"Woody Beal" wrote in message
...
Concur that it does not yield a concrete conclusion, but it does yield a
tendency based on several possible single point failures. If lift fan
doors
don't open, if lift rotor fails to engage properly, if engine fails during
transition to STOVL life gets tough at a very critical and low altitude
moment. These problems (though not identical) are similar to those
experienced in the AV-8B.

Actually, conversion is done at an altitude and speed that, if it fails,
you're still wing-borne. The airplane fails back to a regular engine. Just
pop the TVL forward and continue to fly conventional. THe diciest moment
for the lift-fan system is during clutch engagement, but you don't perform
that in a high-exposure kind of situation. Doors and all that aren't really
a problem, cuz you'll know there's a problem before you expose yourself.

Mechanical failures in the STOVL regime are unforgiving because of their
low
altitude locale.

Yup. But a lot of stuff in the engine/lift-fan system is monitored. Health
checking on the B model propulsion system is way beyond anything that has
been put into service to-date. THe problem here is that health monitoring
tech is really only good for known failure modes. It's the "gee we never
considered that" kind of problems that can get scary. Infant mortality. WIth
the lift-fan system, you'll typically know if you have a mechanical problem
before you go jet-borne. Once transitioning to jet-borne, you just gotta
watch all the critical temps (turbine inlet, exhaust gas....yadda yadda).

Also, much of the unforgiving nature of jet-borne flight has been addressed
through the inceptor mapping. Switching from rates to attitude commands
makes overcontrol type slip-ups much less likely. The F-35B will be much
more forgiving to exhausted pilots.

makes the jet more stable. The complexity of the F-35B when compared to
the
C or the A only gives it an additional option for landing--a complexity
with
several possible single point failures in a critical flight regime.

Keep in mind that the operational environment envisioned for the F-35B is
much more varied than what has been done with the Harrier. So, exposure to
hazards (thinking mainly weather) will be much greater.


Pete
(worked on the X-35B for a couple of years designing the yaw-axis control
laws).