jpdflymhtmlb
Posts: 69
Joined: Sat Jan 07, 2006 1:47 pm

### Hypothetical Question...

Two of them actually. An airplane is getting ready for take-off, and it happens to be full of birds. The pilots, realizing before take-off they are overweight, decide to throw a firecracker in back prior to take off to all the birds start flying. Since they are now flying, would the plane be underweight and be able to make the take-off?

Which now leads to this question...

Same scenario, except the plane is made of chicken wire...

Fly
Landings are just controlled crashes.

Newark777
Posts: 8284
Joined: Thu Dec 02, 2004 6:23 am

### RE: Hypothetical Question...

Oh boy, I remember this thread.

Harry
Why grab a Heine when you can grab a Busch?

darkblue
Posts: 227
Joined: Thu Sep 11, 2003 10:27 pm

### RE: Hypothetical Question...

Newton's 3rd Law: "For every action there is an equal and opposite reaction."

For a bird to fly it must create lift equal to its weight. In a closed fuselage the air that supports the birds is supported by the fuselage. All forces must balance within the fuselage.... Since lift = weight, makes no difference if the birds are flying.

Now for a chicken wire plane (I assume you mean only the fuselage. A wing made of our chicken wire would have some serious issues   )... With nothing to contain the air that is supporting the birds inside the fuselage, you would simply have a very odd looking helicopter. Yes, the aircraft would be lighter.

2H4
Posts: 7960
Joined: Tue Oct 19, 2004 11:11 pm

### RE: Hypothetical Question...

Prediction: 200+ posts.

2H4

Intentionally Left Blank

David L
Posts: 8550
Joined: Tue May 18, 1999 2:26 am

### RE: Hypothetical Question...

Oh, go on then. I'll agree with DarkBlue. Although there'd be some interaction between the airflow caused by all the flapping and the chicken wire it would be minimal. Of course, I wouldn't fancy the birds' chances at 300 kts IAS.

Bobster2
Posts: 1523
Joined: Mon Jan 17, 2005 3:04 am

### RE: Hypothetical Question...

It would be heavier. The firecracker would literally scare the crap out the birds. All the bird droppings would make the plane even more overweight.
"I tell you this, no eternal reward will forgive us now for wasting the dawn." Jim Morrison

David L
Posts: 8550
Joined: Tue May 18, 1999 2:26 am

### RE: Hypothetical Question...

 Quoting Bobster2 (Reply 5):The firecracker would literally scare the crap out the birds. All the bird droppings would make the plane even more overweight.

In the spirit of such discussions, and given the prediction of 200+ posts, I'm going to go ahead and argue that the aforementioned crap was already in the birds when they boarded. Since a lot of it would fall through the chicken wire, the aircraft would be lighter even if the the birds settled on the "floor" (though they might skid around a bit in the aftermath.

aogdesk
Posts: 748
Joined: Wed Jun 09, 2004 2:26 am

### RE: Hypothetical Question...

I'm going to hypothesize that upon seeing the rapidly approaching firecracker travelling at approximately ten feet per second, the rate of bird crap production would increase by a factor of .0013. Upon expulsion of said crap, it would create an increased weight on the airframe.

Ok...I know I'm full of said crap.

Bobster2
Posts: 1523
Joined: Mon Jan 17, 2005 3:04 am

### RE: Hypothetical Question...

Think of a fish tank full of water being weighed on a scale. Everything inside contributes to the total weight. It doesn't matter if an object floats, swims, or sinks to the bottom of the tank; it weighs the same wherever it is.

An airplane is like a fish tank, except it has air inside instead of water.
"I tell you this, no eternal reward will forgive us now for wasting the dawn." Jim Morrison

vikkyvik
Posts: 12043
Joined: Thu Jul 31, 2003 1:58 pm

### RE: Hypothetical Question...

Indeed in the spirit of 200+ posts, I'll postulate that said firecracker would perhaps blow out a window, at which point said birds will be sucked out of said airplane, and therefore said airplane will be less the weight of said birds.

As a friend of mine said upon seeing a photo of a bird that had gotten stuck in the landing gear door of an airplane (don't feel like searching for the photo), "poor bird, doesn't it know it can fly for free?"

~Vik
I'm watching Jeopardy. The category is worst Madonna songs. "This one from 1987 is terrible".

