Lightweigth flywheels - Why?
02-26-2013, 07:15 PM
#31
Rennlist Member
really? in what way? thats a very bold statement, challenging the facts of newton here! 
you are making it a little more complex than it has to be. generally, 5-10lbs of savings on the flywheel, will have different effects of HP costs depending on the gear you are in. 1st might be as high as 20hp, and 5th might be as low as 1-2hp. it all depends on the rate of change of kinetic energy.
No, that is not how it works. the stored energy in the flywheel would have no effect on acceleration oiut of the corner. in order for that to happen, the energy would have to leave the the flyweel in the form of reducing its speed and have it transfter to the rear wheels. thats kind of how the Porsche Hybrid works. the energy in the flwheels have stored energy yes,, but the only case where that can help with acceleration is a clutch dump off the line, or speed shifting where there is a lul between shifts, and in that time, the engine can store energy in the flywheel and then release it upon the next shift. better to have a sequential shift with no time lapse in the end.
this could be debateable. engine braking is more a function of compression and valve timing, but your first statement is not entirely correct either. again, what you get from a ligthweight flywheel is the power savings that goes down substantially with each gear shift. again, 5-10 lbs off a flwheel (at near 10" diameter), might save 20hp in 1st gear but only 1-2hp in 5th. its all about the rate of change of kinetic energy! less the rate of change, the less the weight will effect the net HP.
ahhh, weight of wheel determins the moment of intertia . 
The force of gravity is a constant. The force on an engine changes with throttle and other things. You are confusing yourself.
Here is a factual real world experience answer.
ROAD AMERICA, Wisconsin Turn 5 is a slow left (40-50 mph) followed by a short straight, 100 yards long, uphill, and you must brake before the overhead bridge at the top of the hill because if you do not, then you will go straight OFF into pea gravel. Turn 6 is slightly faster than 5 and also a left.
With a stock flywheel I used to Take corner 5 in second gear and red line shift into third gear about 75 to 80 yards of this 100 yard straightaway.
NOW with a LWFW I make the same redline shift into third at 40 to 50 yards up the the same straightaway. 25-30 yards sooner.
The car is a 996 a GT3. Red line in second is (82-83 mph from memory)
Here is a factual real world experience answer.
ROAD AMERICA, Wisconsin Turn 5 is a slow left (40-50 mph) followed by a short straight, 100 yards long, uphill, and you must brake before the overhead bridge at the top of the hill because if you do not, then you will go straight OFF into pea gravel. Turn 6 is slightly faster than 5 and also a left.
With a stock flywheel I used to Take corner 5 in second gear and red line shift into third gear about 75 to 80 yards of this 100 yard straightaway.
NOW with a LWFW I make the same redline shift into third at 40 to 50 yards up the the same straightaway. 25-30 yards sooner.
The car is a 996 a GT3. Red line in second is (82-83 mph from memory)
Try out these two experiments:
1) A circular plate has the same material, outside diameter and thickness as a circular ring. Obviously the ring weighs much less than the plate.
Put both on the top of a hill and let them start rolling down at the same time. Who would you think gets to the bottom of the hill first, provided they both roll in a straight line? The plate.
Reason being that the potential energy at the top of the hill splits into two energies once they start rolling: One that gives forward motion and one that gives rotation. In a circular plate, the mass is evenly distributed from the middle and out. The mass near the middle doesn't spend as much energy rotating as the mass near the outside. That extra energy is used to give the plate forward motion.
In a ring, the mass is obviously at the outside so more energy is spent on rotating than forward movement.
2) A circular plate has the same material and thickness as another circular plate with a smaller diameter. Obviously the plate with the smaller diameter weighs much less than the plate with the larger diameter.
Perform the same experiment as in # 1). Which plate gets to the bottom of the hill first? Both plates get to the bottom of the hill at the same time.
Even though the mass is different, the speed is the same because the potential energy, kinetic energy and rotational energy is proportional to the mass when two objects have the same shape.
How the heck it translates to flywheels? Well, the flywheels don't actually go anywhere do they. It is all rotation. For wheels though, it's food for thought. Getting the mass closer to the center is more important than the overall wheel weight. Anyway, back to flywheels: at a steady 3.000 RPM, the flywheel has stored potential energy and it has a rotational energy. Since most of us tend to stay at a steady RPM until the apex, when we start accelerating, that's the situation in a lot of corners, lap after lap. Wouldn't that potential energy turn into rotational energy once we start accelerating? If so, wouldn't the ideal flywheel when coming off the apex be heavier with a smaller diameter? Two seconds later, barreling down the straight, a lighter, smaller diameter flywheel would have less moment of inertia and provide quicker acceleration, right?
