Preparation for 3D Modeling

Before I start developing my model in 3D, I need to make my initial sketches more precise. There are several key dimensions used in the Computer-Aided Design workflow that need to be identical across the sketches, to avoid any discrepancies. This includes the ground clearance, total height, and belt line height. It is also important that the height, width, and length have the correct proportional relationship, so the 3D printed model is to scale.

After making the necessary adjustments to the sketches, I am now ready for 3D modeling!

Below are the finalized sketches.

Design Considerations

After further reviewing my sketches, there are some design complications that I will have to address.

Firstly, the air intake system on the body side creates an impression on the doors. It is important that the side glass has enough room to drop into the door structure. This means I cannot add too aggressive indentations to the door's exterior surface, because it would push the interior trim inwards, cramping the occupants.

The side glass cut lines are not defined within the door profile. There are also no door cut lines. Fortunately, car doors are flush with the exterior surface, so door profiles will not change the final, 3D printed product. By contrast, side glass is slightly offset from the adjacent door surface, so cut lines are necessary to make changes to this surface.

A two dimensional model is not good at communicating the variation in depth along the vehicle surface, even with sketches from different views. I will have to wait for the 3D modeling to add more detail.

Occupant Packaging

To set up the occupant package, I must establish some key dimensions and position the SAE 95th Percentile Manikin. Before I can do that, I need to keep these factors in mind:

On a high performance car, the front and rear spindles are positioned to provide optimal weight distribution. I cannot change these to accommodate the occupants.

Crush space is behind the driver for a rear engine vehicle, because there are no hard components in front of the driver. Thus, there must be more room than for just the engine behind the driver's seat.

The dimensions below correspond to the diagram.

1. H-Point to Ground: 325 mm

2. Chair Height: 150 mm

3. Back Angle: 28 degrees

4. Forward Vision Angles: 8 degrees up, 5 degrees down

5. Effective Headroom: 955 mm

6. Shoulder Room: 1350 mm

7. Lateral Location: (from center line) 340 mm

Size and Proportions

In this phase of the design process, I will look at some key dimensions of the model, derived from my sketches, and compare them to similar vehicles. This is known as benchmarking.

The Ferrari LaFerrari is a modern rear engine, RWD supercar. I chose this vehicle for comparison because of the similarity in side profile view to my model.

Exterior Dimensions:

LaFerrari

Length: 185.1"

Width: 78.4"

Height: 43.9″

Wheelbase: 104.3″

Front Track: 66.9"

Rear Track: 64.4"

My Model

Length: 181

Width: 72.

Height: 47

Wheelbase: 105.5

Front Track: 65.

Rear Track: 63.

My Model

LaFerrari Front (not mine)

LaFerrari Side View (not mine)

Package Ideation

Before settling on one design, it is important to explore every possibility at the beginning. After the initial ideation phase, it will be too late to introduce different ideas and start from scratch.

There are two ways to complete the ideation phase for cars.

In one method, the exterior design is developed first to inspire the package layout. The package consists of all of the elements driven by function not appearance, such as the engine, fuel tank, wheels, seating, etc.

It is also possible to start by sketching different layouts for the cargo, occupants, tires, and powertrain. Then ,a loose sketch of the body profile will provide a medium to analyze how different package configurations change the exterior proportions.

Either way, the goal is to explore as many options as possible that satisfy the functional objectives.

I will use the latter method in my ideation phase.

For a high performance vehicle, a powerful engine is a necessity. This effectively eliminates the transverse engine layout, because the engine is constrained by the frame rails. I will consider front and rear-mid engine layouts, FWD and RWD, and also electric motors.

At this stage, exact dimensions are not important. The purpose is to evaluate the resulting proportions of each layout and then chose one or two to develop further.

I chose to continue with the mid-rear engine, RWD layout, which will be the focus of the remaining posts.

Next, I will work out the key dimensions and set up comparisons to similar vehicles.

Model One: Setting Functional Objectives

After spending the past few months studying car design and CAD software, (more to come on that) I will now create my own car! 

In the next ten posts, I will complete design exercises from H-Point, which outline the steps required to build a conceptual vehicle package. My concept will be called the Model 1. 

In the first exercise, I will set out clear functional objectives for the customers, manufacturer, and the market. 

