4.Although the way in which the controls are operated varies from one aircraftto another, a given movement of the control column will always make the aircraftturn in the same direction:Moving the control column forwards makes the aircraft pitch nose down;backwards lifts the nose;Moving or turning the controls to the left raises the left aileron and lowers theright one, making the aircraft roll to the left;Pushing the right rudder pedal deflects the rudder to starboard (right), andcauses the aircraft to yaw to starboard.STICK FORCES5.As aircraft speeds increase, so air flows faster over the control surfaces andthis greatly increases the air loads the pilot has to overcome to move the controlsurfaces. In other words, he must push or pull harder on the controls to move theelevators, etc. The air loads increase as the square of the speed, as you have seenin Chapter 1. These air loads on the control surfaces cause the pilot two mainproblems:33.4.9-2CHAPTER 9Fig 9-1 Control ColumnOperationFig 9-2 Rudder BarOperation
To hold the controls against the air flow could be very tiring, so the designerfits some method of adjustment to the control surfaces which the pilot canoperate in flight. In this way, he trims out the control loads and so can holdthe aircraft in any attitude for a long time without becoming tired.As aircraft speeds increase the forces on the control surfaces become sogreat that the pilot finds it difficult to move them at all. As you have seen,hydraulic power can be used to help the pilot to move the surfaces, or tomove them for him. But before this stage is reached there are variousaerodynamic ways of using the airflow itself to helpthe pilot to move thesurface. Some of the devices which do this are balance tabs, inset hinge andhorn balances.6.There are several methods of operating controls, and these fall into thecategories of manual, power-assisted and power-operated control systems. Thesemay be used in combination with, for example, power-assisted controls being usedfor the rudder and elevators and manual (unassisted) controls for the ailerons, whichoften are easier to move. These various ways of moving control surfaces haveadvantages and disadvantages.For large aircraft and many fast jets, the use of power controls is the only feasiblechoice, because the controls would be so difficult for the pilot to move, and becauseof the control circuits used. For light aircraft and small commercial aircraft, thesimplicity, lightness and cost of manual controls may be used to best advantage,and no power assistance is necessary.For those aircraft between the two extremes, power assistance is often the idealsolution, with some of the control effort being applied by the pilot and some assistanceby mechanical actuators. This takes advantage of smaller actuators, gives the pilotmore feel, since he is still operating the control surfaces directly, and gives a manualbackup if the power-assistance system fails.
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- Summer '18