Designer's Notebook

When is an airplane in trim? At least to the pilot, the airplane is trimmed when no stick force is required to maintain equilibrium. So how do we achieve this? Barnaby Wainfan explains any number of ways to go about it, including the use of trimtabs, spring systems, sparrow strainers and variable incidence tails.

This month Barnaby Wainfan turns his attention to the control system and how various aspects such as linkages, the elevator planform and tail aspect ratio, and trailing-edge treatments affect pitch control.

The diagnosis of pitch sensitivity problems boils down to one of two things: too little static margin or control system problems. This month we discuss how to modify the airplane to fix them;

This month we use the accumulated flight-test data to determine what exactly is causing the unacceptable flying qualities of the airplane so that the best way to fix the problem can be identified;

Flight testing for longitudinal stability problems continues this month as columnist Barnaby Wainfan details tests for stick force as related to trim and stick-free stability of an aircraft. The object is to gather data and analyze it to see if the hypotheses about the nature of the problem hold up under scrutiny.

Columnist Barnaby Wainfan continues his flight-testing discussion by taking up the topic of longitudinal stability. By identifying the origin of the problem, whether it be a control-system issue, a too-small static margin, or a combination of the two, the flight tests he recommends will help to isolate the issue.

Columnist Barnaby Wainfan discusses the factors that affect the longitudinal stability of an aircraft during a variety of maneuvers. Designers make compromises to keep stick forces down so that a pilot can control an airplane, but sometimes they go too far, and light control forces can result in problems that are just as serious as those posed by forces that are too heavy. Whats a designer to do? The most important considerations are presented.

The perils of PIO;

Its an age-old duality: stability versus maneuverability. Many factors go into developing and building any aircraft, and the designers choices will affect a pilots workload, for good or ill. Among the topics discussed are trim, pitch stability and yaw stability;

The author explains how the characteristics of an airplane affect pilot ability to complete tasks, response factors, stability and damping of the airframe to changes in angle of attack, basic stability, trim, control forces, and control power. He also addresses the controversy behind the design of airplanes, their characteristics and the resultant suitability for various types of flying;