What should the minimum spacing be between protruding head rivets?

The minimum spacing between protruding head rivets being set at three rivet diameters is based on industry standards to ensure structural integrity and optimal load distribution. This spacing helps to prevent issues such as shear failure and ensures that the rivets can effectively handle the loads they are subjected to without compromising the surrounding material. By maintaining this distance, it reduces the likelihood of inter-rivet damage and minimizes stress concentrations that could lead to material fatigue over time. This guideline is crucial for maintaining overall airframe strength and durability.