why cant we just add more blades to propellers and rotors to increase thrust?
In: Physics
Propellers use blades that have an airfoil shape, just like aircraft wings. If you put them too close together the airflow from one interrupts the other, so they need to be spread out. In practice that means planes usually have 2 or 3 blades but some have as many a 6.
But let’s imagine that we did add as many propellers as we can fit on a rotor. The airfoil shape doesn’t work as well so we can simplify the blades to be thin angled plates. This creates a bunch of channels that the air can be forced through. But those channels are open on the outside so air is spilling out, let’s put the rotor and blades inside a tube the same diameter so the air is blocked from spilling out the ends. This casing also forces the air to all flow backwards instead of out to the side. But it’s also twisting because of the rotor so let’s put more blades that don’t move inside the casing that will straighten out the flow so all the air moves straight back. We’ve just reinvented the ducted fan.
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