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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The other answers are good. Here are some other design considerations:
1) There is a specific design for a certain kind of 2-blade rotor system that is much simpler to manufacture and also cheaper. This is the teetering/underslung hub found on older H-1s and Bell 206s (among others). This type of design has a number of advantages, but one huge disadvantage called mast bumping. This has the effect of limiting the aircraft’s maneuverability in certain situations and pilots have to be careful not to put the aircraft into flight regimes that can cause it. Mast bumping is very bad, often resulting in the separation of the rotor hub from the aircraft. On rotors with 3 or more blades, a teetering hub is impractical and a fully articulated or rigid hub is used (a 2-bladed aircraft could use this). These are more expensive, more complex with more moving parts, but do not suffer from mast bumping.
2) The number of blades affects vibrations. While this might not be a primary design consideration for how many blades a rotor has, an existing aircraft considering adding more blades will possibly need to redesign the vibration absorbing components of the aircraft.
Why no mention of the width of the rotor blades? I worked on hueys in a air ambulance company Uh1E? Or H any way our sister company was air assault, when I worked with those (avionics) I noticed the blades were considerably wider Uh1M.. but those birds had guns and rocket launchers. I always thought the wide blades were for firing platform stability…. maybe off there. But how does a wider wing play into the power v. Lift v. Blade length?
It’s just like leveling up in a game. Once the helicopter has flown enough hours it is upgraded with two more blades.
The more blades the more experienced helicopter.
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 🙂
Reading through all of these comments, I’ve gone from “well duh, it’s because..:” to “oh wow, I never knew that” rather quickly.
Lift is generated by an object like a helicopter blade slicing through the air, and creating a larger pressure on the bottom than on the top. The more blades, the more lift. In order to go up or down, you actually change the angle of the blade, not make it go faster or slower.
The heavier the helicopter the more blades. The Chinook has 8 (2 sets of 4). Some small helicopters have 4 like the little bird, because they need the performance boost. Most have 4, some medium-heavy helicopters have 6.
There’s also the aspect of gyroscopic precession which is more advanced. More blades makes this more complicated.
It’s a balance of cost (mainly maintenance, the initial cost of another blade isn’t much compared to everything else, weight, and performance).
There’s a lot of things at play here but it comes down to the engine of the helicopter and its intended use. More blades produce more lift without having to rotate as fast but they’re heavier and cause more drag. This means that a large powerful engine can spin them relatively slowly and get the necessary lift but a smaller engine would struggle to spin that rotor. There’s also various other factors like noise and what loads the helicopter is expected to lift or how high it will go. Then we’re putting in even more factors like cost and maintenance ease and complexity.
But to not get too complex the point here is that if a helicopter has “few” rotor blades as opposed to all helicopters having, say, 8 rotor blades, the simple answer is that it doesn’t need to have more. It’s use and capabilities are more than covered with the fewer blades.
Not sure what your talking about but in this situation I’d put my political focus on admin and purchase a level 1 diplo advisor to even out the mana generation.
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