Rudder Input Maneuver

Rudder input maneuver is used to estimate yaw derivatives and rudder control effectiveness. Starting from a trimmed level flight, a doublet or 3-2-1-1 command is applied to rudder pedals keeping the thrust constant. The pulse width of the input signal is appropriately chosen to match the predicted roll-roll frequency.

7.6.1.6 DR Maneuver

The purpose of the DR maneuver is to excite the DR mode of the test aircraft and determine the LD aerodynamic derivatives. Starting from the level trimmed flight (at the chosen flight condition), an aileron stick command is given first and then a command is given to rudder pedals. The command inputs should be either doublet or 3-2-1-1; the thrust is kept constant. The response should be allowed to settle for 5-10 s and the record should be for about 15-20 s, since two consecutive responses (due to aileron and rudder inputs) should be analyzed, preferably in one go. The maneuver is of a short-period kind and the data generated enable the determination of aileron and rudder effectiveness as well as roll/yaw motion-related aerodynamic derivatives (Lp, Lp, Np, Nr). Typical DR maneuver flight-time histories are shown in Figure 7.6.

7.6.1.7 Steady Heading Sideslip Maneuver

In a steady heading sideslip (SHSS) maneuver, starting from level flight, the rudder pedal is applied and held constant to allow the sideslip angle to build up with minimum variation in speed. As the airplane begins to yaw and enter into a skidding turn, it is banked in the opposite direction by applying aileron deflection to maintain a constant heading. As the rudder pedal is further applied, the aileron deflection is adjusted to keep the heading angle constant; the speed variation is marginal. After completing the sideslip maneuver with one rudder pedal, the aircraft is retrimmed and the procedure repeated with the other rudder pedal. This maneuver, along with the DR, can be used to generate the requisite information to assess the aircraft’s directional and dihedral stability. Typical SHSS maneuver flight-time histories are shown in Figure 7.7.