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Ailerons/Roll Control

Most conventional winged aircraft have aileron control surfaces toward the outer ends of the main wings. The ailerons require some kind of hinge plus an actuator mechanism. If extra redundancy is required, each one can be multipart with its own actuator. Since they are in continuous motion during flight, it is important that they be low-drag devices, yet they need to be large enough to provide sufficient roll authority, especially at the low speeds encountered during takeoff and landing. Figure 3.8 shows a typical aileron arrangement, in this case with a two-part control surface but sharing a common hinge spar that supports both aileron parts and the inner wing flap. Notice that planform taper has been achieved by reducing the depth of each of the three control surfaces when moving from root to tip.

We typically design the ailerons to extend over the final 30% of the chord and the outer 50% of the wing. However, if very low landing speeds are required, this may necessitate large flaps extending over more than half of the wing span. In such cases, the available planform space for ailerons can be more limited - if smaller ailerons are to be fitted, care must be taken during the analysis stages to ensure sufficient roll authority will be available, perhaps by increasing the depth of the aileron surfaces to as much as 50% of chord. Note also that the outermost parts of the wing are most affected by the tip vortex, and so the amount or roll control contributed by these parts of the aileron will be correspondingly reduced.

Sometimes, to overcome the drag associated with a flapped aileron, roll control may be achieved by other means, such as via synthetic jets, tiperons, or wing warping - wing warping is how the original Wright brothers aircraft worked. We continue to research such schemes but

UAV that uses wing warping for roll control

Figure 3.9 UAV that uses wing warping for roll control.

UAV that uses tiperons for roll control

Figure 3.10 UAV that uses tiperons for roll control.

generally consider them to be too experimental for routine aircraft builds.[1] Figure 3.9 shows an aircraft that uses wing warping for roll control, and Figure 3.10 shows a tiperon system. In both cases, fences are used to help control tip vortex flows.

  • [1] See, for example, the FLAVIIR project that investigated the use of synthetic jets to control roll, https://www.theengineer.co.uk/issues/september- 2010- online/first- flight-for- flapless- uav/.
 
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