Airbus Invents Turning By Fuel?
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Perhaps Airbus are thinking not in terms of current configs but in terms of less conventional future configurations where fuel shift for trim may be more usual and thus the capability may be more available than on a standard "tube with wings"?
ChristianJ;
The Airbus A330 and A340, all series, (and I suspect the A380) all have fuel tanks in the horizontal stabilizer for the same purposes - trim in cruise. The tanks are empty at takeoff and landing, (IOW, not used for storage). The smaller A320-type do not have such a system.
The B777 (the versions I have data on) do not have such trim tanks, nor does the B767 series.
Your second question re transfer rates was the point I was trying to make - present systems could not transfer fuel at rates which would be required to turn the airplane and control the other forces inherent in such maneuvers. I think it is wholly impractical. Perhaps the Mad Scientist is onto something though...
Do subsonic airliners have fwd and aft (tail) trim tanks?
Can existing fuel pumps move fuel fast enough to obtain any kind of long and lat control? (IIRC a typical fuel pump moves about 2t/min.)
Can existing fuel pumps move fuel fast enough to obtain any kind of long and lat control? (IIRC a typical fuel pump moves about 2t/min.)
The B777 (the versions I have data on) do not have such trim tanks, nor does the B767 series.
Your second question re transfer rates was the point I was trying to make - present systems could not transfer fuel at rates which would be required to turn the airplane and control the other forces inherent in such maneuvers. I think it is wholly impractical. Perhaps the Mad Scientist is onto something though...
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I think your missing the novelty
Why pump a small amount of Fuel a long way to increase the Moment Arm? Why not move the entire Tank a few centimeters instead? Adding rails and tractor jacks would solve the "Rate" problem by moving all the Fuel in the Tank instantly, a short distance.
I have to agree however with Christiaan who questions the attention paid to a small chance risk. There was that -10 that lost its exhaust cone from #2 last month, however. No interruptions in that one, but a stage or two forward.......?
I have to agree however with Christiaan who questions the attention paid to a small chance risk. There was that -10 that lost its exhaust cone from #2 last month, however. No interruptions in that one, but a stage or two forward.......?
Last edited by airfoilmod; 14th Apr 2009 at 19:04.
Following on from that, why not add a device, maybe somewhere at the back where it would be most effective, which could be moved by remote control from the flight deck (or by autonomous command from the flight computers) producing an aerodynamic force which could counterbalance any tendency towards instability?
The Airbus A330 and A340, all series, (and I suspect the A380) all have fuel tanks in the horizontal stabilizer for the same purposes - trim in cruise. The tanks are empty at takeoff and landing, (IOW, not used for storage).
The Stab trim tanks often contain fuel when it leaves the gate. I can't see 2tonne (plus) of JetA1 being used before takeoff. I may be wrong though.
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and what I know about phugoid oscillation
.. with respect, kijangnim, I think that you need to revisit a basic undergrad engineering text in Mechanics of Flight and review what the phugoid solution represents.
I suspect that you are a tad wide of the mark in your comments.
.. with respect, kijangnim, I think that you need to revisit a basic undergrad engineering text in Mechanics of Flight and review what the phugoid solution represents.
I suspect that you are a tad wide of the mark in your comments.
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PJ2: The Airbus A330 and A340, all series, (and I suspect the A380) all have fuel tanks in the horizontal stabilizer for the same purposes - trim in cruise.
Thanks! I presume that translates to: "On long-range a/c, the reduction in fuel burn due to reduced trim drag, more than compensates for the added weight of tanks and pumps" ?
9v-SKA: From what I know, super sonic aircrafts eg. fighters use the movement of fuel for maneuvering during supersonic flight.
No, they don't. Movement of fuel is used for trim, not manoeuvering. You cannot move fuel fast enough to get an adequate response to control inputs.
airfoilmod and FullWings,
Thanks... ROFLMAO
TURIN,
Concorde typically used about 1.3t from gate to line-up, so the much heavier 'biggies' may well use 2t (I've got no figures either).
On Concorde we could "overfill" the tanks (i.e., above MTOW) and hence arrive at th line-up at exactly MTOW.
john_tullamarine ...the phugoid solution...
I have the impression most people are not really aware of what the phugoid is, because under normal circustances the amplitude is so small and the period so large, that either small control inputs or autopilot tend to mask its existence.
CJ
Thanks! I presume that translates to: "On long-range a/c, the reduction in fuel burn due to reduced trim drag, more than compensates for the added weight of tanks and pumps" ?
9v-SKA: From what I know, super sonic aircrafts eg. fighters use the movement of fuel for maneuvering during supersonic flight.
