Cargo Crash at Bagram
SamC130;
Re, "If it's going to occur, it will most likely be during the takeoff roll when aft Gs are most prominent (and they're not that much.) The Gs experienced at rotation are positive, not aft."
Correct.
The longitudinal g's on takeoff are in the order of 0.3 +/-, and on rotation the vertical g is similarly small, around 0.05 to 0.1g bearing in mind that for most aircraft types the accelerometer is placed near the center of the fuselage, (gear well area), although unless there's a recent change, the B777's is mounted in the cockpit.
As we would know, the longitudinal 'g' would be higher than '0' due pitch angle but again not very high. Of course it would be the tied-down mass affected that provides the potential energy against the restraints and not high longitudinal 'g' loads - again, easily understood.
Regarding stall procedures, manufacturers and SOPs, most contributors here who fly likely have a solid working knowledge of responses etc given the extensive treatment of the subject on the AF447 threads,
.
The recorders have likely been read, (they should be in good shape) so I'm optimistic we'll hopefully soon know what happened.
Re, "If it's going to occur, it will most likely be during the takeoff roll when aft Gs are most prominent (and they're not that much.) The Gs experienced at rotation are positive, not aft."
Correct.
The longitudinal g's on takeoff are in the order of 0.3 +/-, and on rotation the vertical g is similarly small, around 0.05 to 0.1g bearing in mind that for most aircraft types the accelerometer is placed near the center of the fuselage, (gear well area), although unless there's a recent change, the B777's is mounted in the cockpit.
As we would know, the longitudinal 'g' would be higher than '0' due pitch angle but again not very high. Of course it would be the tied-down mass affected that provides the potential energy against the restraints and not high longitudinal 'g' loads - again, easily understood.
Regarding stall procedures, manufacturers and SOPs, most contributors here who fly likely have a solid working knowledge of responses etc given the extensive treatment of the subject on the AF447 threads,
.The recorders have likely been read, (they should be in good shape) so I'm optimistic we'll hopefully soon know what happened.
Last edited by Jetdriver; 8th May 2013 at 13:44.
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A Different Theory
We know N949CA was an ex Air France machine, however at some time this airframe has undergone the BCF conversation from a PAX a/c.
Who did this modification.. TAECO, BEDEK , SIAC or another. Maybe a catastrophic structural failure , whether cargo related or not.
Are we seeing the first of a design flaw in the BCF conversion.
Lets see what the big boys at the NTSB un cover
Who did this modification.. TAECO, BEDEK , SIAC or another. Maybe a catastrophic structural failure , whether cargo related or not.
Are we seeing the first of a design flaw in the BCF conversion.
Lets see what the big boys at the NTSB un cover
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re G force experienced during roll/ rotation. Surely once the rotation is complete, the overwhelming force acting on the load would be plain gravity eacting on an inclined plane.
ie classic newtonian mechanics.
So slight accel' during the T/O roll.
Slight +'ve G during rotation, not very significant.
Then, as it starts the climb, plain gravity acting on a load secured to an inclined plane added to the a/c acceleration... surely more force to be resisted here (just after rotate finishes) than at any other?
ie classic newtonian mechanics.
So slight accel' during the T/O roll.
Slight +'ve G during rotation, not very significant.
Then, as it starts the climb, plain gravity acting on a load secured to an inclined plane added to the a/c acceleration... surely more force to be resisted here (just after rotate finishes) than at any other?
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Exhausted
Atomkraft,
When the aircraft starts to climb, it ceases to accelerate. Sorry to divulge this disappointing bit of knowledge about big aircraft performance.
When the aircraft starts to climb, it ceases to accelerate. Sorry to divulge this disappointing bit of knowledge about big aircraft performance.
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Atomkraft is correct, the cargo load does not know whether the longitudinal force applied to its attachment points is caused by the aircraft accelerating down the runway (or in level flight) or caused by gravity while in a climb pitch attitude.
That is because it is the same thing, it even has a name: specific excess power. Either you accerelate level or you climb, the accelerometer in the X axis will register exactly the same amount.
Practically speaking - for having spent countless hours staring at takeoff flight test data - longitudinal acceleration is highest during the first few seconds of takeoff roll. Then there is a slight drop in longitudinal acceleration during rotation and liftoff phases due primarily to increased drag due to lift, but in the grand scheme of things it does not drop markedly at that point.
Not enough to prevent a load shift after VR or liftoff anyway.
That is because it is the same thing, it even has a name: specific excess power. Either you accerelate level or you climb, the accelerometer in the X axis will register exactly the same amount.
Practically speaking - for having spent countless hours staring at takeoff flight test data - longitudinal acceleration is highest during the first few seconds of takeoff roll. Then there is a slight drop in longitudinal acceleration during rotation and liftoff phases due primarily to increased drag due to lift, but in the grand scheme of things it does not drop markedly at that point.
Not enough to prevent a load shift after VR or liftoff anyway.
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Just watched it for the umpteenth time since last week.
