Cargo Crash at Bagram
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FC Eng.
Who do hosties struggle to push the trolleys to the front of the aircraft during climb then?
Why, if they let them go, do they roll aft?
Every day, a schoolday!
Who do hosties struggle to push the trolleys to the front of the aircraft during climb then?
Why, if they let them go, do they roll aft?
Every day, a schoolday!
Alph2z, I do not need to 'prove your data wrong'. You do not have any data for me to prove wrong. Allow me to spell it out for you, as I don't think you fully understand the terms you are trying to use. IAS means indicated airspeed, ie the speed that is indicated on the ASI (airspeed indicator).
Still with me? Now, the IAS is not, has never been, and can never be 'theoretical' - OK? Quite simply, the IAS (indicated airspeed) is the speed that is indicated on the ASI (airspeed indicator).
Now do you understand why do not have any data for me to prove wrong?
Still with me? Now, the IAS is not, has never been, and can never be 'theoretical' - OK? Quite simply, the IAS (indicated airspeed) is the speed that is indicated on the ASI (airspeed indicator).
Now do you understand why do not have any data for me to prove wrong?
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Why have to push beverage cart fwd during climb?
AtomKraft,
The reason that the cabin crew has to push the beverage carts when moving forward during a climb is that the thrust is up, not because of pitch attitude. With thrust set for climb, the force needed to push the carts up the aisle would the same whether climbing at the flight path angle that maintains constant speed (i.e., the normal climb condition), flying level with increasing airspeed, or at some extremely high pitch attitude with airspeed decreasing.
The bottom line is that gravity acts on the airplane and its contents equally so it does not generate forces between the two. In the air, only thrust and aerodynamics generate forces that are sensed by the contents and occupants of the airplane.
One other thing to ponder - if pitch and roll attitude were to determine forces felt within an airplane, how would it be possible to perform a barrel roll with continuous positive acceleration along the body Z-axis?
The reason that the cabin crew has to push the beverage carts when moving forward during a climb is that the thrust is up, not because of pitch attitude. With thrust set for climb, the force needed to push the carts up the aisle would the same whether climbing at the flight path angle that maintains constant speed (i.e., the normal climb condition), flying level with increasing airspeed, or at some extremely high pitch attitude with airspeed decreasing.
The bottom line is that gravity acts on the airplane and its contents equally so it does not generate forces between the two. In the air, only thrust and aerodynamics generate forces that are sensed by the contents and occupants of the airplane.
One other thing to ponder - if pitch and roll attitude were to determine forces felt within an airplane, how would it be possible to perform a barrel roll with continuous positive acceleration along the body Z-axis?
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It's all Newtonian
I experienced an encounter with a galley cart a decade or two back. I was upgraded to first and seated in an aisle seat - 1E IIRC - during a night TO. Since 1F was empty, I was leaning to my right to watch the scenery.
My enjoyment was interrupted by a loud crash just before Vr. A galley cart had come unmoored and, obeying Newton's First Law, tried to stay put while the airplane accelerated around it. It rolled right down the aisle until it bashed against my armrest, delivering its contents on my seat. If I had been sitting upright like a good boy, I might have a broken left kneecap.
Had this event occurred during climb, exactly the same outcome would result; but the cause would be different. The airplane would no longer be accelerating, but the cart would be accelerated by gravity.
My enjoyment was interrupted by a loud crash just before Vr. A galley cart had come unmoored and, obeying Newton's First Law, tried to stay put while the airplane accelerated around it. It rolled right down the aisle until it bashed against my armrest, delivering its contents on my seat. If I had been sitting upright like a good boy, I might have a broken left kneecap.
Had this event occurred during climb, exactly the same outcome would result; but the cause would be different. The airplane would no longer be accelerating, but the cart would be accelerated by gravity.
FCeng: FWIW, pitch (elev/horizontal stab) and roll(aileron) aren't the only control inputs made during a barrel roll. Yaw (rudder pedals / feet) provide the z axis input so that you are in a coordinated turn throughout the maneuver. I suppose the force for each of those airfoil sections is derived ultimately from thrust, which makes the acceleration over the airfoil possible. Beyond that, not getting into that briar patch.
alpha, when you make a claim, support of the claim isn't generally valid when presented as "prove me wrong." Beyond that, no further comment.
alpha, when you make a claim, support of the claim isn't generally valid when presented as "prove me wrong." Beyond that, no further comment.
