By John Routledge

Aircraft rivets

The two major types of rivets used in aircraft are the common solid shank rivets, which must be driven using an air-driven gun and bucking bar; and special (blind) rivets, which are installed with special installation tools. Solid shank rivets are used widely during assembly and repair work. They are identified by the material of which they are made, the head type, size of shank, and temper condition.

The material used for the majority of solid shank rivets is aluminum alloy. The strength and temper conditions of aluminum alloy rivets are identified by digits and letters similar to those used to identify sheet stock. The 1100, 2017-T, 2024-T, 2117-T, and 5056 rivets are the six grades usually available. AN-type aircraft solid rivets can be identified by code markings on the rivet heads. A rivet made of 1100 material is designated as an "A" rivet, and has no head marking. The 2017-T alloy rivet is designated as a "D" rivet and has a raised teat on the head. Two dashes on a head indicate a 2024-T alloy designated as a "DD" rivet. The 2117-T rivet is designated as an "AD" rivet, and has a dimple on the head.

A "B" designation is given to a rivet of 5056 material and is marked with a raised cross on the head. Each type of rivet is identified by a part number to allow the user to select the correct rivet. The numbers are in series and each series represents a particular type of head.

Countersunk head rivets are used where a smooth finish is desired. The 100-degree countersunk head has been adopted as the standard in the United States. The universal head rivet (AN470) has been adopted as the standard for protruding-head rivets, and may be used as a replacement for the roundhead, flathead, and brazier head rivet. These rivets can also be purchased in half sizes by designating a "0.5" after the main length.

Replace rivets with those of the same size and strength whenever possible. If the rivet hole becomes enlarged, deformed, or otherwise damaged; drill or ream the hole for the next larger size rivet. Rivets may not be replaced by a type having lower strength properties, unless the lower strength is adequately compensated by an increase in size or a greater number of rivets. It is acceptable to replace 2017 rivets of 3/16 inch diameter or less, and 2024 rivets of 5/32 inch diameter or less with 2117 rivets for general repairs, pro vided the replacement rivets are 1/32 inch greater in diameter than the rivets they replace.

Rivet edge distance is defined as the distance from the centre of the hole to the nearest edge of the sheet. Rivet spacing is the distance from the centre of the rivet hole to the centre of the adjacent hole. Unless structural deficiencies are suspected, the spacing and edge distance should duplicate those of the original aircraft structure. If structural deficiencies are suspected, the following may be used in determining minimum edge distance and rivet spacing. Special fasteners may require an FAA field approval.

Blind rivets are used under certain conditions when there is access to only one side of the structure. Typically, the locking characteristics of a blind rivet are not as good as a driven rivet. Therefore, blind rivets are usually not used when driven rivets can be installed.

The 2117 rivets may be driven in the condition received, but 2017 rivets above 3/16 inch in diameter and all 2024 rivets are to be kept packed in dry ice or refrigerated in the "quenched" condition until driven, or be re heat treated just prior to driving, as they would otherwise be too hard for satisfactory riveting.

Aerospace fasteners, special fasteners and blind fasteners.

When solid shank rivets are impractical to use, then special fasteners are used. Special fastening systems used for aircraft construction and repair are divided into two types, special and blind fasteners. Special fasteners are sometimes designed for a specific purpose in an aircraft structure. The name "special fasteners" refers to its job requirement and the tooling needed for installation. They are used in fluid-tight areas, on aircraft in air intake areas where rivet parts may be ingested by the engine, on aircraft control surfaces, hinges, hinge brack ets, flight control actuating systems, wing attachment fittings, landing gear fittings, on floats or amphibian hulls below the water level, or other heavily-stressed locations on the aircraft. For metal repairs to the airframe, the use of blind rivets must be specifically authorized by the airframe manufacturer or approved by a representative of the FAA.

Self plugging friction-lock cherry rivets. This patented rivet may be installed when there is access to only one side of the structure. The blind head is formed by pulling the tapered stem into the hollow shank. This swells the shank and clamps the skins tightly together. When the shank is fully upset, the stem pulls in two. The stem does not fracture flush with the head and must be trimmed and filed flush for the installation to be complete. Because of the friction-locking stem, these rivets are very sensitive to vibrations. Inspection is visual, with a loose rivet standing out in the standard "smoking rivet" pattern. Removal consists of punching out the friction locked stem and then treating it like any other rivet. Mechanical-lock rivets have a device on the puller or head which locks the centre stem into place when installed. Many friction-lock rivet centre stems fall out due to vibrations; this in turn, greatly reduces its shear strength. The mechanical-lock rivet was developed to prevent that problem. Various manufacturers make mechanical-lock fasteners such as: Bulbed Cherrylock, CherryMax, Olympic-Loks, and Huck-Loks.