Said earlier, the sequence to stall is like something's holding it back.
I believe that an experienced crew, such as they were, would have corrected a trim issue in time. They made 1200ft, but was it a recoverable trim issue or CofG ?
I only ask, since once established in the climb, it is easy to observe an anomaly, which may be corrected in good time IF one understands the cause.
Load shift (beyond CofG) is not really an option for recovery so near to the ground.
Said earlier, the sequence to stall is like something's holding it back.
I believe that an experienced crew, such as they were, would have corrected a trim issue in time. They made 1200ft, but was it a recoverable trim issue or CofG ?
I only ask, since once established in the climb, it is easy to observe an anomaly, which may be corrected in good time IF one understands the cause.
Load shift (beyond CofG) is not really an option for recovery so near to the ground.
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Hello Atomkraft,
Surely the aircraft accelerates a bit during the whole process from straight and level driving to climb out attitude, it is like trading one for the other.
Once climbout attitude is reached, acceleration stops, you have just set the correct pitch attitude for a constant speed climbout (the old pitch and power game).
Surely the aircraft accelerates a bit during the whole process from straight and level driving to climb out attitude, it is like trading one for the other.
Once climbout attitude is reached, acceleration stops, you have just set the correct pitch attitude for a constant speed climbout (the old pitch and power game).
Last edited by EMIT; 8th May 2013 at 17:29.
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Hi EMIT
Well, I'm no expert but I was just thinking 'at which point would the straps preventing rearward movement of the load be under the greatest strain?'
I don't know the deck angle of the aircraft as rotation finished, but if they were doing a V2 (or V2+10 ) climb it might be 20-25 degrees. A 747 pilot might know, but I guess we dont know the TOW yet which is what will control it.
So, plain old 'inclined plane Newtonian mechanics', would, I think generate the largest rearwards moment for the tie downs to resist, rather than accel' on the rwy or during rotation.
So, once settled in the climb, the force acting to move the load rearward would probably be much greater than during the take off roll. Even a small rearward movement of part of the load might then lead to a larger deck angle, and then to even larger rearwards load on the remaining tie downs.
Just think of 5 25,000 vehicles parked on a 20-25 degree ramp and maybe getting a bit of a shaking.
So, I think they'd be ok until rotated into the climb. Gravity drags the load aft, both pilots grab and push the controls. Gear stays where it is.
Bigger deck angle causes gravity to pull harder on the load.....
Well, I'm no expert but I was just thinking 'at which point would the straps preventing rearward movement of the load be under the greatest strain?'
I don't know the deck angle of the aircraft as rotation finished, but if they were doing a V2 (or V2+10 ) climb it might be 20-25 degrees. A 747 pilot might know, but I guess we dont know the TOW yet which is what will control it.
So, plain old 'inclined plane Newtonian mechanics', would, I think generate the largest rearwards moment for the tie downs to resist, rather than accel' on the rwy or during rotation.
So, once settled in the climb, the force acting to move the load rearward would probably be much greater than during the take off roll. Even a small rearward movement of part of the load might then lead to a larger deck angle, and then to even larger rearwards load on the remaining tie downs.
Just think of 5 25,000 vehicles parked on a 20-25 degree ramp and maybe getting a bit of a shaking.
So, I think they'd be ok until rotated into the climb. Gravity drags the load aft, both pilots grab and push the controls. Gear stays where it is.
Bigger deck angle causes gravity to pull harder on the load.....
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Bigger deck angle causes gravity to pull harder on the load
For any given speed, there is a pitch angle where your aircraft will no longer accelerate, and going past that angle your aircraft will decelerate. For an aircraft having a thrust to weight ratio of one, this angle is 90 degrees.
So what this all means is that the load inside the aircraft gets pulled exactly by the same force regardless of your pitch attitude.
(Apologies for polluting this thread with entry level aeronautical concepts)
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Typical pitch attitude is probably 15-17 degrees, up to maybe 20 degrees.
Ground speed estimates from the video? If you don't know the velocity vector the GS is meaningless. A supersonic airplane going straight up or down has no GS but plenty of airspeed.
Ground speed estimates from the video? If you don't know the velocity vector the GS is meaningless. A supersonic airplane going straight up or down has no GS but plenty of airspeed.
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AtomKraft,
I think you deserve a medal for the patience and moderation you have shown in this thread.
A steeper deck angle does of course increase the horizontal component of the payload, and therefore place a greater load on whatever tie-down/locking system is being used. Were this not the case then Airbus have wasted countless millions in modding the nose gear on the A330-200F to reduce the deck angle from about 1.6° to 0.7°. This relatively miniscule reduction in the inclination of the deck is sufficient to decrease the horizontal component of a 5 tonne pallet load from a level that is unmanageable by handling personnel to a load that they can (literally) handle.
I think you deserve a medal for the patience and moderation you have shown in this thread.