Customers

• Power, speed, and handling are a priority. Comfort less important.
• Two occupants
• Targeted towards car fanatics that are comfortable driving a high-performance car. 
• Modern, Aggressive Vehicle Image

Manufacturer / Brand

• Primary Vehicle in Product Lineup 
• High Investment and Manufacturing Costs
• Annual Sales Volume: 300 (based on competitor's sales volume)
• Internet Marketing and Small Storefronts

Market/Driving Environment:

• All weather driving, only paved roads. 
• Uncompromised engine size, minimum height and front profile for reduced drag.
• Fuel economy won't inhibit performance. 

Up Next: Package Ideation

Exterior Lighting Requirements

There is a wide variety of lights that vehicles must have in different parts of the world.
This post will identify and explain them.



Headlights:
This consists of a high and low beam to illuminate the area in front of the vehicle.
Required in the US and Europe.


Daylight Running Lamps:
Consists of two headlamps that make oncoming vehicles more visible in daylight.
Permitted in US, required in Canada and Europe for some vehicles.


Front Fog Lights:
Two forward-facing lights mounted symmetrically about the center line.
Required in Europe.

Park and Turn Lights:
Parking- Indicate the vehicle's position during parking if the headlights fail.
Turning- Flashes to indicate the drivers intent to turn or for an emergency.
Required in US and Europe.


Side Marker Lights:
Indicate the overall length of the vehicle.
Required in US and Europe


Side Repeater Lamps:
Work with turn signals to show intent to turn or change lanes.
Visible to vehicles travelling alongside.
Required in Europe




Center High Mounted Stop Light:
One rear-facing red light mounted on the vehicle centerline, activated with brakelights.
Required in US and Europe

Back-Up Lights:
For illumination behind the vehicle and to provide a warning signal.
One required, two optional.
White in color.
Required in Europe.

License Plate Lamps:
Used to illuminate the rear license plate to be legible at night.
Required in US and Europe



Taillights:
Brake lights - Red - Indicate the vehicle is slowing down.
Turn Signal - Red or Amber - Flashes to indicate the drivers intent to turn or for an emergency.
A specified portion of the taillight must be mounted on the fixed body (not the trunk lid/hatch).
Clustered into one light assembly.
Required in US and Europe.

Rear Fog Lights: Red- make the vehicle more visible in fog.
One is required, mounted on the driver's or vehicle's centerline. Two are optional.
Not allowed in US, required in Europe.

Thanks for Reading!

Aerodynamics Basics

Aerodynamics is a very technical, in-depth subject, but I will cover the basic principles in this post.

Every package should be set up to allow the vehicle to travel through air as efficiently as possible.

The importance of aerodynamic soundness depends on the type of vehicle. Sports cars need high airflow and downforce improve top speed, handling and engine/brake cooling. Trucks, however, usually have drastically compromised aerodynamics because of their large frontal surface area and underbody structure.

The two most important aerodynamic factors are the drag coefficient (Cd) and total drag. Analogous to the coefficient of friction from AP physics, the drag coefficient (Cd) is an intrinsic property that measures the "slipperiness" of a particular shape, regardless of its size. The total drag is the product of this coefficient and the cross sectional area of the vehicle. This product is a force, which describes the amount of force needed to propel the vehicle.

Airplanes obtain "lift" when the air pressure below the wings exceeds air pressure above the wings. At high speeds, this phenomenon starts to influence the handling and balance of cars too. Spoilers are often applied to maintain consistent down force on the front and read tires, improving traction as well.

Vehicles also need air intake systems to perform several different functions. Engine cooling requires substantial air flow for the cooling modules to work. Cars and trucks usually have very pronounced breathing apertures for this purpose. It is also common for cars to have openings for airflow to cool the brakes. The HVAC (heating, ventilation, and air conditioning) system takes in air from the base of the windshield (aka cowl/plenum), called the cowl screen. Spanning between the a-pillars, the plenum chamber filters the incoming air.

Below are illustrations from H-Point depicting good and poor aerodynamics.

This car's small front reduces drag. The gently contoured roof line, sharp rear-end cutoff, and fared-in rear wheels also contribute to a low drag coefficient.

It doesn't take an aerospace engineer to notice the inefficiencies of a Hummer. The body is large in all dimensions, causing it to push through a lot of air. The sharp changes throughout the body's exterior and the exposed underbody components will create additional drag.

Thanks for reading!