2-Sheet Metal Structures Text

7/22/2019 2-Sheet Metal Structures Text

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SHEET METAL STRUCTURES

2-1 D01

A well designed rivet joint will subject the rivets to

A 1 compressive loads.B 1 tension loads. C 1shear loads.

2-1. Answer C. JSAT 2-51 (AC65-15A)Rivets hold pieces of aircraft skin together, and in a prop-erly designed riveted joint, the rivets support shear loadsonly.

2-2 D01A main difference between Lockbolt/ Huckbolt tension andshear fasteners (other than their application) is in the

A 1 method of installation.B 1 number of locking collar grooves.C 1 shape of the head.

2-3 D01

Alloy 2117 rivets are heat treated

A 1 to a temperature of 910 to 930 and quenched incold water.

B 1 by the manufacturer and do not require heat treatmentbefore being driven.

C 1 by the manufacturer but require reheat treatmentbefore being driven.

2-4 D01The general rule for finding the proper rivet diameter is

A 1 three times the thickness of the thickest sheet.B 1 two times the rivet length.C 1 three times the thickness of the materials to be joined.

2-5 D01The shop head of a rivet should be

A 1 one and one-half times the diameter of the rivetshank.

B 1 one and one-half times the diameter of the manufac-tured head of the rivet.

C 1 one-half times the diameter of the rivet shank.

2-6 D01One of the main advantages of Hi-Lok type fasteners overearlier generations is that

A 1 the squeezed on collar installation provides a more

secure, tighter fit.B 1 they can be removed and reused again.C 1 they can be installed with ordinary hand tools.

2-2. Answer B. JSAT 2-45Huckbolts and Lockbolts are manufactured to the sameFederal Standard. In each case, the tension-type has 4 to 5locking grooves and the shear-type has 2.

2-3. Answer B. JSAT 2-38 (AC65-9A)

The 2117-T rivet, known as the field rivet, is used morethan any other for riveting aluminum alloy structures. Thefield rivet is in wide demand because it is ready for use asreceived, and needs no further heat treating or annealing.

2-4. Answer A. JSAT 2-52 (AC65-15A)As a general rule, the rivet diameter should be not lessthan three times the thickness of the thickest sheet beingriveted.

2-5. Answer A. JSAT 2-53A properly formed shop head is one-half the shank diame-ter high, its diameter is one-and-one-half times that of theshank, and it is concentric with the hole.

2-6. Answer C. JSAT 2-45The hand tools used for installation of Hi-Loks are an openend wrench and hex key (alien wrench).


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Sheet Metal Structures 2-3

2-14 D04

If a new safety belt is to be installed in an aircraft, thebelt must conform to the strength requirements in whichdocument?

A TSOC22. BAR Part 39. C 3

STC 1282.

2-14. Answer A. JSGT 14-3The standards which safety belts must meet are containedin Technical Standard Order C22. The Technical StandardOrder System is covered in FAR 21, Subpart O, TSO, C22.(B) is wrong since FAR Part 39 has to do withAirworthiness Directives. (C) is wrong since conformitywith a standard has little to do with a Supplemental TypeCertificate that is aircraft specific.

2-15 D05

Select the alternative which best describes the function ofthe flute section of a twist drill.

A 3 Forms the cutting edges of the drill point.B 3 Forms the area where the drill bit attaches to the drill

motor.C 3 Prevents overheating of the drill point.

2-16 D05

How many MS20470 AD-4-6 rivets will be required toattach a 10 x 5 inch plate, using a single row of rivets,minimum edge distance, and 4D spacing?

A 354. B356.C 352..

2-15. Answer C. JSAT 2-27 (AC65-9A)The flutes are the valley between the lands. They provide amethod for cooling oil to reach the cutting edges or lips.

2-16. Answer B. JSAT 2-55 (AC43.13-1B)

The rivets identified in this question are

4

/32" in diameter.Minimum edge distance, according to the AC43.13-1B, istwo times the diameter. This gives an edge distance ofone-fourth inch. One-fourth of an inch taken away fromeach side of the plate leaves the dimensions as 4.5" by9.5". With four times the rivet diameter spacing, thespacing will be one-half inch. Because the plate has two4V2 inch sides and two 9

1/2 inch sides (in terms of rivetinstallation), there are 28 inches total to be covered, withV2 inch spacing, or 56 rivets needed.

