Re: Air France Concorde crashes after departing Paris CDG

Date:         19 Apr 2001 16:40:35 
From:         don@news.daedalus.co.nz (Don Stokes)
Organization: Daedalus Consulting
References:   1 2 3 4
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In article <airliners.2001.136@ditka.Chicago.COM>,
Doug Holik <drholik@prodigy.net> wrote:
>
>"Jeremy Harris [RU-UK]" <jgh@uk.sun.com> wrote in message
>news:airliners.2001.112@ditka.Chicago.COM...
>> In article <airliners.2001.78@ditka.chicago.com>,
>> FilipPC.DeVos@rug.ac.be (Filip De Vos) writes:
>> > Part of that drag is the rudder, deflected to compensate for the
>> > assymetric thrust. So my question is, is it possible to make a climbing
>> > turn at a lower speed than 275kt? (turning towards the dead engines)
>
>> Uh, to first order, planes don't turn thanks to the rudder, but thanks
>> to having been banked.
>
>Actually they do turn because of the rudder, why do you think its there?

Turning the rudder just changes where the aircraft is poitinng; it
doesn't change its direction of travel.  If you do this (especially with
swept wings) with the rudder, the aiflow over the wings becomess
assymetric and you risk flipping the thing over.

The rudder is there to control the yaw axis to keep the airflow straight
down the aircraft.  The turn itself is done by banking as the previous
poster said.  Basically, the aircraft's lift, in straight level flight,
is pushing the plane straight up against gravity.  By banking the aircraft,
you adjust the direction of that force so that there's a sideways component
to the force applied.  This sideways force is what changes the direction
of travel and makes the turn.

Without banking, there's very little force being applied to the aircraft
to actually change the direction of flight -- just that applied to the
fuselage and tail, that latter will be just trying to pull the aircraft
straight again.

Mostly the aircraft will be naturally stable and will turn itself with
the changing airflow without help from the rudder.  But for tighter
turns, a bit of rudder input helps keep the aircraft from entering a
dangerous yaw.

The rudder has other uses -- it can offset assymetric power, or with help
from the ailerons actually be used to fly the aircraft in a slight yaw
where you (for example) want to fly straight with respect to the ground
rather than the air, as in the final approach in a crosswind.

-- don