"the Lockheed Martin-built F-35 — which can avoid sensor detection thanks to its special shape and coating — simply doesn’t work very well. The Pentagon has had to temporarily ground F-35s no fewer than 13 times since 2007, mostly due to problems with the plane’s Pratt & Whitney-made F135 engine, in particular, with the engines’ turbine blades. The stand-downs lasted at most a few weeks.
“The repeated problems with the same part of the engine may be indications of a serious design and structural problem with the F135 engine,” said Johan Boeder, a Dutch aerospace expert and editor of the online publication JSF News.
Pratt & Whitney has already totally redesigned the F135 in an attempt to end its history of frequent failures. But there’s only so much engineers can do. In a controversial move during the early stages of the F-35′s development, the Pentagon decided to fit the plane with one engine instead of two. Sticking with one motor can help keep down the price of a new plane. But in the F-35′s case, the decision proved self-defeating.
That’s because the F-35 is complex — the result of the Air Force, Marines and Navy all adding features to the basic design. In airplane design, such complexity equals weight. The F-35 is extraordinarily heavy for a single-engine plane, weighing as much as 35 tons with a full load of fuel." reuters
Most here on SST will not remember the F-111. In the case of that design, the McNamara whizkids decided that having different fighter bomber aircraft for the different services; USAF, US Navy and USMC was wasteful and lacking in elegance from an ORSA applied math point of view. To overcome that awkwardness a shotgun marriage was ordered in which one airplane would be designed, produced and issued to all three services.