2-17 D05Shallow scratches in sheet metal may be repaired by

A 3 buffing. B 3

burnishing. C 3stop drilling.

2-17. Answer B. JSAT 2-84Scratches in aluminum alloy skins encourage corrosion toform, and concentrate the stresses enough that they maycause the part to crack. If the scratch is not too deep, it canbe burnished with a smooth, round-end piece of steel toforce the metal back into the scratch.

2-18 D05

What should be the included angle of a twist drill for softmetals?A. 1183.

B. 903.C. 653.

2-19 D05

When comparing the machining techniques for stainlesssteel sheet material to those for aluminum alloy sheet, it isnormally considered good practice to drill the stainlesssteel at a

A 3 higher speed with less pressure applied to the drill. B3 lower speed with less pressure applied to the drill. C 3lower speed with more pressure applied to the drill.

2-18. Answer B. JSAT 2-27An included angle of 90 degrees should be used fordrilling soft metals such as lead, copper, or very softaluminum and other soft materials such as plastic.

2-19. Answer C. JSAT 2-27 (AC65-15A)When drilling hard metals, the twist drill should have anincluded angle of 1183 , and should be operated at lowspeeds.


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2-4 Sheet Metal Structures

2-20 D05A single lap sheet splice is to be used to repair a section ofdamaged aluminum skin. If a double row of 1/8-inch rivetsis used, the minimum allowable overlap will be

A 43/4 inch.B 413/16 inch.C. 1/2 inch.

2-20. Answer B. JSAT 2-53 (AC65-15A) The minimumedge distance when riveting is two times the diameter ofthe rivet, which in this case is V4". Because this is anoverlap splice, there are two edge distances involved, or a

total of

1

/2". The minimum pitch, or distance between rivets,should be no less than three times the diameter. Thetransverse pitch, or distance between rows, should be about75% of the pitch. In this case, 75% of3/8"is

9/32". The edgedistance total ofa/2", and the transverse pitch of

9/32", gives atotal of25/32" minimum overlap. The only answer that gives atleast this overlap is 13/16 inch.

2-21 D05Which statement is true regarding the inspection of astressed skin metal wing assembly known to have beencritically loaded?

A 4 If rivets show no visible distortion, further investiga-tion is unnecessary.

B 4 If genuine rivet tipping has occurred, groups of con-secutive rivet heads will be tipped in the same direc-tion.

C 4 If bearing failure has occurred, the rivet shanks will bejoggled.

2-22 D05What is the minimum edge distance for aircraft rivets?

A 4 Three times the diameter of the rivet shank.B 4 Two times the diameter of the rivet head. C4 Two times the diameter of the rivet shank.

2-23 D05

When drilling stainless steel, the drill used should have anincluded angle of

A 4 1404 and turn at a low speed.B 41184 and turn at a high speed.C 4 904 and turn at a low speed.

2-24 D05

What is the minimum spacing for a single row of aircraftrivets?

A 4 Three times the length of the rivet shank. B4 Three times the diameter of the rivet shank. C 4Two times the diameter of the rivet shank.

2-25 D05

(Refer to figure 1.) Which of the rivets shown will accu-

rately fit the conical depression made by a 1004 counter-sink?A 3.B 2.

C 1.

2-21. Answer B. JSAT 2-84 (AC65-15A) The presenceof chipped or cracked paint around the heads of rivetsmay indicate shifted or loose rivets. If tipped or loose rivetheads are noticed, they will generally show up in groupsof several consecutive rivets, and will probably be tippedin the same direction.

2-22. Answer C. JSAT 2-53 (AC65-15A) If rivets aretoo close to the edge, the sheet is likely to tear, but if theyare too far back, the edge of the sheet will lift. Acceptedpractice is to have an edge distance of no less than twotimes the diameter of the rivet.

2-23.AnswerA. JSAT 2-27When drilling stainless steel, angles as flat as 150 can beused. Drilling of hard metals should always be done with

the drill turning at a slow speed.

2-24. Answer B. JSAT 2-54 (AC65-15A)The minimum spacing, or pitch, for a single row of rivetsis three times the diameter of the rivet shank.

