Need help with this problem Is the problem 25 from the book

Need help with this problem. Is the problem 2.5 from the book performance and stability of aircraft by J.B. Russell (Chapter 2).

An aircraft has the following characteristics as a function of Mach number at a certain
altitude:

The aircraft has a mass of 90 000 kg and the wing area is 200 m 2. Find the maximum

level flight Mach number if the atmospheric pressure at this altitude is 9.6 kN m -2. (A)

2.5 An aircraft has the following characteristics as a function of Mach number at a certain altitude: 1.9 Mach number 1.7 2.1 0.01 0.00775 0.00875 0.007 No-lift drag coefficient (Lift-dependent coeff.)/Ci 0.56 0.63 0.41 0.46 Thrust (kN) 116 128 131 126 The aircraft has a mass of 90 000 kg and the wing area is 200 m2. Find the maximum level flight Mach number if the atmospheric pressure at this altitude is9.6 kN m 2. (A)

Solution

In this problem,

atmospheric pressure is 9.6 kpa,

the corresponding properties at this pressure are

h = height = 16438.61 m

T = 216.650 K

Velocity of Sound = 295.070 m/s

density = 0.154365 kg/m3

from the table using trial and error method, verifying different Mach numbers for above mentioned properties,

after calculating different Mach number Mach number = 1.7 gives

Mach = 1.7

Velocity of aircraft = 501.619 m/s

Lift of aircraft = mg = 90000*9.81 = 882900 N

Let us verify the Drag for Mach = 1.7

Cd = Cdo + Cdi

= 0.01 + 0.03127

= 0.03127

D = (1/2)*(Cd)*(density)*(Area)*(Velocity)2

D = (0.5)*(0.03127)*(0.15436)*(200)*(251071.1449)

D = 122 KN

which is approximately matches with Mach= 1.7

if we further calculate valuea it decreases considerably

for level flight D = T,

it will be satisfied only by Mach = 1.7 and below