Pilot Mag Quiz

[New Bloke]

In this month’s Pilot Magazine quiz, question 5 has us imagining that a Beluga A300-600 is transporting 3000 kilos of unrestrained live geese. During the flight they all take-off. The magazine suggests that this will have no impact on the weight of the aircraft. Shurly Shome Mishtake.

Let us imaging that each of these geese were sitting on a set of sensors attached to a digital weight read-out. As this mass disturbance took place the scales would drop from 3000 kilos to 0 kilos. Now I agree that if they were all in ground effect there would still be some weight on the aircraft but I maintain the weight of the aircraft would drop and it would shoot up in the air.

I was going to post this in the Private Pilots section but thought it would sit better here.

[GRpr]

New Bloke

You are quite right - the weight of the aircraft will reduce, but not by 3000kg. In trying to be clever (and it is a clever question!) the question master has overlooked one vital point and been hoist by his own petard!!

[eyeinthesky]

I also was a bit surprised at the quiz answer. I agree with you. If they all fly at once then their weight will be reduced from the AUW of the a/c. The problem comes of course when they all crash into the bulkhead and cause a large nose-down pitch!

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"Take-off is optional, Landing is mandatory"

[dragchute]

I think the magazine is correct!

The aircraft has a payload of geese and the fluid in which they are travelling - air. If that fluid is supporting the mass of the geese, since they are now on the wing, has not the mass of the fluid increased because of the altered structure (air+geese)?

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dragchute
email: [email protected]

[GRpr]

dragchute

You've spoilt it by using the word 'mass'!!

In the answer in Pilot, our hoistee says that the 'total weight of the aircraft does not alter one iota'. The 'mass' doesn't, but weight is 'the force of attraction of the earth on a given mass'. As altitude increases, mass remains constant but weight decrases as gravitational force decreases. When the geese take off and gain additional distance from the centre of the earth, their weight will decrease (their mass will of course stay the same).

The decrease in overall weight (albeit only by an iota) will lead to a decrease in wing loading.

As an aside, we always need less than 1g of lift to maintain straight and level flight - and less lift the higher we go!

[Stan Evil]

Aren't you guys forgetting Newton's Third Law? Every action has an equal and opposite reaction. If a 1 kg (9.81 Newton really) goose is flying then the air below it is being forced downwards by a force of 9.81 Newtons. This will have the effect of increasing the air pressure on the floor of the aircraft and decreasing the pressure on the roof by, guess what, 9.81 Newtons. So the aircraft will appear to weigh the same. This is what's known as a 'closed system' - it doesn't matter what you do inside it will maintain its weight.

[Wrong Stuff]

Stan Evil - sounds logical. But if this is true, how come the people standing at the end of runways don't get squished when a 747 goes overhead.

Good example of how close they can get on http://www.aviationpics.de/app/app.htm

OK, so it's not a closed system, but even if all the increased pressure were being dissipated over a much larger footprint I'd intuitively have thought the effect directly underneath would still be significant.

As an aside, what happens to the wing loading if a passenger jumps in the air??

[New Bloke]

Okay,

Now the closed system bit I sort of get, but suppose we now substitute the geese for a large cylinder of helium and 3000 balloons.

No wait, let me think about what point I am trying to make. I shall return

[Stan Evil]

Nice point, Wrong Stuff, I'm having to think about this. However, my quick-and-dirty answer is that lift is mainly suck from the upper surface of the wing. The other point is - try standing under a hovering helicopter or a Harrier - there's certainly a !!!!!load of air going downwards under them.

New Bloke - remember, if it's a closed system and you start blowing up balloons you'll just increase the pressure of the air that's trapped inside the aircraft - the weight remains the same.

[Yogi-Bear]

Try standing under a Tornado on very short final and you won't have to speculate theoretically.

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Yaberdaberdoo. It's OK Boo-Boo.

[dragchute]

GRpr

Sorry if I unwittingly spoilt the direction of the discussion. I wasn’t privy to the original article and the use of the term weight in lieu of mass.

