North American X-15
North American X-15 Nose Art
Dimensions: 40" x 20"
There were 3 North American X-15A's and their construction was titanium and stainless steel. They used some aluminum on the interior of the craft. The X-15A's exterior made use of Inconel-X nickel which is a type of alloy steel. The Inconel could withstand high temperatures. It was important to add a white coating of Emerson ablative material to the external fuel tanks. This material protected the X-15A' from high temperatures during supersonic speeds.
During test flights, the X-15A achieved its greatest speed of Mach 6.7!
The first North American X-15A flight was an unpowered test flight flown by Albert Scott Crossfield, on 8 June 1959.
The first powered flight was also flown by Scott Crossfield on September 17, 1959. Further testing was done with the XLR-99 rocket engine on 15 November 1960.
There was a total of twelve test pilots who flew the X-15A. Among them was Neil Armstrong one of the early pioneers of supersonic flight. Neil Armstrong would, later on, become a NASA astronaut and become the First Man to step foot on the Moon!
The North American X-15 supersonic test aircraft paved the way for our modern fighter jets that we have today.
Is that X-15 Really the Right Color?
The short answer is “No”. There are many reasons the North American X-15 appears black in many photographs, but outdoors in direct sunlight X-15 is an iridescent dark blue. That’s right, blue, or more specifically “gunmetal blue”. Gunmetal blue is the color of iron or iron alloys that have been repeatedly heated to high temperature and then quenched.
The color is a result of a thin layer of magnetite nanocrystals that forms on the surface of the metal. Magnetite, FeO.Fe2O3 is a so-called black iron oxide and is familiar as the “black sand” that is easily picked up with magnets from playground sandboxes. Magnetite forms when iron oxidizes in water as opposed to red iron oxide, Fe2O3, which is common rust formed when iron oxidizes in air. The dark color of the magnetite nanocrystals on iron is the “black” in blacksmith.
The nanocrystals are extremely small, with a width only about 3% of the shortest wavelength of visible light. As the crystals become closely spaced, covering the surface, they absorb most colors of light but produce a metallic blue iridescence. The iridescence is not a pigment color but is due to the structural interference of the crystals with short wavelengths of light, favoring the reflection of blue.
This is similar to the diffraction grating effect that produces a rainbow of colors of the fine lines of a video disk. The magnetite is much harder than the base metal, so the crystals increase the corrosion and scratch resistance of the surface and at the same time give it a very high thermal emissivity (0.925 at 2000oF) facilitating efficient heat rejection. This unusually high thermal emissivity is the crucial enabling factor in X-15’s ability to survive the high temperatures of re-entry without the need for ablative or ceramic coatings.