Long before hitching a ride to the moon aboard Apollo 11, then US Air Force test pilot Neil Armstrong was zipping around in a rocket-powered North American X-15, which to this day remains the fastest manned, winged aircraft ever built. That flight record of Mach 6.72 or 7,274km/h was set by pilot William “Pete” Knight in 1967.
Now, some 59 years later, America still hasn’t fully realised the promise that experimental flight vehicle held for military operations.
Despite many breakthroughs in fields of hypersonic propulsion and high-temperature materials, the air force doesn’t imagine an affordable and operationally relevant surveillance and strike aircraft coming online until the late 2030s.
The storied Lockheed Martin SR-71 Blackbird flew at Mach 3.2, or three times the speed of sound, which is now short of what the air force says it needs to outpace modern interceptors.
Instead, the air branch is pushing hypersonic missiles, powered by the type of air-breathing scramjet engine that propelled the and rocket-boosted Boeing X-51 WaveRider in 2013. Engineless boost-glide hypersonic weapon concepts are also being considered.