On Feb 19, 9:33 am, wrote:
Yesterday on a short sight-seeing x-cntry I noticed the following
flight characteristic of a 1975 C150: whenever I turned to the left,
especially with low power setting, the ball indicated a skid with no
bottom rudder at all.

Explanations I've seen usually are illustrating the danger of skidding
a turn onto final, at high AoA, the typical scenario being tightening
a turn to not overshoot the runway. The inside wing and the rudder are
pointing toward the ground. The ball indicates skid. The pilot gives
more back pressure -- that's where you can get into big trouble.

But I noticed a substantial ball deflection indicating skid with
neutral rudder (shallow turn, not anywhere near critical AoA, by the
way).

In a left turn it seemed to me to take a fair bit of top rudder to
keep the ball centered. That seems weird to me. It doesn't happen in
the 152 or 172 I fly so I'm wondering if other people have seen this
in 150s (or other aircraft) or maybe the ball indicator has a problem?

I remember during my checkride in the same aircraft the ball showed
substantial skid on a demo approach the DE was doing after I had
passed the checkride. He saw it too and corrected, but the plane's
behavior seemed to catch him off guard as well.

You have a broken rudder bar spring. Cessna's springs regularly do
that and will have the airplane uncoordinated, requiring constant
rudder force on one pedal to keep things centered. The unbroken spring
is pulling on one pedal.
The other, more remote possibility, is a worn nosewheel
centering cam. The nosewheel is the rudder's centering system while in
flight on a Cessna single, with the sprung steering pushrods acting as
system centers. Cessna rudder systems are frequently found badly
misrigged, too, since too few mechanics refer to the maintenance
manuals while fixing them.

Dan