Re: Soft ride mode on B747

From:         shafer@rigel.dfrf.nasa.gov (Mary Shafer)
Organization: NASA Dryden Flight Research Facility, Edwards CA
Date:         11 Mar 94 11:57:13 PST
References:   1 2
Followups:    1
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On 10 Mar 94 02:40:00 PST, kwd@netcom.com (Kurt W. Dekker) said:

Kurt> Saurin B. Shroff; x6284 (shroff@cadence.com) wrote: 

: On a recent trip from London to Boston on British Ariways, at around
FL310, : the ride suddenly became rough due to turbulance. The captain
then announced : that the turbulance was unexpected and he has turned
on soft ride mode to : give us softest ride possible (we were being
served lunch then). We were : flying B747.

: Does anyone know what is soft ride mode and how does it work?  After
the : announcement the ride seemed bit softer but not whole lot.

Kurt> Unless it's a simple reduction in forward airspeed [which has
Kurt> attendant increases in airline operating costs, so I doubt that
Kurt> was it!], I say it's a psychological thing.  "The ride will now
Kurt> be smoother with our 'smooth ride' controls enabled" will
Kurt> probably fool around 95% of people into thinking things actually
Kurt> got smoother.  Placebos work.  It's been proven again and again.
Kurt> The mind is a powerful thing.

While the mind is a powerful thing, so are modern flight control
systems.  They have a ride-smoothing mode in the flight control
system--it uses accelerations fed into the FCS computers.  We did a
lot of studies on this using a variable-stability executive jet
aircraft in the mid to late 60's and did find that it was fairly
useful, even though it doesn't make the ride totally smooth.  The ride
is improved enough, however, to reduce motion sickness symptoms.  As
far as I know, the 747 was the first to have this; I don't know what
other aircraft have it.

The F-111 terrain-following mode has the opposite sort of system.  You
can dial in various levels, up to hard ride, to select the amount of
acceleration that you're willing to accept.  I have not tried this
firsthand, but pilots who have assure me that the hard ride really is.



--
Mary Shafer                                                   DoD #362 KotFR   
SR-71 Chief Engineer         NASA Dryden Flight Research Center, Edwards, CA
shafer@ferhino.dfrf.nasa.gov                Of course I don't speak for NASA
 "A MiG at your six is better than no MiG at all."  Unknown US fighter pilot