Wooden Construction in Aviation History

Questions and Answers

What type of truss construction mainly supports compressive loads?

Monocoque

Warren

Semi-monocoque

Pratt (correct)

Which aircraft is famously known as the Spruce Goose?

De Havilland Mosquito

Hughes H4 Flying Boat (correct)

Boeing 747

Cessna 172

What is a defining characteristic of the Warren truss fuselage construction?

Utilizes only wooden components

Carries compressive and tensile loads (correct)

Only uses vertical struts

Incorporates only flat surfaces

What are the secondary components in the Warren truss structure?

Bulkheads Signup and view all the answers

What construction type replaced wood and fabric in commercial aircraft by the late 1930s?

Aluminium Signup and view all the answers

Which of these is NOT a primary component of the Warren truss structure?

Stringers Signup and view all the answers

What was the main purpose of the piano wire stays in the Pratt truss construction?

To carry tension loads Signup and view all the answers

Which of the following aircraft is known for being made entirely from wood?

De Havilland Tiger Moth Signup and view all the answers

What is the primary function of the leading edge in a truss-type wing construction?

To protect the wing from erosion and impact damage. Signup and view all the answers

Which component helps prevent ribs from being crushed in a truss-type wing?

Compression struts Signup and view all the answers

What characteristic is essential for wood to be classified as 'Aircraft Sitka Spruce' grade?

The specific gravity must be no less than 0.36. Signup and view all the answers

What type of forces does a monocoque construction primarily support?

Both tensile and compressive forces Signup and view all the answers

In semi-monocoque construction, what is the role of stringers?

To enhance the load-bearing capacity of the fuselage skin. Signup and view all the answers

What is the main difference between laminated wood and plywood?

Laminated wood has layers running parallel, while plywood has layers at right angles. Signup and view all the answers

What is the typical maximum acceptable moisture content for wood used in aircraft?

15% +/- 2% Signup and view all the answers

Which property does NOT contribute to the strength of wood?

Color of the wood Signup and view all the answers

Which of the following wood types is considered equivalent to Sitka spruce in the Oceania region?

Queensland maple Signup and view all the answers

What role do drag wires play in a truss-type wing structure?

They oppose drag loads pushing the wing rearwards. Signup and view all the answers

What is a common characteristic of semi-monocoque construction compared to monocoque?

It has a load-carrying internal frame. Signup and view all the answers

What are the properties of wood that enhance its suitability for aircraft construction?

Uniformity, strength, and excellent shock resistance. Signup and view all the answers

What is the maximum hole diameter for which a splayed patch can be used?

15T Signup and view all the answers

How should wood be stored to maintain its quality?

Flat with good air circulation in a dry and ventilated area. Signup and view all the answers

What is the primary reason for using a scarfed patch on plywood skin?

It minimizes changes in skin thickness or rigidity. Signup and view all the answers

What is the first step in fabricating a splayed patch?

Tape a small piece of plywood over the damage. Signup and view all the answers

What is the purpose of placing vinyl plastic or waxed paper over the patch after installation?

To allow the glue to cure without interference. Signup and view all the answers

Which type of patching method is described as simple and economical for most working-type airplanes?

Surface patch Signup and view all the answers

What characterizes summerwood compared to springwood?

Dark in color with small fibres and thick walls Signup and view all the answers

Which type of wood has the most living cells?

Sapwood Signup and view all the answers

What is the primary purpose of glues in aircraft structure?

To create joints that maintain structural integrity Signup and view all the answers

What is an important consideration regarding the slope of grain in aviation-quality wood?

It must not exceed a maximum of 1:15 Signup and view all the answers

Why is it crucial to remove casein glue before applying modern adhesives?

It compromises the curing process of the new glue Signup and view all the answers

What is the pot life of plastic resin glue once mixed?

4 to 5 hours Signup and view all the answers

Which wood glue is prohibited for use in primary structure in Australia due to reliability concerns?

Plastic resin glue Signup and view all the answers

What defines the pressing time in the glue bonding process?

The clamping period during glue curing Signup and view all the answers

What is the main property of resorcinol glue once cured?

High resistance to moisture and temperatures Signup and view all the answers

What effects can shrinkage have on sawn wood?

Less significant longitudinally compared to tangentially Signup and view all the answers

Which of the following statements about knots in wood is true?

