Re: Interresting thread in comp.lang.eiffel

[David Gillon <david.gillon@baesystems.com>]

Ken Garlington wrote:

> 
> > > The gains changed abruptly when the aircraft transitioned from
> > > takeoff-and-landing to up-and-away mode. This produced a sudden
> transient,
> > > triggering the start of the PIO. The transition now occurs more
> gradually.
> >
> >    That fixes the primary cause, but not the actual failure mode.  Does
> > the stick now
> > have tactile feedback?

> No -- you don't often get significant tactile feedback from a force-sensor
> side stick connected to a FBW system, such as that on the F-16 or F-22. (In
> fact, the original F-16 stick didn't move at all!) 

IIRC, the YF-16 had a PIO incident during the fast taxi trial and was
only saved by the test pilot lifting off before the oscillation about
the roll axis became severe enough to contact the runway with the
wingtips. He managed to dampen it out once in the air, did a circuit and
landed without further incident. The solution lay in the (analogue) FCS,
not the fixed stick.

There is an undeniable advantage to a moving stick, in that it
immediately demonstrates the last control input if the pilot is
hands-off or in a two crew cockpit. However I don't believe tactile
feedback as a solution to PIO is a workable argument for mandating one.
(Stick-shaker operation as a stall warner is a completely separate
issue).

-- 

David Gillon