flexo
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Copying Flight Of Birds

Sun Nov 09, 2008 8:17 pm

While I'm no expert on biology I wouldn't be surprised if the way birds fly - using the wings for both propulsion and lift - is more efficient than the way we humans came up with - take a fixed wing and attach a propulsion system to it.

So, has there ever been an airplane that used a similar system as birds and did it ever succesfully fly?

[Edited 2008-11-09 12:17:57]
 
osiris30
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RE: Copying Flight Of Birds

Sun Nov 09, 2008 11:15 pm



Quoting Flexo (Thread starter):
While I'm no expert on biology I wouldn't be surprised if the way birds fly - using the wings for both propulsion and lift - is more efficient than the way we humans came up with - take a fixed wing and attach a propulsion system to it.

I'll take a stab at this and say your assumption is wrong. In birds the muscles are the power source in and of themselves. We humans have no such power source, so to fly like a bird we would have to harness a power source and then use a series of pulleys and all manner of things to flap the wing. Every step along the way we would be giving up efficiency.
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vikkyvik
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RE: Copying Flight Of Birds

Sun Nov 09, 2008 11:38 pm



Quoting Osiris30 (Reply 1):

I'll take a stab at this and say your assumption is wrong. In birds the muscles are the power source in and of themselves. We humans have no such power source, so to fly like a bird we would have to harness a power source and then use a series of pulleys and all manner of things to flap the wing. Every step along the way we would be giving up efficiency.

Well, I doubt his basic assumption is wrong. Birds, far as I've heard, are incredibly efficient fliers.

And, humans can indeed use their muscles as a power source. There are, after all, human-powered aircraft. But using our muscles to power wings in the same way as a bird is extremely difficult, if not impossible.

Various people have tried over history to strap on flapping wings, or to make various contraptions that use flapping wings. It hasn't ever worked particularly well, to my knowledge.

Birds' bone structures are incredibly lightweight, which definitely aids them in flying.

I think, in general, it will probably never be feasible to design a flying machine where the wings provide both lift and thrust. Birds have quite a lot of flexibility to adjust their wings and tail in flight, to achieve whatever they are trying to achieve at any given moment. I don't actually know how one would categorize the static and dynamic stability of a bird in flight, but I'd guess they would tend toward neutrally stable - toward areas where humans are only able to fly with the help of FBW.
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N353SK
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RE: Copying Flight Of Birds

Sun Nov 09, 2008 11:39 pm

Look up "ornithopter" on youtube. There are quite a few examples of examples that can't quite get it right.
 
CanadianNorth
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RE: Copying Flight Of Birds

Mon Nov 10, 2008 12:14 am



Quoting Flexo (Thread starter):
using the wings for both propulsion and lift - is more efficient than the way we humans came up with - take a fixed wing and attach a propulsion system to it.

So, has there ever been an airplane that used a similar system as birds and did it ever succesfully fly?

If you want to stretch it a bit, technically helicopters do use their wings (blades) for both lift and propulsion. It does make for a very useful and versatile machine; however, as far as both maintenance and fuel burn go, generally a fixed wing aircraft of comparable size and capacity will be cheaper and more efficient to operate.


CanadianNorth
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osiris30
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RE: Copying Flight Of Birds

Mon Nov 10, 2008 12:32 am



Quoting Vikkyvik (Reply 2):
Well, I doubt his basic assumption is wrong. Birds, far as I've heard, are incredibly efficient fliers.

I should have been clearer.. I meant for humans. As in what is efficient for them won't work nearly as well for us, because we don't have giant muscle motors you can put in a wing.

Quoting Vikkyvik (Reply 2):

And, humans can indeed use their muscles as a power source. There are, after all, human-powered aircraft.

I didn't mean it quite as literally, but having said that, good luck getting across the pond with one of those  Wink

Also, we often forget, I can't think of a single bird that can fly 8000nm on one tank of 'gas'. Our inefficient way of getting around the skies also has advantages. I would be extremely curious to see how long a bird could fly if for example the muscles and bones weren't self repairing (which they will likely never be on something we build.. let's leave out nanotech for now please  Wink ). Alot of what birds can do works because they are living organisms and would likely not work nearly as well if made out of metal (or some other inanimate material).

Using a hummingbird as an example (chosen specifically for their long range flights.. and the fact I could find data online);

A bird that weighs 4grams, consumes 12kcal to fly a distance of 800km in 10 hours.

That equates to; 50208 joules of energy or; 12,552 joules/gram which further boils down to; 15.69 joules/gram/km (phew!).

Now (and apologies for the randomness of the data, again I'm going on what's available, taken from Air France - KLM Sustainability Report 2005/2006), KLM's flight ops in 2005/2006 was 127.6 million giga joules.

For this they carried 11,489 million ton/KM of traffic (it's hard to tell if that includes the weight of the airframe, fuel, etc., but I doubt it does).

So boiling all that down; 1MT = 1,000,000 grams.. so let's cancel that and the million in the GJ yielding;

11,489 million gram kilometers would consume 127.6 giga joules. (I GJ is 1e^9 J)

Dividing a by b, yields: 11.11 joules/gram/kilometer.

