AFRL Successfully Tests Heat-Pipe-Cooled Leading Edges Published Dec. 12, 2006 By Plans and Programs Directorate AFRL/XP WRIGHT-PATTERSON AIR FORCE BASE, Ohio -- AFRL scientists completed thermal validation tests to verify the performance of a heat-pipe-cooled wing leading edge. The effort, which furthers the development of reliable, maneuverable space operating vehicle (SOV) technology, demonstrated a technology readiness level (TRL) increase, advancing the technology's viability from TRL 4 to TRL 5. The heat-pipe cooling technology could have potential application to any type of reentry aircraft or hypersonic cruise vehicle. Heat pipes are metal tubes that evenly distribute heat from one spot on a structure across the structure's entire surface area. This redistribution prevents localized "hot spots" from forming; left unchecked, such hot spots could precipitate component failure. Consequently, AFRL scientists are seeking to incorporate heat-pipe cooling technology into vehicle wing structures. Heat-pipe-cooled leading edges reduce the mass of a wing's leading edge significantly compared to an actively cooled leading edge. Since SOVs require a high degree of maneuverability upon reentry, a small leading edge radius is critical. Researchers tested a heat-pipe specimen constructed of a superalloy (which can withstand very high temperatures) surrounding lithium (which melts at lower temperatures). When the wing becomes hot, as it would during reentry, the lithium within the pipes vaporizes at the hottest areas of the leading edge and condenses into a liquid at the cooler areas. This process distributes heat evenly throughout the leading edge and ensures that materials in the hottest areas do not exceed their temperature limits. To mimic the heat distribution that a structure would encounter in a reentry situation, the researchers used heat lamps to test a heat pipe 4" in width and 36" long. The test successfully verified the pipe's functionality and determined the article's heat transfer capacity.