Jeppesen Oral- Chapter 2 ( Sheet Metal Structures) Flashcards
What is the major type of damage to aluminum structures that is caused by exposure to weather?
Corrosion
Name several methods for forming sheet metal?
Bending, folding, stretching, shrinking, bumping, crimping
What are the dimensions of a properly formed rivet?
Head should be 1.5x the shank diameter (width)
Head should be .5x shank diameter in height
What happens to the stem of a self-plugging (friction lock), rivet, when the rivet is installed?
The stem is pulled until it snaps off and the remaining projecting part is trimmed flush with the head
Name at leas three types of self-plugging mechanical rivets.
Cherry Maxx, CherryLock, Olympic-Locs, Huck
What is the difference between the ticks required to pull a Cherrylock rivet and a cherrymax rivet?
CherryMax only requires one tool for all sizes
Cherrylock, requires different tools for different sizes and heads
Which of the 5 stresses is the most common cause of rivet failure?
Shear
If a 20 24 rivet must be replaces with a 21 17 rivet, how do you determine the size to be used?
For a 5/32” diameter or smaller, use the next larger size 2117 rivet (assuming the edge distance and pitch requirements are met)
Describe the process for determing the total length of a solid rivet for a particular installation.
Add the grip length (thickness of the material being joined together) plus 1.5x diamter
What is the minimum edge distance and spacing that should be used for a single row of protruding head rivets?
Not less than two rivet diameters from the edge
Not less than three diameters apart
How can a mechanic determine whether the countersunk for a flush rivet should be dimpled or drilled?
By the thickness of the top sheet
What action is taken to prevent cracks from forming while dimpling magnesium or some hard sheet metals?
Hot dimpling to preheat and soften metal
What type of damage can occur when using a rivet set that does not properly fit the rivet?
If the radius is too small, the rivet might become damaged
If the set radius is too large it may damage the sheet metal
Why is it important to use the proper size and weight bucking bar when riveting sheet metal?
Bucking bar too big, difficult to control and cause damage
Too light, will not properly upset the rivet prior to work hardening
What procedures should be followed to properly remove a solid shank rivet?
Center punch the rivet and then drill a hole to the base of the rivet head with the same size or one smaller
Use a pin punch to tip off the head and drive out the rest of the shank
What are the two special calculations that must be made when bending sheet metal?
Bend allowance and setback
What are the factors that must be considered in order to determine setback?
Thickness of the material and bend radius
What is done to a corner where two bends intersect to prevent cracking?
Relief holes are drilled into the corner
What are the two reasons for installing a lighting hole n sheet metal wing ribs?
Reduces weight, increase stiffness
Describe a joggle and explain it’s function
Offset formed at an intersection of two or more sheet
Allows multiple sheets of metal to be stacked flat against each other
When preparing an all-metal aircraft, how do you determine what metals should be used?
Use the same metal and thickness
What are three requirements for a repair to a piece of sheet metal aircraft structure?
The repair must restore the lost strength and rigidity, and it must not change the aerodynamic shape of the part.
When making a riveted repair to an aircraft sheet metal structure, which should be stronger, the shear strength of the rivet, or the nearing strength of the metal sheet?
The two strengths should be close to each other, but the bearing strength should be greater.
What type of device is a Cleco fastener?
A patented fastener that is inserted in the rivet holes and is used to hold two pieces of sheet metal together until they can be riveted.
What is the main function of throatless shears in an aircraft sheet metal shop?
Throatless shears are used to cut mild carbon steel up to a 10-gauge and stainless steel up to a 12-gauge. They can be used to cut irregular curves in the metal.
What is the purpose of a sight line when laying out sheet metal to be bent in a cornice brake?
The sight line allows the jaws of a cornice brake to be positioned so the bend made by the brake will start at the bend tangent line.
What kind of metal forming is done by a slip roll former?
Simple curves with a large radius
What kind of metal forming is done by bumping?
Compound curves in sheet metal
What must be done to the flanges of an angle for it to be curved?
The flanges must be stretched for a convex curve and shrunk for a concave curve.
What is meant by the bend allowance used in making a bend in a piece of sheet metal?
The bend allowance is the amount of metal that is actually used in making the bend in a piece of sheet metal.
What determines the minimum bend radius that can be used with a piece of sheet metal?
The thickness of the material and its hardness
What is meant by setback when bending a piece of sheet metal in a cornice brake?
Setback is the distance the jaws bust be set back from the mold line to form the bend.
When hand-forming a piece of sheet metal that has a concave curve, should the forming be started in the center or at its edges?
Start at the edges and work towards the center.
Why should aluminum alloy rivets be driven with as few blows as it practical?
Excessive hammering will work0harden the rivets and make them difficult to drive.
What type of metal should be hot-dimpled?
7075-T6, 2024-T81 alloys, and magnesium alloys should be hot dimpled.
What special precautions must be taken when repairing a radome?
Nothing must be done to the radome that will affect its electrical transparency or its aerodynamic strength
How is the point of a twist drill ground that is to be used for drilling transparent acrylic material?
The cutting edge should be dubbed off to a zero rake angle, and the included angle of the tip should be ground to 140 degrees.
What causes crazing in a piece of transparent sheet metal?
Uneven stresses in the material, usually caused by heat.
What is the purpose of anodizing a piece of aluminum alloy, and how is it applied?
Anodizing is a protective oxide film that is deposited on the surface of aluminum alloy by an electrolytic process.
