Heaver vs. Lighter Flywheel
04-02-2007, 04:36 AM
#61
Originally Posted by fritzD
Torque is an analog of Newtonian Force but applied to rotating bodies. The concept of torque was defined by physicists to make Newtonian analysis on rotating bodies rather than taking into account the forces involved.Yes, it can be called a twisting force. But its more of a vector quantity that can rotate a an object about a pivot point. But, of course, torque is equal to the force perpendicular to the lever times the lever arm. I'm not answering based on my experience as a racer but as an applied physics major. just my 2cents. 
unfortunately there are always too many variables to consider.
04-02-2007, 05:20 AM
#62
Originally Posted by twiggy
this would all work in a prefect world.
unfortunately there are always too many variables to consider.
unfortunately there are always too many variables to consider.
and technically newtons law of gravity doesn't work in the real world either!, but we still accept it as a viable scientific rule because in theory it works
But put the theory into practice in the real world, with variables such as Gravity, resistance etc and Newton's law is not applicable...to an extent i think the same sort of rationality goes with the lightweight flywheel argument. Artificial is correct, TECHNICALLY, but real world issues lead to the "heavy flywheel is best" theory to just not work..hence the lightweight flywheel is better
good discussion though!! i'm not baging or hating anyone
04-02-2007, 06:11 AM
#63
Originally Posted by TomB
and technically newtons law of gravity doesn't work in the real world either!, but we still accept it as a viable scientific rule because in theory it works But put the theory into practice in the real world, with variables such as Gravity, resistance etc and Newton's law is not applicable...to an extent
i think the same sort of rationality goes with the lightweight flywheel argument. Artificial is correct, TECHNICALLY, but real world issues lead to the "heavy flywheel is best" theory to just not work..hence the lightweight flywheel is better
good discussion though!! i'm not baging or hating anyone
But put the theory into practice in the real world, with variables such as Gravity, resistance etc and Newton's law is not applicable...to an extent i think the same sort of rationality goes with the lightweight flywheel argument. Artificial is correct, TECHNICALLY, but real world issues lead to the "heavy flywheel is best" theory to just not work..hence the lightweight flywheel is better
good discussion though!! i'm not baging or hating anyone
Its a tuning option. Not a statement that reigns supreme , which Is why I made the statement in the mtx-4. Because everyone there was always saying lighten the drivetrain up as much as possible. I wanted to show both sides , then people wanted to get technical and well I think we covered that issue.
So a statement saying a lightweight flywheel is better is just not true. Its a tuning option and if your track has the grip , indeed it can be a better thing. If anything Id rather have a smooth idle and reduce weight via the drivetrain on an rc car. Get the benefit of both worlds. Fast spool up in power and regular idle. But then again were using manufacturer flywheels of the chassis not the motor. So its not like the flywheels are really "optimal" for each motor. So I dont see anything wrong with playing around with each motors flywheel and see what works at your track , but perhaps from chassis to chassis there is some "standard" weight in which all chassis manu's shoot for.
04-02-2007, 10:34 AM
#65
What is of most importance in our cars is inertia. As the inertia of a spinning object increases by the square of the rpm high revving objects are much more influenced by inertia than slow turning ones.
As the engine is rotating about 6 times faster than the wheels a gram less weight on a flywheel equals 36 grams on the wheel (at the same distance from the center of rotation). This also means that drilling out a 2 speed axle will save wieight but do very little in rotational inertia (the mass is very close to the rotational axis).
What does this mean for engines?
Our engines idle about 8000 to 10000 rpm (.12 a little higher than .21)
A correctly setup clutch will only start to engage at 20000 and is fully engaged aroung 30000! (calculate at a rollout of 28mm (with 62 tires and normal first gear) you'd be going about 30km/h with 20000 rpm which is about the speed our cars run just after a hairpin).
As rotational mass in objects that have to accelerate very very quickly from 20k to over 40k is very influencial, it is easy to see that a light flywheel is better for acceleration. Topspeed will be no different only attained quicker (possibly due to the quicker acceleration you have more opportunity to accelerate and obtain higher speeds when the length of the straight is the limiting factor).
The above however is only true when the clutch is already fully engaged. When the clutch needs to engage a very light flywheel may not have enough mass to help keep revs up when the clutch engages. So a too light flywheel could make clutch setup (especially very snappy ones) more difficult. Which explains why dragracers use heavy flywheels.
Also a heavy flhywheel will make idle more stable.
As the engine is rotating about 6 times faster than the wheels a gram less weight on a flywheel equals 36 grams on the wheel (at the same distance from the center of rotation). This also means that drilling out a 2 speed axle will save wieight but do very little in rotational inertia (the mass is very close to the rotational axis).
What does this mean for engines?
Our engines idle about 8000 to 10000 rpm (.12 a little higher than .21)
A correctly setup clutch will only start to engage at 20000 and is fully engaged aroung 30000! (calculate at a rollout of 28mm (with 62 tires and normal first gear) you'd be going about 30km/h with 20000 rpm which is about the speed our cars run just after a hairpin).
As rotational mass in objects that have to accelerate very very quickly from 20k to over 40k is very influencial, it is easy to see that a light flywheel is better for acceleration. Topspeed will be no different only attained quicker (possibly due to the quicker acceleration you have more opportunity to accelerate and obtain higher speeds when the length of the straight is the limiting factor).
The above however is only true when the clutch is already fully engaged. When the clutch needs to engage a very light flywheel may not have enough mass to help keep revs up when the clutch engages. So a too light flywheel could make clutch setup (especially very snappy ones) more difficult. Which explains why dragracers use heavy flywheels.
