A320 Single Engine flying - beta target indication
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With bank towards the live engines, an opposing side slip force can be generated
.. being the idea of having a bank input .. which, in turn, provides a lesser Vmc.. However, I suspect that, in the Vmc situation, there will be a residual slip remaining. At higher speeds, where one targets a lesser bank angle (typically around the 2-3 degrees mark) for OEI climb performance, that may not be the case.
.. being the idea of having a bank input .. which, in turn, provides a lesser Vmc.. However, I suspect that, in the Vmc situation, there will be a residual slip remaining. At higher speeds, where one targets a lesser bank angle (typically around the 2-3 degrees mark) for OEI climb performance, that may not be the case.
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With OEI if an aircraft is trimmed for zero side slip it will have some drag due to side loading. The minimum drag position is some slip neutralised by some bank. But how much?Airbus does the calculation for the pilot by creating the beta target which leaves some slip. Pilot just trims the rudder and flies the heading with side stick. This is the minimum drag for optimum OEI performance. Yes as John pointed out there is no bank without aileron but still it is the least drag position.
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vilas
I think we are all saying something similar, but using the wrong words.
Slip is usually displayed using a heavy ball (pea) in a "U" tube (which works well for symmetrical thrust flight.) However aerodynamic slip is better measured using streaming lengths of wool across the canopy.
During steady asymmetric flight with rudder balancing yaw and bank towards the live engines to counteract the rudder generated side slip (according to the wool), then the pea would show "slip". In Airbus, the Beta target replaces the streaming wool.
If we have no aerodynamic side slip (streaming wool / Beta) why would we need any aileron?
The minimum drag position is some slip neutralised by some bank
.... Yes as John pointed out there is no bank without aileron
.... Yes as John pointed out there is no bank without aileron
Slip is usually displayed using a heavy ball (pea) in a "U" tube (which works well for symmetrical thrust flight.) However aerodynamic slip is better measured using streaming lengths of wool across the canopy.
During steady asymmetric flight with rudder balancing yaw and bank towards the live engines to counteract the rudder generated side slip (according to the wool), then the pea would show "slip". In Airbus, the Beta target replaces the streaming wool.
If we have no aerodynamic side slip (streaming wool / Beta) why would we need any aileron?
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With OEI if an aircraft is trimmed for zero side slip it will have some drag due to side loading
Why so ?
The minimum drag position is some slip neutralised by some bank
I can't recall an authoritative source which has minimum drag other than for zero slip.
the pea would show "slip"
I will take the quotes to indicate tongue-in-cheek.
If we have no aerodynamic side slip (streaming wool / Beta) why would we need any aileron?
Beyond my meagre skillset to come up with a convincing two line answer.
However, I refer you to any of the standard references which will take you into headache territory with explanations as to what is going on. You might, for instance, have a read of the USAF FT OEI Good Guts Words.
Why so ?
The minimum drag position is some slip neutralised by some bank
I can't recall an authoritative source which has minimum drag other than for zero slip.
the pea would show "slip"
I will take the quotes to indicate tongue-in-cheek.
If we have no aerodynamic side slip (streaming wool / Beta) why would we need any aileron?
Beyond my meagre skillset to come up with a convincing two line answer.
However, I refer you to any of the standard references which will take you into headache territory with explanations as to what is going on. You might, for instance, have a read of the USAF FT OEI Good Guts Words.
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1. The rudder/vertical stab
2. Everything else (fuselage, nacelles, etc)
The drag on "everything else" is lowest at zero slip, obviously.
But the drag on the rudder is lowest when it is centered. And my earlier post explains why it is closer to being centered not at zero slip, but at some amount of slip with the relative wind vector coming from the good engine side.
So the minimum drag for these 2 components is at different slip conditions, and since the total parasite drag is the sum of both of the components, its lowest point will be at some compromise condition between two conditions.
I had actually never thought of this until reading this thread, or if I did, I would have concluded that the difference is miniscule, and trying to compensate for it would have been cutting with a chainsaw what you measured with a micrometer. But it seems that Airbus thinks it's enough to actually matter.
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John
The reference you have given in that Chapter 11 page 11.9 Fig.11.10 explains what I was trying to say. It gives case 1 EQUILIBRIUM FLIGHT WITH WINGS LEVEL in which the longitudinal axis of the aircraft is not in line with the relative airflow and that creates drag the side force. Case 2 is EQUILIBRIUM FLIGHT WITH ZERO SIDESLIP in which there is some bank
Case 1: 4 = 0 Figure 11.10 shows the forces and moments for Case 1, the zero bank angle case, with the left engine inoperative. The aircraft is in equilibrium with no accelerations. The pilot would note this with constant heading, ball centered, turn needle centered, rudder opposing the inoperative engine and aileron opposite the rudder to keep the wings level.
