8-24] AIRCRAFT MOTIONS 433 



Over the low-frequency range of^LS, iGs] « |Gi|, and the equation becomes 



Jtl = Jls + ~ (8-27) 



Since G1G2 » 1 in the frequency region of interest, Jtl ~ Als as desired. 

 Of course, these relationships hold only if the loop gains are high and the 

 control loops are stable. These are conflicting requirements which are 

 discussed in the following paragraphs where the design of the stabilization 

 loops is covered in detail. 



8-23 AI RADAR ANGLE STABILIZATION 



The primary function of the AI radar control system is to detect a target 

 and to provide tracking information to the interceptor fire-control system 

 about the target's relative position and motion. 



The degree of space stabilization that must be provided depends on 

 {a) the magnitude of the interceptor space motions during an attack and 

 {b) the accuracy with which the target position and rates must be known. 

 These topics are considered in more detail in subsequent sections. 



8-24 AIRCRAFT MOTIONS 



The first step in the design of the stabilization system is to obtain a 

 description of the aircraft angular^^ motions that will occur in the detection 

 and tracking phases of interceptor operation. The basic angular motions 

 are the roll, pitch, and yaw of the aircraft. The origins of these motions 

 may be outlined as follows. First of all, the aircraft must maneuver in 

 accordance with the vectoring commands or the fire-control system 

 commands. Superimposed on these desired maneuvering motions are the 

 oscillatory motions resulting from lightly damped aircraft motions which 

 are excited by the control actions and the tendency of the human pilot 

 (or autopilot) to overcorrect an error. Finally angular motions will be 

 excited by disturbances such as wind gusts and release of armament or 

 other stores {interference motions). 



For purposes of preliminary design of the stabilization loops, these 

 motions may be described in several ways: 



1. By the maximum expected roll, pitch, and yaw angles and angular 

 rates and derivatives. These data can be estimated from attack-course 

 studies and knowledge of aircraft operation. 



2. By the time-response characteristics of the aircraft in yaw, pitch, and 

 roll incident to impulse inputs. This information can be derived from 

 equations which describe aircraft dynamics. 



i^Linear motion is not considered here since stabilization control loops are pricipally con- 

 cerned with angular motion. Linear motion is considered in Paragraph 9-18 in systematic 

 errors. 



