Insulating tiles with interlocking shaped gaps have been developed for use in protecting the leading edges of the wings of aerospacecraft against excessive heating during hypersonic flight (including re-entry into the atmosphere). Other thermal-protection systems have been studied for this application, including those based on active transpiration cooling and heat-sink concepts. These systems have been described extensively in literature during the past thirty years and recently have been proposed for use on two hypersonic vehicles: the National Aerospace Plane (NASP) and the Slender Hypervelocity Aerothermodynamic Research Probe (SHARP). However, because these systems are very heavy and are expensive (millions of dollars) to fabricate and to install, the probability of using these systems in the near term on the surfaces of commercially operated reusable launch vehicles is low.

Figure 1. Damage Occurred in the Gap of a model of a straight-gap pair of tiles without filler that was subjected to a surface temperature of 2,300 °F (1,260 °C) in an arc-jet flow.

Currently, the leading-edge surfaces on such vehicles as the space shuttle orbiter and X-34 reusable launch vehicle use reinforced carbon/carbon and/or ceramic tiles with a straight gap configuration. In straight-gap tile systems, it is necessary to use gap fillers to prevent hot boundary-layer gases from flowing through the gaps and creating what is known as nozzle flow. Because of the limitations of the materials available for making gap fillers, the straight gap configuration is restricted to temperatures no more than about 2,000 °F ≈ 1,090 °C). Without a gap filler, the high-energy boundary-layer gases that are generated along a stagnation streamline (leading edge) during entry into the atmosphere would cause major damage to adjoining tiles and would cause overheating of the structure underlying the tiles. Figure 1 shows an example of damage in the gap of a model of a straight-gap pair of tiles without filler.

Figure 2. Interlocking Tiles, when properly shaped, are less vulnerable to damage in the gaps than are straight-gap tiles.

The interlocking-tile concept (see Figure 2) was proposed to prevent damage in the gaps between tiles. A suitable interlock configuration divides a gap into regions of subsonic and supersonic flow regimes. The flow in the portion of the gap in the area of the stagnation streamline is subsonic. The flows in the portions of the gap in the outer portions of the tile (these portions are called bleed gaps) are in the supersonic regime of the affected leading-edge component. This concept substantially reduces the temperatures down the side wall of the gap by reducing the pressure drop through the gap below a value that can generate nozzle flow. Two patented configurations of this type, called wedge and modular, have been proposed for protecting the leading edges of wings on commercial aerospace vehicles. Tiles of these configurations have withstood arc-jet-flow tests at surface temperatures above 2,800 °F (greater than about 1,540 °C), without incurring damage in their gaps.

This work was done by David A. Stewart of Ames Research Center.

This invention has been patented by NASA (U.S. Patent No. 5,772,154). Inquiries concerning nonexclusive or exclusive license for its commercial development should be addressed to

the Patent Counsel
Ames Research Center
(650) 604-5104.

Refer to ARC-14031.

NASA Tech Briefs Magazine

This article first appeared in the October, 2000 issue of NASA Tech Briefs Magazine.

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