roll inertia, you can enter higher values.