Case 2: ß = 0 Another way to balance the sideforce resulting from rudder deflection is by using the W sin if term in the sideforce equation (11.3). Figure 11.11 shows the forces and moments
for the zero sideslip case.
The aircraft is in equilibrium with some bank toward the operating engine, a constant heading and the turn needle centered. The rudder deflection is in the same direction as in the Case 1, however, less 8r is required. The ball in the turn and slip indicator will be deflected in the direction of the bank angle.
And further it states:Three important conclusions can be made from the previous discussion. First, bank angle can reduce the amount of rudder required to achieve equilibrium. Second, an increase in weight reduces the amount of bank required to reduce the sideslip to zero. Third, this configuration will have the least amount of drag. With ß = 0, no sideforce is generated, and therefore no drag due to sideforce is created
The reference you have given in that Chapter 11 page 11.9 Fig.11.10 explains what I was trying to say. It gives case 1 EQUILIBRIUM FLIGHT WITH WINGS LEVEL in which the longitudinal axis of the aircraft is not in line with the relative airflow and that creates drag the side force. Case 2 is EQUILIBRIUM FLIGHT WITH ZERO SIDESLIP in which there is some bank
Case 1: 4 = 0 Figure 11.10 shows the forces and moments for Case 1, the zero bank angle case, with the left engine inoperative. The aircraft is in equilibrium with no accelerations. The pilot would note this with constant heading, ball centered, turn needle centered, rudder opposing the inoperative engine and aileron opposite the rudder to keep the wings level.
Case 2: ß = 0 Another way to balance the sideforce resulting from rudder deflection is by using the W sin if term in the sideforce equation (11.3). Figure 11.11 shows the forces and moments
for the zero sideslip case.
The aircraft is in equilibrium with some bank toward the operating engine, a constant heading and the turn needle centered. The rudder deflection is in the same direction as in the Case 1, however, less 8r is required. The ball in the turn and slip indicator will be deflected in the direction of the bank angle.
And further it states:Three important conclusions can be made from the previous discussion. First, bank angle can reduce the amount of rudder required to achieve equilibrium. Second, an increase in weight reduces the amount of bank required to reduce the sideslip to zero. Third, this configuration will have the least amount of drag. With ß = 0, no sideforce is generated, and therefore no drag due to sideforce is created
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the pea would show "slip"
I will take the quotes to indicate tongue-in-cheek.
I will take the quotes to indicate tongue-in-cheek.
The ball in the turn and slip indicator will be deflected in the direction of the bank angle.
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We're talking at cross purposes, methinks. A quick review of the thread ..
Not trying to be difficult, folks. Just trying to comes to terms with some stuff which appears strange. Caveat, I am not an AB pilot and understand that the automatics do things a little bit differently than, say, manual flight on the Boeings. Lack of AB knowledge specifics might be at play here ...
Post 2 It indicates minimum drag, not zero side-slip.
Conventional wisdom is that min drag occurs at nil slip condition. Nowhere do I see any authoritative reference to bank so I can only presume that the AB comments relate to wings level climb out which is much the same as for the 72/73 where the pilot manually inputs rudder to centre the wheel. This might give a satisfactory result for the Type but I can't see how it equates to min drag which is going to require a bit of bank. Wings level will result in some residual slip - that's fine - but it ought not to equate to min drag.
Post # 3 beta target centered=optimum side slip=min drag
Similar comments to Post #2
Post # 13 Pilot is required to give rudder input to stop the sideslip
Rudder controls yawing moment. Once that is done (wings level and constant heading) there will remain a residual slip angle
Post # 13 Giving rudder input for zero sideslip will require too much rudder deflection
The rudder input is causing the residual slip. If you input more, what happens to heading and slip angle ? Certainly isn't going to give you nil slip.
Post # 17 For minimum drag (no aileron or roll spoiler deflection) at VMCA, then you would need 5 degrees bank
The bank for control considerations is not for performance, rather it reduces slip and frees up a bit of rudder authority. Can you cite any authoritative reference which supports your suggestion that you will have zero slip in the above situation ?
Post # 17 The aircraft will gradually centre the Beta Target resulting a few degrees of bank
This is the only comment I have seen which suggests that the aircraft will climb out with some bank. If that is the case, typically 2-3 degrees or so, then slip will be around nil and drag minimised. Now, what is the case if you are hand flying it rather than switching in the box ?
The FAST reference makes no observation regarding bank.
Post # 25 So the minimum drag for these 2 components is at different slip conditions, and since the total parasite drag is the sum of both of the components, its lowest point will be at some compromise condition between two conditions.
I think not. To get the nil slip condition will require a combination of rudder and aileron input. No value to be had in trying to separate the bits and pieces.
Post # 26 We are agreed. But is there a point to your post other than to restate the paper's words ?
