066 Poly vs Metal

[bwalker]

I have no idea what you are now talking about. I'm saying what Space is saying, and you're now saying Space is correct... Maintaining the momentum is what we are talking about - RPM....

Dean, Spacemule said what Lake and I have been saying all along. Flywheel weight may effect acceleration/decelleration, but doesnt effect the output or torque curve.
The "simple math" formula I listed above will not prove your point either.
There is no reason to get nasty, is there?

 

[bwalker]

BTW I am waiting for you to "plug in the numbers" and prove us all wrong. If you can do so I will eat crow.

 

[klickitatsacket]

You guys are either purposely doing this for the fun of it or I have given you way too much credit all this time and in Ben's case it wasn't very much to begin with.

First you argue my exact point in other words as if I was wrong; while still admitting I am right.
The biggest problem is that for the most part of this conversation you have substituted torque for torque band. I clearly mentioned the torque band.

Torque band - The RPM Range in which usable power is delevered to the chain.

IF ALL THINGS ARE EQUAL and only the flywheel weight is changed............
A heavier flywheel will give you a wider torque band, less RPM and slower acceleration.

Ben the math is 4th grade level A x B / 5252 = C

I do not want to loose you so I will round the #'s and K.I.S.S.

3 x 14000 / 5252 = 8HP (rounded #'s)
So now let's just throw in a slightly bigger torque #
3.1 x 13553 / 5252 = 8HP (rounded #'s)

So as torque goes up then RPM goes down if HP stays the same.
See still very simple. I hope I have not lost you yet.

Now Does it take more Torque or less torque to move a heavier flywheel? More.
I went ahead and gave you the answer so it wouldn't hurt you this morning.

Now if you have a heavier flywheel and we know it takes more resistance to slow down a heavier object than a lighter one; then we also know that we will have a wider RPM range in which the saw will cut with a heavier flywheel before it falls on it's face.

 

[bwalker]

Quit while you ahead, Dean.

It's sad to see a saw builder with such a weak grasp of such basic physics.

Yep.

 

[bwalker]

IF ALL THINGS ARE EQUAL and only the flywheel weight is changed............
A heavier flywheel will give you a wider torque band, less RPM and slower acceleration.

No, it will not. Weights only change the way the power is delivered(IE over time), not how much power is delivered. If you cant understand this hang up your porting tool.....
BTW I didnt get nasty with you, even though I knew your full of **** from the begining. Do we want to go down this road again?

 

[bump_r]

Now if you have a heavier flywheel and we know it takes more resistance to slow down a heavier object than a lighter one; then we also know that we will have a wider RPM range in which the saw will cut with a heavier flywheel before it falls on it's face.

There's the difference right there. The heavy flywhele will resist slowing "in the wood" for a small period of time. Torque (power output, not inertia) is the SUSTAINABLE speed in the cut.

I can't put a heavy flywheel on my 170 and keep up with my 460. I could for a split second before resistance robbed the inertial energy of the heavy flywheel and the engine output was the sole provider of chain motion.

 

[ShoerFast]

You guys are either purposely doing this for the fun of it or I have given you way too much credit all this time and in Ben's case it wasn't very much to begin with.

First you argue my exact point in other words as if I was wrong; while still admitting I am right.
The biggest problem is that for the most part of this conversation you have substituted torque for torque band. I clearly mentioned the torque band.

Torque band - The RPM Range in which usable power is delevered to the chain.

IF ALL THINGS ARE EQUAL and only the flywheel weight is changed............
A heavier flywheel will give you a wider torque band, less RPM and slower acceleration.

Ben the math is 4th grade level A x B / 5252 = C

I do not want to loose you so I will round the #'s and K.I.S.S.

3 x 14000 / 5252 = 8HP (rounded #'s)
So now let's just throw in a slightly bigger torque #
3.1 x 13553 / 5252 = 8HP (rounded #'s)

So as torque goes up then RPM goes down if HP stays the same.
See still very simple. I hope I have not lost you yet.

Now Does it take more Torque or less torque to move a heavier flywheel? More.
I went ahead and gave you the answer so it wouldn't hurt you this morning.

Now if you have a heavier flywheel and we know it takes more resistance to slow down a heavier object than a lighter one; then we also know that we will have a wider RPM range in which the saw will cut with a heavier flywheel before it falls on it's face.

Your point is very clear Dean!

