# The Green Industry's Resource Center

#101
08-18-2011, 06:50 PM
 Richard Martin LawnSite Fanatic Join Date: Mar 2000 Location: Greenville, NC Posts: 14,689
Let me also add that once slowed down the heavier blade requires more energy (horsepower) to bring it back up to speed. It's a double edged sword. It takes more force to slow it down but once slowed down the heavier blade requires more energy to bring it back up to speed. Inertia works both ways.
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#102
08-18-2011, 07:18 PM
 JDiepstra LawnSite Bronze Member Join Date: Dec 2008 Location: Grand Rapids MI Posts: 1,512
Quote:
 Originally Posted by Richard Martin You're leaving out the effects of gravity. Since the blade is moving strictly in a horizontal plane to gravity it cancels the effects of gravity out. Try stopping the Corvette and then try stopping the semi. It takes significantly more force to stop the 82,000 pound semi then it does to stop the 3,100 pound Corvette. It's called inertia. " Inertia is the resistance of any physical object to a change in its state of motion or rest, or the tendency of an object to resist any change in its motion. It is proportional to an object's mass." http://en.wikipedia.org/wiki/Inertia The heavier blade has more inertia due to it's increased mass.
ok in that case, youre forgetting about friction. Those blades arent spinning freely. U ever tried turning the blades with the belt still in place?
#103
08-18-2011, 07:41 PM
 Snapper Jack LawnSite Senior Member Join Date: May 2010 Location: weaverville, NC Posts: 517
Quote:
 Originally Posted by Richard Martin You're leaving out the effects of gravity. Since the blade is moving strictly in a horizontal plane to gravity it cancels the effects of gravity out. Try stopping the Corvette and then try stopping the semi. It takes significantly more force to stop the 82,000 pound semi then it does to stop the 3,100 pound Corvette. It's called inertia. " Inertia is the resistance of any physical object to a change in its state of motion or rest, or the tendency of an object to resist any change in its motion. It is proportional to an object's mass." http://en.wikipedia.org/wiki/Inertia The heavier blade has more inertia due to it's increased mass.
The thing to remember is the real working force is above that heavy B6 blade,where the working inertia is developed,then transferred to crankshaft and that heavy mass blade absorbs a lot of the transferable working torque that inevitable requires more HP in keeping the same blade speed of a lighter blade at a given RPM. I would rather have a lighter blade backed up by higher engine RPMs where by maximum blade tip speed can be achieved, combined with inertia energy in the blades to overcome the absorbency of power from over grown grass,does this make any sense Engine response time from being bogged down will always be quicker too.
Heavier masses below the crank increases engine stress and causes abnormal wear of the engines internal parts,let alone wear on deck parts. More cons than pros I think.

Last edited by Snapper Jack; 08-18-2011 at 07:47 PM.
#104
08-18-2011, 07:49 PM
 TNGrassCutter LawnSite Bronze Member Join Date: Apr 2010 Location: Tennessee Posts: 1,318
I got my set in today for my Scag WB. I'm kind of disappointed in the lift, I thought there would be more lift, but ill give them a shot. And they are wide and heavy.
Posted via Mobile Device
#105
08-18-2011, 07:53 PM
 JDiepstra LawnSite Bronze Member Join Date: Dec 2008 Location: Grand Rapids MI Posts: 1,512
Quote:
 Originally Posted by TNGrassCutter I got my set in today for my Scag WB. I'm kind of disappointed in the lift, I thought there would be more lift, but ill give them a shot. And they are wide and heavy. Posted via Mobile Device
Are u sure u got g6? The pic shows a lot of lift.
#106
08-18-2011, 08:23 PM
 Ridin' Green LawnSite Fanatic Join Date: May 2011 Location: Michigan Posts: 10,174
I'm not an engineer or mathmatician, but I do know/can hear when my engine "bogs" down, and I can say for sure that heavier blades require a lot more resistance from the grass to slow them down than lighter blades do, and the lighter ones will recover more quickly. The difference in slow down, and thus recovery time never seems to equal the amount of extra drag required to slow them down over the lighter sets in the first place. Another point that needs to be made is that once the baldes are spinning full RPM, it doesn't take any more HP (if even as much) to keep them spinning due to their extra mass/inertia. Also, a lighter blade wil slip on the belt quicker than a heavy blade will since it is more easily held back by thick grass all other things being equal.