2-25.Answer C. JSAT 2-36When a rivet has a 1004 countersunk head, it has a head

whose sides form a 1004 angle. In choice "A" for this ques-tion, there are 2604 of angle shown, if you don't includethe rivet's head. This leaves 1004 for the head of the rivet.


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2-26 D05Which is correct concerning the use of a file?

A 5 A smoother finish can be obtained by using a double cut file than by using a single cut file.B 5 Apply pressure on the forward stroke, only, except when filing very soft metals such as lead or aluminum.C 5 The terms "double cut" and "second cut" have the same meaning in reference to files.


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2-27 D05What is one of the determining factors which permits machine countersinking when flush riveting?

A 6 Thickness of the material and rivet diameter are thesame.

B 6 Thickness of the material is greater than the thicknessof the rivet head.

C 6 Thickness of the material is less than the thickness ofthe rivet head.


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2-26. Answer B. JSAT 2-21 (AC65-9A)Files which have one row of teeth are known as "single-cut", and those with two rows of teeth as "double-cut". Thecoarseness of the teeth are rated from coarse to fine: Coarse cut, bastard cut, second cut, smooth cut, and dead smooth cut.Generally speaking, double cut files are used for removing the most material. When cutting with the file, one should applypressure only on the forward cut, unless the material is soft. In this case the file may be permitted to remain in contact withthe material on the return to help remove chips from the teeth.

2-27. Answer B. JSAT 2-58 (AC65-15A)As a general rule, use the drill or machine countersink method when the thickness of the material is greater than thethickness of the rivet head. If the material is too thin, drill or machine countersinking will grind away too much of thematerial. In this case, dimpling should be used.

2-28 D05When repairing a small hole on a metal stressed skin, themajor consideration in the design of the patch should be

A 7 that the bond between the patch and the skin is suffi-cient to prevent dissimilar metal corrosion.B 7 the shear strength of the riveted joint.C 7 to use rivet spacing similar to a seam in the skin.

2-28. Answer B. JSAT 2-5 and 2-50When repairing a small hole on a metal stressed skin, theriveted joint needs to be designed so that the rivets takethe stress, and not the skin, so if there is a failure, it willbe the rivets that shear and not the skin that tears.


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2-29 D05Which procedure is correct when using a reamer to finish adrilled hole to the correct size?

A 8 Turn the reamer only in the cutting direction.B 8 Apply considerable pressure on the reamer when start-

ing the cut and reduce the pressure when finishingthe cut.

C 8 Turn the reamer in the cutting direction when enlarg-ing the hole and in the opposite direction to removefrom the hole.

2-29. Answer A. JSGT 9-19 (AC65-9A)When a reamer is being used, it should be rotated in thecutting direction only. The reamer should be turnedsteadily and evenly to prevent chattering or marking and

scoring of the walls.

2-30 D05Repairs or splices involving stringers on the lower surfaceof stressed skin metal wings are usually

A 8 permitted only if the damage does not exceed 6 inchesin any direction.

B 8 not permitted.C 8permitted but are normally more critical in reference

to strength in tension than similar repairs to theupper surface.

2-31 D05

When straightening members made of 2024-T4, you should

A 8 straighten cold and anneal to remove stress.B 8 straighten cold and reinforce.C 8 apply heat to the inside of the bend.

2-32 D05

Clad aluminum alloys are used in aircraft because they

A 8 are stronger than unclad aluminum alloys.B 8 are less subject to corrosion than uncoated aluminum

alloys.C 8 can be heat treated much easier than the other forms of

aluminum.

2-33 D05Aircraft structural units, such as spars, engine supports,etc., which have been built up from sheet metal, are nor-mally

A 8 repairable, using approved methods.B 8 not repairable, but must be replaced when damaged or

deteriorated.C 8 repairable, except when subjected to compressive

loads.

2-30. Answer C. JSAT 2-91 (AC43.13-1B)Repairs or splices involving stringers are allowed, but it isespecially important that care be taken when splicingstringers on the lower surface of stressed skin wings. It isin this area of the wing that very high-tension stressesexist.

