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### Author Topic: What would be the mass of an airoplane full of flying birds  (Read 6739 times)

#### Alan McDougall

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##### What would be the mass of an airoplane full of flying birds
« on: 26/06/2008 20:58:55 »
If there were a thousand seaguls in an airplane while its flying, each weighing two pounds a piece, but they were all flying in the airplane, would the airplane weigh 2000 pounds more?

#### lyner

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##### What would be the mass of an airoplane full of flying birds
« Reply #1 on: 26/06/2008 22:51:47 »
The total MASS would always be the same but I think you mean weight. The weight would also be unchanged if the fuselage were sealed. They would be pushing air downwards in order to keep up. The moving air would end up pushing the floor of the plane downwards with a force equal to the weight of the birds.

#### Alan McDougall

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##### What would be the mass of an airoplane full of flying birds
« Reply #2 on: 26/06/2008 22:58:03 »
Right mass and weight are just two words for the same thing. Semantics really.

Of course if one had a sufficiently precise instrument to observe the plane it would be moving minutely in harmony with the up and down pressure of the birds wings

#### lyner

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##### What would be the mass of an airoplane full of flying birds
« Reply #3 on: 26/06/2008 23:12:56 »
Oh no they aren't the same thing. You really must learn some basics my boy! Physics has very precise semantics; with good reason.
Your birds would not be beating their wings synchronously so I imagine the vibrations would tend to average to near zero.

#### Pumblechook

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##### What would be the mass of an airoplane full of flying birds
« Reply #4 on: 27/06/2008 00:00:14 »
A 1 kg mass is always 1 kg but would weigh more or less depending on the gravity acting on it.

#### LeeE

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##### What would be the mass of an airoplane full of flying birds
« Reply #5 on: 27/06/2008 00:56:54 »
Weight is a useless concept - if a bird is flying, does it mean it weighs nothing?  Well, basically, yes it does.  Just consider the mass - that's all that counts.

And also, don't get tied in with the idea that aerodynamic lift comes from downwash i.e. the air deflected downwards from a wing.  If this was the case, a delta-winged aircraft just wouldn't work because the downwash would act behind the wing.

#### Alan McDougall

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##### What would be the mass of an airoplane full of flying birds
« Reply #6 on: 27/06/2008 06:37:23 »
Yes

I stand corrected, of course weight only applies to a scale measurement

#### syhprum

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##### What would be the mass of an airoplane full of flying birds
« Reply #7 on: 27/06/2008 15:45:13 »
I think this was discussed recently in the case of birds in the back of a truck that was about to cross a bridge on the ragged edge of the permissable weight limit.

#### lyner

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##### What would be the mass of an airoplane full of flying birds
« Reply #8 on: 27/06/2008 22:53:20 »
Quote
Weight is a useless concept - if a bird is flying, does it mean it weighs nothing?  Well, basically, yes it does.
No, 'basically' it doesn't. If it is flying the lift is equal to the weight.
If weight is a useless concept then it wouldn't be relevant on the Moon. I believe they found it to be very relevant.
OK if it's not downwash, it's pressure difference that keeps the birds up and that, also will find its way to act on the floor of the plane etc. etc. Either way the total weight will be the same whether the birds are flying or in perches. If they stop flapping for a bit, there may be a very brief reduction, followed by a 'clunk' as they hit the floor.
If the birds didn't add to the load of the plane, I think there is would be some 'free lift' here and that would be a nonsense.

#### Madidus_Scientia

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##### What would be the mass of an airoplane full of flying birds
« Reply #9 on: 28/06/2008 01:51:37 »
Hmmm, but would the flapping of the wings really result in a downward force on the floor or just a momentary tiny pressure increase exerted equally on the inside of the plane? It wouldn't really be "free" lift would it, just the birds are lifting themselves, instead of burdening the plane with their weight?

#### lyner

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##### What would be the mass of an airoplane full of flying birds
« Reply #10 on: 28/06/2008 09:41:28 »
Hmmm, but would the flapping of the wings really result in a downward force on the floor or just a momentary tiny pressure increase exerted equally on the inside of the plane? It wouldn't really be "free" lift would it, just the birds are lifting themselves, instead of burdening the plane with their weight?
But something has to provide an upwards force to keep the birds up. As they are inside the plane, it must be the plane. You can't get forces from just anywhere.

#### Madidus_Scientia

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##### What would be the mass of an airoplane full of flying birds
« Reply #11 on: 28/06/2008 16:28:51 »
Yeah but isn't it the muscles of the birds providing the force? you don't feel the weight of a plane exerted apon you if it flies over you do you?

#### ukmicky

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##### What would be the mass of an airoplane full of flying birds
« Reply #12 on: 28/06/2008 16:43:03 »
Yeah but isn't it the muscles of the birds providing the force? why you don't feel the weight of a plane exerted apon you if it flies over you do you?
And has probably got something todo with why why you don't feel the pressure of all the air above us pushing down with or without a plane or if you go diving the same reason why your body doesn't feel the tons of water above  with or without a ship.
« Last Edit: 28/06/2008 16:47:30 by ukmicky »

#### Alan McDougall

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##### What would be the mass of an airoplane full of flying birds
« Reply #13 on: 28/06/2008 17:05:32 »
OK Weight and mass are not the same thing.

So lets put our aircraft on the ground on top of a huge scale with the birds sitting in their respective seats. They all take of and start flying about in the plane.

1) If there was only one huge bird what would the effect be on the scale?

2) If there were many birds what would be the effect on the scale?

#### yor_on

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##### What would be the mass of an airoplane full of flying birds
« Reply #14 on: 03/03/2009 21:06:14 »
It seems to me as this is a closed environment that the birds must act with a uplifting force equal to the one gravity act upon them to keep up in the air. And that seems to me to mean that the plane if weighted should weight as much with them flying as with them sitting..
(1&2 == same)

#### Alan McDougall

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##### What would be the mass of an airoplane full of flying birds
« Reply #15 on: 03/03/2009 23:14:38 »
yor_on

The mass of course will not differ, but if you placed the plane on a huge extremely accurate bathroom type scale you would observer a very small oscillation the scale momentarily showing heavier and then momentarily light in synchronizing with the flapping of the bird wings

Very similar to you jumping up and down on a bathroom scale

Alan

#### lyner

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##### What would be the mass of an airoplane full of flying birds
« Reply #16 on: 03/03/2009 23:33:34 »
Yeah but isn't it the muscles of the birds providing the force? you don't feel the weight of a plane exerted apon you if it flies over you do you?

The force from the birds' wings must have an equal and opposite force - this is spread all over the floor of the plane - a very small pressure, of course. Likewise, the weight of an aeroplane flying in the vicinity will cause an infinitessimal increase in pressure,locally. But this will make air flow outwards. In the case of the aeroplane cabin, the air can't go anywhere so the pressure on the floor, due to displaced air will, when multiplied by the area, give the weight of the bird.

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##### What would be the mass of an airoplane full of flying birds
« Reply #16 on: 03/03/2009 23:33:34 »

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