Fiberglass Blade Construction Quiz

Rotary Wing Aerodynamics

• AVIA-1035 course
• Course material is about the specifics of rotor blades in helicopters.

Rotor Blades

• Rotor blade design varies significantly depending on the manufacturer, although every manufacturer aims to create the most efficient and economical lifting device.
• Specific helicopter designs influence rotor blade design and construction.

Rotor Blade Design

• Rotor blades commonly feature symmetrical airfoils.

• For stable aerodynamic characteristics, the center of gravity, center of pressure, and the blade-feathering axis must align at the same point along the blade.

• This alignment aids in blade stability during changes in pitch.

• Asymmetrical airfoils are becoming increasingly popular, capable of producing greater lift than symmetrical airfoils with similar dimensions.

• Stability is achieved using a 3° upward angle along the trailing edge section.

• This design approach prevents variations in the center of pressure during changes in the angle of attack.

Rotor Blade Materials

• Common materials include aluminum, steel, brass, and fiberglass.
• Early rotor blades were often made of wood, some of which are still used today.
• Metal followed by composite utilizing several materials then emerged as the preferred construction.

Wooden Rotor Blades

• First generation rotor blades were typically laminated using wood.
• Common wood types include birch, spruce, pine, and balsa.
• Wood combinations were used to improve the aerodynamic shape and structural strength.
• A steel core was positioned within the wooden laminate near the blade's leading edge.
• Fiberglass cloth coated with resin was used as the exterior surface.

Rotor Blades - Protection of Outboard Portions

• Approximately two-thirds of the blade's outboard leading edge is shielded by a stainless steel cap.
• This protection helps prevent abrasion.
• Many rotor blades are in matched pairs; replacing one blade of a pair usually isn't recommended.
• Moisture effects are a potential drawback, but this can be addressed by a short run-up of the helicopter.

Rotor Blades - Metal

• Metal rotor blades (particularly aluminum) have been employed for over 40 years.
• The construction of metal blades varies significantly due to the complexity of manufacturing processes and associated costs.
• Many metal blades feature a hollow extruded aluminum spar that forms the blade's leading edge.
• The use of metal blades is associated with higher quality control processes during construction.

Rotor Blades - Metal (Changes and Maintenance)

• Single blades can be swapped.
• Streamlining is achieved by bonding aluminum pockets to the trailing edge of the spar assembly.
• The blade tip often features an aluminum cap attached to the spar and tip pocket with screws.
• Similar to other types of metal components, metal helicopter blades have a finite useful life.
• Metal rotor blades are subject to stresses in flight and have a limited life expectancy.

Rotor Blades - Composite

• Composite rotor blades (often fiberglass) are composed of a fiberglass blade, with a fiberglass spar.
• Fiberglass blades utilize procured roving spars.
• The composite material is soaked in epoxy resin and wound around a foam core, and is then covered by fiberglass cloth.
• Root reinforcement plates are often added to fiberglass blades.
• Trailing edge foam fillers are part of the blade assembly.
• Aluminum ribs and aluminum foil honeycomb are incorporated into the blade's construction.
• Fiberglass composite blades are protected by stainless steel strips to shield the leading edges from damage.
• Manufacturers typically add balancing weights or counteracting weights at the blade tips to ensure stability.

Rotor Blades - Nomenclature

• Planform: The appearance of the rotor blade viewed from above; this shape can be uniform (parallel) or tapered.
• Uniform planforms are favored for their ease of production.

Rotor Blades - Additional Protections

• Rubber erosion strips are added to the lower surface of blades to act as a shield.
• A steel socket attached to the spar of the blade contributes to securing the blade to its head.
• Blades often have stainless steel tip caps attached with screws to the blade's spar and tip pocket.
• Internal grounding strips are bonded for transference of statically induced electricity.

Rotor Blades - Rotor Stations

• Station zero is invariably situated at the helicopter's rotor mast; numbered station designations move outwards towards the blade's tip.

Blade Construction - Single Pocket

• The "single pocket" or "single fairing" design features a single, complete skin encompassing both the top and bottom of the blade.
•  Each skin extends beyond and behind the spar.
• The construction design is comparatively simplistic and practical because of the minimum need for positioning and securing pockets or fairings during the bonding phase.