2-31. Answer B. JSAT 2-92 (AC43.13-1B)Aluminum members which are slightly bent may bestraightened cold and examined with a magnifying glassfor injury to the material. Reinforce the straightened partsto an extent depending on the condition of the material.

2-32. Answer B. JSAT 2-8 (AC65-9A)Clad aluminum alloys consist of an aluminum alloy corecoated with a layer of pure aluminum, to a depth ofapproximately 51/2% on each side. The pure aluminumcoating affords a dual protection for the core, preventing

contact with any corrosive agents, and protecting the coreelectrolytically by preventing any attack caused byscratching, or from other abrasions.

2-33. Answer A. JSAT 2-51 (AC43.13-1B)Aircraft structural units, which are made from sheet metal,are generally repairable if the repair procedures used bringthe aircraft back to an airworthy condition, and meet therequirements of the Federal Aviation Administration.

2-34 D05A factor which determines the minimum space betweenrivets is the

A 8 diameter of the rivets being used.B 8 length of the rivets being used.C 8 thickness of the material being riveted.

2-34. Answer A. JSAT 2-54 (AC65-15A)Rivet spacing, known as pitch, is determined by thediameter of the rivets being used.


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Sheet Metal Structures

2-40 D05

What is indicated by a black "smoky" residue streamingback from some of the rivets on an aircraft?

A 10 Fretting corrosion is occurring between the rivetsand

the skin.B 10 Exfoliation corrosion is occurring inside thestructure. C 10 The rivets were excessively workhardened during

installation.

2-40. Answer A. JSGT 12-13Fretting corrosion may occur around rivets in a skin, andwill be indicated by dark deposits around the rivet headsstreaming out behind, give the appearance of "rivet smok-

ing".

2-41 D06

The identifying marks on the heads of aluminum alloy riv-ets indicate the

A 10 degree of dimensional and process controlobserved during manufacture.

B 10 specific alloy used in the manufacture of the rivets.C 10 head shape, shank size, material used, and

specifications adhered to during manufacture.

2-42 D06

When an MS20470D rivet is installed, its full shearstrength is obtained

A 10 by the cold working of the rivet metal in forming ashop head.

B 10 only after a period of age hardening.C 10 by heat treating just prior to being driven.

2-43 D06

Which of the following need not be considered whendetermining minimum rivet spacing?

A 10 Rivet length.B 10 Type of material being riveted.C 10 Rivet diameter.

2-44 D06

What is the purpose of refrigerating 2017 and 2024 alu-minum alloy rivets after heat treatment?

A 10 To retard age hardening. B10 To relieve internal stresses. C10 To accelerate age hardening.

2-45 D06

Under certain conditions, type A rivets are not usedbecause of their

A 10 low strength characteristics.B 10 tendency toward embrittlement when subjected to

vibration.C 10 high alloy content.

2-46 D06

A rivet set used to drive MS20470 rivets should

A 10 be nearly flat on the end, with a slight radius on theedge to prevent damage to the sheet being riveted. B

10 have a slightly greater radius than the rivet head. C10 have the same radius as the rivet head.

2-41. Answer B. JSAT 2-38 (AC65-9A)Markings on the heads of rivets are used to classify theircharacteristics. The different markings indicate the compo-sition of the rivet stock

2-42. Answer B. JSAT 2-38Type D or DD rivets are known as "ice box" rivets becausethey must be stored at low temperatures after having beenannealed. Within minutes after being removed from refrig-eration they will begin to age harden. Only after the agehardening process will they achieve their full strength.

2-43. Answer A. JSAT 2-54 (AC65-15A)The length of the rivet has no effect on the rivet spacing.

2-44. Answer A. JSAT 2-38 (AC65-9A)When an aluminum alloy is heated to a specific tempera-ture and quenched in water or in brine, it will not get hardimmediately as steel does, but will gradually become hardand gain its full strength. Rivets made of an alloy such as2017 can have their aging process retarded by storing themin a refrigerator.

2-45. Answer A. JSAT 2-38 (AC65-9A)The 1100 rivet, which is composed of 99.45% pure alu-minum, is very soft. It is generally used for riveting non-

structural parts.

