NASA Dryden Press Release 98-26
May 18, 1998

NASA's F-15B Aerodynamic Flight Facility aircraft is flight testing Thermal Protection System materials for the X-33 Advanced Technology Demonstrator at the Dryden Flight Research Center, Edwards, Calif.

These flights are designed to test the durability of the Thermal Protection System materials at flight velocities for shear and shock loads, providing data to the X-33 Advanced Technology Demonstrator project team. The X-33 is scheduled to begin test flights in July 1999.

"Once again the F-15B exhibits its ability and versatility as a testbed aircraft as it performs this short series of flights to validate the durability of the Thermal Protection System materials planned for use on the X-33," says Roy Bryant, Dryden's F-15B project manager.

The Thermal Protection System material samples, which include metallic Inconel tiles, soft Advanced Flexible Reusable Surface Insulation tiles, and sealing materials are flown attached to the forward-left side position of the F-15B Aerodynamic Flight Facility's Flight Test Fixture II, a device attached underneath the aircraft to carry experiments. In-flight video from the aircraft's on-board video system and chase aircraft photo and video cameras are used to document the condition of the Thermal Protection System materials during flights. Surface pressures over the Thermal Protection System materials are measured by thermocouples contained in instrumentation "islands" to document shear and shock loads on the materials.

Shear loads testing is investigating the air loads acting upon the Thermal Protection System materials under subsonic flight conditions. Shock loads testing is investigating the local impact of the transonic (passing from subsonic to supersonic) supersonic shock wave itself on the Thermal Protection System materials.

"These F-15/X-33 Thermal Protection System flights are part of the X-33 Thermal Protection System qualification process. The X-33 is on a time-critical schedule and these F-15 flight tests are providing data in a very expeditious manner," says Gary Trippensee, Dryden's X-33 project manager. In 1995, the F-15B participated in similar studies of Thermal Protection System durability, but those tests focused primarily on rain impact on the materials. A particle measurement probe, the same used in prior F-104 tests, was installed aboard the F-15B under the Flight Test Fixture II to measure precipitation drop size, distribution and concentration. Edwards AFB weather radar data helped predict rain location and quantity during flight testing. Video cameras on the F-15B documented the test flights.

In 1985, using Dryden's F-104 testbed aircraft, Dryden began testing Space Shuttle Thermal Protection System tiles using a similar test fixture, incorporating both new tiles and tiles that had flown in space on Columbia. The results of F-104 flight tests showed various levels of damage and erosion to the Thermal Protection System tiles when flown through rain. Beginning with "star" cracks in the black face coat of the tile, damage progressed to the formation of pits which penetrate the black glass coating, exposing the white substrate, or supporting material, of the tile. Erosion of the tile substrate was also observed under the most severe test conditions.