Bobster2
Posts: 1523
Joined: Mon Jan 17, 2005 3:04 am

### RE: Hypothetical Question...

I think we're all missing the point here. This was clear case of pilot error, plus they broke the law by carrying firecrackers on the airplane. It's true that we don't know all the details until the investigation is completed, but I'm going to immediately blame the pilots, the airline, and airport security.

(If you really want 200+ messages, the moderators should move this thread to Civil Aviation.)

By the way, it doesn't matter that this thread is hypothetical. The pilots are still guilty until proven innocent.

[Edited 2006-02-14 05:21:09]
"I tell you this, no eternal reward will forgive us now for wasting the dawn." Jim Morrison

jpdflymhtmlb
Posts: 69
Joined: Sat Jan 07, 2006 1:47 pm

### RE: Hypothetical Question...

Since I'm looking for a somewhat serious answer, I guess it's safe to say that in the case where the birds are in a closed environment, they do add to the weight of the airplane regardless of whether they are flying or not. In the case of the airplane being made of chicken wire...structural issues aside, they wouldn't add to the weight, therefore the airplane would be able to make it off the runway? Thanks for the humourous comments too, keep em going if you like...
Landings are just controlled crashes.

Newark777
Posts: 8284
Joined: Thu Dec 02, 2004 6:23 am

### RE: Hypothetical Question...

Harry
Why grab a Heine when you can grab a Busch?

Bobster2
Posts: 1523
Joined: Mon Jan 17, 2005 3:04 am

### RE: Hypothetical Question...

I believe the chicken wire airplane would be like a fish tank in the ocean. Fish could swim in and out of the tank without affecting the weight of the tank, but if you put a rock on the bottom of the fish tank, then the tank would be heavier.
"I tell you this, no eternal reward will forgive us now for wasting the dawn." Jim Morrison

Bobster2
Posts: 1523
Joined: Mon Jan 17, 2005 3:04 am

### RE: Hypothetical Question...

People in the old thread were talking about the birds' flapping wings pushing the air down. Actually, I don't believe the flapping has any relevance.

Imagine the plane carrying flour as cargo. If you ripped open the bags and used fans to fill the air with flour dust, the dust in the air would still add to the weight of the plane even though the dust doesn't have flapping wings.

[Edited 2006-02-14 07:06:11]
"I tell you this, no eternal reward will forgive us now for wasting the dawn." Jim Morrison

flyf15
Posts: 6633
Joined: Tue May 18, 1999 11:10 am

### RE: Hypothetical Question...

Technically, after the firecracker goes off and the birds start flying, the aircraft will indeed be lighter.

In the explosion of the firecracker energy (heat, sound, light, etc) is released. This energy had to come from somewhere, and it came from the mass of the explosives. The resulting mass of the products is going to be slightly less than the mass of the initial substances. e=mc^2

David L
Posts: 8550
Joined: Tue May 18, 1999 2:26 am

### RE: Hypothetical Question...

 Quoting Bobster2 (Reply 8):Everything inside contributes to the total weight. It doesn't matter if an object floats, swims, or sinks to the bottom of the tank; it weighs the same wherever it is. An airplane is like a fish tank, except it has air inside instead of water.

 Quoting Bobster2 (Reply 13):I believe the chicken wire airplane would be like a fish tank in the ocean.

That would be true in a closed system, e.g. a proper fuselage, but this is not a closed system. Air being pushed around by the birds wings would be free to leave the aircraft and only a small amount would interact with the chicken wire.

Bobster2
Posts: 1523
Joined: Mon Jan 17, 2005 3:04 am

### RE: Hypothetical Question...

I'm trying to refine my analogy to make it more convincing.

If you put a fish in a fish tank, the weight of the fish has to be supported by the bottom of the fish tank. If you put a fish in the ocean, the weight of the fish is supported by the entire ocean floor. In both cases, it doesn't matter if the fish is floating on top, flapping its fins, or lying on the bottom.

