From
http://142.26.194.131/aerodynamics1/Lift/Page13.html
Effect of Bank on Radius of turn
Radius of turn is inversely proportional to the tangent of the angle of bank.
r is inversely proportional to Tan(b)
As the Tan of b approaches zero (wings level) tan(b) approaches zero and the radius becomes infinite. Thus, the equation correctly shows that there is no turn with the wings level.
As the Tan of b approaches 90, tan(b) approaches infinity and the radius of turn approaches zero. Thus, the equation indicates that a turn of zero radius can be made at 90 degrees of bank.
Previously we developed the equation LF= 1/cos(b). This equation indicates that the LF becomes infinite at 90 degrees of bank.
Thus, these two equations indicate that it is not possible to make a turn at or near 90 degrees of bank because the forces involved become infinite. Most of us have seen aircraft flying at 90 degrees of bank (and not making infinitely tight turns.) This is possible only by slipping, which was assumed not to be the case when we began this section (examine the first diagram and consider how it would change if the aircraft was slipping.)
Now what was the question again?