But it may be that Ben mentioned it himself , that the weight of the FW would only change the operating characteristics, building as many saws as you have, you explain it well as that it widens the RPM range. Temberwolf also explains this as how a saw should enter the wood for racing.

If I may, reading between the lines, you seem to tend that saws modified to take advantage of the lower RPM, but higher TQ, or "T" would work better with the poly FW, while higher revving HP or "R" modded saws would be slightly more of a candidate for the heaver FW , as that would get a little more usability out of the kinetic energy stored?

One of the best keep secrets of the more consistent NHRA gasoline-class winners is to build there engines for more of a lower RPM, higher TQ design, then the tall-camed over-revving engines of the past. (Same HP, but getting it at a lower speed) As this proves way more constant , it's all about ET's.

 

[B_Turner]

One of the best keep secrets of the more consistent NHRA gasoline-class winners is to build there engines for more of a lower RPM, higher TQ design, then the tall-camed over-revving engines of the past. (Same HP, but getting it at a lower speed) As this proves way more constant , it's all about ET's.

This particularly true with street motorcylces. It is all about usable power.

I'm staying out of the big discussion as I am definitely out of my element. But it seems like some of the arguments would be more relevant in a situation where the load is often interrupted rather than "steady". Like a chopoff saw in 2 by 4s. Not a jab at anyone.

 

[Lakeside53]

But it seems like some of the arguments would be more relevant in a situation where the load is often interrupted rather than "steady". Like a chopoff saw in 2 by 4s. Not a jab at anyone.

Just bottom feeding off 2x4 "short power" needs...

The stored energy in a chainsaw saw flywheel excess to that required by the engine to smoothly perform it's reciprocation is not large. Next time you are cutting a decent size piece of wood, have someone CAREFULLY lean over an push in your decomp. I bet the chain is stopped before you hear the click.

If I knew the moment of inertia for the two crank/flywheel (they are combined; everything else assumed to be constant) I could calculated the energy differential, but them I'd need to know the absorption by the piston on the compression stroke. It isn't 4th grade math.

BTW, the cutoff saw has an "additional flywheel" at the point where energy is delivered - the blade, and if 14 inch steel, very effective! Neat gyro effect.. then try a 20 inch blade - scary!!.

 

[B_Turner]

Just bottom feeding off 2x4 "short power" needs...



BTW, the cutoff saw has an "additional flywheel" at the point where energy is delivered - the blade, and if 14 inch steel, very effective! Neat gyro effect.. then try a 20 inch blade - scary!!.

And for some more scary serious flywheel effect, how about a bandsaw with 36 inch cast iron wheels.

 

[manual]

I have no idea what you are now talking about. I'm saying what Space is saying, and you're now saying Space is correct... Maintaining the momentum is what we are talking about - RPM...

Correct and that would be Momentum without restrictions.
bearing and ring drag also port timing.

 

[Crofter]

Lakeside describes the reason for the flywheel on a saw. It needs to store enough energy at cranking speed in the form of momentum to overcome the forces of compression (and charge induction) till the next power stroke. Much more weight is necessary at this speed than is needed at operating speed because energy stored is a factor of the square of velocity. Some people mention the blade being the flywheel on a mower and how idle is disturbed without it. The fly wheel only receives energy from the starter cord or the piston, not any celestial power. It can only return what it has been given. Without a flywheel on a reciprocating engine there are momentary variations in instantaneous speed of the crank and the flywheel also serves to smooth them out somewhat reducing the pulsating imput to the powertrain. That is a side benefit. The flywheel produces no power of its own PERIOD. Its stored energy can only be given out by the process of losing speed. If the load momentarily exceeds the pistons energy imput the rpm must drop. Tested at any rpm, throughout an engines useable power band there should be no difference in an engines sustainable torque because of variations in flywheel weight.
Now if you want to go down to extremely low RPM like on a trolling outboard ( I think some would go down to 300 RPM) then you must have a heavier flywheel to keep the average velocity high enough to maintain magnet speed for ignition near the end of compression stroke. Same thing Lakeside is talking about. That 4 or 5 lb flywheel is no help to you when you are up on plane!

 

[Kneejerk Bombas]

Lakeside describes the reason for the flywheel on a saw. It needs to store enough energy at cranking speed in the form of momentum to overcome the forces of compression (and charge induction) till the next power stroke.