I believe we can say the same about an airplane. A bird in an airplane is supported by the floor of the airplane, floating, flapping, or standing does not matter. If the skin of the airplane is totally porous and offers no air resistance (hard to image, but this is hypothetical), then a flying bird is no longer in the airplane, the bird is in the ocean of air known as the atmosphere. In the first case, the birds' weight has to be supported by the floor of the airplane. In the second case, the weight is distributed over the large atmosphere and the weight is supported by the Earth.
"I tell you this, no eternal reward will forgive us now for wasting the dawn." Jim Morrison

David L
Posts: 8550
Joined: Tue May 18, 1999 2:26 am

### RE: Hypothetical Question...

 Quoting Bobster2 (Reply 17):A bird in an airplane is supported by the floor of the airplane, floating, flapping, or standing does not matter. If the skin of the airplane is totally porous and offers no air resistance (hard to image, but this is hypothetical), then a flying bird is no longer in the airplane, the bird is in the ocean of air known as the atmosphere. In the first case, the birds' weight has to be supported by the floor of the airplane. In the second case, the weight is distributed over the large atmosphere and the weight is supported by the Earth.

So you're saying that in an aircraft where the skin is "totally porous and offers no air resistance" the weight of the birds is not supported by the floor of the aircraft but by the surface of the earth. I think a chicken wire skin would count as porous!

As I said, there would be a small amount of interaction but the vast majority of the disturbed air would be free to move in and out of the aircraft without interaction. For argument's sake, lets say the surface area of the chicken wire occupies 5% of the area it covers. That means about 5% of the air being pushed down by the birds' wings would collide with the chicken wire in the floor, pushing it down, and about 95% would pass straight through the gap. I'm assuming that boundary layer effects and so on wouldn't affect the result by more than a few percent.

There's a problem with the fish analogy. Whether in a tank or in open water, fish normally have neutral bouyancy - they have the same the same density as the water so don't need to exert a downward force to remain in position.

David L
Posts: 8550
Joined: Tue May 18, 1999 2:26 am

### RE: Hypothetical Question...

 Quoting Bobster2 (Reply 14):People in the old thread were talking about the birds' flapping wings pushing the air down. Actually, I don't believe the flapping has any relevance.

It does. In order to stay off the floor, the birds have to force air downwards to give them an upwards shove. The air moves downwards with a force equal to the weight of the birds (since that's the force keeping the birds' weight off the floor). Therefore a force equivalent to the weight of the birds acts on the floor. If they didn't flap, they'd fall on to the floor and we'd be back to square one.

Bobster2
Posts: 1523
Joined: Mon Jan 17, 2005 3:04 am

### RE: Hypothetical Question...

 Quoting David L (Reply 19):In order to stay off the floor, the birds have to force air downwards to give them an upwards shove.

Right now I'm having trouble defending some of the things I said earlier, so maybe you're right.

This is the point where I like switching to the fish tank analogy because it's easy to visualize and it can't be disputed. Adding any object to a fish tank full of water makes the tank heavier regardless of whether the object sinks or floats. Can anybody possibly disagree with this? If you want to lift the fish tank, it takes more energy when the fish are added.

There has to be some mechanism to keep an object floating in the water. As you said, the density of an object might equal the density of water. Or an object with high density could use a propeller to hover. Or an object could be designed with wings and a propeller to move horizontally. But I don't see how the mechanism makes a difference. In all cases it's quite clear that the object adds weight to the tank and the position of the object inside the tank makes no difference. We know this from experiments.

Now change the water to air, keep the fish tank with a cover on top. The differences in density, viscosity, compressibility, etc don't change the fact that water and air are both fluids. Adding an object to the bottom of the fish tank full of air makes it heavier. But suppose we fill the tank with flies. Is it heavier? Definitely yes if they sit on the bottom and I think yes when they're flying, because if you want to lift the tank it takes more energy with flies inside. I don't think that can be disputed. You can't get something for nothing. But is the tank heavier if you put it on a scale? The more I think about this, the more I'm having trouble with the idea that flies add weight to the tank when they're flying. Since air is invisible and hard to feel, it's more difficult to have intuition about what to expect in this situation, even though it's an analogy to fish in water. Flying in air should be like swimming in water. Right?

Regarding the chicken wire issue: Air molecules are always moving. You can't see them or feel them, but they are absolutely all moving all the time. In the absence of gravity, the direction of movement would be totally random. In the presence of Earth's gravity there are slighly more molecules moving down than up. That's why air has weight. That's why the airplane has to lift the weight of air inside.

