Basic Heli - Lesson 1-3

Helicopters

Classified as rotary wing aircraft, and their rotary wing is commonly referred to as the main rotor or simply the rotor.

Chord

The cross section of the blade of the distance have an imaginary line drawn from the leading edge to the trailing edge.

Airfoils

The blades of the main rotor are the

Relative wind

This is the direction of the airflow with respect to the blade.

Pitch angle

The acute angle between the rotor blade chord and a reference line.

Angle of attack

The acute angle between the chord line of the airfoil and the relative wind.

Lift

The force produced by the airfoil that is perpendicular to the relative wind and opposes gravity.

Drag

The force which tends to resist the airfoil's passage through the air.

Center of pressure

An imaginary point where the result of all aerodynamic forces of the airfoil are considered to be concentrated.

Stall

The condition under which the streamline flow of air separates from the camber of the blade and reverse flow occurs, resulting in an almost complete lost of lift.

Lift variation

Will also vary with the density of the air. Air density is affected by temperature, altitude, and humidity.

Thrust

The force developed by the rotor blades acting parallel to the relative wind and opposing the forces of drag and weight.

Collective pitch

Changing the pitch of all rotor blades in the main rotor system equally and simultaneously and, consequently, the amount of lift or thrust being generated.

Gyroscopic precession

An action occurs 90 degree from the force applied in the same direction as rotation.

Torque

In helicopters with a single, main rotor system, the tendency of the helicopter to turn in the opposite direction of the main rotor rotation.

Blade twist

The variation in the angle of incidence of a blade between the root and the tip.

Dissymmetry of lift

The unequal lift across the rotor disc resulting from the difference in the velocity of air over the advancing and retreating blade half of the rotor disc area.

Tubular, stressed, bonded

Methods of helicopter construction

Tubular Construction

This type of construction is used of early generation helicopter such as Bell 47. Trusses are welded together to form the fuselage.

High strength to weight ratio, Can be repaired at field level

Advantages of Tubular construction

High manufacturing cost, Difficult to hold dimensions to a close tolerance

Disadvantages of Tubular construction

Four longerons

Normally ran the length of the fuselage, taking most of the compressive and tensile loads and kept apart by cross members.

N, X, or W

Cross tubes arrangement

Longerons and cross tubes

Forms the primary structure of a tubular construction

Stressed skin construction

Uses mainly aluminium alloys in its construction and can be either monocoque or semi-monocoque.

Semi-monocoque construction

Consists of a framework of vertical and horizontal members covered with a metal skin.

Bulkheads or formers

Vertical members in a semi-monocoque structure that provide the shape of the fuselage.

Longerons

Heavy longitudinal members that provide the primary strength in a semi-monocoque structure.

Fuselage

Includes the crew and cabin area, windshield, windows, crew and passenger doors, pylon and engine cowlings, and the landing gear.

Tail boom

Includes the baggage compartment, elevator, driveshaft and gearbox covers, vertical fin and tail skid.

Monocoque construction

Involves the construction of a metal or composite material tube or cone without internal structural members where the stressed skin carries the principle stress imposed upon the structure.

Bonded construction

Involves structure whose parts are joined together by chemical methods rather than mechanical, utilizing fibreglass, honeycomb, and other composite materials by the use of adhesives, heat, and pressure.

Engine attachment

Carry the thrust loads in a fixed-wing aircraft structure.

Wing attachment

Carry the lift loads in a fixed-wing aircraft structure.

Helicopter fuselage

Carries both the lift and thrust forces at the same point because the main rotor acts as both the wing and propeller.

Tail rotor

Provides both directional and anti-torque while also producing vibration.

Vertical fin

Takes some of the side load in flight.

AS350/355 fuselage

Uses a combination of various materials and is a semi-monocoque construction consisting of aluminum and fiberglass materials using thermosetting type of resins.

Body structure

The main structural member of the fuselage that carries lift, thrust, and landing loads, and supports all other members either directly or indirectly.

Bottom structure

Attached to the front of the body box structure and made of two cantilevered beams that carry the weight of the cabin and transmit it to the box.

Cabin section

Made almost entirely of synthetic materials such as polycarbonate reinforced with glass fibre, consisting of sub-assemblies like the cabin roof, nose, and vertical members.