In the first two posts, I discussed the Army’s efforts to develop an organic close air support (CAS) capability. In spite of restrictions, the Army considered jet-powered forward air control (FAC) aircraft, which looked very much like fully capable attack aircraft. This met, as expected, with resistance from Air Force leaders, who judged the Army’s jets an unwanted encroachment the junior service’s mission.
Looking back for a moment to Pace-Finletter of 1952, the Army had one other loophole to exploit: “The provisions of this memorandum are not intended to apply to convertiplane-type aircraft, nor will this agreement be interpreted to prohibit the continuing research, development and testing of such aircraft for the Army.”
And what is a convertiplane, you ask? That would be a fixed-winged aircraft capable of vertical take-off and landing (VTOL). Sound familiar? If not, that soon will.
Through the 1950s, the Army experimented with several designs, some radical and others more conventional. None of those types did much more than test theories. Among those experimental types was this odd contraption:
A joint Air Force-Army project, the Avro Canada built the VZ-9 AvroCar by reverse-engineering a crashed UFO recovered from Roswell…. um… NOT! Don’t believe what you hear on the History Channel.
This advanced demonstrator leveraged a pair of conventional jet engines turning a central turbine, with airflow bleed off to the disk edge for control. The “wing” in this case was of course a rounded disk. The craft was a great subject for concept diagrams. Impressive eye-candy for the Popular Mechanics audience for sure.
But the project flopped due to control and stability problems. Probably for the better.
Other convertiplane testbeds offered less radical departures. A joint project with the Navy and NASA, the Vertol VZ-2 used a tilting wing to offer VTOL capability.
The Fairchild VZ-5 of 1959, continued the tilting wing concept. This ugly contraption that only an aerospace engineer could love lead to cleaner designs.
The Bell V-3 introduced tilt-rotor concept, leading to today’s V-22 Osprey over several decades of work.
But none of these prop-driven convertiplanes, even with refinement and better power plants, offered much in the way of speed and weapons payload. Thus the Army looked at other technical innovations for a possible convertiplane FAC, which might eventually offer a CAS capability.
The Air Force had already tested some promising jet VTOL aircraft in the late 1950s, notably the Ryan X-13 and Bell X-14. The X-13 simply landed on its tail, while the X-14 used an early thrust redirection system. But neither option overcame the technical limits of that time, and the Air Force dropped further refinement. Then in 1961 the Army Transportation Research Command, jumped on board and ordered two different jet VTOL types for concept evaluation.
In contrast to the ungainly looking prop-driven convertiplanes, the Lockheed XV-4 Hummingbird appeared trim and streamlined. The Hummingbird used a duct system for the jet exhaust, augmented with cold air through intakes. Exhaust ports in the nose, tail, wingtips and central fuselage provided lift and control. The type actually did fly, in 1962, as seen in the video here (with bonus crash scene at the end!)
But the thrust ducting system failed to provide a useful thrust to weight ratio, limiting the Hummingbird to little more than a concept testbed.
More promising, but more complex, the Ryan XV-5 Vertifan diverted jet exhaust to a set of fans in order to provide vertical lift (actually similar in concept to the AvroCar above). After the first flight in 1964, the Army tested the Ryan fan-jet for several years.
The fan-jet system worked fine in practice. Indeed the principle foreshadowed the system used on the F-35 VSTOL variant. But the setup took up too much room in the small airframe, detracting from any potential combat load.
But, to the chagrin of the Air Force, the Army’s interest with VTOL jets did not cease with the two limited experiments. In 1962, the US entered a joint project with England and West Germany involving the Hawker-Siddeley P.1127 Kestrel VTOL jet. Hawker built the Kestrel around a British requirement for an attack aircraft operating close to the front lines from unprepared locations. The Kestrel used a specially designed Pegasus thrust-vectoring engine for both vertical lift and horizontal thrust. Although the video below fails to mention such, two Army pilots (along with one Air Force and one Navy pilot) joined those from the Royal Air Force and Luftwaffe in a multinational test squadron in 1965-66.
Although very successful during the tests, only the RAF dropped orders, with the service type becoming the Harrier GR.1 (entering service in 1969). West Germany opted to pursue a domestic VTOL design, which ended up stillborn. But the US agencies opted for further tests and refinement. Designated XV-6A, seven Kestrels arrived in the US for more evaluations. Eventually the Air Force and Navy dropped their participation, citing existing programs which met operational needs. The Army remained very interested, administering the additional tests. But eventually, demands from the growing war in Vietnam and pressure from the Air Force pushed the project to closure.
At the close of the last post, I made light that the Army, with no small external pressure, passed on some conventional jet types – each of which proceeded to accumulate very impressive service records with other services and countries. In the case of the “convertiplane loophole,” the Army passed on a very capable VTOL jet which went on to serve the RAF, Royal Navy, USMC, and other nations with distinction. One must wonder if the Army had deployed Harriers in the late 1960s and retained that capability beyond the Cold War (as the USMC did), if the situation, with regard to air support, might differ today.
Concurrent with the fast FAC evaluations and the VTOL jet testing, the Army pursued one additional approach to fixed winged CAS. I’ll turn to that chapter next.