An Internet Guide To Constructing Your Own Race Car.

Tips: Safety & Ergonomics

The following tips and information focus on how to optimize race car safety and ergonomics. Depending on class rules, these suggestions may or may not be valid. Always check your regulations.

General Safety/Ergonomics Design Principles

Safety/Ergonomics Design Tips

General Safety/Ergonomics Design Principals

Safety

Safety in a race car is the art of protecting the human occupant, at whatever cost to the car. Designing the car to be damaged minimally while hindering driver safety is definitely the wrong approach.

So how do we protect the driver? Well first we need to consider the basic physiological weak points of the human body.

The diagram above shows that pretty much any part of the body exposed to the chassis of the race car is at risk. Injuries occur because the body sustains impacts beyond the G (gravities) level that it can sustain.

The brain is particularly succeptible to injury, because it is really just a soft tissue mass stored inside a very solid bone container, the skull. The key to avoiding injury in the brain is to avoid instantaneous decelleration of the skull. That is, when the skull strikes something hard, it decellerates instantaneously. The brain inside unfortunately keeps on moving, causing head trauma.

Neck and spinal injuries also present a serious threat to life and career. These "Connector" type elements in our body are flexible and stretchable, to a point, and can sustain tremendous G loads before breaking. However, depending on angle of impact, they can break rather easily.

Other bone injuries (breakages) are not as life-threatening or career ending, but still are to be prevented. The bones in our arms, legs and spine are designed to be stressed in tension and compression along their length. In the case of impacts they are often stressed in shear or bending, and therefore snap relatively easily.

Safety In Engineering

Safety in race cars consists of optimizing the chassis and bodywork to provide maximum support for normal driving situations, and maximum protection and energy absorption in crash situations.

First, the driver needs to be supported, so movement under normal driving is very limited. This means a seat with lateral head support, a head rest, and good lower and upper body lateral support. Most racing seats provide these three elements.

Secondly, the car's chassis needs to hold the seat and driver in place, in all situations, driving and crashing. This is of course accomplished with a chassis mount for the seat, and a 5 or 6 point harness.

Thirdly, measures must be taken to prevent intrusion into or the crushing of the driver's limbs and extremities. On formula cars, the problem of suspension wishbones breaking and piercing the driver's legs is solved by anti-intrusion panels that prevent pieces of the car from intruding into the driver's cockpit. As well, the cockpit "Safety cell" needs to be very strong. The "Safety cell" is the last piece of material between danger and the driver, and so should be well constructed, and not prone to collapsing onto the driver.

Finally, the car needs to absorb the energy via structures that are crushable. As stated previously, the human body does not like to be decellerated from 80 or 100 km/h to 0 instantly. Therefore, we need to find a way that "quickly" decellerates the body. The only possibilities on a race car are the structures which surround the driver's safety cell. Designing these structures to collapse in an impact ensures that G levels are reduced because the car is literally decellerating over a small distance, instead of ZERO distance.

Below is a diagram:

Ergonomics

Ergonomics, or the study of human-machine interfacing, is important to race cars because the ultimate control of the car belongs to the driver. Poorly placed controls mean the driver must lose concentration on the race, and instead focus on the cockpit.

The ergonomics of a race car cockpit consist of several elements:

• The driver's line of sight - Visibility is of prime importance. The goal in design is to ensure enough of the race track in front is visible, and enough of the action to left and right is visible, through peripheral vision. Of course, the driver also needs to see behind to watch for his/her competition. The mirrors should act as an extension of the visible field.
• The steering wheel - The steering wheel is a tool of leverage. If a steering wheel is too far from the driver, the driver's arms will straighten, and ultimately limit the range of motion easily provided. If it doesn't stop the driver from driving properly, this situation will cause fatigue. If a steering wheel is too close, it will also limit the range of motion and perhaps cause interference with other cockpit controls or supports. The proper distance is largely a matter of comfort and clearance, and usually means the arms are bent at the elbows when driving straight, yet still comfortable when turning the wheel.
• The gauges - The gauges act as vital signs for the car, and as such should be as close to the driver's normal line of sight when looking forward. Forcing the driver to look down at gauges removes concentration from the race. In Formula 1 (a particularly good example), the RPM is displayed with a series of LEDs (Light emitting diodes) that light as the redline is approached. This light sits almost at the very top of the cockpit, in line with the line of sight, allowing the driver to change gears without ever needing to look down.

  A technique frequently used in racing is to rotate the gauges so that all needles or indicators are pointed to the directly vertical position when operating normally. The driver does not need to conciously scan the gauges, but can instead use his/her peripheral vision to determine the state of the car.

• The Pedals - The pedals, like the steering wheel are a leverage item. The driver's legs will tire if not given a position of leverage. Likewise, the driver's legs may tire anyway, due to an inappropriate leverage fulcrum in the actual pedal system. Assuming the pedals and levels are well designed, we can focus on the driver's legs. To be most effective the driver's legs should be bent slightly when the pedals are fully engaged, and should be bent somewhat more when the pedals are not engaged. The calf portion of the leg should probably not be at less than 120 degrees angle in relation to the thigh when the pedals are disengaged. See below:

• Other Controls - Positioning of controls such as the gear shift, kill switch, and adjustment knobs should be carefully considered. It does no good if shifting is hampered by the steering wheel, or if the kill switch is buried away from rescue crew access.

 

Safety/Ergonomics Design Tips

• Use energy absorbing materials in the collapsable crash structure - In lower cost racing cars, most of the car is usually built from mild steel. Using that same mild steel in areas such as wishbones means that impacts will bend the material long before it breaks the material, meaning energy absorption takes place over a longer period.
• For light weight, use a stressed skin over a lightweight core material - crushable zones such as the nose cone on a formula car can be made from balsa, honeycomb or high density styrofoam covered with a stressed skin of composites.
• Triangulate the driver "safety cell" to prevent collapse - The safety cell can be designed in such a way that a catastrophic impact which collapses the safety cell, will make the safety cell expand away from the driver, instead of collapsing it onto the driver. In the case of a frontal impact, this would mean the sides of the cockpit would expand outward, upward and downward, instead of inward.
• Use a clear windscreen or bodywork to increase vision - using lexan or other non-shattering clear material can help increase visibility without compromising the function of the bodywork. In some cases, the driver can be lowered for better CG (center of gravity), and the normally opaque bodywork replaced with clear lexan, to aid in re-establishing the vision field.
• Keep the fuel cell and battery away from the driver and danger. Keeping dangerous items away from the driver is sometimes very difficult. In order to reduce the weight balance change over a race, designers will frequently put the fuel cell at the CG, so that no matter how empty or full it is, it does not cause a front/rear or side-to-side weight bias. However, most drivers don't like to sit next to fuel. Use secured, sealed firewalls between the fuel cell and driver compartment, and further, use the safety cell to protect the fuel cell from outside intrusions.
• Don't scrimp on safety. Use only top quality certified suppliers of safety equipment. The cost is perhaps high, but consider how much you value your life. Fuel cells (Sanctioning body certified), seat belts (5 or 6 point sanctioning body certified only!), and driver safety wear (Nomex, 2 or more layers minimum! -- anything less is like wearing nothing).

Check Back Later For More Safety/Ergonomics Tips.

Got a safety or ergonomic design tip? Send us feedback.

Read some good race car design books (including safety)...