Indian flywheel fins

[J1MS]

If you reduce the gap at the side of the flywheel cowling, you will reduce the efficiency of the fan because the resistance away from the fan and into the head cowl will increase, the fit of the fins to the front face of the cowl is the most important for shifting cooling air.

[ArmandTanzarian]

If you reduce the gap at the side of the flywheel cowling, you will reduce the efficiency of the fan because the resistance away from the fan and into the head cowl will increase, the fit of the fins to the front face of the cowl is the most important for shifting cooling air.

Bearing in mind that this is all guesswork on my part....

The way that the fan operates is to suck air in through the middle which gets pushed to the outside. Surely any gap that allows air to escape in any direction other than into the cylinder cowling is a waste.

[firekdp]

The shape that the increasing gap forms is called a volute, it's job is to convert kinetic energy into pressure energy, this pressure formed at the widest point will force the air over your cylinder. If you take a look at most centrifugal pumps they will have this shape around the impeller.
And technically it doesn't suck. The air thrown outwards by the centrifugal force causes a low pressure at the eye of the pump and it is atmospheric pressure that pushes more air in.

[ArmandTanzarian]

The shape that the increasing gap forms is called a volute, it's job is to convert kinetic energy into pressure energy, this pressure formed at the widest point will force the air over your cylinder. If you take a look at most centrifugal pumps they will have this shape around the impeller.
And technically it doesn't suck. The air thrown outwards by the centrifugal force causes a low pressure at the eye of the pump and it is atmospheric pressure that pushes more air in.

So does that mean that a small gap everywhere you don't want the air to go is the most efficient?

A quick search on google for "volute design" threw up lots and lots of highly complex equations that are way beyond my tiny brain

[firekdp]

As J1MS said, you want the top of the fins close to the cowling, but you need the gap around the periphery of the impeller to allow somewhere for the pumped air to go. This gap increasing all the way to the outlet is the most efficient shape.
Pumps with the casing tight to the impeller all the way around will trap the air between the fins until it reaches the outlet so it will pump much less air.

[minotaur]

....but if you use an af lightened flywheel which is smaller than indian the gap is larger, as the flywheel diameter is smaller, the twist and go scoots have small flywheels and cowls to suit so there must be some reasoning, i'll test this week..

[ArmandTanzarian]

From the limited amount I could get from the scientific papers google produced, the golden rule seems to be that the casing must start as close as possible to the fan and then smoothly expand in the direction of flow. What the most efficient rate of expansion is I'm not clever enough to calculate.

[firekdp]

From the limited amount I could get from the scientific papers google produced, the golden rule seems to be that the casing must start as close as possible to the fan and then smoothly expand in the direction of flow. What the most efficient rate of expansion is I'm not clever enough to calculate.

The gap will be as small as possible just after the outlet because you want all pumped air to go out of the outlet and not around the system again.

[ArmandTanzarian]

Having read a bit more, the original configuration looks pretty good. The gap starts small and widens smoothly to the exit. I guess Mr. Innocenti knew his stuff after all.



However, my original questions have yet to be answered. Do longer fins make any difference and is there a more efficient fan on the market?

[CANbus]

However, my original questions have yet to be answered. Do longer fins make any difference and is there a more efficient fan on the market?

firekdp was spot on with his evaluation on how the flywheel operates,it spins creating a void in the air, atomospheric pressure forces air into the hole. So if we can start viewing the flywheel as a pump we can say longer the fins the bigger displacement the pump has, bigger displacement= more airflow.