Pilot Mag Quiz
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Pilot Mag Quiz
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.
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.
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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"
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"Take-off is optional, Landing is mandatory"
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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
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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
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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!
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!
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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.
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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??
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??
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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.
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.
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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
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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
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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!
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!
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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.
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.
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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.
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.
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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!
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!
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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?
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?
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<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>
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 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
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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?