Last edited by Lonewolf_50; 9th May 2013 at 20:18.
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Gravity on the cart
FCEng84,
Gravity acts on the drinks cart. The reaction force from the floor of the aircraft, through the wheels of the trolley prevents the trolley from plummeting to its doom. In non accelerating flight, it exactly balances the weight of the cart. It's real and you can feel it, just as gravity acts on you and the sofa equally, but there is a reaction force keeping you from falling to the floor - as you say, this certainly means that you can't tell whether you're sitting on the couch, or sitting in a non-accelerating aircraft.
Gravity also acts on the aircraft: per kilogram in exactly the same amount as on the drinks cart. The lift force from the air flowing over the aircraft's wings prevents the aircraft from plummeting to its doom. When there is no acceleration, it exactly balances the weight of the aircraft (which includes the weight of the cart), while thrust exactly balances drag.
To push the cart forwards up the aisle requires work to be done, because it's being taken uphill. When descending, the cart requires work to be done to push it backwards down the aisle, as again it's being taken uphill.
If the aircraft is accelerating, forward, back, or in a turn, then another force - the mass of the cart multiplied by the acceleration - adds vectorially to the cart's weight. This can make it easier or harder to push depending on its direction. As you, say accelerating in a climb will make the push harder, slowing in a climb would make the pushing easier. Just as it does walking down the aisle of a courtesy bus. If a zero-g free-fall trajectory was being flown, then the cart would float up the aisle by itself after being given a gentle push, as the acceleration of the aircraft is chosen to match that of gravity, and the cart free-falls within the plane.
Gravity acts on the drinks cart. The reaction force from the floor of the aircraft, through the wheels of the trolley prevents the trolley from plummeting to its doom. In non accelerating flight, it exactly balances the weight of the cart. It's real and you can feel it, just as gravity acts on you and the sofa equally, but there is a reaction force keeping you from falling to the floor - as you say, this certainly means that you can't tell whether you're sitting on the couch, or sitting in a non-accelerating aircraft.
Gravity also acts on the aircraft: per kilogram in exactly the same amount as on the drinks cart. The lift force from the air flowing over the aircraft's wings prevents the aircraft from plummeting to its doom. When there is no acceleration, it exactly balances the weight of the aircraft (which includes the weight of the cart), while thrust exactly balances drag.
To push the cart forwards up the aisle requires work to be done, because it's being taken uphill. When descending, the cart requires work to be done to push it backwards down the aisle, as again it's being taken uphill.
If the aircraft is accelerating, forward, back, or in a turn, then another force - the mass of the cart multiplied by the acceleration - adds vectorially to the cart's weight. This can make it easier or harder to push depending on its direction. As you, say accelerating in a climb will make the push harder, slowing in a climb would make the pushing easier. Just as it does walking down the aisle of a courtesy bus. If a zero-g free-fall trajectory was being flown, then the cart would float up the aisle by itself after being given a gentle push, as the acceleration of the aircraft is chosen to match that of gravity, and the cart free-falls within the plane.
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Here's a simple way to think of the issue:
Think of a simulator. What does it do to create the impression that its occupants are accelerating? What does it do to create the impression that its occupants are climbing? It does exactly the same thing.
Think of a simulator. What does it do to create the impression that its occupants are accelerating? What does it do to create the impression that its occupants are climbing? It does exactly the same thing.
FCeng84;
and,
I'm missing something here and am prepared to learn if the physics makes sense.
It is true and I agree with you that gravity acts on the airplane and contents equally and that as such gravity is not a "force" per se, except when acting upon something that cannot resist gravity's force with an equal-and-opposite force, (such as a galley trolley on wheels in an airplane in stable, level, non-accelerating flight). Gravity's effects could be measured by strain gauges on the bolts that fasten things to the airframe like engines, seats, gear etc, but nothing moves of course, because it is all fastened together. But not things with wheels for example, which are normally intended to move.
Without massive hydraulic system, the gear can't be raised, not because Nz is so high and remaining so but because the gear weighs a lot, and that is gravity's acceleration rate at work.
So, as an interested student of these things who is by no means an engineer but a mere (ret'd) pilot of these aircraft, I need to ask you what causes an increased effort to push something uphill, (in an airplane or anywhere else there is a gravity field), and further, should such force not also affect anything that is not resisting that same force?
