The North American X-10 was an unmanned experimental aircraft constructed for the top secret Navaho Missile program launched by the US Air Force in the 1950s, that attempted to develop an intercontinental surface-to-surface cruise missile in the face of a growing Soviet threat.

The only Navaho missile classified as an X-plane, unusually the X-10 test vehicle would enjoy far greater success and longevity than its end product, the disastrous XSM-64, which was abandoned after just four launches.

Contents

• Background
• Development
• The X-10
• Missile
• Testing of the X-10 Drone

Background

Before the end of the Second World War, and with the aid of captured Nazi documents, American manufacturer North American commenced a top secret research program conducted at their Technology Research Laboratory codenamed MX-770, that sought to reveal the secrets of long-range supersonic surface to air missiles.

Still a relatively rudimentary technology, in January 1947 North American engineers crafted their first test rocket, the NATIV, which had a range of 500 miles and was the first Navaho missile prototype. Housing one of the earliest missile navigation systems, the Kinetic Double Integrating Accelerometer or KDIA, the NATIV test rocket proved once and for all that the inertial guidance of long-range missiles was possible.

After being assessed by the United States Air Force, in April 1947 a new set of guidelines for a follow-up missile, required to have a 1,000-mile range and which could be armed with a 3,000-pound warhead, were announced.

The first blueprints of this more advanced prototype christened the XSSM-A-2 and powered by two ramjet engines after being blasted off by a rocket booster, were produced by a newly formed division called Aerophysics in 1948, however, evaluations showed that the guidance system still had issues since it was only accurate to within one mile of the assigned target, a fault caused by the process of gyroscopic precession whereby small errors in the gyro rotation built up over time and distance.

Fitted with an improved guidance unit the missile, called the XN-1, was followed by the XN-2, engineered with an experimental stellar-inertial system that used the position of the stars to accurately hit its mark. Development of the missile was accelerated by the news that the Soviet Union had detonated their first nuclear warhead on August 29th 1949, making the creation of a long-range counter-projectile a top priority of the US government, which soon demanded a missile that could travel 5,000 miles.

North American responded by creating a two-stage vehicle, fitted with a detachable rocket booster that would help launch the missile before being jettisoned to decrease weight and increase the range of the projectile. However, following the outbreak of the Korean War on June 25th 1950 the US government would speed up their missile programs significantly more, and in July the Air Force announced another raft of specifications for a new project entitled Weapon System 104-A, which required a missile with an intercontinental range of 5,500 miles, a minimum speed of Mach 3 and which could soar at altitudes higher than 60,000 feet in addition to carrying a payload of 7,000 pounds.

For this purpose, and in order to properly assess the aerodynamic qualities, structure, autopilot, and inertial navigation system of the proposed missile, which would later be designated as the XSM-64, the North American X-10 was created.

Development

Initial designs of the X-10 were drawn up at the start of May 1950, and after extensive wind tunnel tests in February 1951, the first mock-up was produced in May and inspected by members of the United States Air Force Bombardment Aircraft and Guided Missile Board, who approved it for assembly in September.

The first X-10 unit was completed in December 1952 and inserted into a static testing apparatus called the ‘Horizontal Test Facility,’ which simulated loads by attaching hundreds of bicycle spokes to the wings attached to a whiffletree, a mechanism that ensured an equal distribution of force.

In an effort to accurately reproduce the conditions of Mach 2 speed and above when it was flying, a velocity in which the stainless steel body of the X-10 would lose a tenth of its strength due to the effects of aerodynamic heating, an extra 12% of the static load had to add, while double the amount was applied to the aluminium wings which in the same high-speed scenario would lose 50% of their resistance.

Before the X-10 took to the skies however, a series of planes fitted with experimental X-10 components were flown first for proof-of-concept, including an F-86D installed with an early model of the PIX-10 autopilot, a QG-80 drone aircraft modified with the X-10’s radio control system, and the ET-33 Flight control aircraft furnished with the airborne control unit that would remotely maneuver the X-10.

The X-10

With a length of 66 foot and 2 inches, a height of 14 foot and 5 inches, a maximum take off weight of 42,300 pounds, an empty weight of 25,800 pounds, a wing span of 28 foot and 2 inches, and a wing area of 425 square feet, the unmanned X-10 was the first craft fashioned with the low wing delta configuration.

Its nose compartment housed the radio command unit, telemetering apparatus and an autonavigator covered by glass since the guidance system was the stellar inertial unit used for the XN2 that required exposure to the skies, and the misleadingly named warhead compartment, which would be where the final missile packed its ordinance, contained the PIX-10 autopilot, the cooling system, and the nose gear.

It was fed by a forward tank with a capacity of 565 gallons and the main receptacle, which also absorbed the heat produced by the air conditioning system, with enough volume to carry 2100 gallons of jet fuel. It was propelled by two Westinghouse XJ40-WE-1 afterburning turbojet engines, the most powerful in the world at the time, that worked alongside a Sundstrand 30 KVA alternator which generated electric power.

Moreover, it was the earliest aircraft to have converging and diverging inlet ducts for its engines, which were more advanced than the conventional and inefficient shock ducts of the era.

