Why do ceiling fans have 4 or 5 blades, and others have 3 blades?

Do you have the same doubts about why fan lights have 4 or 5 blades and others have 3 blades.

• Maximize energy output. The more fans there are, the more energy is needed for rotation, but if the fans are too few, the air volume generated will not meet the needs.
• Manufacturing optimization. More fan blades means high production costs, and corresponding maintenance costs are also high.
• Rotate dynamic balance.
• Minimize noise.

The fan we usually use is an axial fan, and its blades are odd numbers. This is because if an even number of symmetrical blades are used, and the balance is not adjusted properly, it is easy to cause the system to resonate. If the blade material cannot resist vibration. The fatigue will cause the blade or the mandrel to break, so the design is usually an odd number of fan blades that are asymmetric about the shaft. This principle is commonly used in various fan blade designs including some helicopter propellers.

Electric fans used in households generally have three blades. The shape of the blades is bird wing (design term). This form of blade has a large flow rate, low noise, and conforms to the principle of fluid mechanics. The three blades have a good dynamic balance. It is not easy to produce vibration, thereby reducing the wear of the bearing. Extend the service life and reduce maintenance costs.

In the United States and Canada, the main requirement for ceiling fans is to supplement air conditioning in the summer. In winter, many fans with reverse switches can be flipped to change the direction of rotation in order to suck in cold air from below, thereby sucking warm air from the heater (usually along the wall near the floor or with vents on the floor) You can fill the room under the fan. Therefore, the ceiling fan can maintain soft air circulation in the room.
Also, keep in mind that in American/Canada houses, the ceiling height and volume of the room are very low, about 8 feet, while in South Asia it is 10-12 feet.

The North American fan with 4 / 5 blades are slower. Also, these fans generally have a maximum of 3 speed settings. Also, the fact that they almost always double up as a lighting fixture with 1–4 bulbs under the central hub could be one of the reasons why they need to be slow and stabilized so as not to blow the lights.
The Indian fans have about 5-6 speed settings, are not designed to run in reverse direction and seldom double up as light fixtures. In India, the ceiling fan is used primarily as a stand alone appliance that does not change the actual temperature of the room but produces a perceived cooling effect by forced convection of air in the room.