So when we talk about the chicken wire airplane, the air molecules move through the chicken wire in all directions by themselves. They don't need to be pushed. The air is no longer a part of the airplane because the air molecules have freedom to move. Even if the chicken wire covers 5% of the area, that's really small. I would still say there is no longer an inside or outside of the airplane, the movement of air molecules joins the inside and outside together into one big atmosphere.

[Edited 2006-02-14 22:47:53]
"I tell you this, no eternal reward will forgive us now for wasting the dawn." Jim Morrison

sovietjet
Posts: 2573
Joined: Sat Mar 15, 2003 12:32 am

### RE: Hypothetical Question...

Oh no not this again. If the plane is chicken wire it would weigh less. If it was a real plane then no it wouldn't.

Silver1SWA
Crew
Posts: 4458
Joined: Wed Mar 10, 2004 6:11 pm

### RE: Hypothetical Question...

 Quoting Bobster2 (Reply 10):I think we're all missing the point here. This was clear case of pilot error, plus they broke the law by carrying firecrackers on the airplane. It's true that we don't know all the details until the investigation is completed, but I'm going to immediately blame the pilots, the airline, and airport security. (If you really want 200+ messages, the moderators should move this thread to Civil Aviation.) By the way, it doesn't matter that this thread is hypothetical. The pilots are still guilty until proven innocent.

LOL welcome to my RU list my friend. That was classic...
ALL views, opinions expressed are mine ONLY and are NOT representative of those shared by Southwest Airlines Co.

David L
Posts: 8550
Joined: Tue May 18, 1999 2:26 am

### RE: Hypothetical Question...

 Quoting Bobster2 (Reply 20):If you want to lift the fish tank, it takes more energy when the fish are added.

In a closed system, yes, i.e. if the displaced water stays in the tank the total weight will equal the original weight of the water plus the weight of the fish. However, if you fill the tank to the top then add the fish, the water displaced by the fish will be spilled over the top of the tank. Since the weight of the water displaced is the same as the weight of the fish the total weight won't change. But here we're talking about something with neutral bouyancy.

 Quoting Bobster2 (Reply 20):There has to be some mechanism to keep an object floating in the water.

The mechanism is that the fish has the same density as the water so there's no net upward or downward force. It's the same mechanism that keeps a litre of water "suspended" in a swimming pool.

 Quoting Bobster2 (Reply 20):Or an object with high density could use a propeller to hover. Or an object could be designed with wings and a propeller to move horizontally. But I don't see how the mechanism makes a difference.

If the object has to apply a downward force to remain "aloft" then it doesn't matter how that force is applied. But it's not the same as the fish scenario.

 Quoting Bobster2 (Reply 20):Now change the water to air, keep the fish tank with a cover on top. The differences in density, viscosity, compressibility, etc don't change the fact that water and air are both fluids. Adding an object to the bottom of the fish tank full of air makes it heavier. But suppose we fill the tank with flies. Is it heavier? I think yes, because if you want to lift the tank it takes more energy with flies inside. I don't think that can be disputed. You can't get something for nothing. But is the tank heavier if you put it on a scale? The more I think about this, the more I'm having trouble.

Agreed so far and I would say categorically that the tank would be heavier than the same closed tank with no flies. However, the flies are forcing air down against the floor when they're flying. Think about blowing on a sheet of paper (the air pushed down by the birds' wings) compared to blowing on a sheet of chicken wire. The paper's going to move quite noticeable while you'd be lucky to move the chicken wire very much at all. The downwards force wouldn't act very much on the chicken wire aircraft but would mostly pass through to the air outside.

 Quoting Bobster2 (Reply 20):Air molecules are always moving. You can't see them or feel them, but they are absolutely all moving all the time. In the absence of gravity, the direction of movement would be totally random. In the presence of Earth's gravity there are slighly more molecules moving down than up. That's why air has weight. That's why the airplane has to lift the weight of air inside.

If there were slightly more molecules moving down than up then the air would eventually spread itself out on the floor! Air has weight because it's trying to move down but can't because something's in the way (more air, the planet's surface, etc.) - the same reason that anything more dense that air has weight.

David L
Posts: 8550
Joined: Tue May 18, 1999 2:26 am

### RE: Hypothetical Question...

 Quoting Silver1SWA (Reply 22):Quoting Bobster2 (Reply 10): I think we're all missing the point here. This was clear case of pilot error, plus they broke the law by carrying firecrackers on the airplane. It's true that we don't know all the details until the investigation is completed, but I'm going to immediately blame the pilots, the airline, and airport security. (If you really want 200+ messages, the moderators should move this thread to Civil Aviation.) By the way, it doesn't matter that this thread is hypothetical. The pilots are still guilty until proven innocent. LOL welcome to my RU list my friend. That was classic...

