Newsgroups: sci.aeronautics.airliners
From: drinkard@bcstec.ca.boeing.com (Terrell D. Drinkard)
Subject: Re: Soft ride mode on B747
Date: 20 Mar 94 22:29:58 PST

In article <airliners.1994.992@orchard.chicago.com>,
Kurt W. Dekker <kwd@netcom.com> wrote:
>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.
>
>Unless it's a simple reduction in forward airspeed [which has attendant
>increases in airline operating costs, so I doubt that was it!], I say it's
>a psychological thing.  "The ride will now be smoother with our 'smooth
>ride' controls enabled" will probably fool around 95% of people into
>thinking things actually got smoother.  Placebos work.  It's been proven
>again and again.  The mind is a powerful thing.

I'm sorry I missed this the first time through, our server has been down.

The 747 does indeed have a ride quality system.  It adjusts the gains on
the yaw damper system.  The idea to equalize some of those lateral
accelerations that gusts impart to the aircraft through the vertical tail.
That is, with the ride quality system (actually called the MSAS - Modal
Suppression Augmentation System) off, the cockpit has a nice ride but those
in the aft end of the airplane get moved about a bit.  With the MSAS on,
the cockpit shares in the sideways accelerations, with a decrease in the
felt accelerations by those passengers well aft.  It does not, and cannot,
remove all the accelerations felt by everyone on the airplane.

--
Terry
drinkard@bcstec.ca.boeing.com
"Anyone who thinks they can hold the company responsible for what I say has
more lawyers than sense."