A steeper deck angle does of course increase the horizontal component of the payload, and therefore place a greater load on whatever tie-down/locking system is being used. Were this not the case then Airbus have wasted countless millions in modding the nose gear on the A330-200F to reduce the deck angle from about 1.6° to 0.7°. This relatively miniscule reduction in the inclination of the deck is sufficient to decrease the horizontal component of a 5 tonne pallet load from a level that is unmanageable by handling personnel to a load that they can (literally) handle.
Per Ardua ad Astraeus
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[QUOT=HA]I think you (AtomKraft) deserve a medal for the patience and moderation you have shown in this thread. [/QUOTE] - seconded. There is an awful load of crap being posted here by many others.
Whether your query actually has anything to do with the accident we will have to wait and see.
Let's not forget, folks, seven aviators died in this crash.
Whether your query actually has anything to do with the accident we will have to wait and see.
Let's not forget, folks, seven aviators died in this crash.
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Greatest longitudinal force during initial takeoff roll
The forces felt by an object within an aircraft are those generated by aerodynamic forces and thrust, not gravity. The greatest component along the X-axis is thrust. Thrust is greatest when at low airspeed (engine thrust decreases with speed.
Think about your own experiences while flying. When are you forced back into your seat the most?
Think about your own experiences while flying. When are you forced back into your seat the most?
Atom, at risk of annoying many in this thread:
It appears to me that the point you are trying to make is that with a roughly level pitch attitude (as we roll down the runway gathering speed for takeoff), the vertical load is mostly supported by the pallet, and as attitude increases (rotation, and then climb attitude attained), a percentage of the vertical load (Frame of reference earth, not deck of plane), aka the load from gravity pulling on the mass of the stuff loaded on the pallets, is taken up by the restraints (varying as pitch varies) until climb is over and the plane returns to level flight ... how many degrees nose up that is being a variable with a small magnitude.
That said, and PJ2 making this point
I considered sines of pitch angles to show the magnitude of forces on the restraints, not on the pallets
I considered that a previous poster with some experience tells us that the restraints are typically able to handle 1.5 times the rated load,
and with a bit of back-of-the-napkin figuring arrived at 30 - 45 degres pitch up before you ran into that strap load capacity being put to the test.
This leads me to a catch-22 for offering strap failure on lift off,during initial climb, as a cause, since the limiting load would not be applied until the nose is well up there, but the nose wouldn't have gotten well up there unless someting failed and all that mass moved ...
I may have plugged in the wrong values, however.
With the previous mission being safely launched and landed ... I run into a dead end for the straps being the culprit.
It appears to me that the point you are trying to make is that with a roughly level pitch attitude (as we roll down the runway gathering speed for takeoff), the vertical load is mostly supported by the pallet, and as attitude increases (rotation, and then climb attitude attained), a percentage of the vertical load (Frame of reference earth, not deck of plane), aka the load from gravity pulling on the mass of the stuff loaded on the pallets, is taken up by the restraints (varying as pitch varies) until climb is over and the plane returns to level flight ... how many degrees nose up that is being a variable with a small magnitude.
That said, and PJ2 making this point
The longitudinal g's on takeoff are in the order of 0.3 +/-, and on rotation the vertical g is similarly small, around 0.05 to 0.1g bearing in mind that for most aircraft types the accelerometer is placed near the center of the fuselage, (gear well area), although unless there's a recent change, the B777's is mounted in the cockpit.
I considered that a previous poster with some experience tells us that the restraints are typically able to handle 1.5 times the rated load,
and with a bit of back-of-the-napkin figuring arrived at 30 - 45 degres pitch up before you ran into that strap load capacity being put to the test.
This leads me to a catch-22 for offering strap failure on lift off,during initial climb, as a cause, since the limiting load would not be applied until the nose is well up there, but the nose wouldn't have gotten well up there unless someting failed and all that mass moved ...
I may have plugged in the wrong values, however.
With the previous mission being safely launched and landed ... I run into a dead end for the straps being the culprit.
Last edited by Lonewolf_50; 8th May 2013 at 20:42.
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Just a thought, aircraft is loaded at airport A and flies to airport B loading is neither changed nor anything added her and the goes to C... What if, for example, the aircraft has to do a pretty hard decelleration during landing at B, would the cargo have to be restrapped to avoid any loadshift caused by loosened straps then?
The Forces felt by an object within an aircraft are those generated by Thrust, Aerodanymic Forces and Gravity.
Balance of forces wrt longitudinal axis of the aircraft:
Thrust(airspeed) - Drag(airspeed) - Gravitational Force x sin(Alpha) = Mass x Longitudinal acceleration.
or
SET(airspeed) - Gravitational Force x sin(Alpha) = Mass x Longitudinal acceleration.
So you can trade between Gravtitational Force as a function of AoA and longitudinal acceleration assuming same airspeed.
For the load it will largely 'feel' the same. Largely because the force component vertical to the floor will change with the cosine of the AoA. On the other hand when accelerating longitudinally airspeed will obviously change over time so this is only the momentary effect.
Last edited by henra; 8th May 2013 at 21:40.