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AIRCRAFT WOOD STRUCTURES

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by

Christopher Gonzalez

on 28 January 2014

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Transcript of AIRCRAFT WOOD STRUCTURES

AIRCRAFT WOOD STRUCTURES
Evaluating Wood for Aircraft Use
Aircraft structural wood is cut from the tree in such a way that most of the grain lies at 45 degrees or more to the wide dimension of the wood plank. There are certain defects that aren't acceptable to be used such as cross grain on the wood or using compression wood. Wood is also used as propellers on aircraft.
Glues
Wood aircraft depend entirely on glued joints for their strength. Today there are a number of high strength glues in the market. Plastic resin and resorcinol are generally used on aircraft. When gluing you have to make sure the design of the glue joint is properly made. Also make sure you mixed the glue properly.
Classifications of Wood and Types of Wood.
There are two basic classifications of wood, hardwood and softwood. There are different types of woods used in aviation: Solid wood, laminated wood, and plywood.
Protection and Inspection of Wooden Aircraft Structures
When inspecting an aircraft with wood or made of wood you have to look out for decay and dry rot in the wood. They cause major problems in the wood. You can protect aircraft structure by keeping air and moisture from the wood.
Construction and Repair of Wood Structures
Nowadays wooden aircraft are usually just built by people who have to time to build them and stuff like that. Commercial manufactures have phased out of using wood in the construction of their aircraft.
Wing spar repair and rib spar repairs are the two common things that have to be repaired on aircraft that have wood.
EXTRAS
Unacceptable Wood to Use
Wood with decay cannot be used.
Composite
Something made up of different materials combined in such a way that the characteristics of the resulting material are different from those of any one of the components.

Deciduous
A type of tree that sheds its foliage at the end of the growing season. Hardwoods come from deciduous trees.
Hardwood
Wood from a broadleaf tree that sheds its leaves each year.
Softwood
Wood from a tree that bears cones and has needles rather than leaves.
Laminated Wood
A type of wood made by gluing several pieces of thin wood together. The grain of all pieces runs in the same direction.
1. Wood that comes from a cone-bearing tree is a softwood.
2. Hardwoods are not always more dense than softwoods.
3. The standard for comparing all aircraft structural wood is Stika Spruce.
4. A wood product made of strips of wood glued together in such a way that all the grains run in the same direction is called laminated wood.
5. Wood propellers are made of lamination's of Birch.
6. The in the plies of a sheet of aircraft plywood cross each other at either 45 or 90 degrees.
7. Aircraft plywood with mahogany or birch faces often have cores made of Polar or basswood.
8. The light bands seen in the end of a piece of wood are called spring wood.
9. The desirable moisture content of aircraft spruce is 12 percent.
10. The maximum allowable grain divergence in aircraft spruce is 1:15 .
11. A sound hard knot that is 3/8 inch in diameter in the web of a solid wood wing spar IS an acceptable defect.
12. A pitch pocket 1 inch long , 1/8 inch wide and 3/32 inch deep in the center of a solid wood wing spar IS an acceptable defect.
13. A wood wing spar blank containing some compression wood IS NOT acceptable for use.
14. Nails in a glues joint IS NOT increase the strength of the joint.
15. A properly designed glued joint should be loaded in shear .
16. There should be a time lapse of no more that 8 hours between the final surfacing of the wood and the application of the glue.
17. When preparing solid wood for a glued joint, the surface should not be roughened to help the glue adhere.
18. Final smoothing of the wood surfaces to be joined should not be done with fine sand paper.
19. When using aircraft nails to apply pressure for gluing gussets to a wing rib, the maximum distance between nails is 3/4 inch.
20.A laminated wood spar may be used to replace a solid wood spar if they are both made up of the same quality wood.
21. The majority of the flight loads applied to a wing spar are carried in the caps of the spar.
22. Locations where bolts pass through a wooden spar are reinforced with plywood made of birch.
23. Elongated bolt holes in a wing spar should not be repaired by drilling the hole oversize and using the next larger size bolt.
24. The minimum taper to use when splicing a solid or laminated wood wing spar is 10 to 1.
25. The reinforcing plate over a splice in a wing spar should not be in a location through which the wing strut bolt pass.
26. A small hole in the leading edge of a plywood wing that cleans out to less than one inch in diameter cannot be repaired with a fabric patch.
27. The choice repair for all types of plywood skin damage is a scarf patch.
28. Aircraft woof with a moisture content of less than 20% is not susceptible to decay or dry rot.
29. When a sharp knife point stuck into a piece of aircraft wood pries up a chunk of wood instead of a hard splinter, the wood IS likely infected with decay.

Plywood
A wood product made by gluing several pieces of thin wood together. Grain runs at 90 or 45 degrees.
Veneer
Thin sheets of wood "peeled" from a log. Veneer is used for making plywood.
Annual Rings
The rings that appear in the end of a log cut from a tree. The number of annual rings per inch gives an indication of the strength of the wood.
Springwood
The portion of an annual ring in a piece of wood that is formed principally during the first part of the growing season, the spring of the year. Springwood is softer, more porous, and lighter than the summerwood.
Summerwood
The less porous, usually harder portion of annual ring that forms in the latter part of the growing season, the summer of the year.
Quatersawn wood
Wood sawed from a tree in such a way that the annual rings cross the plank at an angle greater than 45 degrees.
Cap Strip
The main top and bottom members of wing rib. The cap strips give the rib its aerodynamic shape.
Planer
A woodworking power tool used to smooth the surface of a piece of wood.
Jointer
A woodworking power tool used to smooth the edges of a piece of wood.
Gusset
A small plate attached to two or more members of truss structure. A gusset strengthens the truss.
Amateur-built aircraft
Aircraft built by individuals as a hobby rather than by factories as commercial products.
Web of Spar
The part of spar between the caps.
Routed Spar
Repair of wood structure when spars are subjected to bending loads.
Fitting
An attachment device that is used to connect components to an aircraft structure.
Scarf joint
A joint in a wood structure in which the ends to be joined are cut in a longer taper, normally about 12:1, and fastened together by gluing.
Splayed Patch
A type of patch made in an aircraft plywood structure.
Nailing Strip
A method of applying wood to the glue in a scarf joint repair in plywood skin.
Decay
Decomposition. The Breakdown of the structure of wood fibers. Wood that shows any indication of decay must be rejected for use in aircraft structure.
Dry Rot
Decomposition of wood fibers cause by fungi. Dry rot destroys all strength in the wood.
Fungus
Any of several types of plant life that include yeasts, molds, and mildew.
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