# Interlocking Wing-Leading-Edge Thermal-Protection Tiles 

### These tiles are shaped to prevent damage at inter-tile gaps. 

#### *Ames Research Center, Moffett Field, California*

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.

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
(![](media/image1.png){width="0.15555555555555556in"
height="0.11388888888888889in"} 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.

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.

 

![](media/image2.jpeg){width="2.6034722222222224in"
height="1.6979166666666667in"}\
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.

 

![](media/image3.jpeg){width="4.166666666666667in"
height="3.1347222222222224in"}\
Figure 2. **Interlocking Tiles**, when properly shaped, are less
vulnerable to damage in the gaps than are straight-gap tiles.

 

*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.*

*Tech Briefs article published October 2000.*