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What is it that stops man from duplicating Bird Flight as Engineering?

After all, birds do not require separate propullsion! They use the same wings for propulsion and navigation.

My question could be broad. Is it far-fetched ?

With solar energy harnessed and electronic control systems, SHOULD we not take a re-look at bird flight, at least as personal carriers or even as a short-haul option ?

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    $\begingroup$ "After all, birds do not require separate propullsion!" They have a complex muscular system that provides the additional propulsion. We can mimic that in devices the size of birds, but when we scale up to the size of aircraft, moving wings like that becomes a major (power) problem. It is easier (aka fuel efficient) to pull it through the air via engines rather than try to flap 300 feet of wings. Not to mention the up/down motion of the body would be very uncomfortable for passengers. $\endgroup$ – Ron Beyer May 13 '19 at 1:12
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    $\begingroup$ It's actively researched, not for propulsion, but for controls. $\endgroup$ – Antzi May 13 '19 at 2:08
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    $\begingroup$ Have a look at this: en.wikipedia.org/wiki/List_of_largest_birds Notice how the largest flight-capable birds are not far over your weight target, and keep in mind that these devote most of their mass to the purpose of flight, that is, they can carry almost no payload. Further notice that most of the largest examples are soaring birds, dependent on updrafts for endurance. $\endgroup$ – AEhere supports Monica May 13 '19 at 9:22
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    $\begingroup$ See "Bird Flight As The Basis Of Aviation", Lilienthal. $\endgroup$ – quiet flyer May 13 '19 at 15:46
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    $\begingroup$ Possible duplicate of Can planes flap their wings like birds? $\endgroup$ – KorvinStarmast Jun 12 '19 at 17:15
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The movement of the bird wing during the flight is very complex. Not just the trajectory matters, the shape of the wing itself changes as it moves. Angle of attack changes continuously. It is definitely not just about flapping up and down. For a long time, this limited the possibilities of building such machines, while with recent technology it seems possible.

This complex movement also restricts the maximum speed possible, as even small birds cannot beat the wings more than about 80 times per second. The fastest birds, such as the white-throated needletail, may reach 105 mph (168 km/h) in horizontal flight that would not be impressive for an aircraft.

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  • $\begingroup$ Add to that the inherent instability of birds which requires them to adjust their wings fore and aft all the time. $\endgroup$ – Peter Kämpf Jul 1 '19 at 22:33
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It has been looked at. This class of aircraft is called an ornithopter. Scale model ornithopters can be made to work, manned ornithopters are few and far between.

A big problem with a large ornithopter is that you're replacing a static structure (the wing) with a large, reciprocating mass.

  • The structure gets a lot heavier and each joint is a point of failure.
  • you have to convert the high-speed rotating motion of the engines to low-speed linear motion, which means (heavy) hydraulics and large losses
  • imagine the complexity of a wing that's articulated, and at the same time needs to be able to change its profile multiple times per second at each point of its span. You soon end up with an aircraft that can't carry anything because the wing is stuffed with hydraulics.
  • on a bird, the wings are a large fraction of the total area and weight of the bird. It has a small payload. Scaling up the concept only makes this worse (square/cube law).
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  • $\begingroup$ +1 for ornithopter. I hope developing can go forward for very low and slow plus high reliable recreational uses, akin to Hang gliding $\endgroup$ – jean Jun 12 '19 at 17:03
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Much of the early history of attempted flight is about failure inspired by bird flight. It wasn't until the idea of flying stopped trying to incorporate bird-like flapping movements that it started to see any kind of success.

Wing-propulsion is a dead-end for human flight.

In fact, for large birds, wing-propulsion is also not as efficient as it is for smaller birds, because of the way that scaling works - if you double a length, you get four times the area, and eight times the volume (and mass).

Larger birds tend to spend most of their flight soaring, making use of the movement of air itself - and many of them, far from flapping, are able to lock their wings into place.

There are many aspects of bird flight that have successfully informed human flight, but using wings for propulsion is not one of them.

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For the use of wings for both propulsion and sustaining flight, it has already been done as ornithopter

For the use of flexible wing for control, it is currently under research. For example, I can cite the NASA dynamic Control Surfaces and Active Wing Shaping Control.

For the solar energy, I may add that gliders and birds use thermals.

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