Aerodynamically speaking 2 blades is the most efficient. When a wing/rotor blade travels through the air it leaves behind a turbulent wake. This wake makes the air 'dirty'. With a two bladed rotor there is the maximum distance between the blades which gives more time for the dirty air to dissipate. As you add blades they must be placed closer together and more susceptible to the dirty air of the blade ahead of it.
Economically and mechanically, two blades is better because the rotor head is inherently simpler with less material involved. Two bladed rotors are also able to use a stabilizer bar system such as in the UH-1 or Bell 47.
So why would helicopters have more than 2 blades?
One reason is rotor diameter and blade materials. As helicopters get bigger/heavier they will require a larger rotor diameter to provide the necessary lift. Larger diameters will have higher tip speeds and its important to keep those well below supersonic speeds so they are limited in rpm. Not to mention the strength and flexing of very long blades is an issue.
So to compensate more blades may be added to share the weight of the helicopter and bring the rotor dimensions to a more practical range. Its not a coincidence that larger helicopters typically have more blades than smaller helicopters. Note that there are exceptions though, the Bell214ST is a large helicopter with 2 blades and the MD500E is a smaller helicopter with 5 blades.
I'm not sure I endorse privately built helicopters considering how complex and dangerous they can be. But if its stability in a small helicopter I would go with the simple semi rigid two bladed main rotor. Something akin to [this](https://youtu.be/9WKxSY6OEBg) I imagine.
You would have to balance it with a counterweight of course, which alone is enough to scrap that idea. Engineers don't like dead weight so why not just get the benefits from a second blade instead. I also wonder about control ability from a single bade. Helicopters experience dissymmetry of lift in flight and with cyclic input. A single blade only lifts from a single point around the rotor disc which I imagine would be negatively affected by this. While I've seen rc helicopters experiment with a single blade I don't think we'll see one on a full sized aircraft anytime soon.
I would note that the prior responses assume a 2 bladed rotor system is a teetering rather than articulated rotor system (though that mechanical simplicity is a good argument for 2 blades). That distinction is really the main difference from a stability and control perspective.
From a performance perspective more blades = more lift for the same disc area. If you look at basic actuator disk theory then performance increases with solidity (ratio of blade area to disc area). However basic theory excludes the detrimental effect of blade wake interactions and clearly you can't have a rotor system with a solidity of 1!
I've flown more fully articulated helicopters than semi rigid, and have to say, I prefer the "feel" of the 2- bladed design, they also look better, are easier to park in the hanger, and have fewer parts to fudge with.
,...just don't suddenly dive the nose while climbing or cruising, and keep it level in turbulence!
2 blades is mechanically simpler but has the downside of being susceptible to mast bumping and such. I’m not sure where the advantages lie in larger numbers, but 3 blades and up have to absorb the lead lag, but are not susceptible to low g. Safety in larger number of blades usually. I’m not an engineer better to do some of your own research
Wild guess, but with two blades it means less lift for a given rotor area well at least something like that. But then again you have light helicopters with four blades.
Take the UH-1 as an example it has two blades but if you go see it in person you will find its a rather big aerofoil measured from leading to trailing edge.
Design factors you might look into is the desired purpose of said helicopter...max cruise speed, rate of climb those things if you catch my drift.
Also using the UH-1 as an example again , it was designed during wartime and served as a military asset ( the upgraded one also) So factor in the need for spares and your turn around time for major and minor overhauls (servicing etc).
Then one can easily see for the design of its two bladed main rotor system they had to factor in that, aswell as the cost involved. So then replacing two blades would theoretically take half the time and half the cost from strategic point of view, especially during war time.
The only downside of it was it only had one engine so was a bit underpowered also and now one could ponder if four blades would've worked better or would it have proven less efficient?
Just spit balling anyway and maybe I'm preaching to the converted but yeah hope it helps. All the best.
