X-7

The X-7 was built by Lockheed Missiles & Space Company Skunk Works for the US Air Force to test technology for supersonic ramjet engines and missile guidance and control components. Dubbed "the flying stovepipe," the 33-foot-long vehicle had a 10-foot wingspan and was 20 inches in diameter. The X-7 was carried aloft on a plane for aerial launch. The booster attached to the stern of the X-7 was ignited after launch and pushed the vehicle to approximately 1,000 miles an hour. The ramjet engine was mounted under the aft end of the fuselage. The ramjet being tested, slung underneath, then took over the propulsion, and the booster is jettisoned. B-29s and later B-50s were used as launch planes.

In a ramjet, there is no compressor. Instead, the forward speed of the vehicle is employed to “ram” air into the combustor. At supersonic speeds air enters the intake where a diffuser nozzle causes the air to slow down to around Mach 0.2 through a series of shock waves. This sudden slowing creates the pressure needed to operate the engine. Fuel is injected and burned with the aid of a flame holder. Since there is no compressor to power, there is no need for a turbine and the hot gases expand directly out the nozzle. The downside is that the ramjet engine can only work when the vehicle is already moving at a considerable speed. A ramjet produces little thrust below about half the speed of sound and works best when operating at low supersonic speeds (ranging from Mach 1 to 3).

Ramjets always offered far more promise than they actually delivered, and it was not until the late 1950’s that the practical winged ramjet-powered aircraft became a reality, as exemplified by the Lockheed X-7 pilotless testbed, the Boeing IM-99 Bomarc SAM, and the French Nord Griffon technology demonstrator.

First flown in April, 1951, the last of 130 flights occurred in July 1960. There were three main groups doing the engine research and conceptual work; Marquardt, APL/JHU, and GASL. Roy Marquardt himself knew how to draw together a team of rather wild horses and keep them aimed in useful directions. Several companies were involved in engine development and production, and no less than seven major airframe companies were doing active design studies. Operational kerosene fueled ramjets were routinely flying Mach 2-3 in the Bomarc and Talos interceptors. One Marquardt ramjet had accelerated a Lockheed X-7 test vehicle to about Mach 4.7 in an all-out test, holding it at nearly 1 "G" until the fuel ran out. But the recovered engine and airframe were badly overheated, and not reflyable.

Marquardt completed its scheduled production of the ramjet engine for the Bomarc A missile in 1960. As this program phased out, production began immediately on the new RJ43-ll engine, which powered the new Bomarc B missile in successful test flights. This advanced ramjet engine and its predecessor, the RJ43-3, were the only two ramjets in the Nation to have passed the military qualification test.

In mid-1960, final flight testing of the RJ43-ll was completed when the engine met all flight requirements as it propelled the Lockheed X-7 test vehicle on a complex flight. The X-7 has acted as a flying test bed for air-breathing engines. After flight, a parachute recov- ery system lowers missile and engine to earth, where complete evaluation can be made.

During a 13-year testing program, the X-7 had flown and reflown ramjet engines and components, simulating Bomare flight parameters to test and prove the Marquardt propulsion system's reliability before qualifying it for Bomarc service. This test program not only provided production information invaluable to Ogden manufacturing, but in the process established an impressive record for air-breathing engines. Powered by a single ramjet engine, the X-7 reached speeds in excess of mach 4- more than 3,000 miles per hour - and it established a world's altitude record for air-breathing missiles by exceeding 100,000 feet.

More significant than these speed and altitude records is the contribution which the ramjet development and testing programs made to advance the state of missile and engine art. Much invaluable aerodynamic, thermodynamic, special fuels, and materials information has been accumulated as a result of this program.

Utilizing the knowledge of this test program and research activity throughout Marquardt's history, Ogden developed a precision manufacturing plant and related testing facilities. Advance techniques in metal fabrication were developed to a production line basis, and similarly machine-tooling equipment, predominantly tape controlled, allowed the production of precision parts with reduced costs. During the ramjet engine manufacturing program of the RJ43-3 and continuing with the present production of the RJ43-ll, unusual metal-fabrication skills and equipment were amassed. The spin forge machine, which cold-flows metal into various shapes much as a potter does with clay on his wheel, and ex- plosive forming, which blows metal into the shape of a die into which the metal is placed, are two examples of techniques that are being used by Marquardt's manufacturing engineers.

As production techniques kept pace with ramjet engine improvement programs, significant accomplishments in ramjet production were noted. Creating the RJ43-ll engine, now being produced on an assembly line technique at Ogden, required only 3½ years' work rather than the 7 years which were required to bring the RJ 43-3 from conception through the successful completion of the qualification tests.

Because this Utah facility was founded exclusively to produce ramjet engines, the Marquardt technicians and engineers adapted their skills and experience to form a unique team for the efficient and economical production of this unusual propulsion system.

At the end of their missions, the missiles deployed parachutes, and their sharp, aerodynamic nose spikes buried themselves vertically into the ground. Later on, this flight test program suffered its only casualty. Thankfully, it was not serious. There were cattle nearby White Sands in those days. The aerospike nose of an X-7 skewered a steer.