"Teacherjh" wrote in message
...

Isn't it the case, in an earth-centric reference frame, that an object
moving in a straight line, when subjected to a horizontal force
perpendicular to that motion, will move in a circle?


If the force is in fact perpendicular to the MOTION (the course) and not
to the
HEADING. In the case of simply banking, the nose does not move (so the
heading
remains the same) while the course changes (due to the force you are
talking
about). But so long as the nose does not change direction, the force will
not
change direction either and the plane will simply continue in a straight
line,
in a slip.


I'm having a hard time wrapping my brain around this. Maybe the different
reference frames are confusing me.

Let's say I put the plane into a 30 degree bank with ailerons yet maintain
neutral rudder. To simplify things let's say I do this instantaneously.
Right at that moment, the nose is pointing in the original heading. But
what happens as this fairly large (earth referenced) horizontal lift force
acts on the plane; clearly it moves it sideways. But what happens to the
heading, that is messing me up. If the force continues, either it results
in an acceleration which causes increasing velocity or it reaches a terminal
velocity where the force is balanced by drag. Does the slip result in such
large drag so quickly that the net result is similar to a crosswind, or does
the plane act in the medium it is flying in (of course ignoring the earth
below) and have the nose indeed change heading because the plane is now
"climbing" sideways? I know from experience I need a lot of *opposite*
rudder to counteract a 30 degree bank and keep the nose on the same heading
(as in crosswind landings).