2-46. Answer B. JSAT 2-64The radius of the cup of the rivet set must be slightly larg-er than the radius of the rivet head. If it is too small, it willproduce a small indentation on the head of the rivet. If it istoo large, it will produce the same indentation on the skinaround the rivet.


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SheetMetalStructures 2-9

2-47 D06

Heat treated rivets in the D and DD series that are not driv-en within the prescribed time after heat treatment orremoval from refrigeration

A 11 may be returned to refrigeration and used later with-out reheat treatment.B 11 must be reheat treated before use.C 11 must be discarded.

2-47. Answer B. JSAT 2-39 (AC65-9A)Rivets classed as "D" and "DD" become hard within a fewhours of being heat treated. If this happens, they must beheat treated again before they can be used.

2-48 D06

The dimensions of an MS20430AD-4-8 rivet are

A 11 1/8 inch in diameter and 1/2 inch long.B 11 1/8 inch in diameter and 1/4 inch long.C 11 4/16 inch in diameter and 8/32 inchlong.

2-49 D06The primary alloying agent of 2024-T36 is indicated by thenumber

A 1120.

B 1124

C 11 2.

2-47. Answer A. JSAT 2-36The first number following the letter (material code)indicates the diameter of the rivet in 1/32-inch increments.4/32= i/8-inch diameter. The number following the dash is thelength in 1/16-inch increments.

8/16 =1I2inch.

2-49. Answer C. JSAT 2-7 (AC65-9A)The first digit in this aluminum alloy 2024 number indi-cates what the primary alloying agent is. 1000 series would

indicate almost pure aluminum. 2000 series would indi-cate copper as the primary alloying agent. 3000 serieswould indicate manganese as the primary alloying agent,and so on.

2-50 D06Which part of the 2017-T36 aluminum alloy designationindicates the primary alloying agent used in its manufac-ture?

A 1120. B1117.

C 11

2.

2-50. Answer C. JSAT 2-7 (AC65-9A)In the 2xxx through 8xxx groups, the first digit indicatesthe major alloying agent used in the formation of the alloy.A head is the only way to tell what alloy the rivet isactually made of.

2-51 D06A sheet metal repair is to be made using two pieces of0.040-inch aluminum riveted together. All rivet holes aredrilled for 3/32-inch rivets. The length of the rivets to beused will be

A 11 5/16 inch.B 11 1/4inch. C 111/8 inch.

2-51. Answer B. JSAT 2-52 (AC43.13-1B)To properly form the shop head, a rivet should be equal tothe thickness of the material being joined, plus one andone-half times the rivet diameter. Two pieces of .040 mate-rial + 1.5 x .094 will give us a rivet length of .221.Standard rivet lengths are in 1/32increments, and the closeststandard length to .221 would be V4 .

2-52 D06

Most rivets used in aircraft construction have

A raised dot.B 11 smooth heads without markings.C 11 dimples.

2-53 D06

MS20426AD-6-5 indicates a countersunk rivet which has

A 11 an overall length of5/16 inch.B 11 a shank length of5/16 inch [excluding head).C 11 a shank length of5/32 inch (excluding head).

2-52. Answer C. JSAT 2-38 (AC65-9A)There are more rivets made of 2117 alloy than any other.

These rivets are identified by a single dimple on theirhead.

2-53. Answer A. JSAT 2-36 (AC65-9A)The second dash number indicates the rivet's length in six-teenths of an inch. In this case, it is 5/16 .


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2-54 D06Which rivet may be used as received without further treat-ment?

A 122117-T3. B 122017-T3.C12 2024-T4.

2-55 D06

(Refer to figure 3.) Which is the grip length of the flushrivet?

A 122.

b 12 3.

C 121.

2-54. Answer A. JSAT 2-38 i.The reason the 2117-T rivet is so popular is that it is readyfor use as received, and needs no further heat treating orannealing. It also has a high resistance to corrosion.

2-55. Answer B. JSAT 2-36 (AC65-15A)The grip length of a rivet is that portion of the rivet whichis passing through the material.

2-56 D06

Which rivets should be selected to join two sheets of .032-inch aluminum?

A 12 MS20455DD-5-3. B 12 MS20425D-4-3. C 12 MS20470AD-4-4.