Unless I have missed something about aerodynamic forces, your statement, above, is incorrect, isn't it?
All objects with mass are acted upon by gravity such that they would experience a uniform acceleration in the absence of other forces. The concept of weight comes from the force needed to resist the acceleration that gravity would impart if left unchecked. In order for a mass to remain in an unaccelerated state relative to an earth based reference frame a force must be applied to that mass to oppose gravity. Remove that force and the mass will accelerate toward the earth at approximately 9.8 meters per second^2.
Force is measured between objects. In the case of an airplane and cargo, between the body of the aircraft and its contents. Because both the airplane and the cargo are subject to the same gravity field, the force between the two does not represent gravity. There cannot be any force between the airplane and its cargo without some external force acting on the airplane (and here gravity is not a force). On the ground at rest, the external force comes from the gear. In the air the external force comes from the engines and aerodynamic forces. In the air, the forces felt within an airplane have nothing to do with pitch or roll attitude. They are entirely dependent on thrust and the combination of angle of attack, sideslip angle, control surface positions, dynamic pressure (i.e., airspeed), and Mach number.
Force is measured between objects. In the case of an airplane and cargo, between the body of the aircraft and its contents. Because both the airplane and the cargo are subject to the same gravity field, the force between the two does not represent gravity. There cannot be any force between the airplane and its cargo without some external force acting on the airplane (and here gravity is not a force). On the ground at rest, the external force comes from the gear. In the air the external force comes from the engines and aerodynamic forces. In the air, the forces felt within an airplane have nothing to do with pitch or roll attitude. They are entirely dependent on thrust and the combination of angle of attack, sideslip angle, control surface positions, dynamic pressure (i.e., airspeed), and Mach number.
The reason that the cabin crew has to push the beverage carts when moving forward during a climb is that the thrust is up, not because of pitch attitude. With thrust set for climb, the force needed to push the carts up the aisle would the same whether climbing at the flight path angle that maintains constant speed (i.e., the normal climb condition), flying level with increasing airspeed, or at some extremely high pitch attitude with airspeed decreasing.
The bottom line is that gravity acts on the airplane and its contents equally so it does not generate forces between the two. In the air, only thrust and aerodynamics generate forces that are sensed by the contents and occupants of the airplane.
The bottom line is that gravity acts on the airplane and its contents equally so it does not generate forces between the two. In the air, only thrust and aerodynamics generate forces that are sensed by the contents and occupants of the airplane.
It is true and I agree with you that gravity acts on the airplane and contents equally and that as such gravity is not a "force" per se, except when acting upon something that cannot resist gravity's force with an equal-and-opposite force, (such as a galley trolley on wheels in an airplane in stable, level, non-accelerating flight). Gravity's effects could be measured by strain gauges on the bolts that fasten things to the airframe like engines, seats, gear etc, but nothing moves of course, because it is all fastened together. But not things with wheels for example, which are normally intended to move.
Without massive hydraulic system, the gear can't be raised, not because Nz is so high and remaining so but because the gear weighs a lot, and that is gravity's acceleration rate at work.
So, as an interested student of these things who is by no means an engineer but a mere (ret'd) pilot of these aircraft, I need to ask you what causes an increased effort to push something uphill, (in an airplane or anywhere else there is a gravity field), and further, should such force not also affect anything that is not resisting that same force?
Unless I have missed something about aerodynamic forces, your statement, above, is incorrect, isn't it?
Last edited by PJ2; 9th May 2013 at 21:41.
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Gravity is an acceleration also. While standing still on the planet's surface we are constantly accelerating away from the local center of mass, resulting in a force we attribute to gravity.
Gravity is an acceleration also.
Well, it is, and I think that's the point being made. There are two phenomena (for lack of a better word) acting on things - acceleration and gravity. The discussion is about frames of reference; it is not about forces.
I can understand FCeng84's point that gravity is not a "force" per se and acceleration is but the difference is confined to the results of "acceleration" (in all its forms, either gravity, as FCeng84 states) or acceleration through engine thrust, etc. The effects of gravity are felt-seen when something is unable to resist the standard acceleration of gravity.
But an aircraft in stable, level, non-accelerating flight and all it's attachments and contents are still under the effects of gravitational "force", (albeit slightly smaller at cruise altitudes). The machine and contents have "weight", against which the wings provide lift, "resisting" the effects of gravity.
