Control Surface Travel In order for a control system to function properly, it must  be correctly adjusted. Correctly rigged control surfaces  move through a prescribed arc (surface-throw) and are  synchronized with the movement of the flight deck controls.  Rigging any control system requires that the aircraft  manufacturer’s instructions be followed as outlined in their  maintenance manual. Therefore, the explanations in this chapter are limited to the  three general steps listed below:  The range of movement of the controls and control  surfaces should be checked in both directions from neutral.  There are various tools used for measuring surface travel,  including protractors, rigging fixtures, contour templates,  and rulers. These tools are used when rigging flight control  systems to ensure that the aircraft is properly rigged and  the manufacturer’s specifications have been complied with.  Rigging fixtures and contour templates are special tools  (gauges) designed by the manufacturer to measure control  surface travel. Markings on the fixture or template indicate  desired control surface travel. In many instances, the aircraft  manufacturer gives the travel of a particular control surface  in degrees and inches. If the travel in inches is provided, a  ruler can be used to measure surface travel in inches. Protractors are tools for measuring angles in degrees. Various  types of protractors are used to determine the travel of flight  control surfaces. One protractor that can be used to measure  aileron, elevator, or wing flap travel is the universal propeller  protractor shown in  Figure 2-90 . This protractor is made up of a frame, disk, ring, and two  spirit levels. The disk and ring turn independently of each  other and of the frame. (The center spirit level is used to  position the frame vertically when measuring propeller  blade angle.) The center spirit level is used to position the  disk when measuring control surface travel. A disk-to-ring  lock is provided to secure the disk and ring together when  the zero on the ring vernier scale and the zero on the disk  degree scale align. The ring-to-frame lock prevents the ring  from moving when the disk is moved. Note that they start at  the same point and advance in opposite directions. A double  10-part vernier is marked on the ring.  The rigging of the trim tab systems is performed in a similar  manner. The trim tab control is set to the neutral (no trim)  position, and the surface tab is usually adjusted to streamline  with the control surface. However, on some aircraft, the  specifications may require that the trim tabs be offset a degree  or two from streamline when in the neutral position. After  the tab and tab control are in the neutral position, adjust the  control cable tension.  Pins, usually called rig pins, are sometimes used to simplify  the setting of pulleys, levers, bellcranks, etc., in their neutral  positions. A rig pin is a small metallic pin or clip. When rig  pins are not provided, the neutral positions can be established  by means of alignment marks, by special templates, or by  taking linear measurements.  If the final alignment and adjustment of a system are correct,  it should be possible to withdraw the rigging pins easily. Any  undue tightness of the pins in the rigging holes indicates  incorrect tensioning or misalignment of the system. Figure 2-90.  Universal propeller protractor.  1.  Lock the flight deck control, bellcranks, and the  control surfaces in the neutral position.  2.  Adjust the cable tension, maintaining the rudder,  elevators, or ailerons in the neutral position.  3.  Adjust the control stops to limit the control surface  travel to the dimensions given for the aircraft being  rigged.  3 0  2 0 1 0$_{0}$ 1 0 2 0 3 0 1 0 0 1 0 Disk degree scale Ring vernier scale Disk-to-ring lock on ring engages only  when zeros on scales are aligned. Ring adjuster Center spirit level Disk adjuster Ring Ring-to-frame lock Corner spirit level  on frame folded in Disk 2-53