2-57 D06A sheet metal repair is to be made using two pieces of 0.0625-inch aluminum riveted together. All rivet holes are drilled for 1/8-


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inch rivets. The length of the rivets to be used will be

A 13 5/16 inch.B 13 3/16 inch. C 13

5/32 inch.


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2-56. Answer C. JSAT 2-52 (AC65-15A)To join the two pieces of aluminum together, the rivet will need to be .064 long plus l 1/2 times its diameter. The AN470AD-4-4rivet is 1/8 in diameter and

1/4 long. This rivet meets the length requirement.

2-57. Answer A. JSAT 2-52 (AC43.13-1B)

To find the rivet shank length, add the material thickness and then add 1V2 times the rivet diameter. The material required to formthe shop head is .3125 or5/16 total shank length.

2-58 D06

Mild steel rivets are used for riveting

A 14 nickel steelparts. B 14magnesium parts. C14 steel parts.

2-58. Answer C. JSGT 12-9 (AC65-9A)Mild steel rivets are used for riveting steel parts. Metals ofthe same galvanic grouping show little tendency to cor-rode.


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2-64 D06

What type loads cause the most rivet failures?

A 16 Shear.

B 16 Head.C16Bearing.

2-64.AnswerA. JSAT 2-5 and 2-51 (AC65-15A)Shear failure is perhaps the most common of rivet failures.It is simply a breakdown of the rivet shank by forces actingalong the plane of two adjacent sheets, causing a slipping

action which may be severe enough to cut the rivet shankin two. If the shank becomes loaded beyond the yield pointof the material and remains overloaded, a permanent shiftis established in the sheets and the rivet shank maybecome joggled.

2-65 D06Which rivet is used for riveting magnesium alloy struc-

tures?

A 16 5056 aluminum. B16 Monel.C 16 Mild steel.

2-65.Answer A. JSAT 2-38 (AC65-9A)The 5056 rivet is used for riveting magnesium alloy struc-tures because of its corrosion resistant qualities in combi-nation with magnesium.

2-66 D06

Which rivet is used for riveting nickel steel alloys?

A 16 Mild steel.B 16 Monel.C 16 2024 aluminum.

2-67 D06

The length of rivet to be chosen when making a structuralrepair that involves the joining of 0.032-inch and 0.064-inch aluminum sheet, drilled with a No. 30 drill, is

A 16 1/4 inch.B 167/16inch.C 16 5/16 inch.

2-66. Answer B. JSAT 2-39 (AC65-9A)

Monel rivets are used for riveting nickel/steel alloys. Theycan be substituted for those made of corrosion-resistantsteel in some cases.

2-67. Answer C. JSAT 2-52The length of rivet to use is determined by adding togetherthe thickness of the material, and then adding 1V2 timesthe diameter of the rivets to this value. The thickness ofthe material in this case is .096 of an inch. A No. 30 drill is.1285 in diameter, which would take a V8 diameter rivet.One and one-half times the rivet diameter, or3/16 of an inch,plus the thickness of the material, would call for a rivet 5/16of an inch in length.

2-68 D07

(Refer to figure 4.) The length of flat A is

A.16 3.875 inches.B. 16 3.937 inches.C. 16 3.750 inches.

2-68.AnswerC. JSAT 2-71 (AC65-15A)The length of flat "A" is equal to the total length from themold point to the end of the flat, or 4", minus the setback.The setback for a 90end is equal to the metal thicknessplus the radius of the bend. The thickness of the metal, .0625 or V16", plus the bend radius of

3/16", is equal toa/4".

Four inches minus V4" leaves a flat of 3.75"

2-69 D07

(Refer to figure 4.) The amount of material required tomake the 9016 bend is

A 160.3717inch. B 16

0.3925 inch. C0.3436 inch.

2-69. Answer C. JSAT 2-73 (AC65-15A)The amount of material required to make a bend is knownas bend allowance. The bend allowance for a 90 bend maybe calculated using the formula given in the drawing.Simply substitute 3.14 for, .1875 for R, and .0625 for T.Complete the calculations.


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2-70 DO7

(Refer to figure 5, page 2-14.) What is the length of flat A?

A 17 3.9 inches.B 17 3.7 inches.C 17 3.8 inches.

2-71 D07

(Refer to figure 5, page 2-14.) What is the flat layout dimension?