Also a heavy flhywheel will make idle more stable.
04-02-2007, 10:36 AM
#66
Originally Posted by Julius
What is of most importance in our cars is inertia. As the inertia of a spinning object increases by the square of the rpm high revving objects are much more influenced by inertia than slow turning ones.
As the engine is rotating about 6 times faster than the wheels a gram less weight on a flywheel equals 36 grams on the wheel (at the same distance from the center of rotation). This also means that drilling out a 2 speed axle will save wieight but do very little in rotational inertia (the mass is very close to the rotational axis).
What does this mean for engines?
Our engines idle about 8000 to 10000 rpm (.12 a little higher than .21)
A correctly setup clutch will only start to engage at 20000 and is fully engaged aroung 30000! (calculate at a rollout of 28mm (with 62 tires and normal first gear) you'd be going about 30km/h with 20000 rpm which is about the speed our cars run just after a hairpin).
As rotational mass in objects that have to accelerate very very quickly from 20k to over 40k is very influencial, it is easy to see that a light flywheel is better for acceleration. Topspeed will be no different only attained quicker (possibly due to the quicker acceleration you have more opportunity to accelerate and obtain higher speeds when the length of the straight is the limiting factor).
The above however is only true when the clutch is already fully engaged. When the clutch needs to engage a very light flywheel may not have enough mass to help keep revs up when the clutch engages. So a too light flywheel could make clutch setup (especially very snappy ones) more difficult. Which explains why dragracers use heavy flywheels.
Also a heavy flhywheel will make idle more stable.
As the engine is rotating about 6 times faster than the wheels a gram less weight on a flywheel equals 36 grams on the wheel (at the same distance from the center of rotation). This also means that drilling out a 2 speed axle will save wieight but do very little in rotational inertia (the mass is very close to the rotational axis).
What does this mean for engines?
Our engines idle about 8000 to 10000 rpm (.12 a little higher than .21)
A correctly setup clutch will only start to engage at 20000 and is fully engaged aroung 30000! (calculate at a rollout of 28mm (with 62 tires and normal first gear) you'd be going about 30km/h with 20000 rpm which is about the speed our cars run just after a hairpin).
As rotational mass in objects that have to accelerate very very quickly from 20k to over 40k is very influencial, it is easy to see that a light flywheel is better for acceleration. Topspeed will be no different only attained quicker (possibly due to the quicker acceleration you have more opportunity to accelerate and obtain higher speeds when the length of the straight is the limiting factor).
The above however is only true when the clutch is already fully engaged. When the clutch needs to engage a very light flywheel may not have enough mass to help keep revs up when the clutch engages. So a too light flywheel could make clutch setup (especially very snappy ones) more difficult. Which explains why dragracers use heavy flywheels.
Also a heavy flhywheel will make idle more stable.
04-02-2007, 10:44 AM
#67
As an addition.
A heavy flywheel will reduce acelleration because of inertia. This can be an advantage if you do not have the traction to cope with a lot of acelleration. But in those instances you'd probably be better off using a different clutch setup or longer gearing or learn how to use the throttle better.
It is in my humble opinion plain wrong to down tune the cars acceleration potential if you can find a better solution.
Be aware that the slowdown in acceleration off the line might help there but it will slow you down in every other instance where you are accelerating.
A heavy flywheel will reduce acelleration because of inertia. This can be an advantage if you do not have the traction to cope with a lot of acelleration. But in those instances you'd probably be better off using a different clutch setup or longer gearing or learn how to use the throttle better.
It is in my humble opinion plain wrong to down tune the cars acceleration potential if you can find a better solution.
Be aware that the slowdown in acceleration off the line might help there but it will slow you down in every other instance where you are accelerating.
04-02-2007, 05:54 PM
#68
I'm not sure this has been added to the discussion but here's something many missed in the part of this thread I read.
The engine produces a set amount of power. NO part will add power that doesn't alter the fuel or air mixture.
Reducing rotating mass doesn't add power to the engine is maximize the efficiency of getting the power to the ground. The more weight the more power is wasted in moving the part and less power is put to the ground. The engine still makes the same power, it just won't get to the ground and is lost in translation.
The X-Dyno (Nitrodynesystems) uses about an 8lb flywheel, which you would never use on a RC car, and the HP is the same as it would be in the car using the stock flywheel.
What heavier/lighter flywheels do is change the inertia of the system. Sometimes a heavier flywheel is better because it keeps the system from being influenced by outside forces and dropping the engine out of the powerband. Neither of them make more power, the lighter one will simply waste less power and put more to the ground, although that doesnt mean it will be faster on the track.
The engine produces a set amount of power. NO part will add power that doesn't alter the fuel or air mixture.
Reducing rotating mass doesn't add power to the engine is maximize the efficiency of getting the power to the ground. The more weight the more power is wasted in moving the part and less power is put to the ground. The engine still makes the same power, it just won't get to the ground and is lost in translation.
The X-Dyno (Nitrodynesystems) uses about an 8lb flywheel, which you would never use on a RC car, and the HP is the same as it would be in the car using the stock flywheel.
What heavier/lighter flywheels do is change the inertia of the system. Sometimes a heavier flywheel is better because it keeps the system from being influenced by outside forces and dropping the engine out of the powerband. Neither of them make more power, the lighter one will simply waste less power and put more to the ground, although that doesnt mean it will be faster on the track.
04-02-2007, 11:22 PM
#70
Originally Posted by Julius
Also a heavy flhywheel will make idle more stable.
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