All the theortetical/opinion stuff aside for the moment, the G6's for my machine are the same width, and thickness as the stock blades, and the lift isn't any more pronounced than the OEM high lifts has, so spinning them won't be a problem (for me anyways).
#107
08-18-2011, 08:31 PM
 ALC-GregH LawnSite Fanatic Join Date: Mar 2008 Location: PA Posts: 7,053
Quote:
 Originally Posted by JDiepstra ok in that case, youre forgetting about friction. Those blades arent spinning freely. U ever tried turning the blades with the belt still in place?
It does go deeper with what you're saying. I'd have to dig up my notes but in a nut shell, if the object being turns has less weight mass then the object turning it, then it voids out the added inertia. Something like that.
#108
08-18-2011, 09:41 PM
 Snapper Jack LawnSite Senior Member Join Date: May 2010 Location: weaverville, NC Posts: 517
Quote:
 Originally Posted by Ridin' Green I'm not an engineer or mathmatician, but I do know/can hear when my engine "bogs" down, and I can say for sure that heavier blades require a lot more resistance from the grass to slow them down than lighter blades do, and the lighter ones will recover more quickly. The difference in slow down, and thus recovery time never seems to equal the amount of extra drag required to slow them down over the lighter sets in the first place. Another point that needs to be made is that once the baldes are spinning full RPM, it doesn't take any more HP (if even as much) to keep them spinning due to their extra mass/inertia. Also, a lighter blade wil slip on the belt quicker than a heavy blade will since it is more easily held back by thick grass all other things being equal. All the theortetical/opinion stuff aside for the moment, the G6's for my machine are the same width, and thickness as the stock blades, and the lift isn't any more pronounced than the OEM high lifts has, so spinning them won't be a problem (for me anyways).
I'm no engineer either but there's a much bigger overall picture here being that you have to in vision theses mowers of ours as automobiles and that frictional Hp loses are going to occur through the drive train,(these loses simple aren't unavoidable),which in our case would be the belts,deck and the blades would represent the differential. Having dragged raced for several years,I can tell you for a fact that going from a 8 3/4 rear end to 9 3/4 ,that gained masses from the drive gear and pinion gear required more HP to turn at all given RPMs over the lighter 8 3/4 unit. You simply can't have you cake and eat it to when converting over to the G6 blades,you're going to lose something regardless what HP your mowers packing.You just need more HP to sustain the same or higher blade speeds with the G6s on smaller engine displacements is what I'm trying to say.
If you'll do a search on the Meg Mo system,members who tried converting over notice a drop in power to sustain the exact blade speed. I'm in no way knocking the G6s and I just want a lighter blade
#109
08-18-2011, 10:18 PM
 ALC-GregH LawnSite Fanatic Join Date: Mar 2008 Location: PA Posts: 7,053
Quote:
 Originally Posted by Snapper Jack I'm no engineer either but there's a much bigger overall picture here being that you have to in vision theses mowers of ours as automobiles and that frictional Hp loses are going to occur through the drive train,(these loses simple aren't unavoidable),which in our case would be the belts,deck and the blades would represent the differential. Having dragged raced for several years,I can tell you for a fact that going from a 8 3/4 rear end to 9 3/4 ,that gained masses from the drive gear and pinion gear required more HP to turn at all given RPMs over the lighter 8 3/4 unit. You simply can't have you cake and eat it to when converting over to the G6 blades,you're going to lose something regardless what HP your mowers packing.You just need more HP to sustain the same or higher blade speeds with the G6s on smaller engine displacements is what I'm trying to say. If you'll do a search on the Meg Mo system,members who tried converting over notice a drop in power to sustain the exact blade speed. I'm in no way knocking the G6s and I just want a lighter blade
This might be a little radical but do you think drilling holes in the blade would lighten them enough and still be safe to use?
#110
08-18-2011, 10:27 PM
 TLS LawnSite Fanatic Join Date: Jan 2000 Location: N&W Philadelphia Suburbs Posts: 7,938
No.

Turbulence.
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