Aircraft Wood Structures Spokane Community College Airframe

Objectives Understand the different species used in aircraft wood construction Understand the defects found in wood construction

Current Wood Structure Applications Why wood? Strength to weight ratio Disadvantage labor intense Maintenance Bellanca Viking Still used for homebuilts and some production aircraft Standards set for wood used in AC AN quality standards Best wood – Sitka Spruce – uniform, strength and shock resistance Buy from reputable companies – derives from Alaska and B.C. AN-W-2 specifications Other substitutions are acceptable as long as they follow the criteria AC-34-13-1B – outlines SLIDE

Addison’s B-40

Oldest Flying Boeing

Great Lakes 2T1A-2

Fully Aerobatic

Substitutions are acceptable as long as they meet the original characteristics of the original product Must be assessed by the mechanic Must be free of defects SLIDE:

Wood Construction and Defects Shake – Separation or crack Check – Develops during drying

Good wood: Slope of the grain – Slide Growth rings per inch – six minimum in soft woods Exceptions – Port Oxford white cedar and Douglas Fir – Eight minimum Must be true, dry etc. Talk about quality of wood. Plywood – Manufactured form African Mahogany and birch veneers over hardwood cores of bass wood or popular May also be basswood plywood – lighter and more flexible but less structural Bonded 90 degrees to each other Specifications – MIL-P-6070 – calls for testing after immersion in boiling water for 3 hours Laminated wood – Each layer is bonded with the grain running parallel Stronger but less flexible Much more resistant to warping Used for curved components – wing tip bows and fuselage formers

Reasons for rejection Cross Grain – Wood in which the direction of the fibers/grain deviate from a line parallel to the sides in excess of listing. Wavy, curly and interlocked grain – disruption in the grain pattern in the form of waves, bird’s eyes or alternate spirals in excess of limitations. Hard Knots – solid knots which show weakness or decay surrounding them.

Reasons for rejection Pin knot clusters – knots with diameters less than ½ inch in a grouping are not acceptable if the show a large affect on the grain. Pitch pockets – pockets which may or may not contain pitch are not acceptable unless they fall within limitations. Mineral streaks – discoloration which shows excessive minerals in the wood are acceptable only if they show no signs of rot or decay.

Reasons for rejection Checks, shakes or splits – cracks either uniform or disruptive in the grain are reasons for rejection. Compression wood – buckling of the grain that appear as streaks in the surface of the wood and are at right angles to the grain are reason for rejection. Decay – attack by organisms such as fungi and insects and can be powdery (dry rot) or wet are always reasons for rejection.

Inspection What else would you use to inspect a wood structure? Tools: Pick Rule Feeler gauge Mirror, Flashlight What else would you use to inspect a wood structure?