Tech Insight: the Bell racing Helmet

The official Ferrari Competizioni GT drivers take to the track equipped with Bell helmets, whose design philosophy emphasizes function and performance focusing on the essential elements and features needed to enhance driver performance and protection. Development of modern helmet designs have transitioned from hand-made modeling and prototyping to the virtual world where designs like the HP77 are first developed using advanced 3D modeling, computer aided design (CAD) and rapid prototyping. This allows Bell to conceptualize and refine the design, assure physical dimensions and component integration, conduct strength and dynamic analysis, predict impact performance, produce a precise rendering and confirm manufacturing process details before developing prototypes or producing physical tools. Once the design is finalized, CAD files are used to manufacture the aluminum shell tooling, produce the EPS liner tooling and injection molded tooling for specific accessories designed for the helmet. The majority of Bell models have three separate shell/liner combinations per design to optimize helmet fit based on the size and circumference of the head, with each shell size accommodating three hat sizes allowing Bell to offer a wide range of sizing to fit most drivers safely and comfortably.

Testing a racing Helmet. Bell does extensive, ongoing research and development testing to assure helmets like the HP77 are developed with the best possible combination of materials and manufacturing techniques to maximize energy management and driver protection while ensuring they exceed the most stringent helmet standards in motorsports. Testing is a destructive process so only a small percentage of helmets are impact tested after final assembly. To confirm the helmets produced are performing as intended, Bell conducts random sample testing within each production run plus performs incoming material testing by batch and lot prior to releasing materials to production. Testing is performed to industry standards including FIA and Snell, is conducted on a twin-wire drop tower test rig with impacts at various drop heights. The helmet is placed on a specific head form that simulates the size and weight of a human head. Located inside the head form is an accelerometer that measures the peak G’s and the duration of impacts. The accelerometer measures the amount of force that was not absorbed by the helmet. The objective is to reduce the amount of G’s as much as possible while extending the duration of the impact to limit the energy or force transmitted to the head. The HP77 is homologated to the FIA8860-2018 ABP standard and the outcome of a successful test is determined by two parameters: the maximum acceleration measured in “G’s” must be within the standard based on the location and type of impact and the helmet must not exceed a HIC (Head Injury Criterion) indicating a serious or life threatening amount of force. In addition, the area above the visor on the HP77 is subjected to an additional frontal test to confirm the helmet has a high level of ballistic protection above the visor. Additional tests include flame, roll off, chin bar deflection, shell penetration and compliance testing to confirm use with head and neck restraint devices. The goal is to create a protective helmet that absorbs as much energy as possible, limits the overall volume and minimizes the energy transmitted to the head.

Racing Helmet Construction. The first component of the helmet is the shell. Production of the most advanced Bell helmet available in the world, the HP77, starts with a pre-preg kit, a series of pre-preg advanced carbon fiber materials that are die cut in patterns optimized for the shell’s geometry and impact requirements including ballistic materials incorporated into the shell reinforcing the front forehead area of the helmet to prevent penetration. The pre-preg materials are applied into a two-part mold made to the exact shape and dimensions of the helmet in a specific sequence to form the shell layup. The mold is placed in a purpose-built machine that cures the shell through a combination of heat, pressure and time. Bell Racing Helmets uses a proprietary Prepreg Compression Molding (PCM) machine using technology derived from the aerospace industry with pressures higher than common autoclaves. Once inside the machine, homogeneous pressure is applied with the material subject to a temperature cycle to allow the material to reach the highest degree of curing in around 45 minutes. This process combined with the latest carbon fiber materials allows Bell to produce a shell that is lightweight, extremely strong, and resistant to penetration. Once the shell is fully cured the helmet is placed in a fixture to route or cut the eyeport, bottom trimline, vent holes, and shell holes to install the shield hardware. Once routed, highly trained technicians sand the shell by hand to prepare it to be painted and clear coated. An added advantage of Bell’s PCM pressure molding system is it reduces the presence of micro porosity on the shell surface, produces a smoother finish which results in less preparation time and less weight added from fillers used to fix imperfections. The standard HP77 is clear coated using a matte clear finish providing a weight savings of up to 40 grams. Once the shell is clear coated, the shield hardware can be installed, and the shell is ready for custom paint or final assembly.

Energy Absorbing Inner Liner. The second component of the helmet is the liner system. To produce the inner liner, Bell uses a proprietary EPS (expanded polystyrene) formulation with natural rebound for single and multiple impacts designed to absorb as much energy as possible while limiting the forces transmitted to the driver. The bead is pre-expanded to the correct density determined through testing and liners are molded on-site at the Bell Racing Helmets factory in Bahrain to allow for better quality control assuring the liner parts are within weight and specification. The HP77 uses a multi-piece liner system featuring a solid outer ring with two interior liner sections allowing Bell to incorporate different densities in specific areas of the liner to work in conjunction with the carbon shell enhancing the energy management capability of the helmet. Bell also uses EPS and EPP materials in the front face piece of the helmet, extending energy absorbing protective material into the front chin bar of the helmet. Once the liner is molded and assembled, the inner liner along with the left and right front face piece sections are ready for interior padding to be installed.

Building the Interior & Final Assembly. The helmet interior including the fit pad and chin straps form the retention system and are the third component of the helmet. The interior is made using a combination of fire-retardant fabric, foam and aramid material for the chin straps. The fabric pieces are cut in specific patterns to cover the fit pad, face piece, cheek pads and chin straps. The foam for the fit pad and cheek pads are cut in specific patterns and thicknesses depending on the model and size of the helmet. The fit pad fabric and foam is sewn together and glued to the liner assembly while the sewn fabric pieces and foam are assembled and glued to the face piece. The aramid material (Kevlar) for the chin straps are cut in specific lengths for the d-ring and strap sides, the strap end is chemically sealed and the hardware that attaches the chin strap to the shell along with the side that holds the chin strap d-ring is secured to the chin strap assembly using a high-strength bar tacking machine. Bell uses a purpose designed d-ring system that locks the strap in place once fastened and tightened while preventing the d-ring from twisting when using the helmet. The completed liner assembly, face piece assembly and chin strap assembly are ready to be installed in the helmet. Prior to assembly, the helmet shell edges are finished using a fire-retardant rubber molding applied to the shell with adhesive to finish the eyeport and bottom trim line of the helmet. The liner assembly is inserted into the bottom of the shell and rotated into place. Once the liner is inserted, the chin straps are attached to the shell using a rivet system and the face piece assembly is installed. At this point the various accessories including the anti-fog face shield and air intakes are installed in the helmet, and it is ready for final QC inspection. Once confirmed, homologation labels are applied and the HP77 is placed in a helmet bag, boxed and ready for use. However, HP77 helmets that are designated for use in GT racing are further customized with a custom interior developed for the specific driver’s head shape and individual paint and graphics applied to the shell prior to assembly.

3D Head Scan. For the official Ferrari Competizioni GT drivers, Bell improves helmet fit by taking a 3D head scan of the driver and building a custom interior. The process starts with a custom head scan to create an exact 3D model of the driver’s head shape. Bell’s engineers use computer aided design (CAD) to position the scan within the parameters of the inner liner. Using this data, a custom interior is built, conforming to the driver’s head shape to create a secure, perfect fit that eliminates pressure point and enhances the comfort of the HP77.