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Chapter Synopses
Chapter 1 – Basic Principles of Strength Materials
Chapter 2 – Forces in Structures
Chapter 3 – The Nature of Composites
Chapter 4 – The Structural Sandwich
Chapter 5 & 6 – Materials
Chapter 7 – Joining Structures
Chapter 8, 9 & 10 – Open Layups and Foamed Cores
Chapter 11, 12, 13 & 14 – Molded Structures
Chapter 1 – Basic Principles of Strength Materials
 Read Chapter 1 for free (171k, PDF)
Introduces the beginning reader, without mathematics, to the basic principles of any strong material such as steel, wood, or glass, including:
- The definitions and a brief explanation of the concepts of stress, strain, stiffness, and strength.
- Definition of a structure and why wood is a complex structure of hollow cellulose cells.
- Composites as structures.
- Why structures break – the mechanisms of failure and cracking.
- The concept of the work of fracture in propagating a crack.
- Why any practical material can be strong.
- Why thin glass fibers are very strong.
- The concept of toughness as the opposite of brittleness. ^ Top
Chapter 2 – Forces in Structures
Introduces the beginning reader, without mathematics, to the basic principles of bending a beam. The reader is taken through a step-by-step example which explains the forces in a beam for the very simple case where a weight is suspended from a cantilever beam attached to a wall. The reader is shown how the forces in the beam combine to support a load at a distance from the wall. The reader will understand why a thick beam is more efficient than a thin beam and how and where the loads occur. Most important, the concept of shear forces is explained. Buckling of columns and thin sheets is described with particular attention given to the importance of buckling as a limiting factor in aircraft structures. ^ Top
Chapter 3 – The Nature of Composites
Introduces the beginning reader to how and why composites work and why they are strong. A composite is a combination of a strong, stiff base material, usually in the form of fibers, imbedded in a less-stiff matrix. The strength of a single glass fiber is limited by the existence of flaws along its length which reduce the strength to zero at each flaw. Between flaws, a single thin glass fiber is very strong. In a composite, a very large number of glass fibers is used so that the flaws are spread throughout the bulk of the structure and the combined strength approaches the theoretical strength of the unflawed fibers. In homebuilt aircraft construction, we are most interested in the case where the strong material is very thin glass fibers and the wetting matrix is a plastic which is applied as a liquid and which hardens at room temperature. Most builders and pilots are familiar with the failure modes of ductile metals like aluminum and steel or the special characteristics of wood. The contrasting nature of composites in failure is explained, particularly the design requirement that the load should be aligned with the fibers. Effects of environment on composite materials are discussed. ^ Top
Chapter 4 – The Structural Sandwich
Explains why the structural sandwich is particularly well suited to composite construction, where a thin glass skin is combined in a “sandwich” with a much thicker “core” of a light material which carries the necessary shear forces between the skins. The sandwich principle is explained in terms of a simple beam where the light weight “core” is a hollow “egg crate” made from a thin sheet material and the sandwich is closed with a thin skin which carries tension and compression loads. The core, then, carries the shear forces. The conclusion is that a relatively thick sandwich with a light core is a very weight-efficient structure compared with a similar structure which must use solid skins sufficiently thick to avoid buckling. Sandwich cores as described in this book, are usually assumed to be light weight plastic foams, or wood, in special cases. Failure modes of sandwich structures are described. ^ Top
Chapter 5 & 6 – Materials
Chapters 5 & 6 describe the component materials typically used in aircraft-quality composite construction, including the fibers, the plastic matrices, and practical core materials, including foams and honeycomb. Most kit manufacturers and designers of plans-built aircraft specify the use of aircraft epoxy matrix materials, in contrast with the much more widely used polyester resins used in huge quantities by the boat industry and by the mainstream composites industry. The book explains why this choice is made by aircraft builders. These chapters explain the various fiber weaves offered to the homebuilt aircraft community in small lots through the established aircraft supply houses. (A large part of industrial fiber production is not available for amateur use because of special or inappropriate weaves and fabric combinations.) Kit manufacturers may use materials and tools which are not appropriate for the aircraft homebuilder because of the necessary investment in tooling. Kit manufacturers produce excellent parts for assembly by the kit builder and the potential kit builder will want to understand how these parts are made.
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Chapter 7 – Joining Structures
Describes processes and requirements for bonding cured composite structures. Most adhesives sold in home supply stores are not suitable for bonding composite structures because these adhesives depend on an interaction with the atmosphere to cure, usually evaporation of a solvent. Composite structures are gas-tight, so the adhesive must be activated before assembly, which greatly limits the available options, including the use of aircraft glues intended for wood. The aircraft supply houses offer two-part structural adhesives which are specifically designed for bonding cured composite structures and which have the appropriate properties of correct stiffness, ability to adjust to irregularities, and excellent adhesion. These products, and the reasons for them, are discussed. A secondary bond is produced when a new wet layup is continued over and already-cured surface. Examples are given for joining large surfaces, such as are used to assemble such large parts as fuselage turtlebacks and wing skins. Methods are discussed for making hard points such as bolt attachments in a sandwich skin. ^ Top
Chapter 8, 9 & 10 – Open Layups and Formed Cores
Describe the basic composite construction techniques, particularly the methods pioneered by Burt Rutan and continued in later successful aircraft designs. Procedures are described preparing a surface (such as a foam core or the face of a mold), for handling, measuring, and placing glass fiber material on a surface, and wetting it out with the liquid matrix plastic. ^ Top
Chapter 11, 12, 13 & 14 – Molded Structures
These chapters describe composite structures which are assembled from stiff molded surfaces to make hollow structures, such as wings. Conventional commercial practices, as used by kit manufacturers, are described. It is assumed that the home builder will not attempt to duplicate these processes, but should understand them because he may choose to purchase large molded subassemblies, such as fuselage tubs and wing skins, from a kit manufacturer, instead of building them himself. It is practical for the homebuilder to use simple molds (“tools”) formed from sheets of commercially available building materials. Many practical aircraft parts can be molded on a flat tool or a curved tool formed by bending a flat sheet. Hiqh-quality composite structures can be formed on a flat or curved tool under a vacuum bag by the use of simple techniques and with materials available at a home supply store. A small commercial vacuum pump is recommended, but other vacuum hardware is available at hardware stores. ^ Top |
