Composite Blade Construction Quiz

Rotary Wing Aerodynamics

• AVIA-1035 course offered at Fanshawe College.

Rotor Blades

• Design and construction vary between manufacturers, aiming for efficiency.
• Helicopter design dictates specific requirements influencing blade design and construction.
• Blades are typically symmetrical airfoils for stable aerodynamic pitching.
• Stability is achieved when the center of gravity, center of pressure, and blade-feathering axis are aligned.
• This alignment maintains stability as the blade changes pitch.
• Asymmetrical airfoils are becoming more popular, offering greater lift potential.
• Asymmetrical airfoils have a 3° upward angle on the trailing edge for enhanced stability during changing angles of attack.

Rotor Blade Materials

• Common materials include aluminum, steel, brass, and fiberglass.
• Early rotor blades were made of wood, still used in some cases.
• Metal blades followed, then composite blades (latest).
• Composite blades utilise multiple materials.

Wooden Rotor Blades

• First production blades were laminated wood (combinations of birch, spruce, pine, balsa).
• Steel core was positioned within the wood laminations near the blade's leading edge.
• Exterior surface was covered with a resin-impregnated fiberglass cloth.

Rotor Blades - Wood - Additional Information

• Approximately two-thirds of the outboard portion of the leading edge is protected by a stainless steel cap to prevent abrasion.
• Blades are often constructed in matched pairs (due to variations in wood).
• Moisture is a disadvantage and can be mitigated through short helicopter run-ups.

Metal Rotor Blades (Aluminum)

• Been in production for over 40 years.
• Construction varies greatly due to expense and manufacturing methods.
• A typical design has a hollow, extruded aluminum spar forming the leading edge.
• Quality control is a notable advantage during construction.

Metal Rotor Blades - Single Blades Allowed

• Individual blades can be changed without requiring a set.
• Aluminum pockets ensure streamlining along the trailing edge.
• Aluminum tip caps are secured using screws, combining a spar and tip pocket.
• Like other metal components, there's a limited lifespan.

Figure 3-6

• Diagram showing the different parts of a typical metal rotor blade.

Rotor Blades - Metal - Additional

• A steel cuff is bolted to the root end of the spar for blade attachment.
• An abrasion strip made of stainless steel is adhesive bonded to the leading edge.
• A common feature in all blades is bonded construction—a heat and pressure process with advantages.

Fiberglass or Composite Blades

• The main load-carrying member (spar) can be fiberglass or metal.
• A typical fiberglass blade uses a pre-made roving spar, wound with epoxy resin and glass material.
• Fiberglass cloth makes up the blade skins.

Rotor Blades - Composite - Additional Information

• Root reinforcement plates are often added.
• Trailing edge foam filler forms part of the trailing edge (roving strip).
• Fairings (fiberglass-covered bonded aluminum ribs or aluminum foil honeycomb).
• Leading edge fitted with a stainless steel strip protecting it throughout the span.
• Balancing weights are attached to the tip.

Figure 3-7

• Image of a composite blade with an aluminum hollow spar.

Figure 3-7 - Composite Rovings

• Image showing the composite blade root and rovings.

Additional Protection for Blades

• Added rubber erosion strips are bonded to the lower surface of the blade.
• A threaded steel socket attached to the blade spar links it to the rotor head.
• Stainless steel tip caps fastened by screws on the blade spar.
• Internal grounding strips bond to transfer static electricity.

Blade Nomenclature

• The planform describes the blade's shape (top-down view).
• The planform can be uniform or tapered (easier to manufacture).
• Uniform planforms use identical parts to be more efficient.

Figure 3-8

• Diagram of parallel and tapered planforms.

Old Video (of Helicopter Blade Hit)

• (:43) - Length of a video clip.

Uniform Blade Requirements

• Only one stamping die for all ribs is used to reduce cost, one result of a uniform blade.
• Incorporates negative tip twists to create uniform lift across the blade.
• Blade angle remains constant to produce greater lift at the tip.
• Unequal lift causes blade cone or bending.

Tapered Planform Blades

• Create uniform lift across their length.
• Rarely used due to increased manufacturing cost.

Blade Twist

• Blade-element theory applies to rotor blades as well as propellers.
• Rotor blades are usually twisted negatively from the root to tip to distribute lift uniformly.

Blade Skins

• Fiberglass or aluminum layers.
• Thin skin can be damaged easily during handling.
• Mostly constructed from single or multiple pockets .

Blade Root

• The root is the part nearest the center of rotation, attaching to the rotor head.
• Thickened for added resistance to centrifugal forces.

Figure 3-9

• Diagram showing the features of the blade root.

Figure 3-9 - Diagram

• Image depicting the components of the rotor blade root.

Blade Tip Details

• Located furthest from the center of rotation and moves at the fastest speed during operation.
• Blade tip caps have a design that allows for attaching balancing weights.

Figure 3-10

• Diagram illustrating the blade tip features.

Provisions for attaching Balance Weights (Figure 3-10)

• Detailing the locations for attaching balancing weights.

Leading Edge of Blades

• The leading edge is the part that strikes the air first.
• Leading edges are thicker than trailing edges for efficient functioning.
• Blades are coated with an abrasion resistant protective material like a cap to shield from erosion (caused by sand and dust).

Figure 3-11

• Diagram illustrating the leading edge.

Blade Trailing Edge

• The section behind or after the leading edge.
• Thinner and strengthened to withstand ground-handling damage.

Figure 3-12

• Diagram showing the trailing edge of the blade.