I think what I am trying to get to is whether the aim is to fly with bank or just accept the wings level compromise ?
Not trying to be difficult, folks. Just trying to comes to terms with some stuff which appears strange. Caveat, I am not an AB pilot and understand that the automatics do things a little bit differently than, say, manual flight on the Boeings. Lack of AB knowledge specifics might be at play here ...
Post 2 It indicates minimum drag, not zero side-slip.
Conventional wisdom is that min drag occurs at nil slip condition. Nowhere do I see any authoritative reference to bank so I can only presume that the AB comments relate to wings level climb out which is much the same as for the 72/73 where the pilot manually inputs rudder to centre the wheel. This might give a satisfactory result for the Type but I can't see how it equates to min drag which is going to require a bit of bank. Wings level will result in some residual slip - that's fine - but it ought not to equate to min drag.
Post # 3 beta target centered=optimum side slip=min drag
Similar comments to Post #2
Post # 13 Pilot is required to give rudder input to stop the sideslip
Rudder controls yawing moment. Once that is done (wings level and constant heading) there will remain a residual slip angle
Post # 13 Giving rudder input for zero sideslip will require too much rudder deflection
The rudder input is causing the residual slip. If you input more, what happens to heading and slip angle ? Certainly isn't going to give you nil slip.
Post # 17 For minimum drag (no aileron or roll spoiler deflection) at VMCA, then you would need 5 degrees bank
The bank for control considerations is not for performance, rather it reduces slip and frees up a bit of rudder authority. Can you cite any authoritative reference which supports your suggestion that you will have zero slip in the above situation ?
Post # 17 The aircraft will gradually centre the Beta Target resulting a few degrees of bank
This is the only comment I have seen which suggests that the aircraft will climb out with some bank. If that is the case, typically 2-3 degrees or so, then slip will be around nil and drag minimised. Now, what is the case if you are hand flying it rather than switching in the box ?
The FAST reference makes no observation regarding bank.
Post # 25 So the minimum drag for these 2 components is at different slip conditions, and since the total parasite drag is the sum of both of the components, its lowest point will be at some compromise condition between two conditions.
I think not. To get the nil slip condition will require a combination of rudder and aileron input. No value to be had in trying to separate the bits and pieces.
Post # 26 We are agreed. But is there a point to your post other than to restate the paper's words ?
I think what I am trying to get to is whether the aim is to fly with bank or just accept the wings level compromise ?
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On both the EJet and the CSeries. Beta index in the middle puts the ball (trapezoid) and a little bank towards the live engine.
No Idea about AB. It's before my time ;-)
No Idea about AB. It's before my time ;-)
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I think what I am trying to get to is whether the aim is to fly with bank or just accept the wings level compromise ?
It is fly with some bank. The beta when centred gives you optimum slip and you need some bank to maintain heading and together it makes for minimum drag.
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John,
You said you had never seen any authoritative reference to bank. You will find one in Appendix G of Torenbeek's "Synthesis of Subsonic Airplane Design" where he writes:
>It is generally found that the total aysmmetric drag after failure of a starboard engine is minimum for a small negative slip angle, i.e. the airplane slips in the direction of the operative engine. However there is very little drag increment in a flight with zero sideslip. In that condition the most important drag contribution is caused by the vertical tail>
He cites another paper delivered by J G Callaghan of Douglas as part of AGARD Lecture Series 67. (I was there but had forgotten it till checking the reference! - old age)
Callaghan gives a comparative chart showing the various contributions from windmilling, rudder, sideslip, aileron and spoiler. Given the date of the lecture (1974) I think we can safely say it is old technology and a contemporary MDC twin engine design.
Unfortunately his picture has no numerical Y scale, but one can get a good idea of the magnitudes by simple measurement.
For the total aysmmetric drag increment that gives:
Bank/sideslip/drag units
5/-6/5.6
2.5/-2/4.5 (optimum)
1.5/0/4.6 (zero slip)
0.5/2/5.5
0/2.9/6.8 (wings level)
-2.5/6.8/10.9[/B]
You can see from this that the difference between optimum slip and zero slip for this aircraft was pretty damn small! This might not be true for other designs - it all depends on the induced drag factors of the VT and how you use either slip or rudder to generate the corrective yaw. Wings level was definitely off optimum.
You said you had never seen any authoritative reference to bank. You will find one in Appendix G of Torenbeek's "Synthesis of Subsonic Airplane Design" where he writes:
>It is generally found that the total aysmmetric drag after failure of a starboard engine is minimum for a small negative slip angle, i.e. the airplane slips in the direction of the operative engine. However there is very little drag increment in a flight with zero sideslip. In that condition the most important drag contribution is caused by the vertical tail>
He cites another paper delivered by J G Callaghan of Douglas as part of AGARD Lecture Series 67. (I was there but had forgotten it till checking the reference! - old age)
Callaghan gives a comparative chart showing the various contributions from windmilling, rudder, sideslip, aileron and spoiler. Given the date of the lecture (1974) I think we can safely say it is old technology and a contemporary MDC twin engine design.