So unless I'm missing something, FCeng84 is incorrect.
Fascinating.
I can understand FCeng84's point that gravity is not a "force" per se and acceleration is but the difference is confined to the results of "acceleration" (in all its forms, either gravity, as FCeng84 states) or acceleration through engine thrust, etc. The effects of gravity are felt-seen when something is unable to resist the standard acceleration of gravity.
But an aircraft in stable, level, non-accelerating flight and all it's attachments and contents are still under the effects of gravitational "force", (albeit slightly smaller at cruise altitudes). The machine and contents have "weight", against which the wings provide lift, "resisting" the effects of gravity.
So unless I'm missing something, FCeng84 is incorrect.
Fascinating.
Last edited by PJ2; 9th May 2013 at 23:39.
These arguments are now so convoluted that this subject needs to be spun off to The Tech forum for a month
Will we ever know ? Even the voice recorders will, maybe, only tell us what the crew themselves only thought was happening - maybe.
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The big picture
I agree with all suggesting that this discussion has veered off course and needs to get back to the big picture. First and foremost a terrible accident has occurred and people have lost their lives. The least that can be done to honor this loss is to get to the root cause of the disaster and to take steps to reduce the likelihood of a similar event occurring.
Much of this discussion here has been directed at the possibility of cargo shift having played a role in this event. Some on this forum have suggested that an agressive pull-up to a very high pitch attitude during climbout would have put more load on the cargo tie-downs thus increasing the likelihood of a cargo shift. My comments have been in an effort to explain that the X-axis (along the body fore/aft) load exerienced by cargo tie-downs is not dependent on pitch attitude, but rather it is almost exclusively dependent on engine thrust.
Only time and careful investigation will reveal the truth here, but I strongly believe that in the end it will be shown that if cargo shift played a role in this event, the shift occurred during takeoff roll on the runway and not after leaving the ground.
Much of this discussion here has been directed at the possibility of cargo shift having played a role in this event. Some on this forum have suggested that an agressive pull-up to a very high pitch attitude during climbout would have put more load on the cargo tie-downs thus increasing the likelihood of a cargo shift. My comments have been in an effort to explain that the X-axis (along the body fore/aft) load exerienced by cargo tie-downs is not dependent on pitch attitude, but rather it is almost exclusively dependent on engine thrust.
Only time and careful investigation will reveal the truth here, but I strongly believe that in the end it will be shown that if cargo shift played a role in this event, the shift occurred during takeoff roll on the runway and not after leaving the ground.
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Only time and careful investigation will reveal the truth here, but I strongly believe that in the end it will be shown that if cargo shift played a role in this event, the shift occurred during takeoff roll on the runway and not after leaving the ground.
NONE of us (that I'm aware of) are aviation safety experts here on this forum and many are suggesting (speculating??) various scenarios that 'could' have taken place to cause this very sad and tragic accident. Some of the suggestions are logical, in my opinion.
Let's all hope and pray that the NTSB, along with it's partners in Afghanistan get this mystery solved.
Would it be possible - the next time there is a tragic accident / incident that there are two crash threads - one for pilots / engineers and the qualified to post on - the other clearly labelled for irrelevant drivel?
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Originally Posted by 31st Oct 2012, 16:57 #6 (permalink) G&T ice n sliceFrom the FeightDogs forum :
Just adding one from the groundstaff
You're a freight dog CAPTAIN if you have that special extra sense that enables you to ALWAYS offload exactly the one and only pallet that is 110% "must ride"
You're a freight dog CAPTAIN if you have that special extra sense that enables you to ALWAYS offload exactly the one and only pallet that is 110% "must ride"
$$$$$ ?
but I strongly believe that in the end it will be shown that if cargo shift played a role in this event, the shift occurred during takeoff roll on the runway and not after leaving the ground.
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Geez, you pilots should know this stuff in your bones - F = ma, a is acceleration. No acceleration, no net force. That doesn't mean no force - it means they all cancel each other - they are vectors.
A airplane flying at constant speed relative to ground with a positive pitch will be like any other inclined plane (haha). A cart left alone will roll to the back. In that case there is a net force - from gravity - causing it to accelerate.
A airplane flying at constant speed relative to ground with a positive pitch will be like any other inclined plane (haha). A cart left alone will roll to the back. In that case there is a net force - from gravity - causing it to accelerate.