Aircraft Maintenance: Joggle Joint with Doubler

Joggle Joint with Doubler

• A joggle is formed to allow two pieces of metal to be on the same plane, rather than pulling the doubler against the skin with rivets.

Strength of Joints

• The strength of a joint is governed by plate specification, rivet specification, and rivet spacing.
• Plate specification involves selecting a material and gauge that can withstand tensile and bearing loads.
• Rivet specification involves selecting a rivet that can withstand shear loads, with a diameter 2.5 times the thickness of the plate.
• Rivet spacing is determined to give the joint optimum strength characteristics.

Rivet Sphere of Influence

• The sphere of influence of a rivet is the area in which the closed rivet maintains the plates in close proximity, approximately 5D (5 times the diameter of the fastener).
• When the pitch of rivets is 4D, the sphere of influence of each rivet overlaps, providing a fluid-tight joint.

Rivet Positions

• The position of rivets relative to each other and the edge of the sheet material is important.
• Rivets must not be too close together, as an excessive number of holes weakens the joint.
• Rivets must not be too far apart, as there are too few to take the load, causing leakage in pressurized areas.
• Rivets must not be too near the edge of the sheet, as they tear through the material when the joint is under load.

Pitch Circle Diameter (PCD)

• Pitch circle diameter is the diameter of a circle dictated by the pitch of a number of rivets of a given size.
• It is used to determine the diameter of circular repairs.

Rivet Layout

• Single-row layout is used chiefly on attachment and lightly stressed joints.
• Multiple-row layout is common for watertight joints and in places of high stress where thick gauge plate is used.
• Staggered layout is used as an alternative to multiple rows in watertight joints, circular patches, etc.

Riveting Tools and Procedures

• Clearance is important to avoid shaving off the protective oxide coating on the rivet or buckling the sheet metal.
• Air pressure required to operate rivet guns is around 80 lb/in2.
• Retaining springs are used to hold the snap in the gun, but can fail to hold the snap, resulting in serious injury or damage.
• Rivet guns must be handled with care, and the rule is to never play with rivet guns.

Squeeze Riveting

• The squeeze method is used to install large quantities of rivets along an easily accessible edge.

Rivet Sets (Snaps)

• Ensure that the snap used is the correct size for the rivet to avoid marking the rivet head or skin.

Rivet Inspection

• Rivets should be inspected to ensure they are tight and fully formed.
• Rivet heads must not be deformed or cracked, and the surrounding area should be free from distortion and undamaged by the riveting tools.
• Rivets that are obviously not performing their function should be replaced, but replacing rivets that are only slightly below standard might do more harm than leaving them in position.

Faults

• Cracks in the rivet head are not normally acceptable.
• Snap heads formed on the tail of the rivet can result in faults such as a ‘flash’ round the rivet head or small head, accompanied by snap marks on the skin.
• Countersinking too deep, holes out of line, high shop head, clinched shop head, flattened shop head, uneven shop head, skin bulged, swelling between sheets, and open head are all faults that can occur during riveting.