Why air plane propeller consisting of two feathers and the ceiling fan consists of three blades?
Small aircraft with lower power requirements (like a Cessna 152) have a 2-bladed propeller, and as the power requirements increase, the number of blades also increase. There are many turbo-prop planes with 3, 4 and even 5 blades. Lesser blades are easier to move, and reach optimum power settings faster. More blades require more power, but they also deliver more thrust. Small aircraft trade-off the thrust requirement with lighter engines, hence they can make do with 2 blades. A ceiling fan has 3 or 4 blades, in order to maximise the air delivery. You will notice that a 4-bladed fan starts up more slowly than a 3-bladed fan, but it delivers more air.
It’s all about the volume of air that the propeller has to shift. A two bladed aeroplane propeller will provide enough ‘grunt’ to get the aircraft into the air and moving. The propeller has to spin very fast to “grab” enough air and deliver the propulsive energy to do this. The penalty is that the fast moving bade makes a lot of noise, the benefit is that a two bladed propeller is cheaper to make. Aeroplanes are often made with four or more propeller blades. These can deliver a lot of pulling power at lower speeds and are quieter, but they cost more. A ceiling fan does not have to deliver anything like as much energy to the air as a propeller so it is a very different shaped blade which is cheap to make. By giving it three or five blades it turns relatively slowly and so is nice and quiet.
