Figure 2 shows the flight envelope at sea-level for an aircraft of wing span 27.

Question

Figure 2 shows the flight envelope at sea-level for an aircraft of wing span 27.5 m, average wing chord 3.05 m and total weight 196,000 N. The aerodynamic center is 0.915 m forward of the CG and the center of lift for the tail unit is 16.7 m aft of the CG. The pitching moment coefficient is CM = 0.0638 (nose-up positive) Both CM and the position of the aerodynamic center are specified for the complete aircraft less tail unit. For steady cruising flight 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, that is, the only loads on the fuselage structure aft of the CG are those due to the tail lift and the inertia of the fuselage.

Explanation / Answer

Do some of the force and take moments around the CG and solve for theMCGinterms of a level flight moment,ML Flight(does not take into account tail affects) plus thecontribution from the tail. You can relate the generalMCGto theML Flightlinearly to thefacton: MCG= n ML Flight+ Mtail

Hint 2: The pitching moment coefficient at the AC is defined by :0,2221MCcbVM

Hint 3:Solve for the lift at the tail for the given flying conditions on the flying envelope

Hint 4:Once you solve for the moment generated at level flight you can solve for anexpression for theMCGrelated to the flight speed and n

Ans: 1,549,500 Nm at n = 3.5, V = 152.5 m/s

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