Rockwell XFV-12; The VTOL Fighter That Couldn’t

March 17, 2023

The 1970s were a time of great introspection for the US military services. In the light of the draw down of the Vietnam conflict and the final abandoning of the country, the services had to contend with severe issues in funding and personnel quality. And they had to do this with a huge shift in planning priorities, as the US military switched from thinking and spending on largely counter-insurgency doctrine to one once again focused on fighting a conventional or even possibly nuclear war against the Soviet Union in Europe.

For the US Navy, this was particularly problematic. The Navy was the primary conventional power projection force for the United States, mainly through its large fleet of aircraft carriers. This was typified by the commissioning of the USS Nimitz in 1975, the first of a class of nuclear carriers that would be the most powerful warships to have put to sea.

But the US Navy also had the job of keeping global sea lanes open in the event of war breaking out, a conflict that would see the service have to deploy escorts all across the world to deal with the large numbers of Soviet submarines and long-range bombers that would prey upon shipping all across the Atlantic and Pacific.

The US escort fleet at the time was based heavily on old Second World War destroyers and Essex-class aircraft carriers that had been updated in the 1950s and ‘60s but were now badly outclassed by the new Soviet submarines coming into service.

A radical program to overhaul the US Navy’s escort capability was needed and in 1970 the service’s new Chief of Naval Operations, Admiral Zumwalt, proposed that a fresh policy be adopted; the “High-Low” plan. This would see the top end and hugely expensive primary fleet units under development and construction at the time supplemented by larger numbers of smaller, less capable and, most significantly, much cheaper ships that would allow the US Navy to finally retire many of its aging escorts and replace them with more capable vessels.

And key to Zumwalt’s thinking was the potential of a new version of the escort and light carriers that had proven so invaluable during the Second World War; the Sea Control Ship (SCS).

This concept would be a small aircraft carrier, displacing less than 14,000 tonnes fully loaded in contrast to the Nimitz-class’s more than 100,000, and which had the operation of anti-submarine helicopters as its main purpose. This would give far more anti-submarine capability than any single conventional destroyer or frigate, and the SCS’s could form the core of future escort groups.

Indeed, Zumwalt wrote that as eight SCS’s could be built for the cost of a single Nimitz, the SCS seemed a logical way to increase both the US Navy’s escort and flag showing capabilities. Because though the emphasis was on ASW the SCS was still a carrier, and that gave it the possibility of carrying more than just helicopters.

Remembering the lessons of World War Two, where the escort carriers had proven critical in negating the threat posed by enemy long-range naval reconnaissance aircraft, the planners figured that it would great if the new SCS could also carry a small fighter compliment that could drive off or shoot down Soviet scout aircraft if the balloon went up.

The issue was that none of the United States then-current carrier aircraft would be able to operate off an SCS, the design being far too small. But there was another option, one that the US Marine Corps was about to start taking into service; the Hawker Siddeley Harrier, designated by the USMC as the AV-8A.

 

This aircraft was capable of Vertical Take Off and Landing (VTOL), and as such would be able to fly quite happily off of the proposed new SCS. In fact, Marine Corps Harriers were used to demonstrate the concept between 1972 and ‘74 when the assault ship USS Guam was fitted out with a compliment of AV-8s and Sea King helicopters to test out the idea.

But the AV-8A was a very limited design, essentially a light day attack aircraft, with its range, performance and weaponry too limited for it to act as a naval interceptor, and so the advocates of the SCS really wanted something far more formidable to do the job. So, in December 1971 they issued a requirement for a new supersonic VTOL aircraft that should be capable of carrying Sparrow guided missiles and an associated radar for Beyond-Visual Range engagement.

This led in May 1972 to Rockwell receiving a $47-million contract for the construction of two prototypes of their proposed solution – the Rockwell XFV-12.

The XFV-12 was a truly remarkable design. Instead of using thrust vectoring nozzles directly fed from the engine, as with the Harrier, or that of its Soviet contemporary, the Yak-38, which used both vectoring exhausts and static, downward directed jets just to provide VTOL, the XFV-12 used ducts to direct exhaust from the engine through vents in the wings and canards, called the Thrust Augmenter Wing (TAW).

 

In VTOL operation, the rear engine exhaust nozzle would close and vents open in the top of the fuselage, which would both reduce air pressure above the aircraft, assisting with lift, and cool the exhaust gases that were jetting down, in turn preventing damage to the flight deck.

Pretty clever.

Rockwell also really got on board with the whole “doing it on the cheap” theme, which was after all kind off the point of the entire SCS concept. To cut costs and speed production the nose of the XFV-12 was that of the A-4 Skyhawk, while the fuel tank, air inlets and part the wing box were all from the F-4 Phantom.

 

Indeed, Rockwell hoped to build 35% of the new VTOL fighter out of existing aircraft components and parts, all a valuable potential saving.

Naturally, to power any VTOL aircraft you need a substantial engine, and Rockwell chose the Pratt & Whitney F401, essentially a larger, navalised version of the F100 used on the F-15 Eagle. This was being developed to reengine the F-14 Tomcats, specifically the future projected F-14B, and so was a logical choice as it was expected to become the US Navy’s standard fighter engine in the near future.