Thanks to those of you that have bothered to read everything
1) A circular plate has the same material, outside diameter and thickness as a circular ring. Obviously the ring weighs much less than the plate.
Put both on the top of a hill and let them start rolling down at the same time. Who would you think gets to the bottom of the hill first, provided they both roll in a straight line? The plate.
Reason being that the potential energy at the top of the hill splits into two energies once they start rolling: One that gives forward motion and one that gives rotation. In a circular plate, the mass is evenly distributed from the middle and out. The mass near the middle doesn't spend as much energy rotating as the mass near the outside. That extra energy is used to give the plate forward motion.
In a ring, the mass is obviously at the outside so more energy is spent on rotating than forward movement.
2) A circular plate has the same material and thickness as another circular plate with a smaller diameter. Obviously the plate with the smaller diameter weighs much less than the plate with the larger diameter.
Perform the same experiment as in # 1). Which plate gets to the bottom of the hill first? Both plates get to the bottom of the hill at the same time.
Even though the mass is different, the speed is the same because the potential energy, kinetic energy and rotational energy is proportional to the mass when two objects have the same shape.
How the heck it translates to flywheels? Well, the flywheels don't actually go anywhere do they. It is all rotation. For wheels though, it's food for thought. Getting the mass closer to the center is more important than the overall wheel weight. Anyway, back to flywheels: at a steady 3.000 RPM, the flywheel has stored potential energy and it has a rotational energy. Since most of us tend to stay at a steady RPM until the apex, when we start accelerating, that's the situation in a lot of corners, lap after lap. Wouldn't that potential energy turn into rotational energy once we start accelerating? If so, wouldn't the ideal flywheel when coming off the apex be heavier with a smaller diameter? Two seconds later, barreling down the straight, a lighter, smaller diameter flywheel would have less moment of inertia and provide quicker acceleration, right?
Thanks to those of you that have bothered to read everything
As it was told to me, a light weight flywheel will allow the engine to rev faster and easier somewhat like having lighter connecting rods and a lightened crankshaft. Reducing the rotating mass will increase throttle responce and maybe the HP/torque curve of an engine. It also helps with engine braking which can be useful in a racing situation where less foot brake application is required to slow you down. I agree with byprodrivers explaination.IMO
02-26-2013, 07:19 PM
#32
Rennlist Member
in gear, there is the entire mass of the car, and the wheels and tires attached to the engine directly! 5lbs vs the 3000lbs is a drop in the bucket, rotating or not. in idle, thats where you will see most benifits and gains. Quick throttle blips for better engine RPM matching is the advantage.
02-26-2013, 07:27 PM
#33
Rennlist Member
This link takes you through a good explanation of the advantages/reasons for LWFWs
Whether or not they are for your driving style comes down to practice and need
http://www.uucmotorwerks.com/flywhee...heel_works.htm
Whether or not they are for your driving style comes down to practice and need
http://www.uucmotorwerks.com/flywhee...heel_works.htm
03-06-2013, 09:08 PM
#36
Rennlist Member
Having a little knowlege here can be useful, expecially in racing.
on a track, where you are running in 3rd through 5th gears, I gave the effects. in a miata, where the hp is only 100s, 1-5hp can be significant, which would be the effect, just as if the weight was sitting in the car. a drag race where 200lbs is sitting in the car, is more significant than 10 to 20lbs sitting in the car in the higher gears, and that is the actual REAL effects on straight line acceleration for a 7-10lb ligher flywheel for example.
If you rememember we had a discussion a while ago about a guy in a porsche that had 1lb lighter wheels and clamied it saved him a second a lap. under closer inspection, the Data showed there were significant driving style differences in those comparitive laps. In the end, when weight is on the wheel and tire, the difference is as if that weight was 2x it sitting in the car (1.5 on the edge of the rim vs 2x if at the tire diameter for inertial calculations)
so, in that case, 4lb savings on the rim total, was equal to about 8lbs sitting in the car, which is less than the effect of 1hp. Not possible for that to effect lap times by 1 second a lap, by any stretch of the imagination.
It would take a lot more than a lighten flywheel for VR to beat me in anything motorized.