I guess weight could be used in a correct sense if the writer of the original question implied no shift in vertical displacement of the aircraft from the time the Geese were first considered until the time they left their collective perch.

Altitude will of course affect the cabin differential pressure and if the aircraft is at 30,000 feet with a cabin altitude of say 10,000 feet, then when compared with sea level cabin pressure, the payload (mass of air) has reduced. I wonder what the co-efficient of lift is for a goose and if the bird is able to take to the wing in such rarefied conditions. No doubt some wag will have a stab at that!

Stan Evil,

You did of course correctly raise the issue of Newton’s third law. My approach was to bypass the law and simplify the discussion by reference to the combined ‘fluid’ payload.


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dragchute
email: [email protected]

[VLift]

If the aircraft becomes lighter it's operation becomes more efficient in terms of fuel consumption, making geese a very desireable commercial cargo. Only one cheap to hire crewmember needed, a muzzled fox.

[Squealing Pig]

Same idea, bigger scale
Does the earth weigh less with several thousand large aircraft flying at once?


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Push forward - Pigs get bigger
Pull back - Pigs get smaller
Pull back some more - Pigs get bigger again ??

[GRpr]

There seems to be some confusion on this thread between 'weight' and 'mass'.

Weight is the force of attraction of the earth on a given mass. For one to say something weighs 'less' on the moon, one is modifying the definition to produce a 'moon weight': the force of attraction of the moon on a given mass.

The force of attraction is gravity, and the gravitational force between two bodies is proportional to their masses and inversely proportional to the square of the distance between them. The geese exert a gravitational ‘pull’ on the earth, as does the earth on the geese. It just happens the latter is somewhat stronger!! It is not possible to talk about the ‘weight of the earth’, because it is not possible to have a weight relative to the same body that is producing the gravitational pull. The earth has mass.

The mass of a body is the constant of proportionality between the force applied to a body and the acceleration produced proportional to the force. (Ignoring the concept of 'rest mass' as mass does actually vary with velocity ref: the theory of relativity). A body with mass of 1kg will have this mass regardless of location - the surface of the earth, the surface of the moon, or outer space.

So, for an object to have 'weight', we need gravity and mass. Mass is a constant and weight varies with gravity. The earth’s gravity decreases the further we proceed away from it.

If we load an aircraft very precisely to MAUW at sea level, and then very precisely do the same at an airfield at 5000’, we will find we can fit more in ‘by weight’. If you feel like proving this, just weigh something on an accurate balance at sea level, and try the same at the top of Mount Everest - but wrap up warm! However, in aviation operations the difference is immaterial, and everyone feels more comfortable with the word ‘weight’ - they feel they know what it means! (If anyone knows different - eg calculations are done with large aeroplanes to make altitude adjustments to take on more cargo or fuel at, for example, Kathmandu, I would be fascinated to know!)

Turning to our geese.

The total mass of the aeroplane and cargo remains constant when the geese attempt to start their migration. If there was no variation in gravity, then the weight of the aeroplane would stay constant (closed system, downward force of flapping wings, Newton’s third law etc).

However, the poser of the question in Pilot was dealing with ‘precision’ - after all he was talking about very small centre of gravity movements. In his answer he made the classic mistake of talking about the ‘weight’ of the aircraft not altering by ‘one iota’. If one is being precise, then the weight of the aircraft does indeed decrease. The geese become further from the centre of the earth; they therefore weigh less; the downward force to keep them airborne becomes less; the reduction in the downward force on the floor of the aircraft means that the total weight of the aircraft is less - albeit by a very tiny, tiny amount. If the total weight of the fuselage is less, then the wing loading will decrease.

Unfortunately, the altitude of the aircraft is not given. If it was, we could calculate the reduction in weight of the aeroplane when the geese fly around. It would be a very small figure!

Phew!! Got that off my chest. I must have too much time on my hands!! Actually, kicking my heels waiting for a work permit to come through!

[New Bloke]

Okay, now suppose that this aircraft was so cavernous that these geese could fly and not be in ground effect. We wouldn't have a downward pressure on the deck from the flapping wings, okay the air would be still supporting their weight but who says this is a truly closed system.

