Page 292 - Aircraft Stuctures for Engineering Student

Problems 273
is 16.7m aft'of the CG. The pitching moment coefficient is

CM,o = -0.0638 (nose-up positive)
both CM.o and the position of the aerodynamic centre are specified for the complete
aircraft less tail unit.

"t

V m/s

Fig. P.8.3

For steady cruising fight at sea-level the fuselage bending moment at the CG is
600 000 Nm. Calculate the maximum value of this bending moment for the given
flight envelope. For this purpose it may be assumed that the aerodynamic loadings
on the fuselage itself can be neglected, i.e. the only loads on the fuselage structure
aft of the CG are those due to the tail lift and the inertia of the fuselage.

Ans. i 549500Nm at n = 3.5, V = 152.5m/s.
P.8.4 An aircraft weighing 238000N has wings 88.5m2 in area for which
C, = 0.0075 + 0.045C;. The extra-to-wing drag coefficient based on wing area is
0.0128 and the pitching moment coefficient for all parts excluding the tailplane
about an axis through the CG is given by CM -c = (0.427C~ - 0.061) m. The
radius from the CG to the line of action of the tail lift may be taken as constant at
12.2 m. The moment of inertia of the aircraft for pitching is 204 000 kg m2.
During a pull-out from a dive with zero thrust at 215 m/s EAS when the flight path
is at 40" to the horizontal with a radius of curvature of 1525 m, the angular velocity of
pitch is checked by applying a retardation of 0.25 rad/sec2. Calculate the manoeuvre
load factor both at the CG and at the tailplane CP, the forward inertia coefficient and
the tail lift.
Ans. IZ = 3.78(CG), IZ = 5.19 at TP, f = -0.370, P = 18 925N.
P.8.5 An aircraft flies at sea level in a correctly banked turn of radius 610 m at a
speed of 168 m/s. Figure P.8.5 shows the relative positions of the centre of gravity,
aerodynamic centre of the complete aircraft less tailplane and the tailplane centre
of pressure for the aircraft at zero lift incidence.