Wood Structures Flashcards
What species of wood is used as a standard for strength properties in aircraft structures?
Spruce is used as he standard of which all woods are compared.
What type of wood quality must be used in the repair of aircraft structures?
Aircraft quality, and equivalent or stronger than original strength.
What is the difference between laminated wood and plywood?
Laminated wood has layers with parallel grains, plywood has layers with grains at 90 degrees with adjacent plys.
What are the two types of glues used for aircraft wood structure repair?
Casein and Synthetic resin glue. The resin glues that are recommended for wooden aircraft applications are the resorcinol formaldehyde type glues.
What method is used to prepare plywood for bending?
The wood is soaked in hot water and then placed on a form until completely dry.
What are the results of using insufficient gluing pressure when making a wood joint?
Results will normally be thick glue lines indicating a weak joint.
How long should a wood glue joint be kept under pressure before removing the clamps?
Recommended to at least 7 hours at pressure at 85 degrees F. Pressure varies with temperature. Setting time increases with temperature. Full joint strength takes at least two days.
What are some of the various methods used to apply pressure to joints in aircraft gluing operations?
Brads, nails, screws, clamps, and hydraulic or electric power presses.
Why does the strength of a scarf joint depend upon the accuracy of the two beveled surfaces?
Because an inaccurate bevel will reduce the amount of effective glue area.
What type of patch is preferred for repair of stressed plywood skin and why?
Scarf patch, because it has a 12 to 1 slope and uses reinforcements under the patch where glue joints occur.
Are mineral streaks acceptable in aircraft wood?
Yes, provided there is no decay.
How do you determine the moisture content of wood?
Use of a moisture meter. Or, take a sample of wood and weigh it at room temp, then dry at 100 to 105 degrees and re-weigh. Then find percentage of dry weight.
What area of the wood spar may not be spliced?
Under wing attachments, landing gear fittings, engine mount fittings or lift-and-interplane strut fittings.
What kind of joint is generally used in splicing structural members in aircraft?
A scarf joint.
What is compression wood and why is it not acceptable for aircraft structures?
Compression wood has a high specific gravity and has the appearance of excessive growth of summer wood. It is not strong (hard, non-porous).
