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
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