The Mach 3 Monster Bird: XB-70 Valkyrie

On September 6, 1976 (Showa 51), a Soviet (at the time) Air Force MiG-25 Foxbat 'Foxbat' flew into Hakodate Airport. This was the so-called 'Soviet Lieutenant Belenko MiG-25 defection incident.' At the time, for me, the

MiG-25was a 'mysterious fighter jet capable of supersonic flight at Mach 3.' Even though I didn't fully understand how fast Mach 3 was (roughly 1 km per second), it was faster than the Mach 3

F-15 'Eagle' and F-14 'Tomcat' (Mach 2.3–2.5 class), which were touted as the strongest at the time, so to me, it was the 'strongest fighter jet' (perhaps that was just my misunderstanding at the time that higher speed meant greater strength...). Text: tompei

However, after the Hakodate incident, disparaging reports such as 'the MiG-25 is made of iron' or 'it runs on vacuum tubes' became prominent, and various questions arose in my mind. I would later learn that the use of iron (heat-resistant steel) and vacuum tubes was appropriate for the time, but as someone without the relevant knowledge back then, I couldn't understand it. Even so, for me at the time, '


Mach 3' was paramount, and it remained a 'mysterious and amazing fighter jet.'

By the way, around the same time, there was the X-15, which approached Mach 7, but it was an ultra-high-altitude experimental aircraft powered by a rocket engine, so it was not a comparable subject. Even after that, I was drawn to the MiG-25, not the F-15 or F-14.

And that leads to the American supersonic high-altitude strategic bomber prototype that induced its development, the XB-70 'Valkyrie'.

Mig-25 was required to have ultra-high-speed performance of Mach 3 due to the existence of supersonic high-altitude strategic bombers and reconnaissance aircraft such as the XB-70. Of course, the white aircraft, which could fly at

Mach 3 and had its design finalized in 1960, featured movable wings with a unique structure that transformed according to its speed. Its appearance could well be called a monster bird or a bewitching bird.

It had already recorded a maximum speed of Mach 3.08 and a maximum altitude of approximately 22,500m in April 1966. At the rear of the fuselage, six turbojet engines were lined up in a horizontal row.

Although the two prototypes were not equipped with weaponry, the unrealized third aircraft was planned to be equipped with a bomb bay capable of carrying approximately 45,360 kg (for 20 Mton-class hydrogen bombs), a bombing navigation system, and electronic warfare equipment.

Even for the SR-71 (an American high-altitude reconnaissance aircraft) and the Mig-25, which achieved Mach 3 flight, when flying at Mach 3, the aircraft surface temperature reaches about 300°C (enough to melt solder), and if there are any irregularities in shape or airflow stagnation, it becomes even hotter locally. Therefore, the strength of aluminum, a common structural material, would significantly decrease or deteriorate. In the US Mach 3-class


supersonic reconnaissance aircraft SR-71, which was manufactured somewhat later, titanium, which has high strength and heat resistance, was widely used due to improvements in processing technology.

On the other hand, this aircraft and the MiG-25 mainly used heat-resistant steel (iron) in a reliable manner, and for this aircraft, honeycomb-structured heat-resistant steel was used for 68% of the total surface area.

Partly because of such a special structure, the airframe strength was low, and although it was not intended for dogfighting, maneuvers such as turns that would impose high G-acceleration on the airframe were restricted, and it is said that its maneuverability was on par with a civilian airliner (though that was fine for a bomber of that time).

The second aircraft was lost in May 1966 during a promotional flight, which was its 46th flight, when an accompanying F-104N collided with it, causing it to catch fire in mid-air and crash. After that, the first aircraft was transferred to NASA as a test aircraft in March 1967, and its development as a military aircraft ended.

Later, with the mass deployment of intercontinental ballistic missiles, the significance of supersonic high-altitude strategic bombers disappeared, and the entire XB-70 program was cancelled.

Specifications
Empty weight approx. 93,000 kg, maximum takeoff weight approx. 250,000 kg. Length 56.6m x Wingspan 32m x Height approx. 9.4m. Turbojet engines with afterburners (General Electric, thrust 12,800 [kgf]) x 6. Maximum speed (recorded) Mach 3.08, service ceiling (design value) approx. 23,000 [m]. Crew 2. First flight date September 21, 1964 (the second aircraft followed on July 17, 1965). Production quantity 2 prototypes.