why cant we just add more blades to propellers and rotors to increase thrust?
In: Physics
You get diminishing returns in efficiency as you add rotor blades. To retain efficiency you would ideally rather just increase diameter for the same number of blades if more lift is desired. But you do see a fair amount of “just one more blade, bro” in derivative models because it’s cheaper to redesign a hub to add one more of the same blade than it is to put in an all new rotor system of a larger diameter and increase the length of the tail boom. Although with an extra blade you’ve shifted all of the resonant frequencies and may need to stiffen up areas to avoid N/rev vibration. Plus with an extra blade you need more power/torque so you usually do a gearbox and engine upgrade as well. Also in a lot of cases, increasing solidity gets you the same results. Like if you’ve got 4 blades, making each blade 25% wider (chord) does essentially the same thing as adding a 5th blade without changing the structural dynamics as much.
CH-53 and MD-500 are examples of adding an additional blade to gain more lift.
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