Blade Span and Span Line

• Span is the length from blade root to tip.
• The imaginary span line runs parallel to the leading edge, extending from root to tip.
• Blade damage is often described in relation to the span line.

Figure 3-13

• Diagram of a blade with a span line.

Blade Defects along the span line

• Defects that run parallel to the span line are less severe.
• Stress lines don't get disrupted, so these impacts are less damaging.
• Chordwise damage interrupts stress lines.

Chord and Chord Line

• Chord is the width of the blade at its widest point.
• The chord line is an imaginary line extending from the leading edge to the trailing edge, perpendicular to the span line.
• Blade chord line is used as a reference for angular measurements.

Figure 3-14

• Diagram showing the chord of a rotor blade.

Rotor Blade Spar

• The main supporting component of the rotor blade is the spar.
• Spats are constructed from aluminum, steel, or fiberglass.
• Spats extend over the chord line.
• Spats come in various shapes depending on the material and how they integrate with the airfoil.

Figure 3-15

• Diagram showcasing different spar shapes.

Rotor Blade Doublers

• Doublers are flat plates bonded to the root ends of some rotor blades.
• Providing added strength.
• Not all blades need them; many spars provide needed strength.

Blade Top Surface

• The top of the blade, viewed from above the helicopter, is the lower pressure side.
• Usually painted colors like olive drab, grey, or black.

Blade Bottom Surface

• High-pressure side of the blade, facing downward.
• Typically painted a dark, flat black color to reduce glare.

Blade Stations

• The mast is considered station zero.
• Numbers increase as one moves outward to the tip of the blade.

Figure 3-16

• Diagram illustrating blade stations.

Single Pocket or Fairing

• Single-piece top and bottom skins.
• Skins cover the entire span and chord behind the spar.
• A simple one-piece design reducing the number of parts to be bonded.

Blade Construction - Multiple Pockets or Fairings

• Largest rotor blades utilize multiple pockets/fairings.
• The pockets/fairings behind the spar are designed to be replaceable, which may lessen costs.
• This design increases flexibility.

Figure 3-18

• Diagram demonstrating a blade with multiple pockets/fairings.

Blade Internal Structural Components

• Ribs, I-beams, spanwise channels and aluminum honeycomb foil.
• Supporting the blade's skin.

Bonding and Bonds

• Procedure for joining parts using adhesive compounds.
• Minimizes the use of hardware that could weaken the bond.
• Holes should only be drilled at inboard and outboard ends, not in the load-carrying areas.

Blade Construction - Chemical Action

• Bonds can be affected by chemical action (solvents, paint thinners).

Figure 3-19

• Diagram showing the faying surface.

Blade Balance

• Balancing procedure involves using chordwise, spanwise, and tracking weights.
• Placement of weights aligns the blade's center of gravity correctly (the mass and location depend on the manufacturer).

Figure 3-20

• Diagram showing the placements of weights.

Figure 3-21

• Diagram illustrating examples of weights.

Blade Movement Restrictions during Balancing

• Repairers cannot change the weights on most blades.
• Moving weights causes a change in the center of gravity.
• Moving span-wise weights is sometimes permitted, but must be mathematically calculated after weighing.

Blade Construction for Efficiency

• Blades should track on the same level or plane to avoid damage to the helicopter.
• Vibration from misalignment causes damage, reduced comfort and efficiency.

Retaining Blade Track

• Attaching tracking weights in front and behind the feathering axis.
• Allows for movement of blades up or down to match other blades.
• Makes sure all blades follow the same tip path.

Figure 3-23

• Diagram depicting a rotor blade with tracking weights, and the feathering axis.

Blade Construction - Trim Tabs

• Another method for maintaining the same plane of rotation.
• Used typically on tips for maximum speed.
• Sheet metal tabs.

Figure 3-24

• Diagram illustrates a blade with a trim tab.

Blade Construction - Trim Operation

• Bending trim tabs to create a leading edge that rises or lowers.
• Used to adjust the plane of rotations of all blades.

Tail Rotor Blades

• Used for directional control.
• Construction is similar to main rotor blades but with differences in material choice.
• Can be made from aluminum.

Blade Construction - Fiberglass Tail Blades

• Consist of fiberglass sheets bonded to solid titanium spars.

Figure 3-25

• Diagram illustrating the Figure 3-25 construction method.

Metal Blade Construction

• Blades are constructed from shaped metals like aluminum.
• Blade skins are formed around spars.
• Metal blades are usually braced on the inside by honeycomb and ribs.
• Smaller blades may not have these internal structures.

Fiberglass Blade Construction

• Formed around H-shaped titanium spars and supported by aluminum honeycomb.
• Space surrounding the spar is filled with foam plastic.

Blade Balancing - Spanwise Balance

• Some models use washers on the tips, or attaching bolts to balance the spanwise balance.
• Addition or subtraction of washers moves the center of gravity,
• Other models use chordwise adjustment.

Blade Balancing - Additional methods

• Adding weights to the trailing edge of blades, near the cuff end.
• Trammeling aligns tail rotor blades with equal distance at a 2 degree angle.

Rotor Blade Preservation and Storage

• Condemn and dispose of any non-repairable blades.
• Tape holes in blade to prevent moisture and corrosion.
• Remove all external matter using mild soap and water.

Rotor Blade Storage - Additional Considerations

• Place blade records (CARs) into waterproof containers.
• Remove old markings from the containers,
• Marking necessary information on the outside of the containers.

Test your knowledge about fiberglass and composite blade construction with this quiz. Discover the materials, design elements, and balancing techniques used in rotor blade engineering. Perfect for students and professionals interested in aerospace engineering.