# Fuesalge Geometry<no value>

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This page is currently WIP.

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The fuselage can be set up using two different methods: using a *generic* fuselage shape, which is fine for simple aircraft and uses what is essentially a "cigar" shape for the main body, or using the *modern geometry* fuselage shapes, which permit the creation of a more precise fuselage shape. The modern geometry objects also permit the addition of **fuselage parts** like engine nacelles or floats, and even allow the creation of more exotic aircraft like the dual-fuselage [F82 Twin Mustang](https://en.wikipedia.org/wiki/North_American_F-82_Twin_Mustang).

 

Note that you can adjust the required parameters and then *save* in the [SimObject editor](../../../../devmode/editors/simobject-editor/the-simobject-editor/), and the position of the different surface markers will change to reflect the new values, and the goal is to have the surface markers align with the actual shape of the fuselage (and fuselage elements).

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

You can enable [Live Edition](../../../../devmode/editors/simobject-editor/the-simobject-editor/#edition-info) and then select [Auto Resync On Changes](../../../../devmode/editors/simobject-editor/menus/#auto-resync) to see any changes that are made in the editor reflected in the simulation in real-time without the need to save first.

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Before continuing, be aware that - unlike the aircraft wings and other geometry - the modern fuselage geometry objects don't need any of the generic fuselage parameters to be set up first, so if you are using the geometry objects, you can skip the generic fuselage setup (some parameters *are* used to set defaults, but they will need to be edited anyway and so it isn't really necessary to set them up).

 

 

### Generic Fuselage Setup

The generic fuselage shape is essentially a "cigar" shape and will look like this initially:

{{< image-center
    src="images/7_Samples_Tutorials/Tutorials/Define_Flight_Model/geometry/fuselage/fuselage_1_cigar.png"
    alt="The Generic Fuselage &quot;Cigar&quot; Shape" >}}

 

To adjust the fuselage surface sensor positions and their dimensions to the visual fuselage of the aircraft model, you will need to edit the following parameters in the [`[AIRPLANE_GEOMETRY]`](../../../../content-configuration/cfg-files/flight_model.cfg/#airplane_geometry) section of the SimObject editor: **Length**, **Diameter** and **Center** (all in {{< glossterm >}}ft{{< /glossterm >}}):

{{< image-center
    src="images/7_Samples_Tutorials/Tutorials/Define_Flight_Model/geometry/fuselage/fuselage_2_centerpos.png"
    alt="The Fuselage Parameters in The SimObject Editor" >}}

 

These parameters are named [`fuselage_length`](../../../../content-configuration/cfg-files/flight_model.cfg/#fuselage_length), [`fuselage_diameter`](../../../../content-configuration/cfg-files/flight_model.cfg/#fuselage_diameter), and [`fuselage_center_pos`](../../../../content-configuration/cfg-files/flight_model.cfg/#fuselage_center_pos) in the CFG file. As with the wings, you can use the simulation overlays to debug and position the fuselage if you don't have the exact values that you require:

{{< image-center
    src="images/7_Samples_Tutorials/Tutorials/Define_Flight_Model/geometry/fuselage/fuselage_3_genericsensors.png"
    alt="The Fuselage Dimensions In The Debug Overlay" >}}

 

The generic fuselage has 4 rows of surface sensors visible in the debug view which should be placed *and visible* along the model surface, in close proximity to the "shell" of the fuselage (although with the generic shape, some inconsistency is expected).

 

 

### Advanced Fuselage Setup

To switch to using the modern fuselage geometry objects, the generic fuselage object first needs to be **disabled** by *unchecking* the [`enable_aircraft_geometry_fuselage`](../../../../content-configuration/cfg-files/flight_model.cfg/#enable_aircraft_geometry_fuselage) option in the [`[DESIGN_ACTIVATION]`](../../../../content-configuration/cfg-files/flight_model.cfg/#DESIGN_ACTIVATION) section of the [flight\_model.cfg](../../../../content-configuration/cfg-files/flight_model.cfg/):

{{< image-center
    src="images/7_Samples_Tutorials/Tutorials/Define_Flight_Model/geometry/fuselage/fuselage_4_designactivate.png"
    alt="Enable / Disable Generic Fuselage Geometry" >}}

 

