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  • Why The F-35B Is In Trouble
    Posted by Bill Sweetman 3:31 PM on Jan 10, 2011

    Three big issues to be dealt with this week: F-35B, J-20 and bombers. Here goes on the first:

    Defense Secretary Gates announced last week that the F-35B short take-off, vertical landing fighter was "on probation". Coupled with the release of a short summary of actions that follow new program manager VAdm Dave Venlet's review of the program, it points to a challenging couple of years.

    The change to the F-35B plan is major. All but three of the FY11/Lot 5 B-models are cancelled, and another 27 aircraft in FY12 and FY13. Production is being drawn down to the minimum level necessary to preserve a restart option.

    Gates said that solving the unspecified technical issues now afflicting the aircraft "could" add cost and weight; the program office says that it "will", and that it will take two years to "engineer solutions ... and assess their impact."

    This action has been in the works for some time, foreshadowed by comments in September from Lockheed Martin CEO Robert Stevens.

    Gates hit the issue on the nose when he stated that changes could "add yet more weight and more cost to an aircraft that has little capacity to absorb more of either." The current situation has been in the making since the start of the systems development and demonstration program and has to do directly with the basics of a STOVL aircraft.

    Vertical landing is a nonvariable requirement. The required airspeed is zero and can't be adjusted by a few knots to compensate for extra weight. The JSF key performance parameter for bring-back load - corresponding to two 1,000-pound JDAMs and two Amraams - was set early on at a minimal level.

    One reason that Lockheed Martin's shaft-driven lift fan (SDLF) concept was a winner in 1996 and 2001 was that it seemed to offer thrust margin for vertical landing. At the start of SDD, the F-35B was projected to have an empty weight of 29,700 pounds - not a bad place to be in with (then) almost 40,000 pounds of vertical thrust. But, in the weight crisis of 2004, engineers found that the jet had ballooned to a far higher figure (never actually published) at which it could not land vertically with normal fuel reserves, let alone weapons.

    The subsequent redesign clawed back some of the growth, to a goal weight that has since floated up and down around the 32,200-pound mark - at the cost of many detail changes, including smaller horizontal tails and a change in some bulkheads from titanium to aluminum. A little more thrust was coaxed out of the engine, fuel reserves were renegotiated and the F-35B once again met Marine KPPs.

    However, the margin was so tight that the Royal Navy felt it necessary to look at shipboard rolling vertical landing (SRVL) techniques to boost landing weight - a controversial measure that we have been reporting on for almost four years.

    Still, the redesign left a fundamental problem: the bring-back load (around 3,000 pounds) was only 8 percent of the landing weight. The result is that the F-35B couldn't tolerate any OEW growth or thrust shortfall. The engine and transmission are maxed: that's the issue underlying the repeated delays in powered-lift testing, chronicled here and here.

    (Interesting analogy: Concorde, which, in its production version, was designed to cross the Atlantic with a payload that was under 10 percent of its fuel load. Consequently, even a marginal shortfall in cruise efficiency would obliterate its payload, which nearly happened in 1972-74 and was averted only by difficult and expensive refinements to the air inlets.)

    So whatever the F-35B propulsion and structural problems are, they have to be solved without adding weight. At the same time, changing materials and redesigning components will further reduce commonality between the B and the other two versions, putting upward pressure on costs for what is already the most expensive version.

    I suggest the sharp brake that Gates has put on production does not speak to a high level of faith that it can be done. It suggests that the decision to put the STOVL jet on probation, rather than sending it directly to meet Old Sparky, may have been driven by concern that killing both the F-35B and the Expeditionary Fighting Vehicle was a political impossibility, and by a desire to minimize political impact on the entire JSF program.

    The next developments to look for: the outcome of the review of Marine Corps force structure, and the scale and type of resources that will be made available to fix the F-35B.

    Tags: ar99, wellington, tacair, jsf, gates

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