Lockheed X-7

X-7
Role	Experimental aircraft
Manufacturer	Lockheed Corporation
First flight	April 26, 1951
Retired	1960
Primary user	United States Air Force
Developed into	AQM-60 Kingfisher

A Lockheed X-7 on public display in New Mexico

The Lockheed X-7 (dubbed the "Flying Stove Pipe") was an American unmanned test bed of the 1950s for ramjet engines and missile guidance technology. It was the basis for the later Lockheed AQM-60 Kingfisher, a system used to test American air defenses against nuclear missile attack.

Development of the Kingfisher was first initiated in December 1946. The X-7 was called into production by the United States Air Force requirement for the development of an unmanned ramjet test plane with a top speed of at least Mach 3 (2301.1 mph)^[1]

Originally the X-7 project was developed under MX-883 and was titled Model L-151, and was designated the PTV-A-1 but received its official title of the X-7 in 1951.^[1] Despite its first launch being a failure, after re-development of the original ramjet, following test flights were successful.^[2]

Purpose of the X-7

The X-7 laid the foundation for the AQM-60 Kingfisher.^[1] This was a system developed to protect United States soil from nuclear missile attacks.^[2] Being the testbed for a several yearlong projects, the X-7 underwent many structural changes to adapt more closely for its intended purpose.^[1] The Kingfisher was put up against three surface to air missiles designed to test the capabilities of the X-7; SAM-A-7/MIM-3 Nike Ajax, SAM-A-25/MIM-14 Nike Hercules, and IM-99/CIM-10 Bomarc were the missiles used in the tests.^[3] During the testing of the SAMs, the X-7 outperformed the missiles and a very small number of critical hits were achieved.^[2] Due to the pressure and embarrassment put on the military the X-7 project was canned in the mid-1960s.^[2]

Besides the surface to air missile tests, the X-7 project was also used to test communication equipment for acceleration testing, testing aerodynamics, booster propellants, thermodynamics, and parachutes.^[2]

Lockheed X-7 being prepared for loading and test flight. (B-50 seen in background)

Performance and Construction

Performance: Compared to other experimental aircraft the X-7 much more efficiently maximized its speed with its range.^[4] While most experimental aircraft topped off at around 926 knots, the X-7 maximized its speed and range to be more than 200 percent more efficient than the rest.^[4] Comparing the same speeds to that of manned Military aircraft the X-7 held a 633 percent margin.^[4]

Construction: The X-7 was constructed from steel unlike its successors such as the A-12 and YF-10 which used titanium.^[4] These planes had wings constructed from stainless steel but had a fuselage crafted from nickel alloy.^[4] The use of steel was due to the inability of aluminum to handle the air friction at hypersonic speeds, years before the widespread introduction of Titanium.

The engines developed for the X-7/AQM-60 were only designed to operate for a short time, allowing them to be used on small nuclear armed ramjets called the CIM-10 Bomarc. They were redesigned with better materials in order to be used on the hypersonic Lockheed D-21 drone fired off the back of the Lockheed SR-71 Blackbird, or from under the wing of a Boeing B-52 Stratofortress.^[5]

Launch and Recovery of the X-7

Lockheed X-7 buried nose down in the desert

Launch Method: The launch method of the X-7 was an at speed release from the underside of either a B-29 or B-50 carrier plane. (The B-29 was earlier used for bombing runs on Japan during WWII and as transport and cargo carrier, but was later retrofitted to carry the X-7 to its flight position.)^[6] The jet would then take over and build up speed to its top speed of 1000 miles per hour, but was later redesigned to push Mach 4.3 or 2800 miles per hour.^[1]

Recovery method: The recovery method of the X-7 rocket plane was a new and simple design for a test plane of its kind but functioned as designed. A several stage parachute was deployed after the jet had exhausted its fuel supply, slowing its descent toward the desert floor.^[2] Once it had reached the floor, the long metal rod on the end of the nose cone skewered the ground keeping the plane upright and preventing any damage to structure of the X-7. In 1954, the modified X-7 underwent serious changes and was renamed the X-7A-3.^[1] The wing shape was altered, and two small boosters were added to the plane; one under each wing. Due to these alterations, the drop method previously used was changed to make up for these changes. The previous version was a complicated and bulky under wing system while the new design allowed for a simple fuselage mounted dropping system. This system was used until its final flight in July 1960.^[1]

Specifications of X-7A-1^[2]

· Length: 32 feet, 9 inches

· Wingspan: 12 feet

· Height: 7 feet

· Diameter: 20 inches

· Weight: 8000 pounds

· Speed: 2800 miles per hour

· Ceiling: 100000 feet

· Range: 130 miles

· Booster: Alleghany Ballistics Lab. X202-C3 solid- fuel rocket; 467 kN for 4 seconds.

· Sustainer: Ramjet

Specifications of X-7A-3^[2]

· Length: 37 feet

· Wingspan: 10 feet

· Height: 7 feet

· Diameter: 20 inches

· Weight: 8000 pounds

· Speed: 2800 miles per hour

· Ceiling: 100000 feet

· Range: 130 miles

· Booster: X-7A-3/XQ-5: 2x Thiokol XM45 (5KS50000) solid-fuel rocket; 222 kN (50000 lb)

· Sustainer: Ramjet

See also

Related development

• Q-5 Kingfisher (based on the X-7 A-3)

Aircraft of comparable role, configuration and era

• Bomarc

References

External links

Wikimedia Commons has media related to Lockheed X-7.

• Q-5/AQM-60
• "Ramjet test missile takes off on supersonic flight." Popular Science, pp. 142–143.