This will remove the generic fuselage from the simulation, and you can add a fuselage geometry object using the [`[OBJ_AIRGEO_FUSELAGE.N]`](../../../../content-configuration/cfg-files/flight_model.cfg/#OBJ_AIRGEO_FUSELAGE.N) section:

{{< image-center
    src="images/7_Samples_Tutorials/Tutorials/Define_Flight_Model/geometry/fuselage/fuselage_5_addgeo.png"
    alt="Adding A Fuselage Geometry Object To The Simulation" >}}

 

Initially you probably won't be able to see much in the debug view, so we strongly suggest that you first set some generic values just to get the approximate size and shape - specifically the [`size`](../../../../content-configuration/cfg-files/flight_model.cfg/#size%20(OBJ_EA1_FUSELAGE)) and [`element_number`](../../../../content-configuration/cfg-files/flight_model.cfg/#element_number%20(OBJ_EA1_FUSELAGE)) parameters. The size values are used to set the width (x), height (y), and length (z) of the fuselage form (in meters), and the element values are used to define how many surface sensors are going to be used for the definition. Essentially you want to create a cylinder that is the approximate length and width of the aircraft fuselage, eg:

{{< image-center
    src="images/7_Samples_Tutorials/Tutorials/Define_Flight_Model/geometry/fuselage/fuselage_6_cylinder.png"
    alt="The Basic Fuselage Geometry Object" >}}

{{< image-center
    src="images/7_Samples_Tutorials/Tutorials/Define_Flight_Model/geometry/fuselage/fuselage_7_sizeelements.png"
    alt="Setting The Size And Element Number For The Fuselage Geometry" >}}

 

It is important to note that **more surface sensors will not improve the accuracy of the simulation**. In general you want to aim for around 500 sensors for any fuselage object. For example, a small aircraft like the DA62 will use 540 sensors for it's main fuselage (), but then *so will an airliner like the B737 Max*. Adding more than this number of surfaces will **not** improve the aerodynamics simulation and will almost certainly affect the overall performance of MSFS 2024 as it processes the extra sensors for little to no gain.

 

 

#### Shaping The Geometry Object

Once you have roughed out the basic cylinder, it's time to shape or "sculpt" it to match the actual shape of the aircraft as close as possible. This is done using the following three parameters:

-   [`dim_scale_top`](../../../../content-configuration/cfg-files/flight_model.cfg/#dim_scale_top%20(OBJ_EA1_FUSELAGE))
-   [`dim_scale_lat`](../../../../content-configuration/cfg-files/flight_model.cfg/#dim_scale_lat%20(OBJ_EA1_FUSELAGE))
-   [`dim_scale_bottom`](../../../../content-configuration/cfg-files/flight_model.cfg/#dim_scale_bottom%20(OBJ_EA1_FUSELAGE))

{{< image-center
    src="images/7_Samples_Tutorials/Tutorials/Define_Flight_Model/geometry/fuselage/fuselage_8_scale.png"
    alt="The Fuselage Geometry Scaling Parameters" >}}

 

These parameters are used to scale the form of the fuselage sensors along the X-axis (lateral) and Y-axis (top and bottom). Essentially, the length of the fuselage is normalised 1, and then you add "points" from 0 to 1 defining the scale at that point, with the simulation adjusting the surface sensors to match this scale. You can do this by manually adding the points into the table associated with the parameter, however we *strongly* recommend that you use the [Curve Editor](../../../../devmode/editors/simobject-editor/menus/#curve_editor) instead. You can customise the graph view to suit the 0-1 scaling values and then add points into it to adjust the fuselage geometry, for example, the image below shows the curve used for the [`dim_scale_top`](../../../../content-configuration/cfg-files/flight_model.cfg/#dim_scale_top%20(OBJ_EA1_FUSELAGE)) parameter:

{{< image-center
    src="images/7_Samples_Tutorials/Tutorials/Define_Flight_Model/geometry/fuselage/fuselage_9_topscale.png"
    alt="Shaping The Fusealge Geometry Using The Curve Editor" >}}

 

Once you have done this for the three parameters, you will have created the shape of the fuselage using the surface sensors:

{{< image-center
    src="images/7_Samples_Tutorials/Tutorials/Define_Flight_Model/geometry/fuselage/fuselage_10_final.png"
    alt="Example Showing A Final Fuselage Geometry Object" >}}

 

You can then go ahead and repeat this process for any other fuselage elements.

