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WoodStructures
A&P - Airframe - Wood Structures
| Question | Answer |
|---|---|
| What species of wood is used as a standard for strength properties of other species of wood used in aircraft structures? | Spruce is used as the standard of which all woods are compared. |
| Is northern white pine an acceptable substitute for spruce? | Yes, but only if the pine is a larger size to make up for its lower strength. |
| Are knots allowed in aircraft wood? | Knots are allowed if within limitations. Factors that determine if knots are acceptable include the type of knot, location, spacing, and number of knots. |
| What type of wood quality must be used in the repair of aircraft structures? | The wood must be of aircraft quality and equivalent to its original strength or greater. |
| What is the difference between laminated wood and plywood? | Laminated wood and plywood consist of two or more layers of wood which have been glued together. Laminated wood has the grain of all layers approximately parallel. The grain of plywood runs 90° with the adjacent ply. |
| What are two types of glue used for aircraft wood structure repair? | They are 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 in 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. |
| What is the recommended clamping pressure for a glued joint? | 125 to 150 psi. |
| How long should a wood glue joint be kept under pressure before removing the clamps? | Depends on the temperature of the curing room. Recommended temps are 70°F and up. Higher than 70°F will set the glue faster. Ideal temp would be about 85°F for seven hours. Full joint strength develops 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, clamps, or 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. |
| Why is sanding unacceptable when preparing a joint for splicing? | Because the dust created from sanding will clog the pores of the wood, preventing proper penetration of glue. |
| What type of patch is preferred for repair of stressed plywood skin and why? | A well prepped scarf patch is best for plywood, and 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 patched joints. |
| Are mineral streaks acceptable in aircraft wood? | Yes, providing careful inspection fails to reveal any decay. |
| How do you inspect for decay/rot in wood? | Visual (dark discoloration or gray stains), Odor (musty or moldy), Tapping (sharp solid report), Probe (Sharp metal tool), Prying (bonded joints.) |
| How can the moisture content of wood be determined? | You can use a moisture meter, but a more 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 this formula: W1 - W2 / W2 X 100. |
| What area of the wood spar may not be spliced? | it may not be spliced under wing attachment fittings, landing gear fittings, engine mount fittings, or lift-and-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 an excessive growth of summer wood (hard, non-porous). This defect is difficult to recognize and is very detrimental to strength. |
| What are three forms of wood? | Solid, Ply, and Laminate. |
| What are two forms of wood that are acceptable for the repair of wooden aircraft skin? | The plywood and laminated woods are preferred for this application. |
| What would be the greatest number of splices placed into one spar? | Two. |
| What is the largest hole diameter that can be repaired in a plywood wing skin when using a fabric patch? | 1 inch. |
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MyInnerPeace
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