Wood Structures Flashcards
What species of wood is used as a standard for strength properties of other species of wood used in aircraft structures?
Sitka Spruce
What type of wood quality must be used in the repair of aircraft structures?
The wood must be aircraft quality.
What is the difference between laminated wood and plywood?
Laminated wood consists of two or more layers of wood which have been glued together with the grain of all layers approximately parallel.
What are the two types of glue used for aircraft wood structure repair?
Casein glue, plastic resin glue, resorcinol glue, and epoxy adhesives
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?
The results will normally be thick glue lines, which indicate a weak joint.
How long should a wood glue joint be kept under pressure before removing the clamps?
The pressing time will vary depending on the temperature of the curing room. The curing temperatures are from 70°F and up. Higher temperatures will cause the glue to set faster. To be certain that a glue joint is satisfactory, it is recommended that it remain under pressure at about 85°F. for a period of at least seven hours. Full joint strength will develop only after conditioning for at least two days.
What are some of the various methods used to apply pressure to joints in aircraft gluing operations?
Brads, nails, screws, clamp, and hydraulic and 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?
A properly prepared and inserted scarf patch is the best repair for plywood, and is preferred for most skin repairs. It differs from a splayed patch in that the edges are scarfed to a 12 to 1 slope instead of a 5 to 1 slope, and it uses reinforcements under the patch where the glue joints occur.
. Are mineral streaks acceptable in aircraft wood?
Yes, providing careful inspection fails to reveal any decay.
How can the moisture content of wood be determined?
One way is to use a moisture meter. However, the most accurate method is to take a sample of the wood, weigh it, dry it in an oven at a temperature of 100°C to 105°C, reweigh it, and then compute the moisture content by using the following formula.
What area of a wood spar may not be spliced?
It may not be spliced under wing attachment fittings, landing gear fittings, engine mount fittings, or liftand-interplane strut fittings
What type 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 is wood that is characterized by high specific gravity and has the appearance of excessive growth of summer wood. This defect is difficult to recognize and is very detrimental to strength. Reject all material containing compression wood.
