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Which species of wood is considered to be the standard when comparing other woods for use in aircraft structure?
Sitka spruce.
Why must abrupt changes in the cross-sectional area of a wooden structural member be avoided?
Abrupt changes in the cross sectional area of a structural member concentrate stresses and can cause failure.
What is the basic difference between laminated wood and plywood?
In laminated wood all of the grain runs in the same direction, in plywood the grain in the layers cross the others at 90� or 45� angle.
What effect does moisture have on a wood aircraft structure?
Moisture causes the wood to swell and crack as it dries out. It allows fungus to develop in the wood and cause it to decay.
Can northern white pine be used as a substitute for spruce?
Yes, but it must be increased in size to compensate for its lower strength.
Which wood is more inclined to warp, flat grain or vertical grain?
Flat grain.
How do you detect decay in a wood structure?
Stick a sharp-pointed knife blade in the suspect area and pry the wood up. If the wood is good, it will come up as a long splinter; if it is decayed it will come up as a chunk.
Are mineral streaks in a piece of structural aircraft wood reason for rejecting the wood?
No, if there is no evidence of decay in the wood.
How is compression wood identified?
It has a high specific gravity, it appears to have the excessive growth of summerwood, and little contrast between springwood and summerwood.
Is a hard knot, 1/2-inch in diameter allowed if it is in the web of a wing spar?
No, 3/8-inch diameter is the maximum allowable knot, and it must meet severe restrictions.
Are pin knot clusters allowable in aircraft structural wood?
Yes, if they cause only small effect on grain direction.
What kind of glue is recommended for making repairs to a wood aircraft structure?
Synthetic resin or resorcinol glue.
What reference material may be used for acceptable repairs to wood aircraft structure?
AC 43.13-1B, Chapter 1.
How is a scarf splice on a wing spar reinforced?
Solid spruce or birch plywood reinforcing plates are glued to each side of the spar, centered at each end of the scarf.
What is the correct repair to a wooden aircraft wing spar if the wing-attach bolt holes in the spar are elongated?
Splice in a new section of the spar and drill new holes.
What is the minimum taper to use when repairing a wood wing rib cap strip?
12 times the thickness recommended, 10 times is minimum.
How is aircraft plywood prepared for making a compound bend?
Soak the wood in hot water until it is pliable.
What is used to apply pressure to a glued joint when splicing a wood aircraft wing spar?
Cabinetmakers' parallel clamps.
How much pressure must be applied to glue joint in the piece of softwood to produce a strong joint?
125 to 150 pounds per square inch.
What kind of repair is recommended for a hole in the plywood skin of an aircraft wing?
A scarf patch.
What is the recommended taper for a splayed patch in a plywood aircraft skin?
5 to 1.
What is the recommended taper for a scarf patch in a plywood aircraft skin?
12 to 1.
Why should sandpaper never be used when preparing a scarf joint in a wing spar for splicing?
The dust caused by sanding will plug the pores of the wood so the glue cannot get in to for a good bond.
What is the largest hole in a plywood wing skin that can be repaired with a fabric patch?
1-inch in diameter.
Why are light steel bushings often used in bolt holes in a wood wing spar?
The bushing keeps the spar from being crushed when the nut on the attachment bolt is tightened.
How long should a glue joint be kept under pressure when splicing a wood aircraft wing spar?
For at least 7 hours.
Which area of wood wing spar must not maintain any splice?
There must be no splice under wing attach fittings, landing gear fittings, engine mount fittings, or lift and interplane strut fittings.
What is done to a splice in a wood aircraft wing spar to strengthen the splice?
Reinforcing plates are glued to both sides of the splice.
What reference material may be used for acceptable covering methods for fabric-covered aircraft structure?
AC 43.13-1B, Chapter 2.
What are three types of fabric that can be used to cover an aircraft?
Cotton fabric, polyester fabric, and glass fabric.
What paperwork must be completed if an aircraft that was originally covered with Grade-A cotton fabric is re-covered using a synthetic fabric?
The covering must be done according to a Supplemental Type Certificate, and a Form 337 must be executed, stating that all materials and processes complied with the requirements of the STC.
What type of rib lacing cord is recommended or attaching cotton fabric to an aircraft structure?
Waxed linen cord.
What is meant by the selvage edge of a piece of fabric?
It is the woven edge of fabric used to prevent the material unraveling during normal handling.
Why are some portions of the structure of an aircraft dope proofed before they are covered with fabric?
Dope proofing keeps the fabric from sticking to the structure when the first coat of dope is applied. The fabric normally sags enough to touch the structure before it begins to pull taut.
What material is used for inter-rib bracing in a fabric-covered aircraft wing?
Cotton reinforcing tape.
What is the preferred seam used for machine-sewing pieces of aircraft fabric together?
The French fell seam.
Should a sewed seam in the fabric used to cover an aircraft wing run spanwise or chordwise?
Both spanwise and chordwise seams are permissible, but chordwise seams are preferred.
What are two methods of applying the fabric to the wing of an airplane?
The blanket method and the envelope method.
What material is used to cover the overlapping edges of the leading edge metal to protect the fabric?
Cloth tape.
What are two methods of attaching the fabric to the aircraft structure?
By sewing and with a cement.
How are the wrinkles pull out of cotton fabric?
Wet the cotton with water and allow it to dry.
How is polyester fabric shrunk on the aircraft structure?
With heat from an iron.
What type of knot is used for locking the stitches that are used for rib lacing on a fabric-covered aircraft wing?
A modified seine knot.
What determines the spacing of the rib lacing stitches on a fabric-covered aircraft wing?
The never-exceed speed of the aircraft.
When is the finishing tape applied to a fabric-covered wing when it is being recovered?
After the second coat of dope has dried and the nap of the fabric has been sanded off.
What is an antitear strip, and when are they required on a fabric-covered aircraft?
An antitear strip is a strip of the same type of fabric as is used for covering the wings. It is laid over the rib between the reinforcing tape and the fabric. An antitear strip is required for aircraft that have a never-exceed speed in excess of 250 miles per hour.
When are drainage grommets applied when an aircraft is being re-covered?
They are laid into the third coat of dope, at the same time the surface tape is applied.
Where are drainage grommets located on a fabric-covered aircraft wing?
At the lowest point in each bay. It is customary to install a grommet on each side of a wing rib, on the underside of the wing, at the trailing edge.
What is done to cotton and linen fabric to protect it from mildew?
The first coat of dope used on cotton and linen fabric has a mildewcide mixed in it.
How wide should the surface tape be that is used to cover the trailing edge of an aircraft wing?
Three inches wide.
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