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# How much momemt of Inertia will be felt at engine if we attach a disc of moment of inertia X?

## How much momemt of Inertia will be felt at engine if we attach a disc of moment of inertia X?

(OP)
How much momemt of Inertia will be felt at engine if we attach a disc of moment of inertia​ 0.4kgm²at end ?

I would say Zero , because of no unbalance Mass on axis of rotation

### RE: How much momemt of Inertia will be felt at engine if we attach a disc of moment of inertia X?

This is a very vague question.

No matter what, if you have a mass directly coupled to the end of any engine's output shaft, the engine is accelerating (or decelerating) that mass. Whether the mass is balanced or not does not matter. The only way for an engine to operate as if the connected machinery has a moment of inertia of zero is if the connected machinery has a moment of inertia of zero- which is impossible.

### RE: How much momemt of Inertia will be felt at engine if we attach a disc of moment of inertia X?

(OP)
@jgKRI

What if the disc is attached to the outputshaft of gearbox, and if you neglect moment of inertia of gearbox and engine? what will be the feeling of MOI due to Disc at Engine

### RE: How much momemt of Inertia will be felt at engine if we attach a disc of moment of inertia X?

Depends on the ratio of the gearbox- but the reflected inertia cannot be zero.

### RE: How much momemt of Inertia will be felt at engine if we attach a disc of moment of inertia X?

engg35mechie,

Moment of inertia has no effect on anything unless acceleration is present. Is your engine running at a steady speed? If torsional vibration is present, your moment of inertia will affect it.

--
JHG

### RE: How much momemt of Inertia will be felt at engine if we attach a disc of moment of inertia X?

Moment of inertia has no effect? So a flywheel on a combustion engine is useless?
Adding an inertia will change the torsional resonance frequencies. I am not sure what side you mean by the "end" (this is usually the flywheel side) but either end, you will change the crankshaft natural frequency and this may cause a serious problem. It may be a good thing, but also cause the crankshaft to be operated at resonance conditions (which will probably break it)

### RE: How much momemt of Inertia will be felt at engine if we attach a disc of moment of inertia X?

rob768,

A piston engine does not run at absolutely steady speed. It accelerates when the piston fires, and it decelerates under load and under piston compression when the pistons are not firing. The flywheel affects this behavior.

--
JHG

### RE: How much momemt of Inertia will be felt at engine if we attach a disc of moment of inertia X?

(OP)
Hallo thank you for your replies..
What if its the servo motor that drives the gearbox

### RE: How much momemt of Inertia will be felt at engine if we attach a disc of moment of inertia X?

engg35mechie,

The inertia through a gearbox is multiplied by the square of the gear ratio.

--
JHG

### RE: How much momemt of Inertia will be felt at engine if we attach a disc of moment of inertia X?

Drawoh, that is exactly why i think any inertia will have an effect. Hence the question marks..

### RE: How much momemt of Inertia will be felt at engine if we attach a disc of moment of inertia X?

#### Quote (nengg35mechie)

How much momemt of Inertia will be felt at engine if we attach a disc of moment of inertia​ 0.4kgm²at end ?

I would say Zero , because of no unbalance Mass on axis of rotation

I just re-read your post. You can have a high moment of inertia even if your mass is perfectly balanced. The moment of inertia will affect your acceleration when you apply torque. If this is a servo system, you want a low moment of inertia relative to the motor. Otherwise, it will not respond reliably to feedback.

--
JHG

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