It is normal practice to fit control surfaces of some kind to all the lifting surfaces on the aircraft (or in the case of the tail, provide all steerable surfaces). Conventionally, these provide ailerons
Figure 2.4 A typical carbon spar and foam wing with SLS nylon ribs at key locations (note the separate aileron and flap with associated servo linkages).
and flaps on the main wings and elevators and rudders on the tail (Figure 2.4 shows a wing with an aileron and a flap). We mostly opt for simple hinged conventional surfaces but have experimented with Fowler flap mechanisms and main wing morphing for roll control. If “V” or inverted-“V” tails are used, the rudders and elevators become combined, and a suitably mixed control strategy is required to separate the control functions. To make our designs aerodynamically and structurally efficient, the tails adopt the same construction philosophy as the main surfaces: that is, we use a carbon spar onto which small ribs are placed to support a numerically cut foam body. By carrying the spar along the length of the wing, tail, or rudder, this can strengthen the main element against torsional loads while providing a convenient hinge point, as can also be seen in Figure 2.4 (note the pockets for control servos). The surfaces are operated by standard servos attached to the ribs with through-bolted horns with load spreaders where they meet the foam. If redundant systems are required, the functions of a single control surface can be provided with multiple elements each with its own servo, albeit at increased cost and weight.