Mastering Aircraft Spar Repair

Repairing Aircraft Spar: Methods and Considerations

• A damaged spar in an aircraft can be spliced at almost any point, except at certain fittings.
• The damaged spar should not overlap any part of the splice, and reinforcement plates should not interfere with the attachment or alignment of fittings.
• A scarf joint can be used to repair a spar, but it requires precise cutting on both adjoining pieces to achieve full strength.
• The mating surfaces of a scarf joint must be smooth, and various tools can be used to achieve this, such as a plane or a router.
• Another method of cutting a scarf joint involves using a scarf cutting fixture with a router to create a feathered edge.
• Local damage to the top or bottom edge of a solid spar can be repaired by removing the damaged portion and fabricating a replacement filler block.
• Longitudinal cracks in a solid spar can be repaired using plywood doublers that extend beyond the crack.
• Built-up spars can be repaired using plywood reinforcement plates and solid wood filler blocks.
• The wood used for repairs should match the original spar in type and size, and plywood webs should be reinforced with the same type of plywood.
• Splices and scarf cuts must have the correct slope and the face grain should run in the same direction as the original member.
• No more than two splices should be made in a single spar, and if a satisfactory repair cannot be achieved, the spar should be replaced.
• Bolt and bushing holes in aircraft structures must fit snugly, and loose bolts or bushings can cause enlargement of the hole or cracks in close proximity to the holes.