Extreme heat and cold, radical temperature fluctuation, pressure, moisture, ozone and UV radiation are just a few of the hostile elements challenging aircraft design. For engineers at Eclipse Aviation Corp., specifying the O-rings and silicone grommets to achieve state-of-the-art jet engine performance and designing pressurized door seals to achieve FAA certification proved to be major milestones.
The Eclipse 500® very light jet (VLJ) is a revolutionary idea in the aviation industry. The Eclipse 500® functions as a six-person “air taxi,” transporting passengers from point-to-point rather than hub-to-hub as traditional airlines operate. For this concept to be successful, the plane must be very affordable. Eclipse delivers performance at what the company says is a fraction of the cost of its current competition.
In the design of the Eclipse 500® VLJ, Eclipse entered into a long-term contract with the Simrit division of Freudenberg-NOK to supply seals for the program. The two companies worked together on the design and certification of the pressurized door seals and, in conjunction with engine builder Pratt & Whitney Canada Corp. (P&WC), selecting appropriate materials for engine components.
“With rising fuels costs, aerodynamic performance has increasingly become a critical factor,” says Vinay Nilkanth, vice president of business development for Simrit.
“All of the joints where the wings are mounted to the fuselage require aerodynamic seals and need to provide excellent aerodynamic performance and improve the overall efficiency of the aircraft,” he adds.
Simrit worked closely with the Eclipse design engineering staff to design the pressurized door seals, especially in terms of contributing to the CAD design of the aircraft. “We exchanged CAD information and IGUS files to provide recommendations on what to do on the mating components to make it cost-effective and efficient,” says Nilkanth. “We saw a marked improvement in the data as we went through a specification process, so that the design could be FAA certified and contribute to the overall certification of the aircraft.”
Simrit engineers worked collaboratively with Eclipse on a value engineering process and a design review that put the focus on tolerances for components and recommendations in the materials used for the pressurized door seals.
In September 2006, the Federal Aviation Administration gave its full authorization for the Eclipse 500® VLJ. Nilkanth says Simrit is proud of the work done hand-in-hand with Eclipse because, without solving the pressurized door seal issue, certification could have been substantially delayed.
Proper selection of materials, design and technology innovations ultimately helped Eclipse through the certification process.
Eclipse uses two P&WC PW610F turbofans to power the small jet. Since Simrit also works directly with P&WC, it provided technical resources to help with the detailed analysis required for specifying specialized sealing and materials, including silicone grommets and O-rings for the jet engine.
One of the challenges was specifying appropriate solutions to provide both low-temperature performance and lower cost in higher temperature applications. Unlike other commercial aircraft, such as the Boeing 737 or Airbus, the Eclipse 500® flies at slightly lower altitudes where engine temperatures are not as high.
“What we wanted to do was match the performance expectations at various temperatures by carefully selecting the types of materials used,” says Nilkanth.
He says the most challenging aspect of the application was this balancing act of getting close to the high-temperature performance of a larger aircraft, while also achieving lower temperature performance.
“Usually, we need to work on high-temperature solutions, but the higher temperature materials are not as good on the low temperature side,” he says. “Both fuel efficiency and, even more importantly, compatibility with specific jet fuels and lubricants proved to be important to meet the needs of this application.”
Simrit worked closely with P&WC to offer recommendations on material properties and testing to achieve the requirements. Low-temperature characteristics, in particular glass condition temperature, was one criterion used, along with how physical properties performed over a wider temperature range and compression fit.