Ok, so normally it takes more energy to spin something heavy, than light.
And with a fan causing drag in the air, the flywheel effect might be shot down.
so…would CF fan blades be more energy efficent than the wood ones?? They are just flat blades on most, not really any airfoil design. Plus being very light, you can add length to increase air flow.
right? Anthing I’m missing here? I have enough AS4 PEI pre-preg to make TONS of blades, and an autoclave to do it all in!! 
it is correct, same reason wind turbines use composite blades in wind-energy farms.
that and steel blades of that size might weigh a bit extra
You think that I would save any energy though? i’m not sure exactly how things like motors work, relative to what it is attached too. I would play with one, but I don’tthink I can measure the amperage as it is already on the ceiling.
well, obviously more mass requires more energy to spin, however, i’m not sure that the motor wouldn’t just spin faster using the same amount of energy or if it would rotate at the same speed conserving energy.
Like you said, only real way to tell is to check how many amps are being pulled. Ceiling fans are relatively simple to drop a couple inches to be able to check amps, no?
the motor only consumes a certain amount of energy so the watts consumed wouldn’t go down, you would just end up having a more effecient fan by it rotating faster for the same amount of energy input, so yes it would be more energy effecient but not in the way of using less electricity.
you could very well make the fan blades longer but by doing this you would be increasing the moment of inertia, it’s not a linear relationship, so you can’t double the length and have only a doubleing of the moment of enertia, it would be something like a quadrupling of the moment of inertia or something (can’t quite remember)…
Arhhh, physics dont we love it all 
You must also remember that helicopter blades are also a fan like object and that it is also made of a composite material. Must be something beneficial out of it for them to make it that way
Anyways to calculate this whole energy/inertia crap you can use the following formulas.
Power = 2 x Pi x RPM/60 x Torque
Torque = Inertia x Angular Acceleration
Inertia = Mass x Radius of Gyration^2
Now as you can see, if the mass was reduced then the inertia would decrease and then torque will decrease. All of this will cause the power to decrease so yes, in a way it will use less power. The so called speed or “rpm” of the motor wouldnt really increase since most motors run at a synchronized speed of something like 1490rpm etc…
If you were to increase the blade lengths then the radius of gyration would obviously increase and the mass of it would even out with one of a shorter length. In saying that your torque, power etc… would stay the same. You however would have a longer blade length (which is the same mass) and thus should be able to move more air. That however is a whole different sort of calculation …
I don’t think that the current the elecrtical unit is drawing would decrease. I’m quite sure that the current is a property of the elecrtical device, independent of the loads on the motor. putting a lighter blade on the unit would only reduce the parasitic drag(or inertia to be more correct) that the heavier blades are causing, where by increasong the speed at which the motor will spin with lighter blades.
you could very easily test this with any sort of household item that rotatees at a fixed speed by varying the mass of the rotating object. Which you will certianly find that the effect will be an increase or decreas in rotations depending on what the mass and radius form the center of rotation.
Here is a thought experiment: Lets say that the rpm of the motor without any mass of blades to effect it would be the upper limit of it’s rpm and it’s most effecient point. Now pretend we place heavy blades on there, the rpm would decrese, if we lightened the blades then the rpm would increase, but still be less then the rpm without any blades. The amount of energy of the system is constant and dictated by the current the electrical device draws, this is balanced by the rpm at which different masses will rotate.
Yeah you are right about the current part. As there is less load on the blades then the current draw would decrease as the new power required would be less and that the torque required would also be less.
Remember that there is two formulas for power (well in this case anyways)
Power = Current x Voltage (Voltage is fixed thus as current changes so would the power required)
AND
Power = 2 x Pi x RPM/60 x Torque.
They work in conjunction with one another.
That’s the thing I don’t think the current would decrease. The voltage is fixed at 120V ac out of the wall, the current is fixed because the internal resistors and what ever else are the same, so if the current and voltage remain constant so does the power output of the motor, as a reuslt effecting the rotation speed of the blades…
all we have changed are the mass of the blades not the internals of the motor to effectively reduce the current…
Yes you are right, we arent changing the internals of the motor but by reducing the mass and thus the power needed to turn the blades you are also reducing the load in which the motor needs to spin.
Therefore less power needed means less “current” needed/pulled.
And you also need to remember that the “energy” used is not a measure of current (not directly anyways) so you can really use the V= I x R formula. Energy used is measured in “watts” so you use P = I x V
You guys are missing the most important point!
Lighter fan blades will only make it accelerate faster. Its speed is limited by the air drag on the blades, regardless of weight. And heavier blades are MORE efficient at a constant speed becuase it’s more difficult to change their speed (slow them down).
For the same reason, wind turbines have the lightest blades possible because they need to turn a shaft, not be turned by it.
Carbon blades on a cooling fan would only look cool.
BTW, they are used on RC (and full size) helicopters because they are more responsive (aka acceleration) and stiffer.