What helicopter has the most rotor blades?

I have seen 2 rotor blades up to many and wonder when does having more rotor blades become less efficient? What helicopter has the most rotor blades?

What is the definining line between a helicopter and a drone a person can ride in?

• If the blades are longer it has to spin slower to keep the tips from going supersonic. They are also heavier and harder to control – Ron Beyer Apr 22 '19 at 1:59
• @RonBeyer do you think redundancy of having more blades could allow the helicopter to fly with damaged blades? – Muze the good Troll. Apr 22 '19 at 2:04
• Unlikely. Chipped/mildly damaged blades can still fly, but once they fail structurally the entire rotor is unbalanced an no amount of extra blades is going to make it stabilize. It will shake itself apart as soon as it becomes unbalanced enough. – Ron Beyer Apr 22 '19 at 2:09
• when does having more rotor blades become less efficient? -- any number more than one. The problem is if you need more lift then you need to use longer blades but if you cannot increase blade length due to structural issues and/or storage issues then you have no choice but to sacrifice efficiency for more lifting power. A single blade is ALWAYS the most efficient number of blades. – slebetman Apr 22 '19 at 5:13
• Is this blades per hub, or blades per helicopter? Tandem rotor (Chinook et al) or Coaxial rotor helicopters have several hubs, each with the same number/size of blades. – CSM Apr 22 '19 at 9:22

Special mention for Raúl Pateras Pescara de Castelluccio (good article) who was fond of lots and lots of rotor blades, settling on sixteen for most of his designs, although his Model 3 had twenty.

Pescara's helicopters may look a little comical (and dangerous!) but they are an important part of early helicopter evolution, pioneers in the first fully controlled helicopter flights, as well as the first use of the what would be recognised as modern helicopter controls.

Here's a video of Pescara testing one of his helicopters in 1922 wearing a Homburg hat with about 5mm of clearance to his head. He had many setbacks, but persevered. It's visionary, brave guys like him who make advances in aviation.

Here is his Model 3 from 1929: (source1)

• This is actually a comment. But only a heart of stone could refuse a +1 for that picture. – Tim Lymington Apr 22 '19 at 12:12
• Wow. Counter-rotating biplane rotors. What could possibly go wrong? – Bob Jarvis - Reinstate Monica Apr 22 '19 at 12:19
• @TimLymington you're right - answers with good/useful pictures earn more upvotes than plain text answers. Add images to answers for better scores. – Criggie Apr 22 '19 at 13:04
• @TimLymington I have expounded the answer so it's hopefully less comment-like. – Party Ark Apr 22 '19 at 14:28
• Mr Pescara did at least have the sense to fit a head guard to his machine. Very stylish guy, flight testing with that hat! – Cpt Reynolds Apr 23 '19 at 18:59

The most blades I've seen are 8 on the Mi-26.
Source

But the highest theoretical lifting efficiency is achieved with the fewest blades and experiments have been done with single blade rotors (with a counterweight - there were vibration problems that couldn't be resolved).

So in practical terms, the most lift for the least power is achieved with a 2 blade rotor, but the need to absorb more power with a limited desirable disc diameter forces you to add more blades (or you may want a smaller rotor with lots of blades for maneuverability or other reasons, but it's sub-optimal from a horsepower efficiency standpoint).

Put another way, a helicopter like the Mi-26 could probably achieve a fair bit more lifting power for its installed horsepower with a 2 blade rotor, but each blade would seemingly extend off into the next township.

• It's interesting to note that the tail rotor of Mi-26 also has large number of blades (5). – trolley813 Apr 22 '19 at 9:36
• @John K Could you maybe please provide some sources for your statements. Because for example the Ec145 helicopter recently got a new main rotor with five instead of 4 baldes and now it can carry more load with the same engine power verticalmag.com/news/… – hph304j Apr 22 '19 at 13:56
• Added a link to another ASE post where @Peter Kämpf responds with much greater authority than I on the theory. – John K Apr 22 '19 at 17:09
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