No, they don't. Movement of fuel is used for trim, not manoeuvering. You cannot move fuel fast enough to get an adequate response to control inputs.
airfoilmod and FullWings,
Thanks... ROFLMAO
TURIN,
Concorde typically used about 1.3t from gate to line-up, so the much heavier 'biggies' may well use 2t (I've got no figures either).
On Concorde we could "overfill" the tanks (i.e., above MTOW) and hence arrive at th line-up at exactly MTOW.
john_tullamarine ...the phugoid solution...
I have the impression most people are not really aware of what the phugoid is, because under normal circustances the amplitude is so small and the period so large, that either small control inputs or autopilot tend to mask its existence.
CJ
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I've been trying to work out how much weight you can shift in a few seconds using normal plumbing and I can't help feeling that a little fat guy running up and down the aisles might be faster.
cg movement
To Mad (Flt) Scientist.
All right then, I will bite! Yes indeed, cg movement is how you steer a hang glider. But Turin is right also. Load up left wing by moving to that side, increase billow and the drag on the left wing, therefore turn left.
AND you can land a hang glider (but no other fixed wing non VTOL aircraft) with zero kinetic energy.
Excuse me while I polish my tinfoil helmet!
All right then, I will bite! Yes indeed, cg movement is how you steer a hang glider. But Turin is right also. Load up left wing by moving to that side, increase billow and the drag on the left wing, therefore turn left.
AND you can land a hang glider (but no other fixed wing non VTOL aircraft) with zero kinetic energy.
Excuse me while I polish my tinfoil helmet!
Last edited by 911slf; 15th Apr 2009 at 13:25. Reason: Just spotted Turin's post
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Originally Posted by deltayankee
I've been trying to work out how much weight you can shift in a few seconds using normal plumbing and I can't help feeling that a little fat guy running up and down the aisles might be faster.
100kg fat guy running from tail to centre of cabin (assuming no trolley dolleys or trolleys in the way) is 100kg over about 25m in 10 seconds.
2t/min from tail tank to centre tank is 330kg in 10 seconds. Slightly better.
You'll have to get the fat lady to run as well.
CJ
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The NS article has very little information (online, haven't seen the latest edn in the shops here yet)...does anyone have a link to the actual patent application?
There is an art to patents and the use "controlling aircraft by pumping fuel around" is not the core of the patent application but rather the way you express the ideas that make up the claims of the patent. Therefore I guess that Airbus have some clever techniques linking fuel pump operation with the control systems for much more sophisticated and subtle trim than is achievable by the pilots controlling the fuel flow between tanks. In addition to that this patent might really come down to some novel device that sits between the fuel pumps and the FBW system...
Looks interesting and would love to see more of the details
fc101
E145 Driver
There is an art to patents and the use "controlling aircraft by pumping fuel around" is not the core of the patent application but rather the way you express the ideas that make up the claims of the patent. Therefore I guess that Airbus have some clever techniques linking fuel pump operation with the control systems for much more sophisticated and subtle trim than is achievable by the pilots controlling the fuel flow between tanks. In addition to that this patent might really come down to some novel device that sits between the fuel pumps and the FBW system...
Looks interesting and would love to see more of the details
fc101
E145 Driver
TURIN;
I took a look at a fuel sheet I kept, (134,000kgs) and indeed the Trim Tank was loaded with 5050kgs of juice so my recollection is incorrect - fuel is in the TTs at takeoff. If I recall correctly, the TT is empty (or supposed to be) by the time descent begins. Amazing the details one forgets after a year and a bit of retirement!
ChristianJ;
Fully agree. I think most people don't comprehend the nature of phugoid oscillations in transport category aircraft; the mass is substantial (ranging from 50,000 to 400,000kgs approx) therefore the "stasis" (inertia) in cruise flight (700 to 1000fps or so) is significant - the cycle takes time to develop, it takes great anticipation (lead/lag of control input) and careful control handling to stop. Otherwise, one's input is liable to exacerbate the cycle, not stop it. In terms of Dutch Roll, one firm opposite aileron into the roll usually works, but that's not a phugoid. The entire cycle is, as you observe, subtle to begin with.
Having seen large fuel imbalances across the wing in different types and the relative insigificance of such weight differences in terms of controllability, I think any fuel redistribution to intentionally roll the aircraft has marginal aerodynamic and mechanical viability. I can imagine the aircraft beginning to roll "as commanded" and a rapidly-developing need to transfer fuel back to stop the developing roll - again, it would have to be very subtlely done and certainly not by the crew - the airplane would likely simply roll on it's back under manual control unless one is extremely good, careful and experienced at handling these aircraft.
