Flightdeck Friday: V/STOL Dreams

 It is clear that the XFV-12A program will not enhance the image of naval aviation. Note that in this case the outcome was not only predictable, but was in fact predicted. As is so often the case, all of the principals in the decision have moved on in both OSD and the Navy. The task of justification will fall on others and will be difficult. It is to be hoped that the same mistakes will not be made again, although the entire V/STOL program certainly has the potential.

– George Spangenberg, 1977 memo to RADM Ekas, USN (NAVAIR)

 

The 1970’s — disco balls, cardigan sweaters in the White House, double digit inflation and unemployment.  The nation was in the grip of stagflation and post-Vietnam malaise; defense spending and investment was down substantially and traditional big ticket items, like nuclear aircraft carriers, were increasingly difficult to fund.  It was, in a word, an age of diminished expectations.

In the early 70’s an idea surfaced of using smaller ships with an air capability to supplement the big decks, especially for things like convoy duty.  A reduced (much) size “airwing” of a dozen or so ASW helos, 2-3 AEW helos and 6-7 VSTOL fighters would be embarked on these “sea control” ships.  The ASW helos were already in the inventory – SH-2’s or SH-3’s, and AEW helo would be based on one of those, most likely the SH-3 – like the Royal Navy did.  The VSTOL fighter though, would be a problem.  The AV-8A Harrier did not possess an all weather intercept capability, was range and endurance limited and subsonic to boot.  In the convoy escort mission, especially convoys headed to Europe to reinforce NATO forces on the Central front, the escorts and their wards would have to run a gauntlet of long-range, supersonic cruise missiles launched from Bear B/C and Badger bombers as well as SSGN’s like the Juliet:

  

In 1971, in an attempt to jumpstart industry investment in the next generation of transformational weapons and weapons platform (ed. except it wasn’t labled “transformational” back then -SJS), OSD through the Deputy Under Secretary of Defense for Research and Engineering (DDR&E) established a prototyping program.  The intent of this “out of the box” program was intended to produce more competitive hardware with less bureaucratic control, reduce costs, and give SecDef more program options. “Requirements”, and “Specifications” were to be avoided and innovative approaches encouraged. In the words of one DDR&E official the Air Force enthusiastically supported the program, while the Army and Navy were reluctantly brought aboard. Mat-03 (VADM Davies) was the head Navy Prototyper. Some support for the program existed in all segments of DOD by those who believed that “Prototype” funds would be in addition to the normal R&D budget. The more realistic officials recognized that any “added funding” would be small and limited to that one budget.  Noted aerospace engineer, George Spangenberg (BuAer/NAVAIR) was one of the most vocal opponents within Navy, noting in a later memo:

Most of the lessons of history were ignored by those who attempted what they believed to be innovative approaches to defense procurement, but which in fact had all been discarded in the evolution of the naval aircraft acquisition process. Another factor involved in the early years of the program, and one which has been a recurrent problem within my experience, is a belief that the engineers who produce NavAir estimates are congenitally overly conservative, while contractor technical estimates can be achieved if adequate management attention is applied. This belief, as you know, was a major factor in the TFX debacle.  – G.S. (1977 memo)

Initial projects submitted by Navy to the Prototype program were those which were already extant and had received little or no funding within Service budgets.  Chief amongst these was a proposed COD version of the S-3.  Smarting from the rejection, MAT-03 opted to solicit industry directly for two new designs, both of which would be V/STOL in character.  One would be for a sensor platform to serve as the basis for the ASW, AEW and ESM missions and the other, a fighter/attack aircraft.  Both were for basing on the (still on paper) Sea Control Ship (SCS).  The RFP went out to industry in 1972 (accompanied by a requirement to keep the bid proposal to 20 pages max).  Two designs made it to the finals – one from General Dynamics/Convair that was a canard-delta wingform and used a three-bearing, swivel-down main engine based on the  P&W JTF22A-30A (F401 variant) engine and two lift engines in tandem behind the cockpit:

 

The three-bearing swivel nozzle serves to deflect the main engine thrust downwards. Control in the vertical mode would come via bleed air from lift fans driving a reaction control system with nozzles at each wingtip and under the nose. Convair claimed that the 200 would have a get-home capability on the two lift engines alone and STOL landing with one lift engine out.  Armament would be a combination of cannon and two AIM-7 Sparrow’s in semi-recessed locations on the fuselage.

 

While the GD/Convair offering was technologically challenging, by far the more radical and cutting edge design was submitted by North American.  The principle used in the GD/Convair 200 revolved around a similar one used in the Harrier – re-direction of direct thrust from the engine.  It had the virtue of being somewhat straight forward and providing known qualities from operations with the Harrier.  As they were beginning to find out with Harrier ops though ( and similarly the Soviets with the YaK-38 Forger) the effects of the ambient heat on aircraft performance (higher temps forced reduced payloads due to lift engine limitations) and blast/heat effects from the direct lift jets on flightdecks tended to weigh against the direct lift engine method  have a deleterious effect on flightdecks .

North American Aviation weighed in with a radical new design based on an unproven concept – the thrust augmented wing.  Instead of concentrating the vertical thrust in a small foortprint it would instead be re-directed from the main engine via a series of ducts to the wings and canards, providing a larger, but “cooler” foortprint while eliminating the need to carry an extra engine that only operated during part of the flight regime:

Diagram of an Ejector Lift system similar to the one used on the XFV-12A

(Drawing copyright Rolls-Royce Ltd.)

