In one embodiment, a method for reducing drag includes forming a smooth surface on a first portion of a physical object. The method also includes forming periodic riblets on a second portion of the physical object. The method further includes generating a flow over the periodic riblets of the second portion of the physical object and over the smooth surface of the first portion of the physical object. The second portion of the physical object is adjacent to the first portion of the physical object. Each peak of each riblet of the periodic riblets of the second portion of the physical object is located above a plane of the smooth surface of the first portion of the physical object. Each valley between adjacent riblets of the periodic riblets of the second portion of the physical object is located below the plane of the smooth surface of the first portion of the physical object. A length of each riblet of the periodic riblets runs parallel to a direction of the flow.

An envelope portion of an airborne craft comprises a metallic outer wall and a metallic inner wall arranged interior to the outer wall. The outer and inner walls delimit an inter-wall volume configured to support a flow of coolant to cool the outer wall during atmospheric heating of the outer wall.

An envelope portion of an airborne craft comprises a metallic outer wall and a metallic inner wall arranged interior to the outer wall. The outer and inner walls delimit an inter-wall volume configured to support a flow of coolant to cool the outer wall during atmospheric heating of the outer wall.

Methods and apparatus for cooling a surface on a flight vehicle and generating power include advancing the vehicle at a speed of at least Mach 3 to aerodynamically heat the surface. A first working fluid circulates through a first fluid loop that heats the first working fluid through a first heat intake thermally coupled to the surface and expands the first working fluid in a first thermal engine to generate a first work output. A second fluid loop has a second working fluid that receives heat from the first working fluid and a second thermal engine to generate a second work output. The first and second work outputs are operably coupled to first and second generators, respectively, to power primary or auxiliary systems on the flight vehicle.

Methods and apparatus for cooling a surface on a flight vehicle and/or generating power include advancing the flight vehicle at a speed of at least Mach 3 to aerodynamically heat the surface. A supercritical working fluid is circulated through a fluid loop that includes compressing the supercritical working fluid through a compressor, heating the supercritical working fluid through a heat intake that is thermally coupled to the surface, expanding the supercritical working fluid in a thermal engine to generate a work output, cooling the supercritical working fluid, and recirculating the supercritical working fluid to the compressor. The work output of the thermal engine is operably coupled to the compressor, and may optionally be coupled to a generator to produce power. The supercritical working fluid absorbs heat from the surface, eliminating hot spots and permitting use of lighter and/or less expensive materials.

Methods and apparatus for cooling a surface on a flight vehicle and/or generating power include advancing the flight vehicle at a speed of at least Mach 3 to aerodynamically heat the surface. A supercritical working fluid is circulated through a fluid loop that includes compressing the supercritical working fluid through a compressor, heating the supercritical working fluid through a heat intake that is thermally coupled to the surface, expanding the supercritical working fluid in a thermal engine to generate a work output, cooling the supercritical working fluid, and recirculating the supercritical working fluid to the compressor. The work output of the thermal engine is operably coupled to the compressor, and may optionally be coupled to a generator to produce power. The supercritical working fluid absorbs heat from the surface, eliminating hot spots and permitting use of lighter and/or less expensive materials.

A removable battery to provide motive power for an aircraft includes a battery frame and removable, interchangeable battery modules. Each of the battery modules defines module common space through which liquid heat transfer fluid flows during charging of the battery when the battery is removed from the aircraft and through which air as a heat transfer fluid flows during discharge of the battery, as during flight. The module common space also defines a combustion conduit to convey heated air and products of combustion safely outside the battery in the event of a cell fire during flight. The removable battery frame is a structural component of the aircraft.

An unmanned aerial vehicle (UAV) includes a fuselage, electronics disposed with the fuselage, a heat sink, and a solar shield. The heat sink is thermally connected to the electronics and includes a cooling plate disposed on or extends through an exterior surface of the fuselage. The cooling plate is exposed to an external environment of the UAV to conduct heat from the electronics to the external environment via convection. The solar shield extends over the cooling plate and defines an air scoop within which the cooling plate is disposed. The air scoop directs airflow from the external environment across the cooling plate. The solar shield shades the cooling plate from solar radiation to prevent or reduce solar heating of the cooling plate.

An unmanned aerial vehicle (UAV) includes a fuselage, electronics disposed with the fuselage, a heat sink, and a solar shield. The heat sink is thermally connected to the electronics and includes a cooling plate disposed on or extends through an exterior surface of the fuselage. The cooling plate is exposed to an external environment of the UAV to conduct heat from the electronics to the external environment via convection. The solar shield extends over the cooling plate and defines an air scoop within which the cooling plate is disposed. The air scoop directs airflow from the external environment across the cooling plate. The solar shield shades the cooling plate from solar radiation to prevent or reduce solar heating of the cooling plate.

An exterior panel is formed of superplastic materials, including an exterior skin of titanium to accommodate high thermal stresses imposed on hypersonic transport vehicles during hypersonic flight. The exterior skin is fixed to an underlying reinforcing skeletal structure consisting of a superplastic formable reinforcement (SFR) layer, for example a titanium, zirconium, and molybdenum (TZM) alloy, which supports the exterior skin whenever the latter may be heated to temperatures exceeding 1200 degrees Fahrenheit. The exterior panel includes a separate interior skin configured for attachment to a frame member such as a rib, stringer, or spar of the hypersonic transport vehicle. A multicellular core is sandwiched between the exterior and interior skins to impart tensile and compressive strength to the exterior panel. In one disclosed method, the core is superplastic formed and diffusion bonded to the exterior and interior skins.