Rotor Blade Materials and Design Quiz

Rotary Wing Aerodynamics

• AVIA-1035 course
• FANSHAWE

Rotor Blades

• Design and construction of rotor blades differs between manufacturers, but the goal is always to create an efficient and cost-effective lifting device.
• Helicopter design specifications influence the design of rotor blades.

Rotor Blades (Continued)

• Rotor blades are symmetrical airfoils to produce stable aerodynamic pitching.
• Aerodynamic stability is achieved when the center of gravity, center of pressure, and blade feathering axis are aligned.
• The forces acting on the blade remain relatively consistent, creating stability even as the blade pitch changes.

Asymmetrical Airfoils

• Asymmetrical airfoils, while less common, are becoming more popularly used.
• An asymmetrical airfoil blade develops greater lift compared to a symmetrical blade of similar dimensions.
• The asymmetrical design includes a 3° upward angle on the trailing edge.
• This design helps prevent excessive center-of-pressure shift when the angle of attack changes.

Rotor Blade Materials

• Common materials used for rotor blade construction include aluminum, steel, brass, and fiberglass.
• Early rotor blades were often made of wood, a material still used in some instances.
• Metal blades followed, then composite blades became more prevalent. Composite blades use multiple materials to achieve greater efficiency.

Wooden Rotor Blades

• Early blades were often made of laminated wood, using combinations of birch, spruce, pine, and balsa.
• A steel core was placed in the wood laminations near the leading edge.
• The outer surface then gets coated with resin-impregnated fiberglass cloth.
• Often the blades are matched in pairs due to variations in the wood.

Wood Blade Details

• Approximately 2/3 of the outboard portion of the leading edge is often protected by a stainless steel cap, primarily for abrasion resistance.
• The inherent nature of the wood sometimes mandates using matched pairs of blades.
• Moisture can impact the blade negatively although a short helicopter run-up will often correct this issue.

Metal Rotor Blades (Aluminum)

• Metal blades have been in use for over 40 years.
• Variations between manufacturers' constructions are significant.
• A typical metal blade features a hollow, extruded aluminum spar, which largely contributes to the leading edge shape.
• Advantages include quality control during construction.

Metal Blades (Continued)

• Individual metal blades can be replaced without relying on matched sets.
• Aluminum pockets bonded to the trailing section of assembly contribute to streamlined construction.
• Aluminum tip cap is bolted to the spar and tip pocket.
• A blade life limitation is typical for metal blades.

Rotor Blades (Figure 3-6)

• Diagram illustrating the features of rotor blades, including pocket, skin, spar, tip fairing, trailing edge strip, and side plate.

Metal Rotor Blade Details

• A steel cuff bolted to the rotor head end of the spar is common for mounting to the rotor head.
• A stainless steel abrasion strip is often bonded to the blade's leading edge.
• A bonded construction method is common to all blades; this uses a heat and pressure process.

Fiberglass/Composite Rotor Blades

• Either fiberglass or metal spars are the primary load-carrying components.
• The spar is often procured as roving.
• Rovings are thin glass material strips, saturated with epoxy resin and wound around a foam core.
• The blade's skins are created using fiberglass cloth.

Composite Blade Details

• Root reinforcement plates are added to the construction for strength.
• A trailing edge foam filler is added.
• Fairings or pockets are created from fiberglass material bonded over aluminum ribs or a honeycomb.
• A stainless steel strip covers the leading edge to protect against damage.

Rotor Blades (Figure 3-7)

• Diagram showcasing a composite blade with an aluminum hollow spar, composite blade root, and composite rovings.

Rotor Blades (Figure 3-8)

• Diagram illustrating the difference between parallel and tapered planforms.

Rotor Blades (Figure 3-10)

• Diagram providing a depiction of the helicopter blade tip showing the provisions for attaching balance weights at the tip.

Leading Rotor Blade Edge

• The leading edge is the portion of the blade that encounters the incoming air first.
• To function efficiently, leading edges need to be thicker than the trailing edge.
• Leading edges feature a hard, abrasion-resistant cap or coating to withstand erosion from dust or debris.

Rotor Blade Trailing Edges

• The part of the blade that trails or follows behind the leading edge is the trailing edge.
• The trailing edge, often the thinnest section of the rotor blade, is strengthened to prevent damage, which is frequently a result of ground handling.

Span and Span Line (Figure 3-13)

• The span of a blade refers to its length, from root to tip.
• The span line is an imaginary reference line running parallel with the leading edge, from the blade root to the tip.
• Span lines are helpful in designating or specifying repair sections of damage.

Rotor Blades (Figure 3-14)

• Diagram illustates the blade chord.

Rotor Blades (SPAR)

• The spar is the main structural support component of a rotor blade.
• Typically made from aluminum, steel, or fiberglass.
• Spars follow the span line along the blade length.
• Spar shapes vary, depending on the blade's materials and how they fit into the airfoil.

