Page 430 - Aircraft Stuctures for Engineering Student

10.4 Fuselage frames and wing ribs 41 1

Fig. 10.46 Support of load having a component normal to a web.

of open rings so that the interior of the fuselage is not obstructed. They are connected
continuously around their peripheries to the fuselage shell and are not necessarily
circular in form but will usually be symmetrical about a vertical axis.
A fuselage frame is in equilibrium under the action of any external loads and the
reaction shear flows from the fuselage shell. Suppose that a fuselage frame has a
vertical axis of symmetry and carries a vertical external load W, as shown in
Fig. 10.47(a) and (b). The fuselage shell/stringer section has been idealized such
that the fuselage skin is effective only in shear. Suppose also that the shear force in
the fuselage immediately to the left of the frame is Sy,l and that the shear force in
the fuselage immediately to the right of the frame is S,,,2; clearly, Sy,2 = S,,: -
W. Sy,l and S,,2 generate shear flow distributions q1 and q2 respectively in the fuselage
skin, each given by Eq. (10.17) in which Sx,l = Sx,2 = 0 and Ixy = 0 (Cy is an axis of
symmetry). The shear flow qf transmitted to the periphery of the frame is equal to the
algebraic sum of q1 and q2, i.e.
4f = 41 - 42

c
X

W I

(a)
Fig. 10.47 Loads on a fuselage frame.