Therefore, it is reasonable to conclude that for average mission profiles, today's aircraft are not all that bad. Now I've double checked the math, but I might have missed something.
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Viscount724
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RE: Copying Flight Of Birds

Mon Nov 10, 2008 1:02 am



Quoting Osiris30 (Reply 5):
I can't think of a single bird that can fly 8000nm on one tank of 'gas'.

Soime come pretty close.
http://www.msnbc.msn.com/id/27322698/
http://www.guardian.co.uk/environmen.../2008/oct/22/wildlife-conservation
 
osiris30
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RE: Copying Flight Of Birds

Mon Nov 10, 2008 1:12 am



Quoting Viscount724 (Reply 6):
Soime come pretty close.
http://www.msnbc.msn.com/id/27322698/
http://www.guardian.co.uk/environmen...ation

Impressive. But also (and I'm really not disparaging birds here, honest!), much easier at 7days vs. 16 hours. (Drag increase being non-linear and all). Still I couldn't even think of walking 7000km, let alone running it.  Smile
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Starlionblue
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RE: Copying Flight Of Birds

Mon Nov 10, 2008 2:00 am

Great thread.

- Muscles. Artificial muscles are being developed. That is organic constructs that contract and relax on command. Early days though and still very small. Mechanical solutions with pulleys and so forth can work, but have issues compared to the "smoothness" of turbines.
- Adaptable wing. As mentioned birds reconfigure their airfoils continually, both for flapping (power) and for control. The wings can thus adapt readily to various flight regimes. Granted, aircraft don't need to change speeds as often as birds, but this is still and issue. There are experiments with adaptable airfoils (beyond the current high lift devices) but we are far from a wing that is completely morphable and instantly responsive.
- Payload. This might be the killer for practical applications. Birds aren't very efficient cargo carriers. Many of them barely have excess lift beyond their own body weight.
- Movement and vibrations. Birds have evolved to handle erratic movement patterns and vibrations. Humans and their machinery might find it hard to take these movements. At the very least fatigue life would be a consideration.


I think we will see the morphing wing first, as this could give enormous efficiency gains. Flapping for power is possible, but turbines are probably a better solution unless the application is very specialized, for example tiny spy drones disguised to look like insects and birds.
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tdscanuck
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RE: Copying Flight Of Birds

Mon Nov 10, 2008 2:58 am



Quoting Osiris30 (Reply 1):
Well, I doubt his basic assumption is wrong. Birds, far as I've heard, are incredibly efficient fliers.

They're really efficient in their niche, and from mechanical power input to thrust but they're awful at overall efficiency...that's why birds have to eat so much, basically all the time. A turbine cycle is something like 30-40% efficient on the thermodynamics side, and somewhere in the 85-95% on the mechanical-to-thrust side.

Birds are very good at the latter, but the conversion from food energy to mechanical energy is a lot worse in biological organisms than in jet engines.

A bird also physically can't fly at airliner speeds...if we took airliner technology and scaled it down to bird speeds we'd have absurd efficiency.

Birds don't have the benefit of rotary joints...if they did, you'd probably see propulsion systems more akin to what we use. There are some marine microorganisms that do have a "bearing" and use spinning propulsion rather than flapping. Birds also have something that we are just starting to touch...a fully adapative wing with a very fast, very accurate, learning control system.

Tom.
 
osiris30
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RE: Copying Flight Of Birds

Mon Nov 10, 2008 3:02 am



Quoting Starlionblue (Reply 8):
Adaptable wing. As mentioned birds reconfigure their airfoils continually, both for flapping (power) and for control. The wings can thus adapt readily to various flight regimes. Granted, aircraft don't need to change speeds as often as birds, but this is still and issue. There are experiments with adaptable airfoils (beyond the current high lift devices) but we are far from a wing that is completely morphable and instantly responsive.

Agreed, this is the most 'interessting' area of development. Flapping for propulsion (unless, as you say for very specific profiles) is actually less efficient using the numbers I could find online (see above, as compared to your average turbine powered AC, and the numbers probably look even better for turbine powered craft if I had bothered figuring out AC + Fuel weight).

One area birds do have an advantage though is that for long flights they burn fat, and (again from what I could find online) it takes 3G of hydrocarbon based fuel to equal the energy in 1.3G of fat. So from an energy density standpoint, the fuel tank on birds is vastly superior to our current tech.
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osiris30
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RE: Copying Flight Of Birds

Mon Nov 10, 2008 3:06 am



Quoting Tdscanuck (Reply 9):
They're really efficient in their niche, and from mechanical power input to thrust but they're awful at overall efficiency...that's why birds have to eat so much, basically all the time. A turbine cycle is something like 30-40% efficient on the thermodynamics side, and somewhere in the 85-95% on the mechanical-to-thrust side.

Wrong person quoted Tom :P

I actually think aircraft are more efficient (energy used vs. work done) than birds, based on what I could find online (and the disregards the actual conversion from source fuel to work energy... my numbers are just energy burn).
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Starlionblue
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RE: Copying Flight Of Birds

Mon Nov 10, 2008 4:28 am

Another interesting aerial organism is the bat. It flies on the same principles as a bird, but unless my guess is wrong the wing is less adaptable. There are no feathers to spread on the up stroke, for example. Mechanically less complex, if you will. Perhaps easier to model. AFAIK current flapping wing experiments have more bat-like "solid" wings than bird-like "feathered" wings.