Rotor Blades (Figure 3-15)

• Diagram illustrating the different rotor blade component features, including the various spar configurations, and balancing weights.

Rotor Blades (Doublers)

• Flat, plate-like reinforcements bonded to both sides of the root end, to strengthen the blade where it connects to the rotor head.
• Not all rotor blades utilize doublers; some spars are designed with sufficient thickness to meet these strength requirements.

Rotor Blades (Top)

• The top side of the blade, facing away from the aircraft when viewed from above.

Rotor Blades (Bottom)

• The bottom side of the blade; also called the high-pressure side.
• Typically painted a matte black to reduce glare or reflection in the aircraft interior.

Blade Stations (Figure 3-16)

• Diagram describing the different blade stations.

Single Pocket or Fairing

• Usually consists of a continuous skin that follows the span and chord of the blade.
• It is positioned behind the spar; this is simple and easy to manufacture.

Blade Construction (Multiple Pockets)

• Most large rotor blades use a multiple pocket design; these are often more expensive.
• The internal pocket structure is replaceable if damaged, which extends the useful life of the blade.

Internal Blade Components

• Additional components, such as ribs, I-beams, spanwise channels, and aluminum honeycomb foil help strengthen blade skin.

Blade Construction (Bonds and Bonding)

• Bonding is a process that joins multiple parts together using adhesive.
• It minimizes the need for holes in the blade, reducing weakening to the blade components.

Blade Construction (Bonds and Bonding - Continued).

• However, bonding materials can degrade in the presence of certain solvents, such as paint thinner or other cleaning solvents.

Blade Construction (Figure 3-19)

• Diagram depicting the faying surface in composite blade construction.

Blade Balance

• Three balance weight types used: mass, chordwise, and spanwise weights are used to ensure balance.
• Mass balance weights are often installed during blade manufacture.
• Chordwise balance is generally about 25% of the blade chord length. Weight and placement vary by manufacturer.

Blade Construction (Figure 3-20)

• Diagram illustrating the position of the different balance weights.

Blade Construction (Figure 3-21)

• Diagram illustrating the various types of mass balance bars.

Blade Construction (Movement of weights is not allowed)

• Movement of weights not usually allowed on a blade, but when allowed should cause a compensating shift in weight.
• Spanwise balance weighs will move the center of gravity.
• This shift in location must be considered when making adjustments to the blade.

Blade Construction (Blade Tracking)

• Blades must be assembled and balanced on the same plane of rotation.
• Imbalance leads to decreased performance and damage to the aircraft.

Blade Construction (Trim Tabs)

• A device to adjust the blade to achieve the correct plane of operation.
• Less expensive than tracking weights.

Blade Construction (Figure 3-24)

• Diagram describing the method of adjusting for blade tracking by using offset trim tabs.
• Adjust the trim tabs till all the rotor blades are on the same plane of rotation.

Tail Rotor Construction

• Used for directional control only.
• Made from metal (typically aluminum) or fiberglass.
• Their assembly is similar to main rotor blades, depending on the material used.

Blade Construction (Blade 3-25)

• Illustration of typical fiberglass tail blades.
• Spars are frequently titanium.

Metal Blades

• The blade skins are typically formed around and bonded to the spar components.

Fiberglass Blades

• The blade skins are typically formed around and bonded to H-shaped titanium spars.

Blade Balance (Spanwise)

• Blade balance is often adjusted with washers.
• If the blade is unbalanced, adding or subtracting washers on the blade tips, or at blade attachments, are used.

Blade Balance (Other models used chordwise)

This involves adding weights to specific areas behind the spanwise balance screws.

Blade Construction (Trammeling)

• Fully articulated tail rotor systems require a trammel procedure before being balanced.
• The process involves aligning tail rotors evenly with a 2-degree lead angle.

Rotor Blade Preservation and Storage

• Non-repairable or damaged blades must be condemned and disposed of properly.
• Tape or cover all holes in the rotor blade to prevent moisture damage.
• Clean the blades by thoroughly removing foreign debris with a mild soap and water solution.

Rotor Blade Preservation and Storage (Additional Details)

• Protect eroded or rust-prone exterior surfaces with corrosion preventive coatings.
• Protect vulnerable areas such as bolts, bushings, and other exposed metal surfaces with corrosion preventive coatings.
• Secure the rotor blades within a shock-mounted support during packaging.
• Seure the packaging lid.

Rotor Blade Preservation and Storage (Records)

• Ensure relevant manufacturer's documents (such as CARs), relevant materials, and other helpful records are stored with the blade, typically within a waterproof bag and inserted into the container record tube.
• Remove previous markings related to prior shipments.

Rotor Blade Preservation and Storage (Information on container)

• Stencil the blade's National Stock Number (NSN) model, and serial number onto the container's exterior surface, for easy identification.

Test your knowledge about the materials and design features of rotor blades. This quiz covers various aspects including types, bonding, and protective elements associated with fiberglass, metal, and wooden rotor blades. Challenge yourself with questions about construction, advantages, and characteristics of each type.