Principles of Flight

Introduction

This chapter examines the fundamental physical laws governing the forces acting on an aircraft in flight, and what effect these natural laws and forces have on the performance characteristics of aircraft. To control an aircraft, e it an airplane, helicopter, glider, or balloon, the pilot must understand the principles involved and learn to use or counteract these natural forces.

Bernoulli's Principle

Bernoulli's Principle of Differential Pressure: as the velocity of of a moving fluid (liquid or gas) increases, the pressure within the fluid decreases. This principle explains what happens to air passing over the curved top of the airplane wing. A practical application of Bernoulli's Principle us the venturi tube. The tube has an inlet that narrows to a throat and an outlet section that increases in diameter toward the rear. The diameter of the outlet is the sames as that of the inlet. At the throat, the airflow speeds up and the pressure decreases; at the outlet, the airflow slows and the pressure increases.

As the wing moves through the air, the flow of air across the curved top surface increases in velocity creating a low-pressure area.

Angle of Attack

The term angle of attach is defined as the angle between the wing chord line and the relative wind. The wing chord line is a straight line from the leading edge to the trailing edge of the wing. The relative wind is the direction of airflow relative to the wing when the wing is moving through the air.

The angle of attack at which an airplane wing stalls will remain the same regardless of gross weight. A given airplane wing will always stall at the same angle of attack regardless of airspeed, weight, load factor, or density altitude. Each wing has a particular angle of attack (the critical angle of attack at which the airflow separates from the upper surface of the wing and the stall occurs.