 

It should be noted that there is one additional shaping parameter that can be used: [`dim_offset_middle`](../../../../content-configuration/cfg-files/flight_model.cfg/#dim_scale_top%20(OBJ_EA1_FUSELAGE)). This parameter works like the other ones, as it is based on the normalised length of the fuselage geometry object and requires two values (offset in meters and position between 0 and 1). The values given here are used to *offset* the surface sensors along the length of the fuselage to create more complex and curved shapes, for example:

{{< image-center
    src="images/7_Samples_Tutorials/Tutorials/Define_Flight_Model/geometry/fuselage/fuselage_11_offset.png"
    alt="Example Of Surface Sensor Offsets" >}}

 

 

#### Setting Up The Aerodynamics

One of the major features of using the geometry objects for the fuselage is the ability to set up the aerodynamic properties of the "surfaces" that comprise the shape. A surface in this context is a plane generated from the surface sensor normal, and you can define the aerodynamics for these surfaces using the following parameters:

-   [`surface_cx`](../../../../content-configuration/cfg-files/flight_model.cfg/#surface_cx%20(OBJ_EA1_FUSELAGE))
-   [`surface_cx_tangent`](../../../../content-configuration/cfg-files/flight_model.cfg/#surface_cx_tangent%20(OBJ_EA1_FUSELAGE))
-   [`surface_cx_normal`](../../../../content-configuration/cfg-files/flight_model.cfg/#surface_cx_normal%20(OBJ_EA1_FUSELAGE))
-   [`surface_cx_efficiency`](../../../../content-configuration/cfg-files/flight_model.cfg/#surface_cx_efficiency%20(OBJ_EA1_FUSELAGE))

 

These parameters are explained in detail in the [Note On Surface Cx](../../../../content-configuration/cfg-files/flight-model/flight-model-physics-obj/#surface_cx), and so we won't go into that here. However we will quickly give a rough idea of how to apply some *approximate* values based on the fuselage shape and the **measured drag coefficients** shown below (note these are only *some* of the shapes that have pre-calculated values and you can find others on the internet):

{{< image-center
    src="images/7_Samples_Tutorials/Tutorials/Define_Flight_Model/geometry/fuselage/fuselage_12_cdshapes.png"
    alt="Shape Vs Drag Coefficient Diagram" >}}

 

The idea here is to look at your aircraft from the direction of one of the three axis, then check the shape you see against that given above, and then add the shown value into the corresponding axis of the parameter. Note that you are NOT adding it to the "look" axis, but the axis of the visible plane! So:

-   Viewing from the back &gt; X-axis plane
-   Viewing from the side &gt; Z-axis plane
-   Viewing from the top &gt; Y-axis plane

 

In the example below we are looking along the Z axis (from the back of the aircraft) and so the shape we see is that of the plane along the X-axis:

<img src="images/7_Samples_Tutorials/Tutorials/Define_Flight_Model/geometry/fuselage/fuselage_13_cessnashape.png" class="center" />

 

In this case the shape formed is closest to the "short cylinder" base shape (see the list above) and so we get an *initial* X component of 1.15, which can then be plugged into the X component of the [`surface_cx`](../../../../content-configuration/cfg-files/flight_model.cfg/#surface_cx%20(OBJ_EA1_FUSELAGE)) and [`surface_cx_normal`](../../../../content-configuration/cfg-files/flight_model.cfg/#surface_cx_normal%20(OBJ_EA1_FUSELAGE)) parameters. You can then do the same for the Y and Z components of these parameters.

 

For the other parameters, unfortunately there is no "simple" way to get base values as they require complex computations done in an air tunnel or a fluid dynamics simulation. However, for the [`surface_cx_tangent`](../../../../content-configuration/cfg-files/flight_model.cfg/#surface_cx_tangent%20(OBJ_EA1_FUSELAGE)) you can start with value of 0.04 for each and then - through testing - tweak the components as necessary. For the [`surface_cx_efficiency`](../../../../content-configuration/cfg-files/flight_model.cfg/#surface_cx_efficiency%20(OBJ_EA1_FUSELAGE)), you can start with the following values:

-   For X you can use the {{< glossterm >}}oswald_efficiency_factor{{< /glossterm >}}, or - if not known - set it to 1.0 initially.
-   For Y you can use the {{< glossterm >}}oswald_efficiency_factor{{< /glossterm >}}, or - if not known - set it to 1.0 initially.
-   For Z, set to 1.0.