You know there's actually some good freebie models to try this on... The framerate also effects how this appears, real footage will also reflect this behavior too - with different rates among film cameras and video equipment.

Anyways, now I'm gonna have to post my old examples done with one of my helicopter models. One thing to note though, doing this with motion blur takes forever if you don't have a renderfarm. (I suggest using a minimal samples setting. The extra frames needed for stronger blur don't effect video as much as they do stills. But they do cost quite a bit in time.) Cutting down on other render properties helps a bit though if the rotor blur effect is something you want to push through. (Especially if the animation is going to be compressed anyways.)

Helicopter Animation Test

Helicopter Animation Test 2

Also looks somewhat realistic if you set the spin modifier to somewhere around 3-4 turns per second, which is about 200-240 RPM. This reflects what the main rotor typically spins at on a average helo. Then the tail rotor also tends to be a fixed ratio of that, 1/4 or 1/2 turn for every turn of the main rotor. Also it's very easy to spin up or idle down in Carrara by changing the spin modifier property for the rotors at the right times in the timeline.

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Barbequed Pixels?

Your friendly neighborhood Wings3D nut.
Also feel free to browse my freebies at ShareCG.
There might be something worth downloading.