Even if it is, if all the geese now start to glide at the same time, a higher pressure would be generated under the wings, but a lower pressure above. :. Because this craft is so huge the pressure on the floor of this craft would remain the same.

I think.

I just doesn’t seem right that the only difference would be due to the decrease in gravitational pull because they increased their altitude.

[dragchute]

New Bloke,

Let me pose this scenario. You have a vat that ’weighs in’ at 50 kg, sitting on a set of scales. You add 100 litres of water to the vat causing the scales to now read 150 kg. You float a 10 kg block of timber in the vat. Will the scales now read 150kg or 160 kg or somewhere in between? Of course they will reflect the full increase of 10 kg because the fluid is now supporting the block!

A plane load of geese is sitting on a weighing device on the ramp. The geese are perched. If the geese suddenly take to the wing, inside the aircraft, what change will the scales register. None, because the air within the cabin is now supporting the geese. The mass of the air and the geese is still supported by the aircraft structure! It makes no difference if the fluid + solid is water/timber or air/geese. The combined mass of the fluid and solid is unchanged. The scales are simply measuring a bunch of molecules and are unable to determine the actions/reactions of those molecules.

Hope this helps.

[Mariner9]

Dragchute, IMHO you're wrongly combining Archimedes & Bernoulli's theorems.

In order to generate lift, the Geese expend energy. This energy will combine with the aircraft energy to generate total lift. Therefore lift is increased/apparent weight is decreased.

Dunno about the effect of all the geese **** though!

[New Bloke]

Dragchute, I think that the analogy that you use is flawed because the fluid (water) you are talking about, has a weight when it is within the fluid I am talking about (air).

To carry the analogy on, if within your Vat we placed a submarine full of water, within the submarine we placed a brick that lay on the floor of the sub. Now we exert energy upon that brick and lift it from the floor of the submarine. I think we would all agree that the total VAT weight remains the same, however the buoyancy of the submarine has now increased.

Or am I talking out of my bum?

[Zeke]

<font face="Verdana, Arial, Helvetica" size="2">
In this month’s Pilot Magazine quiz, question 5 has us imagining that a Beluga A300-600 is transporting 3000 kilos of unrestrained live geese. During the flight they all take-off. The magazine suggests that this will have no impact on the weight of the aircraft. Shurly Shome Mishtake.
Let us imaging that each of these geese were sitting on a set of sensors attached to a digital weight read-out. As this mass disturbance took place the scales would drop from 3000 kilos to 0 kilos. Now I agree that if they were all in ground effect there would still be some weight on the aircraft but I maintain the weight of the aircraft would drop and it would shoot up in the air. </font>

The aircraft will have a marginally lower weight but the mass will not change if the geese all decided to fly at the same time. I should point out that the changes in weight we a re taking about here are VERY small.

The reason for the weight decrease is that the geese will move slightly further away from the Center of Mass (COM) of earth.

As you know the gravity formulae is gravity=G*M1*M2/R^2, as the geese move slightly further away from the COM of earth the gravity acceleration will SLIGHTLY decrease (as a function of 1/R^2).

As you know the weight of an object is give by weight=gravity*mass, as the gravity reduces slightly the weight reduces slightly. The best example of this is in astronauts who are large distances away from earths COM, their mass remains unchanged, but their weight has reduced significantly as a function of 1/R^2.

This is fairly basic physics, what they are saying is analogous to saying that a hovercraft overcomes gravity to float above the ground, we know this is not that case. Using the hovercraft analogy, does a person sitting on a hovercraft weigh less when the hovercraft is floating above the ground ? Does a persons mass change ?

The answers to these two questions are yes, SLIGHTLY as I have said above as you a moving away from earths COM by the smallest amount, no you don’t lose any mass.

The mass of the aircraft remains unchanged if you view the aircraft and its contents as a control volume, then the aircraft can been seen as point mass based upon its COM.

Sorry to disappoint you, but if this was the case Boeing and Airbus would have air seats to levitate everyone above the floor to reduce the takeoff weight.

