Rotor Blade Construction Quiz

Rotary Wing Aerodynamics

• AVIA-1035 course
• Focuses on rotor blade aerodynamics

Rotor Blades

• Design and construction vary between manufacturers, but all aim for efficiency and cost-effectiveness.
• Helicopter design dictates specific requirements for rotor blades, influencing their design.

Rotor Blade Design

• Most blades are symmetrical airfoils to create a stable aerodynamic pitch.
• Stability is ensured when the center of gravity, center of pressure, and feathering axis are aligned.
• The constant alignment of these forces across blade pitch changes yields flight stability.

Asymmetrical Airfoils

• Asymmetrical airfoils are becoming more common
• This design is capable of producing greater lift compared to symmetrical airfoils.
• Aerodynamic stability achieved with a 3° upward angle on the trailing edge.
• This design counteracts excessive center of pressure shifts

Rotor Blade Materials

• Common materials include aluminum, steel, brass, and fiberglass.
• Initial blades often used wood, still used in some applications.
• Metal blades were used next, followed by composite designs incorporating multiple materials.
• Composite blades are the most recent design.

Wooden Rotor Blades

• First production blades employed laminated wood from various species (birch, spruce, pine, balsa).
• A steel core was placed within the wood laminations near the leading edge for reinforcement.
• A resin-impregnated fiberglass cloth covers the exterior surfaces.

Wooden Blade Details

• Two-thirds of the outboard leading edge covered with stainless steel caps for abrasion prevention.
• Blade pairs are often a matching set for construction consistency; a single blade is not easily substituted.
• Moisture affects wood blades; this can be mitigated by a brief helicopter run-up.

Metal Rotor Blades (Aluminum)

• Have been used for over 40 years.
• Construction varies considerably among manufacturers and over time.
• Typical blades use an extruded hollow aluminum spar forming the leading edge.
• Quality control during construction is an advantage.

Metal Blades - Design Details

• Single blades can be replaced without a matched set.
• Aluminum pockets bonded to the trailing edge help with streamlining.
• An aluminum tip cap is fastened using screws, enhancing assembly efficiency.
• Metal blades have a limited lifespan due to flight stresses.

Rotor Blades - Diagrams

• Diagrams (Figures 3-6, 3-7, 3-8, 3-9, 3-10, 3-11, 3-12, 3-13, 3-14, 3-15, 3-16, 3-17. 3-18, 3-19, 3-20, 3-21, 3-22, 3-23, and 3-24) depict blade components and construction features.

Fiberglass/Composite Rotor Blades

• Fiberglass is a primary material for construction.
• The spar can be made of fiberglass or metal.
• Roving material impregnated with epoxy resin is wound around a foam core.
• Fiberglass cloth makes up the blade skins, providing rigidity and protection.

Rotor/Blade Reinforcement/Additions

• Root reinforcement plates are added to fiberglass blades.
• Trail edge foam filler and additional roving strips to the trailing edge reinforce stability.
• Fiber coverings that add fairing and streamline the blade.
• The leading edge of the fiberglass blade is protected by a stainless steel strip.
• Balancing weights are added to the blade tip during manufacturing.

Rotor Blade - Aluminum Hollow Spar Design

• Featured in Figure 3-7, highlighting structural details.

Rotor Blade - Composite Roving Design

• Depicted in Figure 3-7, showing the blade root details.

Rotor Blade - Other Details

• Additional protection with rubber erosion strips bonded to the underside of the blade.
• Steel socket for attaching the blade to the rotor head.
• Stainless steel tip caps fastened to the spar and tip pocket.
• Internal grounding strips for static electricity transfer to the aircraft.

Blade Nomenclature

• The planform is the blade shape viewed from above.
• Uniform planforms are common for easier construction.
• Tapered planforms give better lift throughout the blade.

Rotor Blade - Span and Span Line

• Span is the distance from root to tip, a crucial measurement.
• Span line is an imaginary line that runs parallel to the blade from the root to the tip.
• Damages are often reported relative to the location on the span line.

Rotor Blade Defects

• Defects parallel to the span line are less critical; the chordwise stress affects the entire blade.

Chord and Chord Line

• Blade width measured at the widest point, the chord.
• Chord line an imaginary line from leading to trailing edge, perpendicular to the span line.
• Used as a reference line for angular measurement.

Spar Construction

• Spar, the primary support structure, is often made of aluminum, steel or fiberglass.
• Usually D-shaped, forming the airfoil leading edge.
• Shape varies based on material and blade design fit.

Blade Construction - Other Components

• Internal structural components include ribs, I-beams, spanwise channels, and aluminum honeycomb foil for strength.

Bonding

• Bonding methods reduce hardware needs, which usually weaken the structural bond.
• Bonding surfaces called faying surfaces.
• This process is not susceptible to chemical damage or many cleaning solvents.

Blade Construction - Single Pocket

• Uses a single, continuous skin for top and bottom construction
• Skin wraps across the entire span and chord from behind the spar.
• Simple design minimizes the number of joining points (pockets) or fairings during bonding.

Blade Construction - Multiple Pocket

• Most large-rotor blades use multiple pockets or fairings behind the spar
• Repairs only require replacing pockets or fairings instead of the entire blade, making repairs more efficient and cost-effective.

Blade Balance

• Three types of balancing weights (mass chordwise, spanwise, and tracking) are used to ensure proper balance and distribution.
• Mass balance bars are bonded to the leading edge of the blade.
• Balance ensures that the center of gravity is about 25% of the chord.
• Manufacturer-specific methods, shapes, and locations for balance vary.

Blade Movement Restriction

• Usually, helicopter blade weights are fixed and not easily repositioned or adjusted.
• Changing weights affect the center of gravity.
• Spanwise weights affect the center of gravity to move outward or inward.

Blade Construction & Efficiency

• Rotating blades should track on the same level plane for efficiency and vibration-free operation.
• Tracking deviations cause vibrations leading to damage and reduced comfort.
• Air turbulence caused by blade rotation also reduces performance.

Blade Construction - Trim Tabs

• Trim tabs are used to fine-tune the blade's position in the plane of rotation.
• Placement is typically at the blade tip for the necessary aerodynamic reaction.

Tail Rotor Blades

• Tail rotor blades are used for directional control in helicopters.
• Metal blades are built similarly to the main rotor blades with aluminum extrusions, hollow extrusions, and sheet channels.
• Fiberglass tail rotor blades use fiberglass sheets and solid titanium spars.

Blade Preservation and Storage

• Maintenance instructions for rotor blade handling, storage, inspections, and documentation.
• Condemn blades with nonrepairable damage.
• Tape blade holes and inspect for damage.
• Clean the blade external surfaces.
• Protect surface areas from erosion or corrosion.
• Secure blades and containers after cleaning and repairs.
• Document critical information such as NSN, model, and serial number.