Knots result from the tree's growth and limbs Signup and view all the answers

Which of the following glues requires specific temperature ranges during the curing cycle?

All types of glue Signup and view all the answers

What is a critical safety measure when using glues in the workplace?

Wearing protective clothing when necessary Signup and view all the answers

During which phase of the glue bonding process is the joint assembled?

Closed-Assembly Time Signup and view all the answers

Which tool is recommended for inspecting glue lines in wooden structures?

A magnifying glass Signup and view all the answers

What should the moisture content of wood be to avoid compromising its strength?

Between 8% and 20% Signup and view all the answers

What might a dull thudding noise indicate during a tap test?

Possible delamination of the plywood Signup and view all the answers

What indicates a possible failure of a bonded joint during prying?

Movement between the wood members of the joint Signup and view all the answers

When inspecting the internal structure of wooden aircraft, where is deterioration most likely to begin?

The lowest point inside the structure Signup and view all the answers

Which is a sign of potential wood decay during inspections?

Mushy or soft feel when probing Signup and view all the answers

What is the function of a moisture meter in the inspection of wooden structures?

Checking the moisture content of the wood Signup and view all the answers

What might a split or tear in the fabric covering of an aircraft indicate?

Potential internal damage to the wooden structure Signup and view all the answers

What action should be taken if glue lines show signs of separation?

Slip a feeler gauge into the separation if possible Signup and view all the answers

What is the purpose of using a tap hammer during inspections?

To check for sound quality and integrity of the wood Signup and view all the answers

What could indicate compression failure in a wooden structure?

Visible cracks across the grain of the wood Signup and view all the answers

What is the effect of dirt collecting in low points inside aircraft structures?

It retains moisture against the wood, potentially causing rot Signup and view all the answers

What is the main role of a carpenter's bradawl in the inspection process?

To probe soft or hollow areas in wood Signup and view all the answers

What is essential for ensuring a strong glue bond in wooden structures?

Properly preparing the wood surface Signup and view all the answers

What factor influences the joint strength when using glue on wood?

Clamping pressure applied during curing Signup and view all the answers

Which preparation technique is specifically noted as inappropriate for wood gluing surfaces?

Using sandpaper to smooth the joint Signup and view all the answers

Which type of pressure method can be used to create strong glue joints?

Mechanical and hydraulic presses Signup and view all the answers

What should be avoided when preparing wood surfaces for gluing?

Having planer marks on the surface Signup and view all the answers

What is the recommended clamping pressure for hardwoods when using resorcinol glue?

150 to 200 psi Signup and view all the answers

How should one apply glue to the joint surfaces prior to joining them?

Apply a smooth, even coat Signup and view all the answers

What is the purpose of using nailing strips when hand-nailing joints?

To distribute pressure over a larger area Signup and view all the answers

Why should wood pieces be kept in the same room for at least 24 hours before gluing?

To equalize their moisture content Signup and view all the answers

Which of the following statements about glue penetration is accurate?

Even glue penetration leads to a stronger joint Signup and view all the answers

What measures should be taken to minimize fire hazards in the shop area?

Maintain cleanliness and control dust and fumes Signup and view all the answers

What is the purpose of applying pressure to a joint after glue application?

To achieve a uniform distribution of glue Signup and view all the answers

What should be done immediately after removing the clamping pressure from a glue joint?

Inspect the joint and clean squeezed-out glue Signup and view all the answers

What safety equipment should be worn when machining and applying glues?

Respiratory, eye, and skin protection as needed Signup and view all the answers

What type of varnish is most recommended for providing excellent protection on surfaces?

Two-part epoxy varnish Signup and view all the answers

Why is it crucial to avoid applying sealer over areas where glue will be applied?

Most glues will not bond satisfactorily to sealers. Signup and view all the answers

What should be done to prepare end-grain surfaces prior to applying a finish?

Apply a thinned coat of sealer. Signup and view all the answers

What are the primary objectives of applying finishes to exterior wood surfaces?

To provide protection against weathering. Signup and view all the answers

Which of the following is NOT a common defect in wooden structures?

Over-staining Signup and view all the answers

What is the effect of prolonged exposure to water on finishes?

Causes finish failure. Signup and view all the answers

What is one reason for stress damage in wooden structures?

Over-tightening of bolts. Signup and view all the answers

What is an effective method for sealing bolt holes in wooden structures?

