Aircraft Wood: Types and Usage

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Questions and Answers

Why is aluminum currently favored over wood in modern aircraft construction, despite wood's historical significance?

  • Aluminum structures can be created faster with automated processes, while wooden structures need significant handcrafting. (correct)
  • Aluminum has a naturally superior strength-to-weight ratio compared to all types of wood.
  • Aluminum is less susceptible to decay and fungal growth, requiring less maintenance.
  • Aluminum is more readily available and cost-effective than high-quality wood suitable for aircraft.

In laminated wood construction, what is the primary benefit of orienting the grain of each thin wood piece in the same direction?

  • It maximizes the wood's resistance to twisting and warping under stress.
  • It reduces the overall weight of the component compared to using a single solid piece of wood.
  • It simplifies the gluing process, ensuring a stronger bond between layers.
  • It allows for the creation of larger structural components from smaller pieces, maintaining consistent strength along the length. (correct)

In plywood construction, why are the layers of wood veneer glued together with the grain of each successive layer oriented at an angle?

  • To enhance the wood's natural resistance to moisture absorption and prevent swelling.
  • To reduce the amount of adhesive needed for bonding the layers together.
  • To create a more aesthetically pleasing finish with varied wood grain patterns.
  • To evenly distribute stresses and strains, which increases overall strength and stability in multiple directions. (correct)

Why is Sitka spruce the most common wood used in aircraft structures?

<p>It maintains favorable strength relative to its weight; is available in large sizes; and has relatively few defects. (D)</p> Signup and view all the answers

Although Douglas fir has superior strength properties compared to Sitka spruce, why is it not as commonly used in aircraft construction?

<p>Douglas fir is heavier, more difficult to work with, and prone to splitting. (A)</p> Signup and view all the answers

What characteristic makes balsa wood suitable as a core material in sandwich-type panels for aircraft?

<p>Its extremely light weight provides rigidity. (C)</p> Signup and view all the answers

Why is straight grain a critical requirement for wood used in aircraft structures?

<p>Straight grain wood ensures that the wood fibers are aligned to evenly distribute stress along the longitudinal axis. (D)</p> Signup and view all the answers

Why are spike knots particularly problematic in aircraft wood?

<p>They disrupt the wood's grain structure more severely than other knots, significantly reducing its strength. (D)</p> Signup and view all the answers

According to FAA standards, what does grain slope refer to in the context of aircraft wood, and what is the maximum allowable slope?

<p>The deviation of the wood fibers from the longitudinal axis; maximum allowable slope is 1:15. (D)</p> Signup and view all the answers

How do pitch pockets affect the structural integrity of wood used in aircraft?

<p>They slightly weaken the wood due to small openings filled with resin reducing wood's cross-sectional area. (D)</p> Signup and view all the answers

What is compression wood, and why is it undesirable in aircraft construction?

<p>Wood formed when a tree leans during growth, resulting in denser and weaker wood, which means it is unsuitable for structural applications. (C)</p> Signup and view all the answers

What distinguishes a check from a shake in wood, and why are both considered defects in aircraft structural components?

<p>A check runs across the annual rings and occurs during seasoning, while a shake involves separation along annual ring boundaries. Both weaken the wood. (B)</p> Signup and view all the answers

What is a split in wood, and why is it considered a critical defect in aircraft structures?

<p>A split is a lengthwise separation of wood fibers, indicating a serious structural weakness that makes the wood unsuitable for aircraft. (A)</p> Signup and view all the answers

What causes stains in wood, and why is recognizing them important in aircraft maintenance?

<p>Fungal decay, which can compromise structural integrity, so stains indicate areas where the wood's strength is compromised. (A)</p> Signup and view all the answers

How can decay in wood be prevented, particularly in the context of aircraft construction and maintenance?

<p>Ensuring proper seasoning and dry storage to inhibit the growth of decay-causing fungi. (A)</p> Signup and view all the answers

Flashcards

Solid Wood

Wood made of one solid piece cut from a log, used for wing spars.

