Dynamics of Aircraft Flight

6 Aircraft Characteristics

6.1. Aerodynamics problems posed by aircraft

The fields of application of aircraft are varied. No single aircraft can cover them all, so there is no “ideal” configuration with perfect characteristics to meet all needs.

The problems to be solved for the design of a civilian aircraft, a military aircraft, a microlight or a drone are not of the same nature. Depending on the needs, an optimum for one or more characteristics will be sought to the detriment of others, considered secondary.

Commonly, the search for optimum qualities concerns the following points:

• – the drag;
• – maneuverability or the creation of lift;
• – stability;
• – the resistance of structures from mechanical and thermal points of view.

6.1.1. Drag

In order to have long range or achieve maximum speeds, an aircraft must have as little drag as possible.

Most of a flight (the so-called “cruising” flight) is carried out at a load factor n = 1 and, therefore, at low incidence, without significant changes other than path corrections. In this case, the search for a minimum drag coefficient is a priority. This drag is divided into four parts:

• – pressure drag (or supersonic wave drag);
• – friction drag;
• – base drag;
• – accessory drag.

The first term indicates that the component, along the longitudinal axis of the integral of the pressures on the aircraft, “base excepted”, is not zero. A body drag can be assigned to each element of the aircraft (body, wings, control surfaces, etc.).

The second term ...