Blade Construction - Multiple Pockets/Fairings

• Many large rotor blades are designed using the "multiple pockets" or "multiple fairings" method.
•  The construction is more complex than the single pocket design.
• The distinctive design feature is the modular arrangement of pockets and fairings in the structure of the blade behind the spar.
• The significant advantage of this design is its modularity, allowing only the damaged component to be substituted without having to replace the entire blade.
• This modular concept lends inherent flexibility and thus, reduces vibration.

Blade Construction - Internal Structures

• Rotor blades commonly feature internal structural elements such as ribs, I-beams, spanwise channels, and aluminum honeycomb foil to enhance support of the blade skin.

Blade Construction - Bonding

• Bonding is a composite material bonding strategy.
•  Bonding is a process that connects two or more components using adhesive compounds to produce a seamless joint.
• A primary advantage of bonding is the minimization in the use of bolts, rivets, and screws.
• The design technique is also used to avoid generating holes, thereby minimizing stress concentrations.
• One notable exception being at the inboard and outboard assembly points of the blade.

Blade Construction - Blade Damage Prevention

• Many substances, such as paint thinners or cleaning solvents, can negatively affect the integrity of bonds.

Blade - Balance

• The process of balancing helicopter blades involves using weights to align the blade to prevent deviation from a predetermined flight path or predetermined angle of rotation.
• Three different forms of balancing weights can be incorporated into the design: chordwise, spanwise and tracking.
• The application of weights is most frequently done during the construction process.

Blade - Blade Movement

• Adding or subtracting spanwise weights can adjust the center of gravity (CG) towards or away from the blade's tip.

Blade - Design Standards

• For optimal operation and to decrease the likelihood of structural damage, all rotor blades are expected to track at a similar level around the plane of rotation.
• This alignment strategy aims to reduce the impact of vibrations on the helicopter's components.
•  Vibration and tracking performance have a direct correlation with performance and reduced operational and mechanical strain.

Blade - Preservation & Storage

• Damaged blades should be decommissioned and disposed of.
• Damage should be addressed and any holes in the blades should be taped to prevent damage from humidity or environmental contaminants.
• Cleaning using a soap and water mixture is crucial to prevent the accumulation of environmental contaminants or debris.
• Coating with corrosion preventative is also required to prevent corrosion associated with environmental contaminants.

Rotor Blades - Tip and root sections

• The blade tip is the outermost section of the blade, furthest from the center of rotation, and operating at the highest speed.
• The blade tip cap facilitates attaching weight as needed for balancing.
• The blade root is the section nearest the center of rotation.
• The root is heavier and thicker to withstand high centrifugal forces.

Rotor Blades - Leading Edge

• The leading edge is the section that initially encounters the airflow, with the leading edge typically being thicker in comparison to the trailing edge.
• This edge is typically shielded by abrasion-resistant coverings to prevent damage from exterior environmental contaminants or debris.

Rotor Blades - Trailing Edge

• The trailing edge trails the leading edge and is usually thinner compared to the leading edge.
• The trailing edge is typically reinforced to resist damage, particularly when the blade is operating at ground level,.

Rotor Blades - Chord and Span Line

• The blade chord is the width of the blade measured at its widest point.
• The chord line is the imaginary line extending from the blade's leading edge to the trailing edge and perpendicular to the span line.
• The chord line and associated information are used as references in relation to measurements regarding angles or degrees.

Rotor Blades - Spar

• The spar forms the main structural support.
• Common materials include aluminum, steel, or fiberglass.
• The spar invariably extends along the span line, and it is often constructed in a D-shape to form the blade's leading edge.
• Spar shape varies based on the blade's material.

Rotor Blades - Trim Tabs

• Trim tabs can be used to modify the rotor's alignment for superior operation.

Rotor Blades - Tail Rotor

• These are solely focused on directional control.
• Tail rotor construction is similar to main rotor construction.
• Materials are often aluminum.

Blade Construction - Materials

• Composite blades use fiberglass or glass reinforced material(s), the spars are made of metal (e.g., titanium).

Additional Concepts/Information

• Modern Rotor Blades