Fiberglass Blade Construction Quiz

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Questions and Answers

What is the main load-carrying member of a fiberglass blade?

Metal Spar (correct)

Fiberglass Cloth

Fiberglass Spar (correct)

Foam Core

What material is used for the skins of a typical fiberglass blade?

Roving

Fiberglass Cloth (correct)

Foam Core

Epoxy Resin

What is typically used for the fairing or pockets of a fiberglass blade?

Stainless Steel

Fiberglass Covered

Aluminum Ribs

Both A and B (correct)

What material protects the leading edge of a fiberglass blade?

Stainless Steel Strip Signup and view all the answers

What is the purpose of the steel socket threaded to the blade spar shank?

To attach the blade to the rotor head Signup and view all the answers

What is the purpose of the internal grounding strips bonded to the blade?

To protect the blade from static electricity Signup and view all the answers

What is the blade planform?

The shape of the blade when viewed from above Signup and view all the answers

What are the two types of blade planforms?

Parallel and Tapered Signup and view all the answers

What is the purpose of mass balance weights?

To guarantee that the blade is balanced chordwise. Signup and view all the answers

What is the main reason manufacturers prefer uniform planform blades?

They are easier to manufacture due to the use of consistent parts. Signup and view all the answers

What is a disadvantage of uniform planform blades in terms of lift distribution?

Uniform planform blades produce more lift toward the tip. Signup and view all the answers

What is the primary reason why fewer manufacturers use tapered planform blades?

Tapered planform blades are more difficult to manufacture due to varying parts. Signup and view all the answers

What is the purpose of negative twist in rotor blades?

To create a more uniform lift distribution along the blade span. Signup and view all the answers

What is the main purpose of the blade root?

To attach the blade to the rotor head and withstand centrifugal forces. Signup and view all the answers

Why is the blade skin susceptible to damage?

It is made of thin fiberglass or aluminum. Signup and view all the answers

What are the two main types of construction for main rotor blades?

Single-pocket and multiple-pocket Signup and view all the answers

Which design feature is used in rotor blades to compensate for the uneven lift distribution caused by the tip moving faster than the root?

Negative twist Signup and view all the answers

Which of these options are correct about the spar of a rotor blade? (Select all that apply)

It is often made of aluminum, steel, or fiberglass. Signup and view all the answers

Where are doublers located on a rotor blade?

At the root end of the blade. Signup and view all the answers

What is the purpose of the chord line on a rotor blade?

To serve as a reference for angular measurements. Signup and view all the answers

Why are defects paralleling the span line of a rotor blade often considered less serious than chordwise damage?

Stress lines move parallel to the span line, minimizing disruption to the blade's structure. Signup and view all the answers

Which of the following best describes the top of a helicopter rotor blade?

The low-pressure side of the blade, typically painted olive drab, flat grey, or flat black. Signup and view all the answers

What is the most accurate definition of the chord of a rotor blade?

The width of the blade at its widest point. Signup and view all the answers

Which of the following is NOT a common consequence of chordwise damage on a rotor blade?

Interference with the smooth flow of air across the blade surface. Signup and view all the answers

Which of the following accurately describes the purpose of doublers on rotor blades?

To reinforce the blade and provide additional strength at the root end. Signup and view all the answers

What is the primary reason for ensuring all rotating blades track on the same level or plane of rotation?

To reduce vibration and maintain flight stability. Signup and view all the answers

What happens when blades fail to track correctly?

All of the above. Signup and view all the answers

Where are tracking weights typically located on a rotor blade?

Near the feathering axis at the blade tips. Signup and view all the answers

What is the primary function of trim tabs on a rotor blade?

To fine-tune the blade's angle of attack to achieve proper tracking. Signup and view all the answers

How do trim tabs influence the position of a rotor blade in its plane of rotation?

By creating a small aerodynamic force on the blade, shifting its trajectory up or down. Signup and view all the answers

How are tracking weights used to adjust the blade's position during repair?

By shifting the position of existing weights along the blade. Signup and view all the answers

What is the primary advantage of using trim tabs over tracking weights for blade tracking?

Trim tabs are cheaper to manufacture and install than tracking weights, making them a more cost-effective option. Signup and view all the answers

What happens to the center of gravity of a rotor blade when weight is subtracted from it?

It moves inward, towards the feathering axis. Signup and view all the answers

What material covers the exterior surface of certain rotor blades?

Resin impregnated fiberglass cloth Signup and view all the answers

What is an advantage of wooden rotor blades?

Abrasion protection at the leading edge Signup and view all the answers

What is a disadvantage associated with wooden rotor blades?

Effects of moisture on the blade Signup and view all the answers

What feature distinguishes metal rotor blades from wooden ones?

Can be replaced individually without matching Signup and view all the answers

What type of construction is common to all rotor blades?

Bonded type construction Signup and view all the answers

Which component is typically used in the leading edge of a metal rotor blade?

Aluminum pockets Signup and view all the answers

What is a characteristic of the hollow, extruded aluminum spar in metal rotor blades?

Forms the leading edge Signup and view all the answers

What is a common feature on the leading edge of metal rotor blades to prevent wear?

Stainless steel abrasion strip Signup and view all the answers

Study Notes

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

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Description

Test your knowledge on the construction and materials used in fiberglass blades, focusing on their key components. This quiz covers everything from load-carrying members to the various design features of rotor blades. Perfect for students and professionals in aerospace engineering.