I forgot to mention that - agreed!

DC10GUY
Posts: 2590
Joined: Fri Feb 18, 2000 5:52 am

### RE: Hypothetical Question...

Sounds like 2 problems. 1st, bad load plan/ weight & balance not correct, 2nd, Cargo not properly tied down.... Oh yeah one more thing.... Does it really matter ?
Dc10guy.
Next time try the old "dirty Sanchez" She'll love it !!!

vikkyvik
Posts: 12043
Joined: Thu Jul 31, 2003 1:58 pm

### RE: Hypothetical Question...

 Quoting Bobster2 (Reply 20):But suppose we fill the tank with flies. Is it heavier? Definitely yes if they sit on the bottom and I think yes when they're flying, because if you want to lift the tank it takes more energy with flies inside. I don't think that can be disputed. You can't get something for nothing. But is the tank heavier if you put it on a scale? The more I think about this, the more I'm having trouble with the idea that flies add weight to the tank when they're flying. Since air is invisible and hard to feel, it's more difficult to have intuition about what to expect in this situation, even though it's an analogy to fish in water. Flying in air should be like swimming in water. Right?

The flies, whether they're flying or sitting on the bottom of the tank, are adding their combined weight to the tank. However, if the flies were to suddenly stop flapping, from the time that they stop to the time that they impact the bottom of the tank, their weight will not register on the scale, due to them being in freefall and nothing supporting their weight. So you'll see the weight on the scale decrease, then increase back to the starting weight (with a small spike as the flies impact the bottom of the tank).

~Vik
I'm watching Jeopardy. The category is worst Madonna songs. "This one from 1987 is terrible".

Bobster2
Posts: 1523
Joined: Mon Jan 17, 2005 3:04 am

### RE: Hypothetical Question...

 Quoting David L (Reply 23):If the object has to apply a downward force to remain "aloft" then it doesn't matter how that force is applied

I'm having a problem with that argument. I thought birds fly by creating a pressure differential above and below their wings, causing an upward pressure that conteracts gravity. The pressure differential only exsists close to the wings. I can't imagine that birds flying 5 feet or so above the floor are going to push the floor down toward the ground. If your "downward force" theory is correct, it seems to me that it only works if the birds are right over the floor, so what happens if they stay near the ceiling?

(Birds do push air, but the force is generally applied to the rear so they fly forward.)
"I tell you this, no eternal reward will forgive us now for wasting the dawn." Jim Morrison

2H4
Posts: 7960
Joined: Tue Oct 19, 2004 11:11 pm

### RE: Hypothetical Question...

We musn't forget to factor in the loss of feathers resulting from the shock and surprise of the firecracker.

In addition, each individual bird's thrust vector would be different, and very few would be perpendicular to the aircraft's flight path. Amidst the chaos, birds would be bumping into and maneuvering away from one other, resulting in diagonal and even horizontal thrust vectors.

2H4

Intentionally Left Blank

vikkyvik
Posts: 12043
Joined: Thu Jul 31, 2003 1:58 pm

### RE: Hypothetical Question...

 Quoting Bobster2 (Reply 27):I'm having a problem with that argument. I thought birds fly by creating a pressure differential above and below their wings, causing an upward pressure that conteracts gravity. The pressure differential only exsists close to the wings. I can't imagine that birds flying 5 feet or so above the floor are going to push the floor down toward the ground. If your "downward force" theory is correct, it seems to me that it only works if the birds are right over the floor, so what happens if they stay near the ceiling?

Technically speaking, the effect of birds (or airplanes, or whatever) is felt from the wing all the way to the ground. However, it is distributed over a large area, and therefore, you don't actually feel the effect of an airplane flying above you (unless it's low).

In addition to the pressure difference, the wing also turns the airflow downward. This is a requirement for flight, as every action has to have an equal and opposite reaction. This downward airflow will encounter the air below it, and push that air downward. This effect will spread out and continue to move downwards, until it hits the ground, where it will be spread out enough that it's hardly noticeable.

