The limitation on the Harrier's operations when performing VTOL operations was due to the need to use demineralized water injection to help cool the engine intake air during vertical flight. There is only enough of it onboard for approx. 90 seconds of flight, so that is what causes the limit and the "black" exhaust when in hover. With the F-35B, the only theoretical limit would be on if there were bearing temperatures to care for and fuel. There is no need to augment the intake air as was stated previously. This is why the lift fan design is much preferred but was never really feasible due to performance loss in the engines to drive the lift fan and the problems with part tolerance control for reasonable cost. With modern capabilities in CNC machining and even 3D metal printing, many of these issues have been resolved allowing for an acceptable performance loss and reliable operations of the drive train.
Testing will bear out how rugged the system is, but from the initial testing series, it seems to be holding up well as they are conducting vertical and STOVL operations on a regular basis, meaning little work is being needed between flights to "fix" any issues.
The Inspector wrote:
Ya mean like early versions of the R/R RB-211 on L-1011's?
Umm, the only problem the RB211 had in development was that the original composite fan
blades weren't up to snuff and the titanium blades had problems too with their metallurgy. The fans themselves were fine.
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