1-3. FAMILIARISATION WITH AIRCRAFT / AIRCRAFT CAPABILITIES

EXERCISE 1-3

FAMILIARISATION WITH AIRCRAFT / AIRCRAFT CAPABILITIES

AIM:

To familiarise the student with the helicopter, its structure, systems, main components and controls, drill and checklists.

THEORY:

BASIC AERODYNAMICS

There are four forces acting on a helicopter in flight. They are lift, weight, thrust, and drag. Lift is the upward force created by the effect of airflow as it passes around an aerofoil. Weight opposes lift and is caused by the downward pull of gravity. Thrust is the force that propels the helicopter through the air. Opposing lift and thrust is drag, which is the retarding force created by development of lift and the movement of an object through the air.

Chord Line:

An imaginary straight line between the leading and trailing edge of an aerofoil section

Pitch Angle:

The angle between the chord line of the rotor blade and the reference plane of the main rotor hub, or the rotor plane of rotation.

Angle of Attack:

The angle between the aerofoil chord line and the relative wind.

Resultant Relative Wind:

Airflow from rotation that is modified by induced flow.

Rotational Relative Wind:

The component of relative wind produced by the rotation of the rotor blades.

Induced Flow:

The component of air flowing vertically through the rotor system, resulting from the production of lift.

Centre of Pressure:

The centre of pressure is to lift what centre of gravity is to weight. The centre of gravity of an object may be defined as the point through which all weight forces are said to act. Consequently, the centre of pressure may be defined as the point on the chord line through which all the aerodynamic forces are said to act.

Feathering Axis:

The straight-line axis between the root of the blade and its tip, about which the blade can alter its blade angle.

Lift:

The production of lift through the deflection of the relative airflow as it passes an aerofoil is the result of changes in the atmospheric pressure, which occur around the surface of that object. When a streamlined flow is made to speed up to get past a body the atmospheric pressure in that area will decrease and the opposite will occur in those areas where the flow is made to slow down.

Blade Sailing:

Blade sailing is a problem with low rotor RPM during start up and shut down producing insufficient centrifugal force on the rotor blades and flapping, caused by the wind, becomes excessive. The problem is worse when the wind is gusting. Two bladed rotors are more vulnerable to blade sailing than three or more blades. This is due to the fact that the advancing blade travelling into wind flaps up with great force due to increased lift, but in the opposite sense, the retreating blade flaps down with the risk of a blade wildly flapping striking the tail boom or causing a danger for anyone in the immediate vicinity.

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