Birds push air downward and to the rear (probably more downward than rearward, as they don't have to fight gravity to move forward). As an example, a 747 wing has to carry 800,000 lbs. to counter the weight, but the engines only need to provide ~200,000 lbs. of thrust to counter the drag.

~Vik
I'm watching Jeopardy. The category is worst Madonna songs. "This one from 1987 is terrible".

David L
Posts: 8550
Joined: Tue May 18, 1999 2:26 am

### RE: Hypothetical Question...

 Quoting Bobster2 (Reply 27):it seems to me that it only works if the birds are right over the floor, so what happens if they stay near the ceiling? (Birds do push air, but the force is generally applied to the rear so they fly forward.)

But there's a downward component. If they propel themselves upwards there must be a force downwards greater than their weight. When they're in "level" flight they must be applying a downwards force equal to their weight. Where does that downwards force go? Each molecule moved by the wings won't reach the floor in that move but they'll push the molecules below them downwards and the molecules at the bottom will push on the floor.

 Quoting Vikkyvik (Reply 26):So you'll see the weight on the scale decrease, then increase back to the starting weight (with a small spike as the flies impact the bottom of the tank).

That's right. Just like someone jumping up and down on the floor.

Bobster2
Posts: 1523
Joined: Mon Jan 17, 2005 3:04 am

### RE: Hypothetical Question...

The pressure differential created by a moving wing disipates quickly. The high pressure air mixes with the low pressure air. You guys may be right but I'm still not convinced that a bird or an airplane pushes on the ground any more than a rocket to the Moon pushes against the Earth. Birds need to be very efficient in order to fly. I can't imagine they are wasting energy by pushing on the ground if they don't have to.
"I tell you this, no eternal reward will forgive us now for wasting the dawn." Jim Morrison

VirginFlyer
Posts: 4462
Joined: Sun Sep 10, 2000 12:27 pm

### RE: Hypothetical Question...

Would it make any difference if the birds were all running on treadmills?

V/F
Having trouble with a malware spam popup advert on A.net mobile site? Share details at viewtopic.php?f=12&t=1363111

"So powerful is the light of unity that it can illuminate the whole earth." - Bahá'u'lláh

vikkyvik
Posts: 12043
Joined: Thu Jul 31, 2003 1:58 pm

### RE: Hypothetical Question...

 Quoting Bobster2 (Reply 31):Birds need to be very efficient in order to fly. I can't imagine they are wasting energy by pushing on the ground if they don't have to.

That's the point - they aren't wasting any energy. They aren't attempting to create a noticeable force on the ground; that's just the result (or cause) of the lift they're generating. The air is supported by the ground; otherwise, gravity would force it toward the center of the earth. Therefore, anything that's being supported by the air is also being supported by the ground.

 Quoting VirginFlyer (Reply 32):Would it make any difference if the birds were all running on treadmills?

Haha, good one.

~Vik
I'm watching Jeopardy. The category is worst Madonna songs. "This one from 1987 is terrible".

David L
Posts: 8550
Joined: Tue May 18, 1999 2:26 am

### RE: Hypothetical Question...

 Quoting 2H4 (Reply 28):We musn't forget to factor in the loss of feathers resulting from the shock and surprise of the firecracker.

But the bulging eyes and stars circling their heads would counteract that. And, as we all know from cartoons, any bird which suddenly loses its feathers is magically adorned with a few sticking plasters.

 Quoting 2H4 (Reply 28):Amidst the chaos, birds would be bumping into and maneuvering away from one other, resulting in diagonal and even horizontal thrust vectors.

But there would still have to be a net downwards component equal to the weight of the birds.

Bobster2
Posts: 1523
Joined: Mon Jan 17, 2005 3:04 am

### RE: Hypothetical Question...

 Quoting Vikkyvik (Reply 33):anything that's being supported by the air is also being supported by the ground.

OK. It's easy to see that with the fish tank, but it's harder to comprehend with air.

So if we have too many birds, can't we have Dick Cheney shoot the extra ones? Just make sure to clip the wings so they can't fly, then he won't miss.
"I tell you this, no eternal reward will forgive us now for wasting the dawn." Jim Morrison

2H4
Posts: 7960
Joined: Tue Oct 19, 2004 11:11 pm

### RE: Hypothetical Question...

 Quoting David L (Reply 34):But there would still have to be a net downwards component equal to the weight of the birds.

