Helicopter Blade Mechanics Quiz

Rotor Wing Aerodynamics

• Presented in a course AVIA-1035 at Fanshawe college.

Rotor Blades

• Design and construction vary by manufacturer, but all aim for efficiency and cost-effectiveness.
• Helicopter design specifics dictate blade requirements, influencing design and construction.
• Most blades are symmetrical airfoils ensuring stable aerodynamic pitching.
• Aerodynamic stability ensured when center of gravity, center of pressure, and blade-feathering axis align.
• This consistent alignment maintains stability as the blade's pitch changes during flight.

Asymmetrical Airfoils

• Less common, gaining popularity; producing greater lift over a comparable symmetric airfoil.
• Increased lift achieved through a 3° upward angle on the trailing edge section.
• Prevents excessive center-of-pressure shift during changes in the rotor blade's angle of attack.

Rotor Blade Materials

• Common materials used include aluminum, steel, brass, and fiberglass.
• Early rotor blades were made of wood, a common material still used in some contemporary models.
• Following wood, metal and composite blades became prevalent. Metal blades have a longer history, and composite blades are contemporary.

Wooden Rotor Blades

• First production used laminated wood (birch, spruce, pine, balsa).
• A steel core was integrated near the blade's leading edge.
• Exterior surfaces were coated with resin-impregnated fiberglass cloth for protection.
• Typically used in matched pairs, due to wood variations.
• Can be vulnerable to moisture damage and thus some short run-ups may be needed.

Metal (Aluminum) Rotor Blades

• Been in use for over 40 years.
• Construction varies greatly due to manufacturing expenses and the variety of manufacturers.
• Usually a hollow extrusion of aluminum serves as the spar in the blade forming the leading edge.
• Quality control during construction is a major advantage.
• Blades can be changed independently of other blades in a set.

Metal Rotor Blades (Continued)

• Aluminum pockets bonded to the trailing edge enhance streamlining.
• Aluminum tip cap secures the blade tip.
• Similar to other metal components, blade life is determined by stresses and wear during flight.

Composite Rotor Blades

• The load-carrying component is made of either fiberglass or metal.
• A typical fiberglass spar relies on procured roving spar (glass strands).
• Roving is imbued with epoxy resin and wound around a foam core.
• Outer layers are fiberglass cloth.
• Root reinforcement plates are added for structural integrity.

Composite Rotor Blades (continued)

• Trailing edge frequently utilizes further roving strips
• The blade's skin might be covered with a fiberglass fairing/pocket (single or multiple), or aluminum honeycomb material for insulation and structural support.

Rotor Blade - Additional Components

• Leading edge is often reinforced by a stainless steel abrasion strip.
• Steel cuff attaches rotor blade to the head.
• Internal grounding strips conduct static electricity away to prevent damage to the helicopter's electronics.

Rotor Blade Nomenclature: Planform

• The planform of a rotor blade is its shape as seen from above.
• Uniform or tapered planforms are common shapes, the latter being more challenging to manufacture.
• Uniform shapes are often favored due to the relatively simple manufacturing process.

Rotor Blade - Figure 3-8 (Uniform/Tapered Planform)

• Diagrammatic representations show uniform and tapered planforms.

Rotor Blade - Figure 3-10

• Represents blade tip with balance weights and blade tracking mechanisms

Rotor Blade Leading Edge

• The blade portion encountering air first, also commonly referred to as the front edge.
• Must be shaped thicker than the trailing edge for proper aerodynamic function.
• Often reinforced with hard abrasion-resistant material.

Rotor Blade Trailing Edge

• Part of the blade following the leading edge.
• Usually thinner than the leading edge.

Rotor Blade Span and Span Line

• A span of a rotor blade is measured from root to tip.
• A span line is an imaginary line running parallel to the leading edge, from root to tip.
• Crucial for damage location and classification during repair.

Rotor Blade Chord and Chord Line

• A chord of a rotor blade is its width at its widest point.
• The chord line is an imaginary line running between leading and trailing edges, and perpendicular to the span line.
• Often used as a reference line for angular measurement.

Rotor Blade Spar

• The primary support component of a rotor blade.
• Typically made of aluminum, steel, or fiberglass, extending along the span line.
• Often D-shaped to form the leading edge of the airfoil.

Rotor Blade Doublers

• Typically flat plates bonded on the root end of certain rotor blades to provide added strength, particularly against centrifugal forces.

Rotor Blade - Top

• The underside of the blade facing away from the ground when situated on the rotor.

Rotor Blade - Bottom

• The counterpart of the top, seen from below during ground viewing.
• Often painted a dull black to reduce glare inside the crew compartment.

Blade Stations

• The rotor blade sections are numbered, starting from the mast (station 0) and progressing towards the tip, increasing in number.

Single Pocket or Fairing Blade Construction

• The skin is a cohesive single piece from the top to bottom, covering the entire span and chord, which is also located behind the spar.
• Requires fewer parts than multiple-pocket constructions.

Multiple Pockets or Fairings Blade Construction

• Large rotor blades often characterized by multiple pockets or fairings behind the spar.
• This structure allows only the pocket/fairing to be replaced in the event of damage, making it potentially cost-effective.

Blade Balance

• Three main types of balancing weights (chordwise, spanwise, and tracking) are used to balance blades, generally fixed into position on the leading edge during manufacturing process.

Blade Trammeling

• Necessary for fully articulated tail rotor systems before balancing.
• Involves aligning blades to an equal distance, with a 2° lead angle, before balancing.

Rotor Blade Preservation and Storage

• Maintaining rotor blades involves several steps:
  • Condemning and discarding damaged, non-repairable blades.
  • Repairing/patching/covering holes with protective tape
  • Removal/cleaning of debris from the surface.

Rotor Blade Outboard Preservation and Storage

• Protecting blade outer surfaces from erosion and corrosion through surface coating
• Protecting exposed metal components with a corrosion coating
• Securing blades in shock-mounted supports/containers before storage.

Additional Rotor Blade Information

• Maintaining records to identify the rotor blade.
• Identifying and noting blade damage with respect to the span line.