The Anatomy of a Manikin (yes, this has to do with cars)

Most of you have probably seen the crash test dummies used to test airbags and other crash safety systems. Automotive designers use a similar device, called a manikin. These aren't dragged out of an Old Navy, they have very specific geometries that reflect the body of a 95th percentile US male (97.5th percentile, including women). The Society of Automotive Engineers (SAE), with the help of other organizations, has collected data on the size, proportions, and movement of the human body to develop this manikin. Designers usually set up the interior space using the 95th percentile manikin to ensure that almost everyone can fit. This diagram from H-Point highlights all of the key features.

The most important part is the h-point, (hence the book's title) also called the seating reference point. This point's location determines the occupant's position relative to the vehicle. The lower the h-point, the lower the occupant is sitting and the further out his/her legs are stretched longitudinally. This relationship between the h-point and the rest of the body creates what is called the SAE accommodation curve, shown in the above diagram.

Notice how no matter where the h-point is on the curve, the feet stay almost in the same longitudinal position, with the torso and legs always in a natural sitting position. This is key when setting up the driver's height and posture. This curve does not apply to rear occupants, however, as their space is often constrained by the total length of the vehicle. This is because the vehicle's length is dependent on the couple distance, which is the horizontal distance between front and rear occupants' h-points. Thus, limits to the vehicle's length will impact rear occupants' space the most.

The following anatomical features are also important for establishing the occupant's environment.

The accelerator heel point is the lowest vertical point of the manikin. For this reason it is used to establish the floor and step-in height.

The ball of foot point is used to determine how much crush space is needed in front of the driver. As discussed in a previous post, crush space is the space  that will compress on impact between the occupants and the exterior surface of the car.

It is essential that every occupant, regardless of their size, has good visibility. For this, SAE developed the 95th percentile eye ellipse, within which 95% of drivers' eyes will be located. Using this ellipse, designers can position the windshield to ensure good visibility.  

Nobody wants a car that doesn't provide enough head room. Designers use the SAE 95th percentile head contours, a volume that represents the amount of head room a 95th percentile occupant needs. This also incorporates space needed for head movement and seat track movement.

Lastly, the thigh center-line is used to position the steering wheel.

That's all for now: up next is interior design!