Applying an appropriate sealer before bolt installation. Signup and view all the answers

Why is shop cleanliness emphasized when using finishes?

For health and safety and product performance. Signup and view all the answers

What characteristic is associated with dry rot in wood?

Softness and discoloration. Signup and view all the answers

What is a good practice before applying a finish to avoid contamination?

Ensure surfaces are clean and free from glue squeeze-out. Signup and view all the answers

Which type of failure occurs when the wood surrounding a strong bond fails over time?

Structural failure around the bond Signup and view all the answers

In what context is a thinned coat of finish primarily used?

To ensure better penetration into wood grain. Signup and view all the answers

What is a key indicator of wood deterioration that should be noted during inspections?

Musty or mouldy odours Signup and view all the answers

What must be ensured during the repair of an aircraft's wooden structure?

The rigidity and aerodynamic shape must match the original structure Signup and view all the answers

How many splices are allowed in a single solid wood spar?

Two splices Signup and view all the answers

What is the maximum depth for damage removal on a solid laminated spar during repairs?

One-quarter of spar thickness Signup and view all the answers

What is the recommended taper ratio for scarf repairs of solid or rectangular wood spars?

1:10 or 1:12 Signup and view all the answers

What is the proper procedure for repairing a longitudinal crack in a solid wood spar?

Scrape away the finish and glue reinforcing plates to both sides Signup and view all the answers

What should be included in the repair information for wooden structures?

Information from the AMM, SRM or AC 43.13-1B/2A Signup and view all the answers

For wing rib repairs, what material is commonly used?

Spruce strips Signup and view all the answers

What is the maximum extension allowance for reinforcing plates on a scarf joint?

6 times the thickness of the spar Signup and view all the answers

What is an important aspect to avoid when repairing plywood skins?

Abrupt changes in cross-sectional areas from patch shapes Signup and view all the answers

What procedure should not be performed until the splice on a spar is completed?

Drilling new boltholes in the spar Signup and view all the answers

What type of spar requires careful attention to its unique design when repairing?

All of the above Signup and view all the answers

Study Notes

Wooden Construction in Aviation History

Modern ultra-light and home-built aircraft still utilize wooden construction techniques.
Historic models like the De Havilland Tiger Moth remain operational for joy flights, highlighting the ongoing need for qualified aircraft maintenance engineers.
Completely wooden aircraft, such as the Hughes H4 Flying Boat and De Havilland Mosquito, demonstrate longevity and safety in service.

Types of Wooden Airframe Construction

Three primary types of wooden airframe constructions are Truss, Monocoque, and Semi-monocoque.
The Pratt truss fuselage uses wooden longerons and struts to create a rigid frame, with specific tension and compressive load settings.
The Warren truss features longerons supported by diagonal members, allowing for both compressive and tensile loads.

Wing Components and Construction

Major components of wooden truss-type wing construction include the leading edge, front spar, rear spar, compression struts, ribs, drag wires, and anti-drag wires.
The leading edge typically uses materials like plywood or sheet metal for protection against erosion.
Compression struts prevent structural failure from the lateral pulling of spars, while ribs shape the wing, supporting non-load-bearing skin.

Monocoque and Semi-Monocoque Construction

Monocoque uses the outer skin to support loads, lacking an internal frame.
Semi-monocoque features a skin that supports some loads, reinforced by internal structural elements like formers and bulkheads.

Common Aircraft Wood

Sitka spruce is the standard reference wood for aviation structures due to its strength and durability.
In Oceania, woods like Hoop pine and Queensland maple serve as acceptable substitutes for Sitka spruce.

Laminated Wood and Plywood

Laminated wood, made from layers of solid wood with parallel grains, offers enhanced strength and resistance to warping.
Aircraft-grade plywood consists of veneers bonded with alternating grain directions to provide rigidity.

Wood Properties and Testing

Moisture content critical to wood strength should ideally be at 15% +/- 2%, with kiln drying recommended to eliminate moisture-related issues.
Wood density measurements help assess the quality of timber used in constructions.
Brittle and splitting tests verify the integrity and direction of wood grain, essential for safety.

Wood Preparations and Safety

Storing conditions for wood should be dry and well-ventilated to maintain quality.
Preparing wood surfaces for gluing requires thorough cleaning and equalizing moisture content for strong bonds.