Cheers

:rolleyes:

[Sensible]

dragchute has it right I'm afraid chaps! You see, most people believe that air weighs nothing and that anything suspended in it weighs nothing also. The fact is that whatever is in the airplane, whether it be air, water or solid - including feathers has a weight and it matters not whether the matter is lighter or heavier than air, it all weighs the same no matter what position it occupies within the space. In the scenario where the wood floats on the vat of water, does the vat weigh more or less when the wood becomes waterlogged and sinks to the bottom of the vat?

[Checkboard]

The aircraft will be lighter by one or two pilots when the CAA finds out that they were carrying unrestrained live animals! ;)

[Mariner9]

For all the chaps who think the weight is unchanged.....

If all the geese flew to the front of the aircraft, would the pilot have to re-trim due to change in CG?

I think not.

The geese are flying, and are supported in the air due to pressure differentials generated in by their wings. They are not displacing their own weight in air, as would be the case if they were floating.

Pressure exerts the same force in all directions, not just down. Therefore the geese's mass is no longer acting in a 1g downward force, therefore 'weight' of the aircraft + contents has decreased.

In theory, the aircraft would then start to increase altitude...not sure what the CAA would make of the Pilot's excuse of a level bust due to pax!

The

[Zeke]

Mariner9

<font face="Verdana, Arial, Helvetica" size="2">
If all the geese flew to the front of the aircraft, would the pilot have to re-trim due to change in CG?
</font>

The answers is yes. The reason for it is this, if you had no geese in say the first 5 meters of the hold, then move the 3000 kg into the space while flying the density of the fluid being supported by the fuselage in that volume increases, hence an increase in mass, and in increase in weight, therefore a change in CG.

<font face="Verdana, Arial, Helvetica" size="2">
The geese are flying, and are supported in the air due to pressure differentials generated in by their wings. They are not displacing their own weight in air, as would be the case if they were floating.
</font>

Your idea is correct where the geese would be in contact with the free stream air (fluid), such as in the bird cage.

In this case the geese are not in direct contact with the free stream air, and therefore cannot exert a force on it. The mass of air is fixed inside a controlled volume. The load of the aircraft and all its contents is transferred to the free stream air (fluid) via the wings and the small amount of lift produced by the fuselage.

If you are wondering where the energy is going that the geese are delivering to the air if its not significantly changing the aircraft weight…. It is converted to heat, noise, and friction between the air molecules inside the aircraft.

For all practical purposes the weight of the aircraft does not change, as I have indicted above the weight will reduce but only by the smallest amount.

Cheers

:rolleyes:

[Throtlemonkey]

If a hellicopter was hovering inside the aircraft the weight would remain unchanged due to the downforce acting on the cabin floor being equal to the weight of the chopper. Mariner9 if that chopper hovered on up to the front of the aircraft the c of g would change. hellicopters work in allmost the same way as ornithopters (what birds are).

[Mariner9]

Sorry guys, but I dont buy this 'downthrust' theory.

Lift is generated by pressure differentials across aerofoils, and not by downthrust (except on a hovering harrier!)

Perhaps the airforce could organise an experiment to check this out. After all, the navy investigated the effect of aircraft on penguins!

[dragchute]

Mariner9,

Forget about all this pressure differential theory. Simplify the problem. We have a sealed aluminum cylinder containing atoms. Some atoms form geese and some form air – and no doubt they are all in motion. If the atoms with a greater mass move towards one end of the cylinder then it will tip the balance in that direction.

Supposing our cylinder is football shaped. We fill it with atoms from two metals, aluminum and lead in molten form. Suppose too that the lead atoms congregate at one end of our football shaped cylinder. Will it sit level or will it tilt in the direction of the heavy metal? That is the big picture!


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dragchute
email: [email protected]

[Night Rider]

The weight of the aircraft will not change at all - the force generated by the geese flapping their wings to stay airbourne is transmitted to the air and will still be felt on the floor of the aircraft - thus producing no change in weight!!!

