M. Borri, L. Trainelli
A
Simple Framework for the Study of Airplane Trim and Stability
AIAA paper no. 2003-5620
presented at the AIAA
Atmospheric Flight Mechanics Conference and Exhibit, Austin, TX, USA, Aug
11-14, 2003.
Abstract
We develop a reformulation of the study of airplane trim
and stability intended mainly for teaching purposes. This approach yields a
slightly different form of the governing equations with respect to that
commonly adopted in the literature and in education programs. Under hypotheses
of linear, low subsonic, steady-state aerodynamics in symmetric flight, the
constitutive laws for lift and pitching moment are rewritten in homogeneous
form and appropriate characteristic points are introduced: the first is the
well known neutral point, while the second is termed the control point. This
allows for a reduction of the complex system of aerodynamic forces acting on
the airplane to an equivalent one consisting in only two applied forces. Basic
considerations of trim and stability are easily carried out within this framework
by simple, intuitive reasoning upon the resulting force distribution patterns.
In order to help the reader to familiarize with this approach, applications to
level flight in both the stick-fixed and stick-free settings, as well as to
maneuvering flight, are briefly addressed.