Whirl Wheels

Electric Fans

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, 2003-05

Here are some photos of electric fans with variety of blade designs.

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Traditional fan blades. Featuring round triangular blades with large surface area.
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Holmes brand, featuring straight back edge, metal blades. The cutting edge is convex, curved like a knife. It spins clockwise. The back edge has a fixed flap.
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Patton's industrial fan. Large fans usually use metal blades. Notice that the cutting edge is concave, scythe-like. (it spins clockwise.)
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Two Vornado fans. Both spins clockwise. Right: This Vornado features flower-like, overlapping, thick, metal blades.

Vornado fans tend to have a boat-propeller styled blades; fat and small with deep attack angle. The brand Vornado has always been making fans of this style. Its name makes one think of vortex and tornado. Its ads make-believe that the design can generate current that cycles the whole room without changing blow direction. This one spins clockwise.

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This Airwave brand model features a fancy curved penta-blades. Cutting edge is concave.
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This Bionaire has a very different design. It has six thin scythe-like blades with concave edge, and with a rim that connects all blades.
electric fan electric fan
Ceiling fan, almost always having flat rectangular board as blade. The number of blades are usually from 3 to 5.

Here is an ad for ceiling fans: ad image. Particularly notable is the “Malibu Star ceiling fan” that is selling for some seventeen hundreed dollars. Its hub is ostensibly a bicycle sprocket, and its blade consists of silk fabric made taut by the tension of bent fiber-glass rods. In this fan, efficiency of looks is more important than the function of air-generation. Here is another page of the ad: ad image 2.

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Exhaust fan. Notice the symmetry of the leafs, allowing the fan to spin both ways with equal effectiveness. (photo courtesy of electric-fan.com.)
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This unusual fan has the rotation plane in a convex way. The blades are curved backwards, as if to blow wind not just straight-forward but outward like radiation. The edge of the blade that cuts air is concave. (the fan turns clockwise)

In general, i think that metal blades generate the most noise, and traditionally shaped fans that has wide area generate the most current (most efficient). Traditional shaped fans with their plastic blades tend to be the lightest and cheapest as well. I think all the fancily shaped blades are only for the looks.

Can any aerodynamics student or engineer summarize the blade design situation? That is, number of blades, attack angle, shape of blades (warped, flat), edge shape of blades (concave/straight/convex), surface area… what makes whiling blades noisy?

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