Can a microscopic insect fly by flapping rigid wings?

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SUMMARY

This discussion centers on the feasibility of microscopic insects, specifically those around 10 microns in size, achieving flight using rigid wings. The conversation references Purcell's scallop theorem, which states that non-reciprocal motion is necessary for net forward movement at low Reynolds numbers. The implications of this theorem suggest that flying robots at this scale may need to adopt helicopter-like mechanisms for lift. Additionally, the discussion mentions the DARPA Nano Hummingbird and a recent Nature paper that explores untethered flight with wings flapping in the XY plane.

PREREQUISITES
  • Understanding of Purcell's scallop theorem
  • Familiarity with Reynolds number in fluid dynamics
  • Basic knowledge of aerodynamics and flight mechanics
  • Awareness of millimeter-scale flying robots like DARPA's Nano Hummingbird
NEXT STEPS
  • Research the application of Purcell's scallop theorem in micro-aerodynamics
  • Explore the mechanics of helicopter flight and its relevance to microscale robotics
  • Study the effects of Reynolds number on flight performance
  • Examine the design principles of millimeter-scale flying robots
USEFUL FOR

Aerodynamics researchers, robotics engineers, and anyone interested in the mechanics of flight at the microscale will benefit from this discussion.

Dishsoap
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TL;DR
Are insects at low Reynolds number capable of flying by flapping rigid wings?
While in quarantine, I've been reading a lot about some millimeter-scale flying robots, like DARPA's Nano Hummingbird and others. I'm noticing that a lot of millimeter-scale flying robots flap their wings like a fly, and I'm wondering if it's even possible to use this motion to move if the fly were much smaller (say, 10 microns in size) with rigid wings. In that case, the Reynolds number is much lower, and Purcell's scallop theorem dictates that non-reciprocal motion must be used to have a net motion forward (up, in this case).

That being said, I know virtually nothing about aerodynamics/flight, so I'm curious if there's a reason why the scallop theorem wouldn't apply to upwards motion (lift). Or, if it does, does this mean that flying microscale robots would have to essentially be a helicopter? I notice that this recent Nature paper on untethered flight has the wings flapping in the XY plane (where Z is up), I wonder if this is the reason.
 
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Dishsoap said:
I'm wondering if it's even possible to use this motion to move if the fly were much smaller (say, 10 microns in size) with rigid wings. In that case, the Reynolds number is much lower, and Purcell's scallop theorem dictates that non-reciprocal motion must be used to have a net motion forward (up, in this case).
Rigid wings don't imply reciprocal motion. It depends on how many degrees of freedom they have.
 
I had to look up the smallest flying insect, Kikiki, 0.15 mm, fuzzy wings.
 

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