Ultrahot, pressurized combustion gases within the National Aerospace Plane (NASP) engine needed to be sealed to prevent them from leaking past the movable engine panels to rear engine cavities and causing the engine or entire aircraft to fail. The need to seal the hot gases and distortion of the engine's sidewalls required the development of a device nearly as flexible as a rubber O-ring yet able to operate at over 2000 °F. The advanced, High-Temperature, Flexible Fiber Preform Seal is one very important step in that direction.
This seal is braided of emerging high-temperature ceramic fibers or superalloy wires into a flexible, flow-resistant seal. It has been used for numerous NASA applications since it was patented in 1992. The patented technology was used by GE in the joint NASA/Department of Defense/GE Integrated High Performance Turbine Engine Technology (IHPTET) program. This hybrid rope seal successfully sealed the perimeter of advanced nickel-aluminide turbine vane airfoils, allowing the vanes to grow relative to the supporting structure, thus overcoming the thermal shock failure experienced with the conventional sealing approach. In a successful full-scale Joint Turbine Advanced Gas Generator (JTAGG) engine test, the high-temperature turbine vane/seals, in combination with several other advanced technologies, contributed to meeting the program goals of reducing specific fuel consumption by 20 percent and increasing the engine power-to-weight ratio by 40 percent.
The invention is being evaluated by Pratt & Whitney as a potential replacement for sealing interfaces between large nozzle turning vanes and flow-path fairing elements (see the figure) for the F119 engine that will be used in the F22 fighter, the country's next-generation premier fighter. Pratt & Whitney tested the seal in a full-scale engine (Fall 1997), and after 24 hr of testing the seals showed no signs of degradation.
Seal Requirements
In addition, Williams International is evaluating the seal for an advanced turbine engine, and AlliedSignal Inc. is considering using the seal as part of an industrial gas turbine generator for auxiliary electric power. Lewis researchers helped qualify the seals for subsequent engine and industrial system tests.
NASA is developing a future replacement for the space shuttle and will be testing many of the technologies on an experimental vehicle, the X-33. The X-33 contractor team is exploring possible use of the NASA rope seals for sealing the joints between the aerospike engine nozzles and the joints between the vehicle's heat-resistant thermal tiles.
Although the seal was developed for aerospace uses, it is being evaluated for industrial applications as well. Under a reimbursable Space Act Agreement, NASA Lewis is working with Praxair, a major U.S. producer of industrial gases, to adapt the seal technology for use in the company's high-temperature, proprietary industrial gas systems. Other potential future applications include sealing furnace doors, heat exchangers, and continuous-casting and glass-processing equipment.
The seal is able to bend around sharp radii (about equal to the seal's diameter) conforming to and sealing complex components. In addition, the seal exhibits low leakage, retains resilience after high-temperature cycling, and can support structural loads.
For more information, be sure to check our web site.
Lewis contact: Dr. Bruce M. Steinetz, (216) 433-3302,
Bruce.M.Steinetz@grc.nasa.gov
Author: Dr. Bruce M. Steinetz
Headquarters program office: OASTT
Programs/Projects: Propulsion Systems R&T, HITEMP
Special recognition: The 1996 Government Invention of the Year was awarded to Dr. Bruce Steinetz and Mr. Paul Sirocky (retired) for co-developing the advanced, High-Temperature, Flexible Fiber Preform Seal. This is the first time Lewis has won this NASA-wide competition since 1988 when Harold Sliney won the award for his high-temperature solid-film lubricants.
Previous articleLast updated April 15, 1998, by Nancy.L.Obryan@nasa.gov
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