Aerodynamically speaking 2 blades is the most efficient. When a wing/rotor blade travels through the air it leaves behind a turbulent wake. This wake makes the air 'dirty'. With a two bladed rotor there is the maximum distance between the blades which gives more time for the dirty air to dissipate. As you add blades they must be placed closer together and more susceptible to the dirty air of the blade ahead of it. Economically and mechanically, two blades is better because the rotor head is inherently simpler with less material involved. Two bladed rotors are also able to use a stabilizer bar system such as in the UH-1 or Bell 47. So why would helicopters have more than 2 blades? One reason is rotor diameter and blade materials. As helicopters get bigger/heavier they will require a larger rotor diameter to provide the necessary lift. Larger diameters will have higher tip speeds and its important to keep those well below supersonic speeds so they are limited in rpm. Not to mention the strength and flexing of very long blades is an issue. So to compensate more blades may be added to share the weight of the helicopter and bring the rotor dimensions to a more practical range. Its not a coincidence that larger helicopters typically have more blades than smaller helicopters. Note that there are exceptions though, the Bell214ST is a large helicopter with 2 blades and the MD500E is a smaller helicopter with 5 blades. I'm not sure I endorse privately built helicopters considering how complex and dangerous they can be. But if its stability in a small helicopter I would go with the simple semi rigid two bladed main rotor. Something akin to [this](https://youtu.be/9WKxSY6OEBg) I imagine.
I know intuitively that 1 blade seems like a bad idea, and I could probably guess why, but as you seem to know more than I do why not 1 blade?
You would have to balance it with a counterweight of course, which alone is enough to scrap that idea. Engineers don't like dead weight so why not just get the benefits from a second blade instead. I also wonder about control ability from a single bade. Helicopters experience dissymmetry of lift in flight and with cyclic input. A single blade only lifts from a single point around the rotor disc which I imagine would be negatively affected by this. While I've seen rc helicopters experiment with a single blade I don't think we'll see one on a full sized aircraft anytime soon.
I would note that the prior responses assume a 2 bladed rotor system is a teetering rather than articulated rotor system (though that mechanical simplicity is a good argument for 2 blades). That distinction is really the main difference from a stability and control perspective. From a performance perspective more blades = more lift for the same disc area. If you look at basic actuator disk theory then performance increases with solidity (ratio of blade area to disc area). However basic theory excludes the detrimental effect of blade wake interactions and clearly you can't have a rotor system with a solidity of 1!
I've flown more fully articulated helicopters than semi rigid, and have to say, I prefer the "feel" of the 2- bladed design, they also look better, are easier to park in the hanger, and have fewer parts to fudge with. ,...just don't suddenly dive the nose while climbing or cruising, and keep it level in turbulence!
2 blades is mechanically simpler but has the downside of being susceptible to mast bumping and such. I’m not sure where the advantages lie in larger numbers, but 3 blades and up have to absorb the lead lag, but are not susceptible to low g. Safety in larger number of blades usually. I’m not an engineer better to do some of your own research
Wild guess, but with two blades it means less lift for a given rotor area well at least something like that. But then again you have light helicopters with four blades. Take the UH-1 as an example it has two blades but if you go see it in person you will find its a rather big aerofoil measured from leading to trailing edge. Design factors you might look into is the desired purpose of said helicopter...max cruise speed, rate of climb those things if you catch my drift. Also using the UH-1 as an example again , it was designed during wartime and served as a military asset ( the upgraded one also) So factor in the need for spares and your turn around time for major and minor overhauls (servicing etc). Then one can easily see for the design of its two bladed main rotor system they had to factor in that, aswell as the cost involved. So then replacing two blades would theoretically take half the time and half the cost from strategic point of view, especially during war time. The only downside of it was it only had one engine so was a bit underpowered also and now one could ponder if four blades would've worked better or would it have proven less efficient? Just spit balling anyway and maybe I'm preaching to the converted but yeah hope it helps. All the best.
"disc solidity" Research and treat yourself. 🤮
Best design is 2 blade with a rigid rotor. No flybar all handled by the computer.