Novel coating fireproofs helicopter deck structures
All aircraft are manufactured to increasingly strict weight requirements. Light weight means lowered fuel consumption, which saves costs and reduces CO2 emissions. The main material currently used for aircraft bodies is carbon fibre reinforced plastic (CFRP). Despite this material’s general suitability for aircraft frames, it is not suitable for every part. A helicopter engine deck is the platform that supports the engines above the cabin. The deck usually consists of two compartments, one for each engine. These compartments are separated by a firewall, which is a physical barrier between the engines intended to stop a fire in one engine spreading to the other. As firewalls can be subjected to extreme temperatures, CFRPs are unsuitable because they would rapidly combust. Therefore, firewalls are still made of metal, although that entails excess weight.
The first fire-resistant CFRP
The perfect solution would be a fireproof CFRP firewall. Thus, the EU-funded HEFESTO project (funded within the framework of the CS-Joint Undertaking), developed a material suitable for engine decks and firewalls. “We have developed a lightweight laminate that coats underlying CFRP structures,” explains Gonzalo Garcia Fuentes, project coordinator. “Yet it achieves the degree of fireproofing mandated by the aerospace ISO 2685 standard.” Beyond direct fireproofing, the coating also ensures that the CFRP beneath never exceeds 120 degrees Celsius. Therefore, in the event of fire, the material will retain structural strength long enough for the aircraft to land safely. The laminate is also cheap to make, using materials available in the market. The combination of the laminate and CFRP may achieve, in the best case studied, weight savings of 10-20 % compared to metal firewalls.
New application method tested
The team also developed a new engineering process for applying the laminates to a CFRP firewall prototype. The method allows application of the laminate to a firewall’s complex shapes, including along corners and joints, and also around fittings or other through-wall elements. In parallel with developing the material and application methods, researchers also proposed redesigned aircraft structures, and introduced innovative assembling procedures for the new materials. As a secondary effect, the redesign simplifies the installation of elements and fittings to the structure. The combination of new design and materials cannot be retrofitted to existing aircraft. Instead, these developments would appear on a new generation of aircraft due in 4 to 5 years. The laminate coating could theoretically be applied to any CFRP aerospace structure. Researchers tested the developments according to the strict ISO 2685 standard. In part, this requires aircraft structures to withstand kerosene-fuel fires while under intense mechanical vibration. Having successfully passed those tests, the product has achieved technology readiness level 5-6, meaning that the concept is proven. Next, the HEFESTO team will be identifying any potential weaknesses in the approach, and re-engineering where necessary. “In parallel,” adds Garcia Fuentes, “we are studying the patentability of the result, and evaluating different models of exploitation.” The outcome will be helicopter engine decks and firewalls made of lightweight CFRP that are also fireproof to an aviation standard. This will make future helicopters more fuel efficient.
Keywords
HEFESTO, firewall, CFRP, coating, helicopter, laminate, fireproof, weight saving, carbon fibre reinforced polymer
