NAVWEPS OO-BOT-BO  STABILIJY AND CONTROL  the critical speed, with some limited amount  of force applied by the pilot (usually the limit  of lateral force is assumed to be 30 lbs.), the  Pb  ailerons cannot be held at full deflection, ~~  drops, and rate of roll decreases.  In this exam-  ple, the rolling performance at high speeds is  limited by the ability of the pilot to maintain  full deflection of the controls.  In an effort to  reduce the aileron hinge moments and control  forces, extensive application is made of aerody-  namic balance and various tab devices. How-  ever, 100 percent aerodynamic balance is not  always feasible or practical but a sufficient  Pb  value of -  must be maintained at high speeds.  ZV  given to the airplane size.  For geometrically  similar airplanes, a certain deflection of the  I!!.  ailerons will produce a fixed value of zlr mde-  pendent of the airplane size. However, the  roll rate of the geometrically similar airplanes  at a given speed will vary inversely with the  span, b.  If  Thus, the smaller airplane will have an ad-  vantage in roll rate or in time to accelerate  through a prescribed angle of roll.  For ex-  ample, a one-half scale airplane will develop  twice the rate of roll of the full scale airplane.  This relationship points to the favor of the  small, short span airplane for achieving high  roll performance.  Pb -  ~-constant  p=(constant) 7  (  )  Rather than developing an extensive weight  lifting  program mandatory for all  Naval  Aviators, mechanical assistance  in lateral con-  trol can be provided.  If a power boost is  provided for the lateral control system, the  rolling performance of the airplane may be  extended to higher speeds since pilot effort  will not be a limiting factor.  The effect of a  power boost is denoted by the dashed line  extensions of figure 4.30.  A full powered,  irreversible lateral control system is common  for high speed airplanes. In the power oper-  ated system there is no immediate limit to the  deflection of the control surfaces and none of  the aberrations in hinge moments due to com-  pressibility are fed back to the pilot.  Control  forces are provided by the stick centering  lateral bungee or spring.  An important variable affecting the rate of  roll is the true airspeed or flight velocity, V.  If a certain deflection of the ailerons creates a  Pb  specific value of -7  the rate of roll varies  2V  directly with the true airspeed. Thus, if the  roll helix angle is held constant, the rate of  roll at a particular true airspeed will not be  affected by altitude.  The linear variation of  roll rate with airspeed points out the fact that  high roll rates will  require high airspeeds.  The low roll rates at low airspeeds  are simply  a consequence  of the low flight speed and this  condition may provide a critical lateral con-  trol  requirement for satisfactory handling  qualities.  A problem particular to the high speed is  due to the interaction of aerodynamic forces  and the elastic deflections of the wing in  torsion.  The deflection of ailerons creates  twisting moments on the wing which can cause  significant torsional deflections of the wing.  At the low dynamic pressures of low flight  speeds, the twisting moments and twisting  deflections are too small to be of importance.  However, at high  dynamic pressures, the  deflection of an aileron creates significant  Figure 4.30 illustrates the typical rolling  paformance of a low speed airplane.  When  the ailerons are at full deflection, the maximum  roll helix angle is obtained. The rate of roll  increases  linearly with speed until the control  forces increase to limit of pilot effort and full  control deflection cannot be maintained.  Past  303 