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                      PART III - HANDLING
                      
        (b)   Trim changes
        
              From the diagram it can be seen that as speed increases
              to about 0.90M there is a progressive nose-up change of
              trim.  Between 0.90M and 0.94M a nose-down trim
              change followed by a nose-up trim change occurs the
              aircraft being almost back in trim again by 0.96M.  At
              higher speeds as the aircraft becomes supersonic the trim
              again changes to slight nose-down.
              
        (c)   Changes in stick force and tailplane and elevator
              effectiveness
              
               (i)  As mach no. is increased beyond 0.92 the
              elevator becomes less effective.  This is particularly
              evident at transonic speeds when even large elevator
              deflections have a delayed and reduced response.  The
              tailplane may be used to assist in manoeuvring, although
              its effectiveness is somewhat reduced.
              
              (ii) Since the effectiveness of the elevator decreases as
              mach number increases, greater deflections are required
              to manoeuvre.  Consequently the stick forces increase.

        (d)   Transonic flight
        
              Practice transonic flights should be made by putting the
              aircraft into a 30° to 40° dive with the tailplane trim set
              at 1° nose-down.  At 0.97M very slight wing drop may
              occur which can easily be counteracted with aileron; if
              the dive angle is too shallow the aircraft will reach a
              maximum speed of 0.97M, at which speed the elevator
              is not effective enough to increase the angle of dive.
              
        (e)   Recovery from transonic dives
        
              During recovery the throttle should be closed.  The air-
              brake may be used; its extension causes moderate buffet-
              ing and a nose-up change of trim.  It is not very effective
              in reducing speed.  Recovery can be made without using 
              the tailplane trim, but jack stalling may occur(see para.
              73 (c)).  However, trimming nose-up decreases the
              angle of deflection between the elevator and the tailplane
              thereby unstalling the jack and enabling further stick
              movement to be applied.  Normally it should not be
              trimmed more nose-up than 0°.  This is because it is

74

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