Hard facts about lightened flywheels

[mrcrsr]

The point alot of people miss is it takes power to accelerate mass, that's why in a drag racing situation the lighter flywheel accelerates the boat quicker. Once the engine is up to speed it is not taking additional power to operate a heavier flywheel, but from a longevity standpoint a lighter flywheel is better, not having all the weight hanging off the top of the crankshaft, let alone what happens when the prop comes in and out of the water with the flywheel trying to twist the crankshaft

[FMP]

Take a 5hp motor with a 5 lb wheel ,run it a 4000rpm. Now replace that wheel with a 5000 lb wheel and see if it can maintain 4000rpm. Or build a flywheel which can draw mass from the outer edge toward the center while rotating.

A student stands on the center of a rotating platform that has frictionless bearings. He has a 2.0 kg object in each hand, held 1.0 m from the axis of rotation of the system. The system is initially rotating at 10 rpm. Determine a) the initial angular velocity in radians per second, b) the angular velocity of the sytem in radians per second after the objects are brought to a distance of 0.20 m from the axis of rotation, c) the change in the rotational kinetic energy of the system as the objects are pulled closer to the center of rotation. d) What causes the increase in rotational kinetic energy? (Assume that the moment of inertia of the platform + student remains constant at 1.0 kg m ².)
Solution:

a) Use 1 rev = 2 radians and 1 minute = 60 seconds to convert:

10 rev/min	=	(10 rev/min )(2 rads/rev )(1 min /60 s )
	=	1.05 rad /s.

b) Use conservation of angular momentum. We therefore need to compute the initial and final moments of inertia of the system:

Ii	=	I (student + platform) + mri2 + mri2
	=	1.0 kg m 2 + (2.0 kg )(1.0 m )2 + (2.0 kg )(1.0 m )2
	=	5.0 kg m 2

If	=	I (student + platform) + mrf2 + mrf2
	=	1.0 kg m 2 + (2.0 kg )(0.2 m )2 + (2.0 kg )(0.2 m )2
	=	1.16 kg m 2.

Determine final velocity using conservation of angular momentum:

Ii = If.

So that:

	=
	=	x 1.05 rads/s
	=	4.5 rads/s.

c) The change in kinetic energy is:

KE	=	KEf - KEi
	=	If - Ii
	=	(1.16 kg m 2)(4.5 rads/s )2 - (5.0 kg m 2)(1.05 rad /s )2
	=	11.8 J - 2.75 J
	=	9.05 J.

d) As the student pulls the object in toward the center of rotation, he is doing work on the system. This work goes into increasing the kinetic energy of the system.

[Mr. Demeanor]

Take a 5hp motor with a 5 lb wheel ,run it a 4000rpm. Now replace that wheel with a 5000 lb wheel and see if it can maintain 4000rpm..

It would be able to maintain 4000rpm it would just take a LONGGGG time to get it up to 4000 rpm.

[FMP]

An infinite mass wheel and an infinitely small HP will take infinite time

[XstreamVking]

What I wanna know is, how do those ice skaters spin so damn fast with out a flywheel.....

[Mr. Demeanor]

What I wanna know is, how do those ice skaters spin so damn fast with out a flywheel.....

[FMP]

Was going to post one with real nice shape just to give an example to the question above.

[XstreamVking]

That is not what I had in mind. I was thinking more like FMP.

[Krazymaan]

The hardest fact about lightened flywheels... They look cool.

[Mr. Demeanor]

I know! My poor motor looks so sad. Kind of like its wearing an ugly hat.

[Mr. Demeanor]

Its only good for playing ring toss now.

[Classic18]

We have never expected a lightened flywheel to make more top end horse power in fact it should make less. The #1 point in a lightened flywheel is to stop the top of the crank from coming off at 10,000 RPM. or for that matter at 8000 RPM. But what your test really doesn’t show is the torque gain on acceleration dew to spinning up a lighter mass. In an F1 boat a lightened flywheel is a noticeable gain in acceleration off the turn. On my dyno, as long as the motor is accelerating, the lightened flywheel will make 10 more HP over the stock S3000 type.

we run lighter recip mass on A sedans (pistons, flywheel...) for the increase in a Cel after a corner. Same physics...guess Newton knew what he was talking about. Not really any top speed increase, in fact slight negative

[Classic18]

What I wanna know is, how do those ice skaters spin so damn fast with out a flywheel.....

By using the product of moment of inertia and rotational speed

[FMP]

By drawing mass to center axes of rotation. Sample problems above

[tlwjkw]

i've been told for years n years tha lite weight came about for "slowin' down" ta turn more than any other reason.... any other benefit was jus icin'........