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Pull back and the houses get smaller - pull back a bit more and the houses get bigger!

[RVR800]

I havent read the article but

IMHO

Force (Weight) = Mass X Acceleration

Acceleration = 9.81 (a constant on Earth)

The weight of the Aircraft includes the
weight of the air contained in it

e.g The weight of 22.4 litres of Nitrogen at STP is 14 grammes (this is 71 percent of air)
Add in the oxygen etc and its say 20 grammes
for the same volume

Incidentally:
The vertical component of weight for this gas is greater then the outside atmosphere at cruising altitude due to pressurisation

The vertical component of lift for the birds
is equal to their weight

The weight is supported on the molecules
of Nitrogen etc in the cabin. The downwards component of molecules colliding is represented as pressure on the bottom surface of the cabin (like the Tornado)

Therefore

The weight is the same as it was when it
took off is it not ?

[Mariner9]

&lt;&lt;The downwards component of molecules colliding is represented as pressure on the bottom surface of the cabin (like the Tornado)&gt;&gt;

If the air in a cylinder is compressed by a downwards motion of, say a piston for instance, the pressure is exerted equally in all directions, not just downwards. It is not possible to exert a pressure in one direction on a fluid (or gas)

An aerofoil generates most of the movement of the air molecules on the upper wing surface, and that is not in a downward direction anyway.

[chicken6]

RVR800

You said the acceleration due to gravity is a constant on earth, how does "on" Earth relate to flying? PS I don't think it is constant at 9.81 m/s/s anyway, the Earth is not a perfect sphere and at the Equator there is more mass 'underneath' the body whereas at either pole the mass of the Earth is more spread out sideways than straight 'down'.

New Bloke

Only PART of the total lift from an aerofoil is generated by the pressure distribution. Some of it also comes from the coanda effect, ie throwing air down by curving the top part of the aerofoil produces an equal+opposite reaction of throwing the aerofoil up. Think of a propellor (another aerofoil) - are you saying that standing behind the propellor there should be no propwash because "it's only the pressure distribution" that causes thrust from this propellor?

And can you explain a bit more about the glide bit?

And the last point for everyone who thinks ground effect makes a difference - I don't because it's ALL THE SAME AIR. Doesn't matter how far away from the floor it is, the downforce is still acting on the air from the geese wings. Maybe it's spread out, maybe it's not. Ground effect WOULD be significant if the 'system' i.e. the aeroplane cargo hold was open.

This is interesting! Certainly makes people careful with the words they choose.

[Mariner9]

I agree that only pert of the total lift from an aerofoil is generated by the pressure distribution. However this part of the lift reduces the downwards force (ie weight) of the geese. Therefore total weight is reduced.

[Jed A1]

Mariner9 No offence mate but I'm glad to see you are not a flying instructor. Weight cannot change since it is Mass x Acceleration Due to Gravity. Neither of these can change.

Lift is generated to equal or exceed weight - thus geese go up or remain at same altitude.

The change in gravity due to the distance from COM is negligble. It really is worth ignoring in this instance. Imagine the aircarft flying at 100'.

In the grand scheme of things the parcel of air and geese inside the aircraft does not change in mass and thus weight. All the geese are doing is expending energy to move around the aircraft just as a human would walking around the aircraft.

[Sliced Pan]

You all make mountain out of molehill. Anything in a plane adds to it's weight, including the air inside it and anything that air happens to be supporting.

Pan :)

[212man]

Now, what if the pilot opens a window to get rid of the smell, thereby equalising the air pressure with the outside? (apart from lots of high speed geese being ejected through the hole).

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Another day in paradise

[Jed A1]

212 man opening the window doesn't matter.

Air exerts a force in all directions. up down and sideways. Some of that force may be exerted on the air outside of the window (nett change nil). All we are concerned with is the difference between the downward and upward force's of the air. Remember the air supports the geese. The aircraft supports the air.

[212man]

Oh really? so if you place a hollow tube on some scales, then inserted a lead pipe into the tube, without touching the sides you think the scales would show an increase in weight? I think not (same analogy).

