Pilot Mag Quiz
Guest
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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
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
Guest
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Mariner9
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.
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
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If all the geese flew to the front of the aircraft, would the pilot have to re-trim due to change in CG?
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If all the geese flew to the front of the aircraft, would the pilot have to re-trim due to change in CG?
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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.
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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.
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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
Guest
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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).
Guest
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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!
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!
Guest
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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]
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]
Guest
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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!
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Pull back and the houses get smaller - pull back a bit more and the houses get bigger!
Guest
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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 ?
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 ?
Guest
Posts: n/a
<<The downwards component of molecules colliding is represented as pressure on the bottom surface of the cabin (like the Tornado)>>
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.
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.
Guest
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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.
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.
Guest
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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.
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.
Guest
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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.
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.
Guest
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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
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Another day in paradise
Guest
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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.
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.
Guest
Posts: n/a
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
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
Guest
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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.
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.
Guest
Posts: n/a
212man,
Your analogy with balloons and lead weights makes Mr Archimedes and his principles redundant!
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dragchute
email: [email protected]
Your analogy with balloons and lead weights makes Mr Archimedes and his principles redundant!
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dragchute
email: [email protected]