Problem 5.50 The hydrofoil boat has an A-36 steel propeller shaft that is 30 m l
ID: 2327162 • Letter: P
Question
Problem 5.50 The hydrofoil boat has an A-36 steel propeller shaft that is 30 m long. It is connected to an in-line diesel engine that delivers a maximum power of 2500 kW and causes the shaft to rotate at 1700 rpm. The outer diameter of the shaft is 200 mm and the wall thickness is 10 mm G 75 GPa (Figure 1) Figure 1 r of t Part A Determine the maximum shear stress developed in the shaft. Express your answer to three significant figures and include the appropriate units. A Value Units I Submit My Answers Give Up Part B What is the "wind up, or angle of twist in the shaft at full power? Express your answer using three significant figuresExplanation / Answer
part (A)
shear stress= T x r / J
where T = Torque acting on the shaft
r = distance from the centre to the stressed surface
J = Polar moment of inertia
for a given problem maximum shear stress will be acting on the outer surface at maximum torque condition
max torque T = Max power x 60 / 2 x pi x N
max power = 2500 kw
N = 1700
Substituting given values ; max torque T = 14043 n-m
J = pi x (D4 - d4) / 32
where D = outer diameter = 200 mm
d = inner diameter = 180 mm
substituting given values we get J =5.4 x 10-5
shear stress= T x r / J
substituting above calculated max torque (T) , J and r
we get Max shear stress = 26 Mpa
part (B)
Angle of twist = L x T / J x G
L = length of the shaft = 30 m
T = max torque = 14043 n-m
J = polar moment of inertia = 5.4 x 10-5
G = modulus of rigidity = 75 Gpa
substituting above values we get angle of twist = 0.104 radians
angle of twist = 5.96 deg