Isn't the weight of the crankshaft enough?
I thought the flywheel was only to move air for cooling, engaging the recoil, and spin the magnet for electricity, and the new polymer flywheels are designed as light as possible to still be able to accomplish these three tasks.

 

[klickitatsacket]

see this is the part that is driving me nuts.

I have never said that the flywheel weight adds torque. I never said that it adds power. I said that it lowers the RPM and changes the width of the torque band.
Now Crofter made lakes point that "up on the plane" the weight of the flywheel ads nothing. My point is that under load it makes all the differance; this point was also made by crofter.

Saw racers shave weight of their flywheels all the time to get better RPM and their torque bands are so thin that the average person would play he11 getting it to cut.

 

[bwalker]

I said that it lowers the RPM and changes the width of the torque band.
[/QUOTE
It does not chage the power curve or torque curve one iota and it doesnt lower rpm.

 

[Lakeside53]

Isn't the weight of the crankshaft enough?
I thought the flywheel was only to move air for cooling, engaging the recoil, and spin the magnet for electricity, and the new polymer flywheels are designed as light as possible to still be able to accomplish these three tasks.

The "Polymer" Flywheels aren't as light as you think...

The 066 Polymer wheel weights exactly 1 pound. The exact same diameter 044 flywheel Aluminum flywheel is 14.5 ounces. It's not the weight that really matters but the moment of inertia, which is a function of the distance the center of mass is from the center of rotation.

The polymer wheel has it's mass evenly distributed along the outside of the wheel as a band of laminated steel about 9mmx14mm.

The Aluminum wheel has most of it's mass as two lobes - one with magnets and one without, and then the fins/body.

If I was to hazard a guess, the Polymer wheel has the higher moment of inertia.... and remember, the crank that mates to the polymer is beefier....

If I wasn't at home sick I do two things : I'd go get an 066 wheel, weigh it, and I'd take a couple of pictures of both types. Anyone want to help?

 

[Lakeside53]

Saw racers shave weight of their flywheels all the time to get better RPM and their torque bands are so thin that the average person would play he11 getting it to cut.

Do you think the "other" racing mods have have something to do with the narrower power band?

 

[Crofter]

see this is the part that is driving me nuts.

I have never said that the flywheel weight adds torque. I never said that it adds power. I said that it lowers the RPM and changes the width of the torque band.
.
Does it take more or less torque to move a heavier rotaional mass and maintain spead? Any one? Any one? Any one? Yes, you kid in the back sleeping. Uhhh???? More? Yes. You can go back to sleep now.

Dean you maintain that it takes more torque to accellerate and maintain RPM of a heavier flywheel. It only takes torque momentarily to accellerate and then no more energy to maintain. You have a faulty premise here.

You also maintain that RPM must of necessity be lower with a heavier flywheel. That is an incorrect assumption which you are treating as fact. Only accelleration rate will be decreased.

You are using the anectodal evidence that racers shave the flywheel to achieve higher RPM as an assumed proof of your position. They shave weight to ensure the spoolup will be complete before they hit the wood for the first cut cold start and that Rpm will recover in the tenth of a second during switchovers. There is also the problem of crank breakage at extreme high RPM and as Lakeside mentioned is reduced by reducing the reluctance and substituing a lighter flywheel. That is the reason for the lighter flywheel. Not to produce higher RPM but to keep the saw from destroying itself at the high RPM. Again a faulty conclusion about what is cause and what is effect. The flywheel weught does not directly affect an engines top rpm; it does not affect its torque; and therefore the horsepower. (since torque X RPM = horsepower), Only its accelleration / decelleration charicteristics change. If torque, rpm and horsepower are not affected, I cannot understand how you can say that power band is changed since it is a firm product of all the others. You also cannot say that because one certain saw (of the same basic description) that had a certain weight flywheel was faster or slower was so because of the flywheel weight. As many have pointed out many other things than the flywheel could have been the cause of your observations. Again, simply not useable as proof.

I am beginning to think Dean is just toying with us and does not believe at all what he has been trying to convince us of. Dean, you cunning devil

 

[bwalker]

You have a faulty premise here.

You also maintain that RPM must of necessity be lower with a heavier flywheel. That is an incorrect assumption which you are treating as fact. Only accelleration rate will be decreased.

Yes, and Yes.:bang:

 

[Lakeside53]

and yes..