Would there really have to be, though? The relative wind experienced by each bird would be very erratic, and each bird would have to continously adjust for turbulence and airflow produced by it's neighbors.

For example, when a bird gets blown back from a grouping of birds in front of it, that bird could simply hold still for a moment, and glide on the airflow. In this case, that bird's weight would be supported at least in part by the relative wind and the corresponding Bernoulli effect. It wouldn't ALL be Newtonian physics in there.

We must also take into account the aerodynamic interference of the walls surrounding the group or birds. The relative wind and airflow next to a wall would be very different from that of a point in the middle of the flock.

2H4

[Edited 2006-02-15 02:47:26]
Intentionally Left Blank

vikkyvik
Posts: 12043
Joined: Thu Jul 31, 2003 1:58 pm

### RE: Hypothetical Question...

Now what if the birds were in an A340? It only gets in the air because of the curvature of the earth, right? So if birds are flying in an A340, how does that affect the airplane's weight? I vote that since it's actually the earth that's doing the work here, the birds would increase the weight of the earth instead of the plane.

~Vik
I'm watching Jeopardy. The category is worst Madonna songs. "This one from 1987 is terrible".

2H4
Posts: 7960
Joined: Tue Oct 19, 2004 11:11 pm

### RE: Hypothetical Question...

 Quoting Vikkyvik (Reply 37):Now what if the birds were in an A340? It only gets in the air because of the curvature of the earth, right?

On that note, I predict the birds would prevent an IL-86 from taking off at all.

2H4

Intentionally Left Blank

David L
Posts: 8550
Joined: Tue May 18, 1999 2:26 am

### RE: Hypothetical Question...

 Quoting 2H4 (Reply 36):The relative wind experienced by each bird would be very erratic, and each bird would have to continously adjust for turbulence and airflow produced by it's neighbors.

In localised patches that's true but overall the forces would balance out.

 Quoting 2H4 (Reply 36):In this case, that bird's weight would be supported at least in part by the relative wind and the corresponding Bernoulli effect. It wouldn't ALL be Newtonian physics in there.

But if the bird is being drawn up by the air pressure then air must be drawn down somewhere (i.e. behind the trailing edge of the wing) to balance the forces - a different situation to a piston sealed in cylinder where air would have to be removed from the system to lower the pressure on the top surface.

 Quoting Vikkyvik (Reply 37):I vote that since it's actually the earth that's doing the work here, the birds would increase the weight of the earth instead of the plane.

David L
Posts: 8550
Joined: Tue May 18, 1999 2:26 am

### RE: Hypothetical Question...

 Quoting Bobster2 (Reply 35):So if we have too many birds, can't we have Dick Cheney shoot the extra ones? Just make sure to clip the wings so they can't fly, then he won't miss.

What's the weight of a lawsuit?

Bobster2
Posts: 1523
Joined: Mon Jan 17, 2005 3:04 am

### RE: Hypothetical Question...

It's easy to accept the explanation that the air supports the birds and the plane supports the air. Or, when the plane is open, the air spills out and has to be supported by the earth.

The thing that makes this discussion so much fun is that we insist on making it so much more complicated. At one point I was thinking how the birds displace air from the plane and the birds weigh more than the displaced air so the plane is therefore heavier, and then I started wondering what happens if the birds are squashed into a tiny volume so they displace negligible air. And another time I was trying to visualize the motions of individual air molecules. And then I was thinking that the birds essentially change the average density of the air since they are more dense than the surrounding air even though they are not made out of air. When you think about it too much it's easy to convince yourself that simple explanation has to be wrong.
"I tell you this, no eternal reward will forgive us now for wasting the dawn." Jim Morrison

seanp11
Posts: 281
Joined: Tue Jan 10, 2006 6:16 am

### RE: Hypothetical Question...

 Quoting Flyf15 (Reply 15):Technically, after the firecracker goes off and the birds start flying, the aircraft will indeed be lighter. In the explosion of the firecracker energy (heat, sound, light, etc) is released. This energy had to come from somewhere, and it came from the mass of the explosives. The resulting mass of the products is going to be slightly less than the mass of the initial substances. e=mc^2

A firecracker exploding is a chemical reaction, so that ever so famous equation you posted doesn't hold true. The energy released in a firecracker exploding is the energy in the bonds between its constituent atoms. The mass of the reactant firecracker has to be equal to the mass of all of the products.

zeke
Posts: 10949
Joined: Thu Dec 14, 2006 1:42 pm

### RE: Hypothetical Question...

 Quoting Jpdflymhtmlb (Thread starter):Since they are now flying, would the plane be underweight and be able to make the take-off?

