Page 268 - Aircraft Stuctures for Engineering Student

8.5 Normal accelerations 249

Two cases arise: the first involving a steady pull-out from a dive and the second, a
correctly banked turn. Although the latter is not a symmetric manoeuvre in the
strict sense of the word, it gives rise to normal accelerations in the plane of symmetry
and is therefore included.

8.5.1 Steady pull-out

Let us suppose that the aircraft has just begun its pull-out from a dive so that it is
describing a curved flight path but is not yet at its lowest point. The loads acting
on the aircraft at this stage of the manoeuvre are shown in Fig. 8.11, where R is
the radius of curvature of the flight path. In this case the lift vector must equilibrate
the normal (to the flight path) component of the aircraft weight and provide the force
producing the centripetal acceleration V2/R of the aircraft towards the centre of
curvature of the flight path. Thus

or, since L = n W (see Section 8.4)

(8.15)

At the lowest point of the pull-out, e = 0, and
V2
n=-+I (8.16)
gR

V
Fig. 8.1 1 Aircraft loads and acceleration during a steady pull-out.