I recently had a chance to sit right next to a bat at the Bali Zoo. My first impression after saying "cooool" was that there was a LOT of wing and quite a small body. Much more wing compared to your typical. Granted, I've only seen the one, but I think bats are less efficient fliers overall-

Quoting Osiris30 (Reply 10):

One area birds do have an advantage though is that for long flights they burn fat, and (again from what I could find online) it takes 3G of hydrocarbon based fuel to equal the energy in 1.3G of fat. So from an energy density standpoint, the fuel tank on birds is vastly superior to our current tech.

Yepp. Fat is an incredibly good energy store. Not very practical for "faster burn" I guess.  Wink
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2H4
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RE: Copying Flight Of Birds

Mon Nov 10, 2008 4:33 am

The real question is, how would a bird perform on the conveyor belt?

2H4
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osiris30
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RE: Copying Flight Of Birds

Mon Nov 10, 2008 5:06 am



Quoting Starlionblue (Reply 12):
Granted, I've only seen the one, but I think bats are less efficient fliers overall-

I would have agreed with you, until I went to look it up:

Quote:
Bat wings are highly articulated, with more than two dozen independent joints and a thin flexible membrane covering them.

...

Quote:
Birds and insects can fold and rotate their wings during flight, but bats have many more options. Their flexible skin can catch the air and generate lift or reduce drag in many different ways. During straightforward flight, the wing is mostly extended for the down stroke, but the wing surface curves much more than a bird’s does – giving bats greater lift for less energy. During the up stroke, the bats fold the wings much closer to their bodies than other flying animals, potentially reducing the drag they experience. The wing’s extraordinary flexibility also allows the animals to make 180-degree turns in a distance of less than half a wingspan.


http://www.sciencedaily.com/releases/2007/01/070118161402.htm

Quite an interesting read actually, especially with the vortex information. If I'm reading that right the vortex is moved rather radically during the up stroke which would reduce drag significantlly.
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9VSIO
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RE: Copying Flight Of Birds

Mon Nov 10, 2008 7:50 am



Quoting 2H4 (Reply 13):
The real question is, how would a bird perform on the conveyor belt?

2H4

Generally speaking, it would be so bewildered by it moving backward that before it knew what was going on, the poor bird would have been flung off the belt, landing badly with a concussion. Quicker thinking, more intelligent birds would have read a thread on a popular aviation website discussing this and seen a show on TV regarding taking off from a conveyor belt and would have opened (or should it be extended) its wings before realising that it was a futile manoeuvre as it has legs, not wheels and would still be flung off regardless.

The pigeon, however, will merely beat its wings at the merest movement of the belt and flutter off.

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Starlionblue
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RE: Copying Flight Of Birds

Mon Nov 10, 2008 9:50 am

Very interesting Osiris30!

Quoting 9VSIO (Reply 15):
Quicker thinking, more intelligent birds would have read a thread on a popular aviation website discussing this and seen a show on TV regarding taking off from a conveyor belt and would have opened (or should it be extended) its wings before realising that it was a futile manoeuvre as it has legs, not wheels and would still be flung off regardless.

 rotfl   rotfl   rotfl   rotfl   rotfl 
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osiris30
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RE: Copying Flight Of Birds

Mon Nov 10, 2008 3:02 pm



Quoting 9VSIO (Reply 15):
Quicker thinking, more intelligent birds would have read a thread on a popular aviation website discussing this and seen a show on TV regarding taking off from a conveyor belt and would have opened (or should it be extended) its wings before realising that it was a futile manoeuvre as it has legs,

Nah I gotta disagree... the smart bird would just turn around and spread its wings  Wink
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vikkyvik
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RE: Copying Flight Of Birds

Mon Nov 10, 2008 5:13 pm



Quoting 2H4 (Reply 13):
The real question is, how would a bird perform on the conveyor belt?



Quoting 9VSIO (Reply 15):
The pigeon, however, will merely beat its wings at the merest movement of the belt and flutter off.

I don't know how the pigeons would do, but I think I'd hate to be the one who has to clean off the conveyor belt after they've been on it.....
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BAE146QT
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RE: Copying Flight Of Birds

Mon Nov 10, 2008 6:23 pm

This is all very interesting indeed. Nice reference re: bats there Osiris - thank you.

Figured I'd throw this into the mix;

http://www.airliners.net/aviation-fo.../read.main/228245/?threadid=228245

It's a long thread, but there's some interesting stuff in there - especially from Doclightning - about the structure (and efficiency or otherwise) of a bird's chosen aerodynamic behaviours.
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RussianJet
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RE: Copying Flight Of Birds

Mon Nov 10, 2008 7:16 pm



Quoting 2H4 (Reply 13):
The real question is, how would a bird perform on the conveyor belt?

Terribly - it doesn't have wheels, although it can power its feet whereas an aircraft doesn't drive its wheels.
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