Negative, considered a closed volume in the physics sense, the mass of the birds, air in the aircraft, and aircraft remains unchanged.

The weight on takeoff is irrelevant, the aircraft is certified for a maximum mass takeoff.
Human rights lawyers are "ambulance chasers of the very worst kind.'" - Sky News

David L
Posts: 8550
Joined: Tue May 18, 1999 2:26 am

### RE: Hypothetical Question...

 Quoting Zeke (Reply 43):Negative, considered a closed volume in the physics sense, the mass of the birds, air in the aircraft, and aircraft remains unchanged.

I'm not sure I agree it's a closed system if the fuselage is made out of chicken wire - air is free to enter and leave the system.

From what I can remember of ther first time I was involved in a discussion like this, don't try visualising too hard unless you want a few weeks off work.

2H4
Posts: 7960
Joined: Tue Oct 19, 2004 11:11 pm

### RE: Hypothetical Question...

Question: How many of the birds are female, and what is the likelihood the firecracker will cause such shock that they instantly lay eggs?

This could have a profound effect on their takeoff performance.

2H4

Intentionally Left Blank

David L
Posts: 8550
Joined: Tue May 18, 1999 2:26 am

### RE: Hypothetical Question...

 Quoting 2H4 (Reply 45):How many of the birds are female, and what is the likelihood the firecracker will cause such shock that they instantly lay eggs?

Can the eggs fit through the chicken wire (without being pushed)? If they laid the eggs "hard enough" I guess they might scramble their way through anyway.

David L
Posts: 8550
Joined: Tue May 18, 1999 2:26 am

### RE: Hypothetical Question...

 Quoting David L (Reply 46):If they laid the eggs "hard enough"

I meant "with enough force" rather than "hard-boiled", d'oh! My brain hurts.

jpdflymhtmlb
Posts: 69
Joined: Sat Jan 07, 2006 1:47 pm

### RE: Hypothetical Question...

Ok, good to see so much response on this, thanks for all the replies, but now I have a new question...

Lets say the birds are nailed down to their perches in the chicken wire airplane...it is still overweight, pilots throw a firecracker back, birds start flapping...will it be underweight and able to lift off now?
Landings are just controlled crashes.

David L
Posts: 8550
Joined: Tue May 18, 1999 2:26 am

### RE: Hypothetical Question...

 Quoting Jpdflymhtmlb (Reply 48):Lets say the birds are nailed down to their perches in the chicken wire airplane...it is still overweight, pilots throw a firecracker back, birds start flapping...will it be underweight and able to lift off now?

In that case they'd be applying an upward force to the aircraft by moving air down through the aircraft so the load would be lighter. This is rather like a European or African swallow trying to carry a very large coconut.

If the fuselage were closed, i.e. normal, the air wouldn't be ejected downwards so there would be no net movement relative to the system. All the movement would be within the system... so no difference to the weight... so no coconut.

### Who is online

Users browsing this forum: 747classic, Bing [Bot] and 1 guest

### Popular Searches On Airliners.net

Top Photos of Last:   24 Hours  •  48 Hours  •  7 Days  •  30 Days  •  180 Days  •  365 Days  •  All Time

Military Aircraft Every type from fighters to helicopters from air forces around the globe

Classic Airliners Props and jets from the good old days

Flight Decks Views from inside the cockpit

Aircraft Cabins Passenger cabin shots showing seat arrangements as well as cargo aircraft interior

Cargo Aircraft Pictures of great freighter aircraft

Government Aircraft Aircraft flying government officials

Helicopters Our large helicopter section. Both military and civil versions

Blimps / Airships Everything from the Goodyear blimp to the Zeppelin

Night Photos Beautiful shots taken while the sun is below the horizon

Accidents Accident, incident and crash related photos

Air to Air Photos taken by airborne photographers of airborne aircraft

Special Paint Schemes Aircraft painted in beautiful and original liveries

Airport Overviews Airport overviews from the air or ground

Tails and Winglets Tail and Winglet closeups with beautiful airline logos