As the title says, why do Hueys have 2 blades, while most others have 4, or the Sea Stallion has 6? And if you put 6 on a 4, does that mean more lift and better performance?
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There’s a couple of things at work here but I’ll try to keep it simple. Obviously any force needed to generate lift is going to be applied to the blades. Now that’s a lot of force right? As you want to increase the amount of life a helicopter has, you need to increase the surface area of the blades or the speed at which the spin. The problem is the speed of sound is a major issue because once blades get moving that fast there’s tons of forces on them from spinning as well as disturbances in the air once the speed of sound is broken from the resulting sonic boom. This can very easily destroy the blades and a helicopter with broken blades becomes a falling rock at that point.
It’s important to note that as the length of the helicopter’s blades increase so does the speed of the blades at the tips. An easy way to visualize this is imagine your body is the helicopters rotor and your arms are the blades. Now hold them straight out and spin 360 degrees. Now your shoulders, elbows, and hands all did the same 360 degree movement. The thing to note is the distance in which they covered during that time. Your hands moved a lot further than your shoulders did, so they were traveling at a higher rate of speed. This concept applies with helicopter blades as well.
Ok so why do some helicopters have 2 longer blades and some have 4 or 6 shorter blades. That has to do with design and size of the engine. For a big helicopter you may use 2 blades for the sake of simplicity and cheaper cost. You’ll use an engine that has lots of power to spin these 2 heft blades but not have to spin them as fast.
For a smaller helicopter you’re looking for more performance you’ll choose an engine that an spin the rotor at a higher rate of speed. Then instead of using giant blades, you’ll use multiple shorter blades. That way you can spin them faster without breaking the speed of sound while increasing the number of blades adds surface area for more lift. It also makes the helicopter have a smaller footprint which is nice. It comes at a cost though. More rotors spinning faster is more complex and therefore more expensive. Another plus to more blades is higher amounts of blades tends to make less noise, although a helicopter will never be actually quiet.
At the end of the day it really just comes down to what you need the helicopter to do and how much you’re willing to spend. Huey’s and their 2 big ass blades are old school coming out over 60 years ago. Being military they are as you’d expect simple and cheaper. The military likes things to be as simple, easy to use, and cheap as possible. If you’re Uber wealthy and you’re looking to buy a helicopter to get from place to place like Kobe did (rest in peace bud), then you’re willing to spend more to get a more complicated to build and service bird that flies faster and quieter.
Another interesting fact about helicopters is they don’t actually change the rate at which they spin their blades. Which I find incredibly interesting and cool. In a helicopter you basically increase the engine speed to the ideal operating speed and you leave it there. It’s not like a car where you give it more speed to go faster. The blades spin at the same speed whether it’s just hovering 10 feet off the ground or going max speed. What changes whether the helicopter is moving or not is the angle of the blades in addition to the blades spinning around the rotor they rotate as well to change their angle to make it move 🙂
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