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Another day in paradise

[Zeke]

212man,

You are incorrect.

Your analogy is irrelevant as the lead pipe is being supported by some external means.

The aircraft is supporting the load of the cargo, and transmits this to the free stream air via the wings etc in the air, or the undercarriage on the ground.

:rolleyes:

[212man]

I accept that was not entirely a correct analogy. Try these:

take a large hollow pipe and place it on some scales, then take a bunch of helium balloons with lead weights beneath them (where the lift =weight) and float them into the tube (not touching the sides). Will the weight registered on the scales rise? Of course not. Then, with all the balloons inside, seal the tube off with flat discs at each end, any change? no. Then, by remote control (well, some how!) burst the balloons; now the weight will change.

Alternatively, take your a/c on the ground, with the wheels on scales, and get a load of tame geese to fly into the cabin through an open door. Do you think the weight on the scales will rise with each goose entering? Then close the door, no change. Then get the pilot to ask over the PA that all the geese kindly stop flying and sit down. Then the weight will rise.

Sorry about the odd situations, but it is an odd question in the first place, which seems to need simple answers. The phrases that spring to mind are "ignorance is bliss" and " a little knowledge is a dangerous thing".

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Another day in paradise

[Mariner9]

No offense taken Jed, and you're right, I'm not a FI, but hope to be soon. Suggest all you wannabes get your ppl's quickly!

You're wrong about weight though..it can of course change, simply through acceleration for instance.

Mass is a different matter entirely, as somebody already pointed out earlier in this thread.

The geese's energy keeps them flying, they are not 'supported' by the air. If they stopped expending energy they would land very quickly.

[dragchute]

212man,

Your analogy with balloons and lead weights makes Mr Archimedes and his principles redundant!

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dragchute
email: [email protected]

[chicken6]

(Bell?) 212man

Your analogy again has a subtle flaw - a helium balloon is an aerostat, not an aerodyne. There is no action or reaction on the air from an aerostat (static), whereas there is from an aerodyne (dynamic).

[212man]

No action or reaction on the air? that's novel, so what's supporting the balloon? When you lie in a swimming pool doing starfish impressions, is there no hydrostatic force acting on your lower body to counteract the weight?

Dragchute, if my analogy ignores Archimedes, so does the asertion that the force from the geeses wings will apply itself to the a/c floor. Any rise in air pressure would vent through the open window.

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Another day in paradise

[dragchute]

212man,

Re-read my reply - my comment had referred to your first analogy. If you have a sealed container filled with various compounds such as helium, lead, air or what ever, the mass of those compounds remains constant regardless of what actions or reaction occur within.

I made no comment regarding your second analogy.

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dragchute
email: [email protected]

[helimutt]

Now that my tears have abated somewhat (tame geese being behaved in an aircraft and doing as they're told!?)!! whatever next?
Is there someone who can give a simple answer to the initial question as it's now doing my head in with all of the different theories. I agree with 212man at the minute but can be swayed.
carry on.

[helimutt]

Now that my tears have abated somewhat (tame geese being behaved in an aircraft and doing as they're told!?)!! whatever next?
Is there someone who can give a simple answer to the initial question as it's now doing my head in with all of the different theories. I agree with 212man at the minute but can be swayed.
carry on.

[captain206]

212 man,

agreed.

everyone else,

prove him wrong, I cant!

[212man]

Ah Shucks!
thanks, nice to know I'm not alone in my thoughts. I always think that before getting tied up in forgotten 4th form physics, it's a good idea to look at the practicalities of the situation and how they relate to other instances (eg nautical?). Otherwise, I can feel 'Houghton and Carruthers) being pulled from the bookshelf and dusted off.

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Another day in paradise

[Jed A1]

Air behaves like a liquid.

Imagine a glass with water in it. At the bottom are granuals of sand. The water and sand has a weight. Stir the glass up (supply energy) and the sand becomes suspended in the water.

The sand and water still weight the same. This is despite the heavier granules of sand not touching the bottom.

