FLYWHEEL AND GOVERNORSHORT QUESTION ANSWERS
FLYWHEELS AND GOVERNOR
SHORT QUESTION ANSWERS
Question answers help in understanding
in a better way. Flywheels stores energy
when in excess during the working stroke.
Flywheel supplies back energy in suction,
compression and exhaust strokes.
Question answers help
in practical applications with
ease. It also help in making improvements.
What is a flywheel?
It is heavy wheel which stores excess ROTATIONAL energy during power stroke. It releases energy during exhaust, suction and compression strokes. Time duration of storage and release of excess rotational energy is small.
Q. Compare the different types of flywheels.
A.
Comparison of high and low speed flywheels
Sr. No. 
High speed flywheels 
Low speed flywheels 
1. 
Speed is 30000 to 60000 RPM 
Speed is less than 10000 RPM 
2. 
Light weight 
Heavy weight 
3. 
Easy commissioning and requires less maintenance 
Tedious commissioning and requires heavy maintenance 
4. 
Easy starting 
Tedious starting 
5. 
Easy shut down 
Tedious shut down 
Q. What are advantages of having elliptical
section of the flywheel arm?
A.
This bending moment lies in the plane of rotation of the flywheel. The arm axis also lies in the plane of rotation. Thus the axis should be as large as possible. In a circular section it is equal to the radius. But in case of an elliptical section, the arm major axis can be as large as twice the minor axis. Flywheel arm with elliptical section having major axis twice the minor axis can resist twice the bending moment. It is not obtainable with any other shape of the arm cross section. Thus only elliptical section for the flywheel arm is selected.
Q. What are main considerations for the selection
of material of a flywheel?
A.
It is based on the type of stresses produced. Due to centrifugal force arm comes in tension. There is a tensile stress due bending of arm which is due to torque. There is a reversal of stress due to reverse motion of the flywheel which causes fatigue. Thus the main considerations in the selection of the material are

(i) High tensile strength

(ii) High fatigue strength
Q. What is fluctuation of speed? What is the coefficient
of fluctuation? What is coefficient of steadiness? What
is mass moment of inertia of the flywheel?
A.
(a) Fluctuation of speed
The difference between maximum and minimum speed during a cycle is
called the fluctuation of speed. Recall the speed of the engine is not the
same during suction, compression, power and exhaust strokes. This
fluctuation of speed can be reduced by having a large mass moment
of inertia ‘I’ of the flywheel.
(b) Coefficient of fluctuation of speed
It is the ratio of maximum speed to mean speed.
C_{s} = (N_{max} —N_{min})/N_{mean}
Where N is RPM
The range of C_{s} for various types of machines is given below:
Sr. No. 
Type of machine 
Coefficient of fluctuation of speed, C_{s} 
1. 
Crushing machines 
0.20 
2. 
Electrical machines(direct drive) 
0.002 
3. 
Electrical machines 
0.003 
4. 
Engine with belt transmission 
0.03 
5. 
Pumps 
0.05 to 0.03 
6. 
Machine tools 
0.03 
7. 
Gear wheel machines 
0.02 
8. 
Hammering machines 
0.2 
9. 
Automobile (normal speed) 
0.1 
10. 
Automobile (Idling) 
0.2 
11. 
Paper, textile and weaving machines 
0.025 
12. 
Rolling and mining machines 
0.025 
13. 
Spinning mill 
0.10 to 0.02 
14. 
Punching, shearing and power presses 
0.10 to 0.15 
15. 
Flour mill machines 
0.02 
Less value of the coefficient of fluctuation of speed is desirable.
© Coefficient of steadiness
It is equal to the reciprocal of the coefficient of fluctuation of speed. Its symbol is ‘m’.
Coefficient of steadiness =m = 1/C_{s}
(d) Mass moment of inertia
I = KE / C_{s} ω_{mean}^{2}
Where ω_{mean} is the mean angular speed
KE = Kinetic energy
Mass moment of inertia of various types of flywheels is given below:
(i) Disc type of flywheel
I =(1/2) Mr^{2} = Mk^{2}
where k = r/ 2
Where r is the radius of the disc and k is the radius of gyration
(ii) Rim type flywheel
I = Mr^{2 } =Mk^{2} k = r_{m} =mean radius
Where M is the mass of the flywheel
M is 90 % rim mass and 10 % mass of hub and arms
Governors