Laminated Wood

Wood made of thin pieces glued together with the grain running in the same direction, allowing for larger components.

Plywood

Wood consisting of layers of thin veneer glued together with the grain crossed at an angle for strength.

Hardwood

Trees with broad leaves; one of the two basic species of wood used for aircraft construction.

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Softwood

Trees with needle-like or scale-like leaves; one of the two basic species of wood used for aircraft construction.

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Spruce

A lightweight and strong wood commonly used in aircraft structures.

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Douglas Fir

A heavier wood with high strength properties, but more difficult to work with than Spruce.

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Noble Fir

A wood slightly lighter than Spruce and used on structural parts.

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Northern White Pine

Wood with excellent working and gluing characteristics, but lower strength than spruce.

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Balsa Wood

Extremely light wood used as a core material for sandwich panels requiring light weight and rigidity.

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Birch

A heavy hardwood with very good shock resistance, used for reinforcement plates and propellers.

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Straight Grain

Wood fibers that are oriented parallel to the material's longitudinal axis.

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Knots

A point where a branch grew from the tree trunk, weakening the wood.

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Pitch Pockets

Small openings within the annual rings of a tree that weaken the wood slightly.

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Compression Wood

Non-concentric annual rings caused by leaning during growth, making the wood dense and weak.

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Study Notes

  • Nonmetallic structural materials were significant in early aviation, but aluminum's introduction led to their decreased use.
  • Aluminum is the most common material for aircraft construction and repair today.

Wood

  • Wood is used less in modern aircraft due to the higher cost of labor-intensive construction compared to sheet metal.

Types of Wood

  • Solid wood is used for some aircraft wing spars and rigid parts.
  • Solid wood is made from a single piece cut from a log and commonly used for bulkheads, landing gear, and spars.
  • Laminated wood consists of two or three thin pieces glued together with grains running in the same direction.
  • Laminated wood allows splicing for larger components like spars from smaller pieces.
  • Plywood is made of at least three layers of veneer glued together with alternating grain angles of 45 or 90 degrees.

Species of Wood

  • Two main species used for aircraft are hardwood from broad-leaved trees and softwood from coniferous trees.
  • Sitka spruce is the most common aircraft wood due to its lack of defects, high strength-to-weight ratio, and availability in large sizes.
  • Douglas fir has greater strength properties than spruce but is heavier, harder to work, and prone to splitting.
  • Noble fir is lighter than spruce with equal or superior properties, except for hardness and shock resistance.
  • Noble fir is used for parts under heavy bending and compression, such as spars and cap strips.
  • Northern white pine has excellent workability and gluing characteristics, but lower strength than spruce.
  • Balsa is a very light wood from South America used as a core material in lightweight, rigid sandwich panels.
  • Birch is a heavy hardwood with good shock resistance.
  • Birch is recommended for plywood face plies on wing spars and wooden propellers.

Quality of Wood

  • Wood for aircraft structure must have a straight grain, meaning fibers are parallel to the longitudinal axis.
  • Knots indicate where branches grew from the trunk and can be round, oval, or spiked.
  • Spike knots are cut parallel to a branch, weaken the wood, and are not allowed in aircraft construction.
  • FAA standards permit a maximum grain slope of 1:15
  • Pitch pockets are small resin-filled openings within tree rings that slightly weaken the wood.
  • Compression wood has wide summer-growth rings due to compressive stress during growth, making it denser and weaker.
  • Checks are cracks across annual rings during seasoning.
  • Shakes are separations between annual rings.
  • Splits are lengthwise separations caused by tearing wood fibers.
  • Wood with these defects (checks, shakes, and splits) is not allowed in aircraft structure.
  • Decay stains appear as streaks in the grain, extending from the decayed area.
  • Decay is caused by fungi in damp wood and prevented by proper seasoning and dry storage.

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