Glue Bonding Process

Pot life, open-assembly time, closed-assembly time, and pressing time are crucial phases in the glue bonding process.
Common types of glues for aircraft include casein (obsolete), plastic resin, resorcinol, and epoxy resins, with varying properties and applications.

Clamping and Application Techniques

Proper clamping is essential for ensuring strong joint bonds without excessive or inadequate pressure during the curing period.
Various methods, including hydraulic presses and hand-nailing, can apply pressure while avoiding wood damage.

Health and Safety Practices

Awareness of toxic potential from glues necessitates proper personal protective equipment (PPE) during preparation and application.
Workplace cleanliness and safe practices help mitigate risks associated with dust and fumes from woodworking processes.### Preservation of Wooden Structures
Protect timber and joints post-assembly to prevent brittleness and rot from moisture.
Apply approved varnish or lacquer to all surfaces, following manufacturer instructions.
Ideal varnishes include two-part epoxy resins for excellent protection and compatibility with coverings.
Important to remove excess glue before finish application to prevent incompatibility with paints and finishes.

Finishing Wood Surfaces

End-Grain Surfaces: More absorbent, requiring extra sealing to prevent moisture entry.
Apply thinned sealer for maximum penetration; follow with full-strength coats for a glossy finish.
Interior Surfaces: Aim to protect against moisture changes; seal contact points with metal.
Use one thinned coat of varnish for penetration, followed by two full-strength coats.
Exterior Surfaces: Must resist weathering and UV exposure; require more durable finishes due to external conditions.

Sealing Bolt Holes

Bolt holes present moisture entry points; sealing them is crucial to prevent decay and corrosion.
Apply sealer before bolt installation and ensure it’s fully cured.

Health and Safety Precautions

Many finishes can be toxic; follow manufacturer’s Safety Data Sheets (SDS).
Use personal protective equipment (PPE) to avoid skin/eye contact and inhalation.
Maintain good ventilation to disperse fumes during finishing processes.

Common Defects in Wooden Structures

Dry Rot: Begins at the tree base; infectious and must incinerate affected wood.
Splitting/Cracking: Caused by shrinkage rates or external forces.
Bond Failure: Results from improper bonding, moisture exposure, or using incorrect glue.
- Types include cohesive bond failure, adhesive failure, and structural failure.
Finish Failure: Loss of protective coating leading to decay, intensified by moisture and UV light.
Stress Damage: Arises from excessive loads or overtightened bolts.

Inspection Methods for Wooden Structures

Effective inspection requires familiarization with appropriate tools for defect identification:
- Torch, magnifying glass, inspection mirror, bradawl, plastic mallet, feeler gauges, moisture meter.
Visual Inspections: Critical for spotting surface issues; may use additional aids like borescopes.
Internal and External Visual Inspections: Look for fabric tears that indicate wood damage, check glue lines for separation.

Moisture and Condition Tests

Use a moisture meter to check moisture content (optimal range: 8% to 20%).
Tap testing reveals structural integrity; hollow sounds may indicate internal issues.
Probing with a bradawl can confirm decay; soft areas require repair.
Odor detection can signal moisture or rot presence.

Repair Procedures for Wooden Structures

Repairs must restore strength and rigidity; use original materials unless obsolete.
Wing Spar Repairs: Unique designs dictate tailored repair procedures; certain areas require full replacement if damaged.
Specific Repairs:
- Longitudinal cracks can be fixed with spruce or plywood plates.
- Taper the ends of repairs to distribute stress and avoid weak points.
Wing Rib Repairs: Involves ensuring spruce strips effectively transmit air loads.
Plywood Skin Repairs: Follow specified guidelines (e.g., AMM, SRM) for structural integrity and stress distribution.

Types of Plywood Repairs

Splayed Patch: Used for small holes in thin plywood skins, applying tapered patches to match the original material.
Surface Patch: Quick repair method using fabric cover; not aesthetically optimal but practical.
Scarfed Patch: Preferred for major repairs, preserving skin thickness and rigidity; requires precise matching of angles for strength.

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Explore the significance of wooden construction in aviation history through this quiz. Learn about historic aircraft like the De Havilland Tiger Moth and their ongoing maintenance needs. Assess your knowledge on aviation construction methods and their legacy in modern aviation.