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So, english isn't my first language, so I probably couldn't find any kind of information about it due to not being able to define what I'm asking.

Anyway, helicopter blades are normally like this:

enter image description here

An "off-center" helicopter blade would be like this:

enter image description here

I'm quite ignorant about aerodynamics and I couldn't find anything about it, so I hope someone here knows if a design like that would have any kind of advantages whatsoever.

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    $\begingroup$ Given the physics involved, they will try to straighten themselves out, putting a lot of stress at the 90 degree joint, causing that joint to either fail or have to be very over-designed. $\endgroup$
    – Ron Beyer
    Commented Mar 13, 2022 at 2:11
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    $\begingroup$ Plus it’d make controlling collective and cyclic pitch much more difficult. $\endgroup$
    – Jim
    Commented Mar 13, 2022 at 5:32
  • $\begingroup$ I see other disadvantages, but you're asking for advantages; if the idea is to understand why they're the way they're, you can edit to ask for the disadvantages instead. $\endgroup$
    – user14897
    Commented Mar 13, 2022 at 11:38
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    $\begingroup$ Just curious, but what do you think the advantages might be? $\endgroup$
    – Michael Hall
    Commented Mar 13, 2022 at 15:23

2 Answers 2

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There is a theoretical advantage of an L shaped rotor blade insofar as it behaves like a swept wing, and so it's able to operate at a higher mach number where its velocity is highest, at the tip.

The problem is the blade as pictured would need to be massively heavy to be able to resist centrifugal forces trying to straighten it, and the torsional forces trying to make it twist it in ways you don't want.

So, since we only need that sweep angle where the velocity is highest, at the tip, we simply sweep the tip of the blade instead of from the root, like BERP tip.

So what you are showing is actually being done, but just with the dogleg in the blade swapped out to the other end since that is the zone that benefits from it, although even with that tip, as pictured below, you will notice the entire planform is shifted forward to place the mean center of lift of the swept section closer to that of the straight section, to minimize the torsional and bending side effects of the offset.

enter image description here

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It is actually being used, be it as far as I know only on RC helicopters.
The blades are mounted on an offset hinge, meaning they actually straighten out, as @RonBeyer suggests. The advantage there is the lack of mass behind the impact as the rotor accidentally impacts an object, which is hard to prevent on these helicopters.

Whether it would provide any advantage on a life size helicopter, I do not know. Without the hinge, I suppose it would flutter quite fiercely. With the hinge it might serve to get the blades out of the way as passenger move in or out of autonomous electric air taxis.

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