A large part of the activities when building aircraft is drilling holes and handling bolts, which usually go into the drilled holes. Aircraft kits are nowadays pre-punched, this means that all (well, almost all) holes are already in the skins or ribs.
These holes were sometimes undersized meaning that cleco's can be installed but rivets will not. You will have to enlarge the holes during assembly and alignment. Some kit manufacturers are supplying their kits pre-drilled to the correct size these days.
For an aircraft structure to be able to withstand the designed loads the bolts need to be torqued to the correct value. We will provide you with some tips for using proper procedures for installing and torquing AN bolts.
Throughout the building process there will be numerous instances where bolts are used to fasten parts or materials together. In some cases it may be for the builder to determine the correct length of the bolt to be used.
But whatever you do: ONLY use aviation grade bolts in your project and torque them to the correct values!
The "Rule of Thumb" for determining bolt length is that the bolt must be long enough to pass through the parts or material being fastened together so that:
More precise determinations of grip length are found in a number of books including the Standard Aircraft Maintenance Handbook (its a must have for builders, published by Jeppesen Sanderson Inc.).
The bolts used in aircraft are about .001 to .003 inch smaller than their nominal diameter. This permits them to be installed in a properly drilled hole. The bolt should lie solidly against the surface of the material. Any burr must be removed before it is inserted and the shank (grip) should extend entirely through the hole, no threads should be in contact with the bearing surfaces, see above.
Most applications with bolts require the use of a washer, use the specified type and torque to the specifications of the manufacturer.
The following information is provided for reference when using AN grade hardware. Most of the time torque values are done to feel. But this table does provide a good outline. Occasionally bolts, other than a standard bolt will be called out for use in the builders manual. Please ensure that these special bolts are used where needed. The aircraft designer selected these as they provide the strength for the connection where a standard bolt can not provide this.
Standard torque table (in inch/lbs):
|Fine thread series||Coarse thread series|
|Bolt Size||Standard Nuts||Shear Nuts||Bolt Size||Standard Nuts||Shear Nuts|
|10-32||20 - 25||12 - 15||8-32||12 - 15||7 - 9|
|1/4-28||50 - 70||30 - 40||10-24||20 - 25||12 - 15|
|5/16-24||100 - 140||60 - 85||1/4-20||40 - 50||25 - 30|
|3/8-24||160 - 190||95 - 110||5/16-18||80 - 90||48- 55|
|7/16-20||450 - 500||270 - 300||3/18-16||160 - 185||95 - 110|
|1/2-20||480 - 690||290 - 410||7/16-14||235 - 255||144 - 155|
|9/16-18||800 - 1000||480 - 600||1/2-13||400 - 480||240 - 290|
|5/8-18||1100 - 1300||660 - 740||9/16-12||500 - 700||300 - 420|
|-||-||-||5/8-11||700 - 900||420 - 540|
Reference: Standard Aircraft Maintenance Handbook.
Certain standards are to be followed when installing bolts in aircraft, some of these recommendations are here:
Standard nuts (amongst others) are: MS20365, AN310, AN315. Shear nuts are: MS20364, AN320, AN316, AN23-31