A 17 6.6 inches. B 17 7.0 inches. C17 6.8 inches.


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2-70. Answer B. JSAT 2-70 (AC65-15A)Calculating setback formulas is accomplished using the value obtained from a "K" chart.

2-71. Answer C. JSAT 2-70 (AC65-15A)

The flat pattern layout for a 90 bend should be accomplished by the following steps. First calculate the setback using theformula given (.312). Then deduct the setback from the first overall dimension of flat A (2.688). Calculate the bend allowanceusing the formula given (.441). Deduct the setback from the overall dimension of the flat B (3.688). Add these three values toget the length of the flat pattern layout.


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2-72 D07If a streamline cover plate is to be hand formed using a form block, a piece of dead soft aluminum should first be placedover the hollow portion of the mold and securely fastened in place. The bumping operation should be

A 19 started by tapping the aluminum lightly around theedges and gradually working down into the center. B 19 distributed evenly over the face of the aluminum atall times rather than being started at the edges orcenter.

C 19 started by tapping the aluminum in the center until ittouches the bottom of the mold and then working outin all directions.

2-73 D07A piece of flat stock that is to be bent to a closed angle of 1519 must be bent through an angle of


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2-74 D07

When a piece of aluminum alloy is to be bent using a min-imum radius for the type and thickness of material,

A 22 less pressure than usual should be applied with themovable (upper) clamping bar.

B 22 the layout should be made so that the bend will be9022 to the grain of the sheet.

C 22 the piece should be bent slowly to eliminatecracking.

2-74. Answer B. JSAT 2-69 (AC65-15A)The sheet metal we use for aircraft construction andrepair was formed from an ingot of aluminum alloypassed through a series of rollers until it was reduced to

the thickness needed. In the process of rolling, the metalassumes a grain structure which is easy to see in a pieceof sheet aluminum alloy. When laying out a pattern, thebends in the metal should be made across the grain asmuch as possible.

2-75 D07

The flat layout or blank length of a piece of metal fromwhich a simple L shaped bracket 3 inches by 1 inch is tobe bent depends upon the radius of the desired bend. Thebracket which will require the greatest amount of materialis one which has a bend radius of

A 221/2 inch.B 221/4 inch..

C 221/8 inch.

2-75. Answer C. JSAT 2-69 (AC65-15A)The smaller the bend radius in an L-shaped bracket, thegreater the amount of material needed to make the bracket.If the bracket is made from 1/8 sheet metal, with a bendradius of1/8 , the flat layout would need to be 3.742 long.As the bend radius becomes greater, the length of the flatlayout becomes less.

2-76 D07

If it is necessary to compute a bend allowance problemand bend allowance tables are not available, the neutralaxis of the bend can be

A 22 found by adding approximately one half of the stockthickness to the bend radius.

B 22 represented by the actual length of the requiredmaterial for the bend.

C 22 found by subtracting the stock thickness from thebend radius.

2-76. Answer A. JSAT 2-70 (AC65-15A)The line along which the portion of sheet being bent doesnot shrink or stretch is called the neutral axis of the metal.It is not located exactly in the center of the sheet, but isactually about 44.5% of the sheet thickness from the insideof the bend. For practical purposes, we can consider this tobe in the center.

2-77 D07

Unless otherwise specified, the radius of a bend is the

A 22 radius of the neutral axis plus one half thethickness

of the metal being formed.B 22 inside radius of the metal being formed.C 22 inside radius plus one half the thickness of themetal

being formed.

2-78 D07

The sharpest bend that can be placed in a piece of metalwithout critically weakening the part is called the

A 22 minimum radius of bend.

B 22 bend allowance.C 22 maximum radius of bend.

2-79 D07

The most important factors needed to make a flat patternlayout are

A 22 radius, thickness, and mold line. B22 the lengths of the legs (flat sections). C22 radius, thickness, and degree of bend.

2-77. Answer B. JSAT 2-70 (AC65-15A)The radius of bend on a sheet of material is the radius ofthe bend as measured on the inside of the curved material.