Here, the high-energy hot gas forced fresh air from above through the ejector flaps at a ratio of 7.5:1 to boost thrust by 70 percent. The ejector flaps could be raised or lowered to provide a smooth transition between vertical and horizontal flight.

The Navy opted for the North American proposal after a very brief review of the bids (about two weeks).  NAA proposed to save some construction costs for the prototype by using components from the A-4 and F-4 – hence the familial similarity in the nose and intakes.  Unfortunately, the DNA from those two stellar naval aircraft did not make the transition.

  

Almost immediately the program began running into engineering problems and cost overruns.  Delay built upon delay and it wasn’t until 1977 that the protoype rolled out of the factory to begin flight tests.  A second protoype had already been cut due to cost overruns.

  

The Navy unveiled its new XFV-12A vertical/short takeoff and landing research aircraft at the Rockwell International facility in Columbus, Ohio on 26 August 1977. Aircraft ground testing in July 1977, and suspended tether trials conducted in 1978.  One problem — the damn thing couldn’t fly, period.

  

In early 1978, tethered hover tests of the full-scale XFV-12A were carried out by a joint team of NASA, Navy, and Rockwell personnel. During 6 months of tests, it became apparent that major deficiencies existed in the XFV-12A for hovering flight, including marginal vertical thrust. Lab tests were interpreted to show that 55% augmentation could be anticipated, but differences from the lab models to the full scale system caused the actual augmentation to be only 19% for the wing and 6% for the canard.

  

Although the augmentation of flow at the wing augmentors was as predicted, large losses in the internal ducting and corners of the propulsion system seriously degraded the net thrust to the extent that only 75 percent of the weight of the vehicle could be supported in attempts to hover.   It was worse than a turkey — it was a dodo, in all the sense of the word.

Having evidently not learned the lesson from the TFX ordeal, the Navy opted for the North American design.  Early in the prototype development phase it became apparent that there were going to be issues with this aircraft.  The hard lesson (not) learned was the necessity for solid requirements going into the design process.   The lack of rigor and forethought in the development of requirements, and epitomzed by the abbreviated RFP response and short turnaround for evaluation of bids (two weeks) led to such disconnects as giving up potential weapons carriage locations owing to the use of thrust augmented wings which necessarily eliminated wing mounted harpoints except (possibly) fo wingtip pylons for AIM-9 Sidewinder’s.  On a larger basis, it belied a lack of forethought and intellectual rigor at the senior leadership levels within the Navy — though not existent at the time, the early equivalent of PowerPoint Rangers had convinced the powers-that-be that an all V/STOL force was the way to go with little consideration of the technological and engineering challenges that lay in wait, nor more critically, of capabilities that would be given up.  A glance at the chart below shows the burgeoning weight problem, hamstrung by engine limitations and a subsequent,  widening divergence between the Navy model and the prototype:

A contemporary analysis based on the above chart noted that:

From this tabulation, it can be concluded that there is no possibility of a fleet V/STOL fighter emerging from the program. Note that with the same engine rating, the maximum vertical take off gross weight is the same for both “prototype” and “service” models, while the difference in empty weight and equipment is approximately the same between the two models. The DLI fighter radius can be used as an indicator of capability. On the first Navy check of the design, in 1972, the service model had no capability with approximately 5000 lb. discrepancies between the contractor and Navy estimates of both weight and lift force. Later the differences in lift capability were reduced by eliminating suck down and reingestion effects and increasing the engine rating used. Navy estimates of a future fighter capability peaked at about the end of 1973 when it was estimated that a small amount of fuel could be lifted off in addition to fighter armament, giving a slightly positive radius of action. Since that time it will be observed that the vertical take off gross weight has decreased by about 3000 lb. which would eliminate the fuel allowance, again achieving no capability.

That same analysis went on to conclude that the Lift-plu-Lift/Cruise concept, as epitomized by the GD/Convair Model 200, provided the best and most promising route to superconic cruise V/STOL capability.  The same analysis went on to acknowlege that while some objected to carrying the weight of the lift engines into combat, the fact was that that weight was small compared to the weight penalties associated with the thrust augmented wing and that the latter had been estimated to have the poorest T/W ratio for any of the V/STOL propulsion arrangements which had been studied.  It did call for new lift engine development to precede any lift-plus-lift/cruise aircraft development.

Epilogue

The XFV-12A never flew, yet continued tethered ops for a while with NASA until it was placed in storage and then eventually scrapped.  Still, the allure of supersonic V/STOL flight lurked until the advent of the JSF competition when it was finally brought to reality – in a lift-plus-lift/cruise configuration via Lockheed/Martin’s X-35:

 Perhaps the best summation of the XFV-12 fiasco is a viewgraph used by George Spangenberg in a 1981 presentation on requirements-based capabilities and dvelopment of naval aircraft.  Note the “honor roll” of programs on the left side of the slide:

“The first slide is an all purpose title page, used in a few programs of the past, which share with V/STOL, the problem of being easy to delineate, but difficult to reduce to practice.”

and this also:

“The Chief of Naval Operations in 1976 announced a plan to transition to an all V/STOL force, after he was advised that V/STOL designs equal in capability to CTOL could be produced at no significant increase in cost. The source of that advice was not identified except as coming from “the technical community”. That advice falls into my category of “bum dope”.”

and finally this sage bit of philosophy:

Should serve as a lesson-learned, just like the TFX, for those who would build future forces on pretty Power Point charts, slick brochures and gossamer veil of “requirements” that lack intellectual and engineering rigor.

Not to put too fine a point to it, that is…