NASA's F-15B #836 is a two-seat version of the F-15, which is a high-performance, supersonic, all-weather fighter airplane. The F-15B is used as a test-bed aircraft for a wide variety of flight experiments. In support of this use, a flight-test fixture (FTF) (see Figure 1) was developed to provide a space for flight experiments in a region with known aerodynamic conditions.

The FTF has been flown in many flight experiments during the past several years and can be modified to satisfy a variety of research requirements. For example, the X-33 project requested assistance in exposing specimens to shear and impinging shock loads for validation and flight qualification of the X-33 thermal-protection-system (TPS) materials in a flight environment. X-33 TPS materials for this experiment ranged from metallic panel materials (supplied by BF Goodrich) to a variety of advanced flexible reusable surface insulation (AFRSI) specimens supplied by NASA Ames Research Center. Transition seals and flight-test instrumentation islands were also incorporated into the specimens to demonstrate the durability of these components. Some of the specimens were thermally cycled in an arc-jet tunnel prior to flight test in order to simulate thermal loads expected on the X-33 vehicle.

Figure 1. The Flight-Test Fixture is a fully instrumented test article mounted on the centerline of the lower fuselage of an F-15B airplane. The fixture is 107 in. (2.72 m) long, 32 in. (0.81 m) high, and 8 in. (20 cm) wide, with a 12-in. (30.5-cm) elliptical nose section.

The two forward left side panels on the FTF were replaced by a large carrier plate in order to simplify the installation of the various TPS specimens and thereby enable quick changes in configuration between research flights. Specimens were installed in the various quadrants of the carrier plate (see upper part of Figure 2), depending on the desired configuration for each flight. Forward specimens were generally used to look at the effects of shock-impingement loads previously identified at forward locations at transonic speeds. Specimens in the aft locations were used to document the effects of shear loads.

Six configurations were flight-tested at a maximum mach number of 1.4 and dynamic pressures as high as 790 lb/ft2 (37.8 kPa). Flight tests were conducted at altitudes as low as 5,000 ft (1.5 km) to obtain the higher shear loads and as high as 35,000 ft (10.7 km) for supersonic testing. Surface pressures were obtained to document flow conditions and loads on the specimens. In addition, in-flight video and detailed pre- and post-flight photos were used to document the conditions of all specimens. This highly successful flight-test series was completed in May 1998 as part of the overall flight qualification of the X-33 TPS.

>Figure 2. Specimens of Exposed Materials from the X-33 launch vehicle and the external tank of the space shuttle were mounted on the carrier plate of the flight-test fixture.

Several months later, the Shuttle External Tank Project from Marshall Space Flight Center saw the results of the X-33 test and requested use of the same carrier plate to expose specimens of the shuttle external tank insulation to a simulated shuttle launch environment at speeds up to mach 1.5 and altitudes up to 60,000 ft (18.3 km) Six specimens were flown to simulate the thrust-panel rib structure and foam where the shuttle solid rocket boosters are attached to external tank. Several types of foam insulation configurations and rib orientations (see lower part of Figure 2) were tested by use of similar instrumentation and video documentation. This flight-test series was successfully completed in less than two weeks in January 1999.

The X-33 and Shuttle External Tank Proj-ects were both able to gain significant benefits from the flight-test results obtained by use of the F-15B FTF with a carrier plate as a research platform. Flight results were obtained quickly and efficiently and provided valuable data toward flight qualification with an increased understanding of the durability of the tested materials in flight environments.

This work was done by David Richwine, Craig Stephens, Kirsten Carpenter, Michelle Greslik, and David McAllister of Dryden Flight Research Center. No further documentation is available. DRC-99-11