I took a look at a fuel sheet I kept, (134,000kgs) and indeed the Trim Tank was loaded with 5050kgs of juice so my recollection is incorrect - fuel is in the TTs at takeoff. If I recall correctly, the TT is empty (or supposed to be) by the time descent begins. Amazing the details one forgets after a year and a bit of retirement!
ChristianJ;
I have the impression most people are not really aware of what the phugoid is, because under normal circustances the amplitude is so small and the period so large, that either small control inputs or autopilot tend to mask its existence.
Having seen large fuel imbalances across the wing in different types and the relative insigificance of such weight differences in terms of controllability, I think any fuel redistribution to intentionally roll the aircraft has marginal aerodynamic and mechanical viability. I can imagine the aircraft beginning to roll "as commanded" and a rapidly-developing need to transfer fuel back to stop the developing roll - again, it would have to be very subtlely done and certainly not by the crew - the airplane would likely simply roll on it's back under manual control unless one is extremely good, careful and experienced at handling these aircraft.
Why?????
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that either small control inputs or autopilot tend to mask its existence.
.. can recall some Argosy pilots years ago who couldn't work out why the aircraft had speed oscillations on autopilot during cruise .. a short brief on phugoids sorted that out.
.. can recall some Argosy pilots years ago who couldn't work out why the aircraft had speed oscillations on autopilot during cruise .. a short brief on phugoids sorted that out.
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Trim
To me the phugoid is similar to a natural tendency for the a/c to roll. The cure for uncommanded roll is Dihedral. There is no similar solution for pitch linked excursions. Except for constant inputs balancing Center of lift and cg. There is no natural tendency for an aircraft to seek stable pitch in flight without a designed interruption of deviation. So many of the current crop of accidents involve Pitch, the design arena is so far inadequate to taming this most important characteristic.
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An Idea
First thought about turning with fuel was ahh B.S. The trim tanks on several aircraft have a long time to transfer fuel and it could never be accomplished for sucessful flight.
Reasoning.
1. the obvious fuel transfer is slow
2. quantity changes depending on phase of flight, how do you calculate it to a specific quantity when a pilot would probable prefer to land heavy with plenty of missed approach fuel... many variables here.
3. we have spent years creating bafflels and fuel schedules to prevent fuel from effecting the aircraft's flight chararistics.
The last problem may be the solution, what if the plan is not to pump fuel from tank to tank but to simply allow gravity to do it's job within that tank when desired and pump it in the opposite direction when not. Complex, probably never know when it is broken until you need it (like a dump valve) but completely possible.
How about them "phugoid oscillations"?
Reasoning.
1. the obvious fuel transfer is slow
2. quantity changes depending on phase of flight, how do you calculate it to a specific quantity when a pilot would probable prefer to land heavy with plenty of missed approach fuel... many variables here.
3. we have spent years creating bafflels and fuel schedules to prevent fuel from effecting the aircraft's flight chararistics.
The last problem may be the solution, what if the plan is not to pump fuel from tank to tank but to simply allow gravity to do it's job within that tank when desired and pump it in the opposite direction when not. Complex, probably never know when it is broken until you need it (like a dump valve) but completely possible.
How about them "phugoid oscillations"?
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Wing Loading
And then there's wing loading. The wings lift most of the mass of the a/c, including fuel load. The largest stress on the wings is at T/O, when heavy.
Assumably, Wing tanks will be carrying fuel on T/O. With less than full fuel at T/O, the wings should still contain fuel, as the portion of TOW represented by fuel is better managed when its weight is directly borne above the Lift.
An empty wing stresses (bends more) when asked to leverage all weight when it is empty of fuel. Cruise, same. Splitting the mass (Fuel) at the fulcrum, the wing root, reduces stress and adds life to the wing structure.
But this hasn't anything to do with turning. An increase aft in cg allows the tail to support more mass also, reducing AoA at cruise, reducing drag, increasing fuel efficiency, also nothing to do with turning with Fuel apportionment.
AF
Assumably, Wing tanks will be carrying fuel on T/O. With less than full fuel at T/O, the wings should still contain fuel, as the portion of TOW represented by fuel is better managed when its weight is directly borne above the Lift.
An empty wing stresses (bends more) when asked to leverage all weight when it is empty of fuel. Cruise, same. Splitting the mass (Fuel) at the fulcrum, the wing root, reduces stress and adds life to the wing structure.
But this hasn't anything to do with turning. An increase aft in cg allows the tail to support more mass also, reducing AoA at cruise, reducing drag, increasing fuel efficiency, also nothing to do with turning with Fuel apportionment.
AF