The X-10 was also the first jet aircraft to have a thrust-to-weight ratio of more than a half at 0.51, helping it to achieve a top speed of Mach 2.08, a maximum range of 818 miles, and an altitude ceiling of 50,000 feet. In comparison to a Lockheed F-80 Shooting Star, which could reach an altitude of 25,000 feet in 7 minutes, it could ascend to 35,000 feet in just 6.7 minutes, and when deploying its afterburner could rise as fast as 20,000 feet a minute.

Missile

The X-10 flight program was begun in May 1953, starting rather inauspiciously at Edwards Air Force Base after the crane employed to hoist the x-plane from the truck to the ground accidentally dropped it, causing minor damage to the main gear.

Nevertheless, before the X-10 made its maiden voyage it was the first subject to several preliminary assessments, undertaking a handful of taxi tests in September 1953 to establish its various landing, steering, and stopping qualities, resulting in an accident on September 21st in which the parachute was inadvertently activated by engine vibrations, before becoming engulfed in flames after passing across the engine exhaust of the afterburner.

March 11th 1955 was the date of another mishap involving the X-10 number 3, which blew up at the exact moment the landing gear began retracting after an engineer had accidentally wired the mechanism instead to the self-destruct sequence, which was usually activated 30 seconds after the engines stopped working.

Apart from these incidents, the tests were deemed successful, and before long the X-10 was moved into the flight testing phase, making its debut on October 14th 1953 after several malfunctions with the radio control system had been fixed, and finishing its initial testing period with its fifteenth flight on March 24th 1955.

During this time, the X-10 showed remarkable potential, demonstrating a top speed of Mach 1.84, the reliability of the PIX-10 autopilot, as well as the successful development of the auto-approach and landing system.

Furthermore, the X-10 set a number of world records, becoming the fastest turbojet-powered vehicle in the world on September 28th 1954 after it reached a speed of Mach 1.84, with many deploring the fact that it was unmanned such as one test pilot, who affirmed:

“If North-American would put a saddle I would fly it.”

The flying program was next moved from Edwards Air Force Base to the Air Force Missile Test Centre (AFMTC) at Cape Canaveral, the only military base authorizing planes to fly in a straight line at over 1,500 miles without passing over a civilian populace, a factor that would greatly contribute to the secrecy of the classified Navaho program as the X-10 as it entered the next round of evaluations.

The AFMTC however, also had a few disadvantages, the most notable of which, in comparison to the hard-packed lake bed at Edwards, was the area of soft sand located beyond the runway, meaning that an X-10 overshoot would have considerably more destructive consequences.

It was a drawback pertinently felt during the X-10’s first flight at Cape Canaveral on August 19th 1955, when upon landing the brake did not activate, causing the x-plane to veer off the runway into the sandy area, where a torn fuel receptacle then engulfed the craft in flame. A grand total of 6 X-10s would be subsequently lost either by accident or design.

The X-10 made its final test flight on November 20th 1956, concluding a successful program that had witnessed the first automatic landing at Cape Canaveral on February 3rd 1956, the first-ever turbojet-powered flight to reach Mach 2 on February 29th 1956, the first entirely inertial flight of an unmanned missile on July 18th 1956, as well as the earliest known example of an inertial flight of a missile from launch to impact on November 20th 1956.

Other significant accomplishments included the exhibition of a dive-in-attack strategy, later incorporated into the G-26 and G-38 missiles, performed by an X-10 plummeting into the sea at a speed of Mach 1.25, as well as a demonstration of the efficacy of Cape Canaveral’s earliest radar tracking system, which was able to track a Mach-2 air vehicle at altitudes of over 45,000 feet.

Testing of the X-10 Drone

The results of the X-10 confirmed the aerodynamic advantages of its design and were later employed in the development of the considerably less successful XSM-64 Navaho missile beginning in 1956.

However, the US Air Force was not done with the X-10 at this point, and between 1958 to 1959 the 4 remaining X-10s were reimagined as high-speed and high-altitude drones that were to act as targets for the Bormac and Nike surface-to-air missiles.

Three were destroyed, but surprisingly not in the manner intended. The first X-10 crashed and burned after a brake failure, the second was obliterated after its parachute failed to eject on landing, and the third hurtled down to earth and blew up after suffering a catastrophic electric generator malfunction mid-flight. The last surviving X-10 was saved from a similar fate and was instead transferred to the US Air Force Museum at Wright-Patterson Air Force Base, where it can still be seen today.

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Specifications

• Crew: None
• Length: 77 ft (23 m)
• Wingspan: 28 ft 2 in (8.59 m)
• Height: 14 ft 5 in (4.39 m)
• Empty weight: 25,800 lb (11,703 kg)
• Max takeoff weight: 42,300 lb (19,187 kg)
• Powerplant: 2 × Westinghouse XJ40-WE-1 turbojets, 10,900 lbf (48 kN) thrust each
• Maximum speed: 1,300 mph (2,100 km/h, 1,100 kn)
• Service ceiling: 45,000 ft (14,000 m)
• Rate of climb: 5,224 ft/min (26.54 m/s)

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