The aircraft has an all-metal semi-monocoque fuselage of 58 feet 3 inch in length. The fuselage is of conventional semi-monocoque construction, and has a central pod and lateral twin-boom configuration. The F-15 airframe contains 25.8 percent titanium by weight, most of it concentrated around the engines and in the inboard sections of the wings. The three main wing spars and the bulkheads connecting them and the frames of the engine pods are of titanium. Aft of the forward main wing spar, the fuselage skin is also of titanium. The cantilever booms outboard of each engine which carry the twin fins and horizontal stabilators are made of titanium, as are the stabilator attachments and the spars of the fins. There is a titanium firewall between the two engines to prevent a fire in one engine from spreading to the other.
The heart of the aircraft structure is a set of four carry-through frames which run across the central fuselage, each with holes cut into them to allow the engine air intake ducts to pass through. At each end, they form the main attachment points for the wings, the three aft frames being attached to the three wing spars, and the forward point attaching to a leading-edge member. Machined titanium frames in the rear fuselage maintain structural integrity and provide the main mountings for the engine installation....
...The tail unit of the F-15A is an all-metal structure consisting of twin fins and rudders made of boron composite skin over honeycomb material.