Essentially the geese are disolved in air after they have supplied there own energy to move around the system.

This is the same as helium balloons and lead bars being essentially dissolved in the same air.

At the surface of Earth air pressure is the result of all the particles above in a unit column of air. If these particles increase in mass or weight then pressure at the surface increases. It's the same inside the aircraft.

Mariner9, I take your point about acceleration being able to change.

[Zeke]

Jed A1

Air is a liquid. A liquid by definition is a substance that can resist shear only in motion. A fluid is a substance that deforms continuously under the action of an applied shear force or stress. The process of continuous deformation is called flowing, or as it is applied to air flow.

I would like to commend you on a well thought our and relevant analogy you presented with respect to the sand and the water.

212man

Your analogy of the lead pipes and balloons is again incorrect. If you increase the mass of a control volume the weight increases as weight = mass x acceleration (gravity).

Using your own example, if you were to seal off the container with the lead and balloons in it, and extract all the gas you would agree that the weight would increase. As you know the weight of the extracted gasses would have to added to the tube and lead weight to get the weight of the entire control volume (tube+lead+extracted gas).

:rolleyes:

[New Bloke]

It seems to me that those suggesting the weight remains the same can only do so by using an analogy that has two different fluids. Jed A1’s glass full of water and sand works with two fluids that have different weights but this is not analogues to the original question. To be so the glass and sand would be in a fish tank full of water, now swirl the sand around and what would happen to the weight of the glass? Having said all that a physicist friend of mine has read this thread and sent me the following:

“
The total mass of the aircraft when in flight is equal to the mass of the aircraft plus , the mass of its :
fuel
passengers
pilot
geese
water
poo in the toilet
and air in the cabin and holds.

The total flying weight of the aircraft is equal to the above total mass multiplied by the gravitational field strength, at that point in space above the Earth. Mass X Gravity (mg)

It does not matter whether the geese are asleep on the floor or on the wing. The total mass of the aircraft and its contents remains the same. Not strictly true because it is using fuel and losing mass and therefore weight every moment.

You might think that flying around the cabin removes their weight but this is an illusion.

Think of the birds as being suspended in a fluid filled tube such as some plastic beads in a jam jar of water.

As the birds fly there are many forces acting upon them:
frictional drag
Lift due to pressure difference as the air flows over their wings
Upthrust from the air due to the displacement of a mass of air
A weak gravitational pull between their own mass and that of the aircraft The forward thrust of their wings on the air

All of these forces will have equal and opposite reaction forces (Newtons ThirdLaw) at some point in this complex system.

They are all, however, relative to the air in the aircraft and the aircraft itself. As such they do not change the overall mass or weight of the system that is the aircraft in flight.

Hope this helps,

Clearly you are not busy enough if matters such as this distract you.”

He has a point in his last paragraph ;)

[chicken6]

dragchute

I think 212man was talking to me then!

212man

Sorry, just stirring a little bit, nothing serious!

While I'm here though, you said:

"Alternatively, take your a/c on the ground, with the wheels on scales, and get a load of tame geese to fly into the cabin through an open door. Do you think the weight on the scales will rise with each goose entering? Then close the door, no change. Then get the pilot to ask over the PA that all the geese kindly stop flying and sit down. Then the weight will rise."

So you're saying that should the geese begin to fly again (with all doors and windows closed) the weight will decrease? By the weight of the birds, or are you going to put the change of CoM in there as well? You just described a closed system and said the wieght will change when the geese land.

Is this in the original question (no open door or window) or in your scenario where you opened the window?

[212man]

Chicken6,
I was intending to refer to the window ope situation, hence my original question about openeing the windo. As soon as you do, it ceases to be a closed system. Quite evidently if you strapped a rocket to the a/c and shot it into space (with the window closed and the a/c pressurised) the whole would act as one. If the windows is open, I feel that the situation changes (apart from a. the geese suffocating b. their blood boils and c. they have nothing to fly in). Seriously, even in the atmosphere I think the situation is different.

I agree with the physicist, it's a bit sad to be dealing with this topic.

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Another day in paradise