Section 3. Aerodynamics of an airplane Topic 14. An interference of an airplane parts

After assembly of the aircraft separate parts into single whole their streamlining and aerodynamic characteristics change. It is caused by mutual influence of these parts named as an interference. We can distinguish the interference of three types: 1) between the lifting and poorly lifting elements (wing and fuselage, tail-plane and fuselage, nacelle and wing and others); 2) between the lifting elements (wing and tail-plane); 3) between jets of engines or props and parts of the aircraft. Let's find out physics of the interference of the aircraft various parts.

14.1. Geometrical characteristics of an aircraft

The external shapes of an aircraft and its parts, their sizes and mutual arrangement which provid obtaining of the necessary aerodynamic characteristics are called as aerodynamic configuration.

The aircraft aerodynamic configuration is characterized by presence of some separate parts, their mutual positionment and geometrical features. The following aerodynamic configuration of the aircraft are the most widespread.

Aircraft are distinguished by number of wings onto biplanes and monoplanes. The biplane configuration contains two wings located one above another. This structure was widely used at the beginning of aircraft development. Now majority of airplanes are constructed witn the monoplane configuration or with one wing.

There distinguishes the normal airplane configuration, canard configuration, configuration “tailless” and “a flying wing” by presence and location of horizontal tail unit.

Horizontal tail of normal configuration is located behind the wing. This configuration provides the favorable conditions for flow about wing, however horizontal tail is in the zone of disturbed flow caused by wing and on some modes can lose the efficiency.

In the canard configuration the horizontal unit places ahead of a wing and works in an undisturbed flow, but it effects onto flow about wing. This influence can be both negative or positive depending on the horizontal tail shape both wing and their mutual arrangement.

The airplanes of the configuration “tailless” have no the horizontal tail and the configuration “flying wing” besides actually have no fuselage and vertical tail.

For monoplanes we can differ three configurations depending on wing installation by fuselage altitude: low-wing monoplane, mid-wing monoplane and high-wing monoplane.

Vertical tail, as a rule, is installed in a tail part of the airplane. Depending on number of fins the aircraft can be designed on single-finned, twice-finned and multi-finned configurations, and on number of fuselages the aircraft can be designed on the single-fuselage and twice-fuselage configurations.

The power plant essentially influences on external shape of modern aircraft. The engines can be mounted in a wing, on a wing, under a wing, under a wing on pylons, in a fuselage, under a fuselage, on a horizontal tail unit, in a fin.

In the aircraft aerodynamic configuration its separate elements (wing, fuselage, horizontal tail, vertical tail, engine nacelles etc.) influence each other. Therefore, the aerodynamic characteristics of these elements will vary in aircraft system and at the isolated streamlining.

We distinguish a positive and negative interference, depending on whether total aerodynamic characteristics are improved (in certain sense) or became worse. This circumstance is necessary for taking into account while aerodynamic designing.

Physical features of interaction of lifting surfaces (such as wing, horizontal tail) with a fuselage, engine nacelles with a wing and fuselage, wing and horizontal tail will be considered below. There are other kinds of interaction, for example, jets of the air prop or turbo-prop engines with elements of the aircraft, influence of the cargo plane onto dropped freights, influence of ground or water surfaces onto the aircraft aerodynamic characteristics etc.