2-78. Answer A. JSAT 2-70 (AC65-15A)The radius of bend of a sheet of material is the radius of thebend as measured on the inside of the curved material. Theminimum radius of bend of a sheet of material is thesharpest curve, or bend, to which the sheet can be bentwithout critically weakening the metal at the bend.

2-79. Answer C. JSAT 2-70 (AC65-15A)In order to make a flat pattern layout, the technician mustknow the radius of the bend, because this must be account-ed for when calculating bend allowance. The thickness ofthe material is needed so the technician can calculate thesetback, and thickness is also accounted for in calculatingbend allowance. The degree of bend is also needed whencalculating bend allowance.


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2-16 Sheet MetalStructures

2-80 D07

A piece of sheet metal is bent to a certain radius. The cur-

vature of the bend is referred to as the

A 23 bend radius. B23 bend allowance. C23 neutral line.

2-81 D07

You can distinguish between aluminum and aluminumalloy by

A 23 testing with a 10 percent solution of caustic soda.B 23 filing the metal.C 23 testing with an acetic acid solution.

2-82 D07

The purpose of a joggle is to

A 23 decrease the weight of the part and still retain thenecessary strength.

B 23 increase obstruction for a sheet or an extrusion. C23 allow clearance for a sheet or an extrusion.

2-83 D07

When bending metal, the material on the outside of thecurve stretches while the material on the inside of thecurve compresses. That part of the material which is notaffected by either stress is the

A 23 mold line.B 23 bend tangent line.

C 23 neutral line.

2-84 D07

(Refer to figure 6.) Determine the dimensions of A, B, andC in the flat layout.Setback = .252Bend allowance = .345

A A= 1.252B = 2.504C = 1.752.

B23 A =.748

B = 2.252C = 2.004.

C A= .748B = 1.496C = 1.248.

2-80. Answer A. JSAT 2-70 (AC65-15A)The bend radius for a piece of sheet metal is always to theinside of the metal being formed, unless otherwise stated.

2-81. Answer A. (43.13-1B) (AC65-9A)Aluminum alloy sheets are marked with the specificationnumber on approximately every square foot of material.If for any reason this identification is not on the material,it is possible to separate the heat-treatable alloys fromthe non-heat-treatable alloys by immersing a sample ofthe material in a 10% solution of caustic soda. The heat-treatable alloys will turn black due to the copper content.

2-82. Answer C. JSAT 2-82 (AC65-15A)

A joggle is an offset formed on an angle strip to allowclearance for a sheet or an extrusion.

2-83. Answer C. JSAT 2-70 (AC65-15A)Bending a strip compresses the material on the inside ofthe curve and stretches the material on the outside of thecurve. However, at some distance between these twoextremes lies a space which is not affected by either force.This is known as the neutral line or neutral axis.

2-84. Answer C. JSAT 2-70 (AC65-15A)The dimension for flat "A" is its mold line of 1 minus thesetback. The setback is given in this question as .252, sothe dimension of flat "A" is .748 . The dimension for flat"B" is its mold line of 2 minus two setbacks (one at eachend), or 1.496 . The dimension of flat "C" is its mold lineof 1.5 minus the setback, or 1.248.


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SheetMetalStructures 2-17

2-85 D07

(Refer to figure 6.) What is dimension D?Setback = .252Bend allowance = .345


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A 253.841. B 25 3.492. C 4.182


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2-88 D07On a sheet metal fitting layout with a single bend, allow for stretching by


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A 28 adding the setback to each leg.B 28 subtracting the setback from one leg.C 28 subtracting the setback from both legs.

2-89 D07

The aluminum alloys used in aircraft construction are usually hardened by. which method?

A 28 Heat treatment.B Aging.C 28 Cold working.


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2-88. Answer C. JSAT 2-71 (AC65-15A)When accounting for the total flat layout dimension when the object has a single bend, the two flats forming the bend mustboth have the setback subtracted from their mold line dimension, and then the bend allowance is added in.

2-89. Answer A. JSAT 2-8 (AC65-9A)

Heat treatment is a series of operations involving the heating and cooling of metals in the solid state. Its purpose is to changea mechanical property or combination of mechanical properties so that the metal will be more useful, serviceable, andsafe for a definite purpose. By heat treating, a metal can be made harder, stronger, and more resistant to impact.

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2-Sheet Metal Structures Text