This engine produced more than 28.000lbf in afterburner, which would have given the XFV-12 an expected top speed of Mach 2, far superior to the other VTOL aircraft flying.

Naturally, a price had to be paid somewhere, and the use of the TAW system meant that no locations were available for mounting weaponry under the inner wing, it being considered, understandably, a bad idea to vent hot gases over ordnance.

 

So, the XFV-12 was limited to weapon pylons on its rather thin fuselage and on the outer wing, meaning that weapon load was limited to either two AIM-7 Sparrows and two AIM-9 Sidewinders on the fuselage or four Sidewinders on the outer pylons, supplemented with 20mm Vulcan cannon.

But this all represented a more formidable air-to-air armament than the AV-8’s, which at the time had no radar and nor anything much more than the ability to carry two AIM-9s.

So all in all, the XFV-12 seemed like a really interesting idea, and certainly garnered a fair bit of attention. If anyone has read the Cold-War-Gone-Hot novel “Chieftains”, the author has them in service with the RAF

Certainly, with the growing interest in VTOL operations at the time and the theory that a sudden Soviet strike could knock out many of NATO’s European airfields, it is entirely possible that the XFV-12 may well have found buyers on land not just at sea.

The only problem was is that it didn’t work.

Cost overruns, hardly a surprise given the global economic situation in the 1970s, meant that the second prototype was cancelled, but in 1977 the XFV-12 was able to begin ground testing. These soon concluded that there may be an issue, and the aircraft was shipped to the NASA Impact Dynamics Research Facility in Langley, Virginia in early 1978.

This was the facility that the Apollo astronauts had conducted their training at and housed a huge gantry that the XFV was harnessed to in order to safely test whether the aircraft was capable of vertical take off.

 

And here the more limited knowledge of fluid dynamics available at the time showed itself to be a problem. While the scale test aircraft had shown that the thrust augmenters on the TAW wing would provide enough additional boost to allow the aircraft to be capable of vertical take-off, on the real thing the supplemental boost was nowhere near enough to lift the aircraft. In fact, the system only produced about 75% of the necessary power.

Rockwell persisted in trying to get the aircraft capable of VTOL flight, but the whole concept just simply couldn’t be made to work. Additionally, Zumwalt had retired in 1974 and with him went a lot of the impetus for the SCS and High-Low plan.

Instead the control of US Navy policy fell back under the sway of Admiral Rickover and his disciples, who believed firmly in the imperative of building the most capable ships possible, advocating the “quality over quantity” argument that was essentially the very opposite of Zumwalt’s ideas.

With Rockwell unable to get the XFV-12 to perform and this other doctrinal faction largely in control of policy, plus mounting cost issues with the program, in 1981 the US Navy cancelled the XFV-12.

But it might not have had to be that way. From the beginning Rockwell focused on demonstrating the VTOL aspect of the aircraft’s performance, hardly a surprise because that was its raison d’etre. But this meant the aircraft never even got to fly in either conventional nor Short Take Off/ Vertical Landing modes (STOVL).

And that may represent the great lost opportunity for the XFV-12 and Rockwell. Because theoretically, the aircraft had the potential to have been a real beast of a dogfighter.

 

Though it didn’t have enough power to conduct Vertical Take Offs, it had plenty for conventional flight and probably enough to make controlled vertical landings, especially with lightened loads after flying. Indeed, Bob Gulcher, who was the chief engineer for the XFV-12, said that he was convinced that the aircraft would have made an excellent short take-off and vertical landing fighter.

As a further irony, the year after the XFV-12 was cancelled, the capability of both STOVL aircraft and small carriers for their operation was demonstrated by the British during the Falkland’s War, where Harriers proved utterly critical to the campaign. And it is notable that the Harriers acted in a STOVL manner, using short take off for carrying ordnance and landing vertically – a mode of operation that the XFV-12 was perfectly capable of conducting.

The 1980’s saw a host of new “Harrier Carriers” commissioned by several navies, all of whom bought the Harrier, either from the British or Americans, and also saw the much-improved AV-8B Harrier fielded, which added BVR missile capability to the versatile aircraft. Ironically, most of these new light carriers were based directly on the American blueprints for the proposed SCS.

So, the XFV-12 really does seem to have missed it’s mark by the slimmest of margins and also stays subject to speculation.

 

Erik Simonsen, writing in Boeing Frontiers magazine, theorises that by not actually flying the XFV conventionally to Langley, something it should have been perfectly capable of doing, but instead shipping it via a Supper Guppy freighter, Rockwell missed an opportunity to demonstrate the aircraft’s flying capabilities, something that may have given it more of an edge when it came fighting the falling axe.

Of course, all speculation, and maybe the damn thing would have crashed, which no doubt Rockwell decided to avoid risking when they flew it as cargo.

But it does make the XFV-12 a particular intriguing “what-if” aircraft.

 

Sources/Related

XFV-12A history

a108354

https://en.wikipedia.org/wiki/Rockwell_XFV-12

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