Horizontal stabilizers serve three purposes: 1.) flight stability; 2.) flight path alteration in pitch direction (i.e. descending or climbing); 3.) aileron effect enhancement in roll direction (i.e. rolling).

While with most of the aircrafts horizontal stabilizers are fixed and moveable surfaces provide pitch control, in case of the F-15 horizontal stabilizers rotate as a whole. For economical reasons, left and right stabilizers are purposefully designed to be interchangeable.

They are connected to the left and right booms of the aft fuselage via a single connection point and are rotated by hydraulic actuators (developed by National Water Lift). When there is no hydraulic pressure in the actuators, the stabilizers can be moved even by hand, though not very easily.

Driven by the F-15's semi-fly-by-wire system called CAS (Control Augmentation System), horizontal stabilizers can rotate independently from each other giving the aircraft greater flight stability and crisper reactions when maneuvering. If left alone (not controlled by CAS) the horizontal stabilizers would remain aerodynamically stabilized in neutral position when in level flight.

The leading edge of the horizontal stabilizer has a special 'sawtooth' shape, which was not there upon initial design of the F-15. It appeared later during flight tests in order to eliminate harmful resonances at supersonic speeds. Now it is a quite special outer feature to all models of the Eagle. It is worth mentioning, that although this sawtooth does its job well, it is a very high stress part of the aircraft and it tends to rip away sometimes - a typical flight damage to the F-15 which often remains unnoticed by the pilot as the CAS compensates for the loss of the sawtooth.

The outer sections, leading and trailing edges of the horizontal stabilizers are made from aluminium, while the inner section is made from boron/epoxy composite material, this latter providing structural strength. Note, that boron fibers are cancerous if they get into the bloodstream, this is an issue during manufacturing and during maintenance (if the horizontal stabilizer is broken or cracked for some reason).

Technical Data

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