Unfortunately his picture has no numerical Y scale, but one can get a good idea of the magnitudes by simple measurement.
For the total aysmmetric drag increment that gives:
Bank/sideslip/drag units
5/-6/5.6
2.5/-2/4.5 (optimum)
1.5/0/4.6 (zero slip)
0.5/2/5.5
0/2.9/6.8 (wings level)
-2.5/6.8/10.9[/B]
You can see from this that the difference between optimum slip and zero slip for this aircraft was pretty damn small! This might not be true for other designs - it all depends on the induced drag factors of the VT and how you use either slip or rudder to generate the corrective yaw. Wings level was definitely off optimum.
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Hi John.
I would like to withdraw that statement. It was badly constructed.
On Boeings, you can feel the point when no aileron is required. (Hence no roll spoilers deployed)
On Airbus, you can't feel that point. (Hence Beta Target)
See: http://www.dream-air.ru/new/pilotam/...or_support.pdf
Page 139.
"Hence in order to indicate the amount of rudder required to fly properly with an EO at T/O, the measured SIDE SLIP index is SHIFTED on the PFD by the residual side slip computed value, and displayed in blue instead of yellow, and called BETA TARGET; by pressing the rudder pedal to center the BETA TARGET index, the pilot will fly with the RESIDUAL SLIP as required by the EO condition. Thus theA/C will fly at constant heading with roll surfaces retracted."
Post # 17 For minimum drag (no aileron or roll spoiler deflection) at VMCA
On Boeings, you can feel the point when no aileron is required. (Hence no roll spoilers deployed)
On Airbus, you can't feel that point. (Hence Beta Target)
See: http://www.dream-air.ru/new/pilotam/...or_support.pdf
Page 139.
"Hence in order to indicate the amount of rudder required to fly properly with an EO at T/O, the measured SIDE SLIP index is SHIFTED on the PFD by the residual side slip computed value, and displayed in blue instead of yellow, and called BETA TARGET; by pressing the rudder pedal to center the BETA TARGET index, the pilot will fly with the RESIDUAL SLIP as required by the EO condition. Thus theA/C will fly at constant heading with roll surfaces retracted."
Last edited by Goldenrivett; 26th Jul 2017 at 11:48. Reason: link
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Dog Tired
This is getting as silly as it usually does.
If you don't trust beta in an Airbus and you don't believe what JT has to say, then you might as well admit to being a martian.
If you don't trust beta in an Airbus and you don't believe what JT has to say, then you might as well admit to being a martian.
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It's an airplane, it should fly more or less the same, Airbus or not.
On engine failures in the sim (A320) I do more or less the same I did on earlier not-so-automated types: Rudder in the correct sense, bit of bank into the live engine, trim the rudder. That's it.
I use B target more to try and help me with the rudder inputs, I bank the airplane anyway. It's worked so far with no particular annotations from instructors.
Re: use of TOGA with low weights and speeds. Vilas said the regulatory performance is met with flex. Airbus FCTM advises to take consideration of the use of TOGA in such cases and that it will "require precise handling". I'd use it but only after initial reactions from the aircraft have been neutralised. However, it seems applying the thrust increase while the aircraft is still on the ground (for the scenario in which you are after V1 but not yet airborne) seems a bit easier to control.
On engine failures in the sim (A320) I do more or less the same I did on earlier not-so-automated types: Rudder in the correct sense, bit of bank into the live engine, trim the rudder. That's it.
I use B target more to try and help me with the rudder inputs, I bank the airplane anyway. It's worked so far with no particular annotations from instructors.
Re: use of TOGA with low weights and speeds. Vilas said the regulatory performance is met with flex. Airbus FCTM advises to take consideration of the use of TOGA in such cases and that it will "require precise handling". I'd use it but only after initial reactions from the aircraft have been neutralised. However, it seems applying the thrust increase while the aircraft is still on the ground (for the scenario in which you are after V1 but not yet airborne) seems a bit easier to control.
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Thanks folks .. now I'm up to speed on the story.
OG, I was hoping that you might wade in, good sir. Have located your references and they will keep me busy for a while .. I can well see why you might have remembered the AGARD event ... guess I'll have to swot up on supersonic predictions as well ...
Interestingly, I think that the majority of FT folks probably adopt the nil slip idea as min drag. Vessbot, it appears I was a bit behind the intimate bits of the detail .. mea culpa and thanks.
This is getting as silly as it usually does.
Well, yes, and no. The main value of Tech Log to PPRuNe folk is that dummies, such as I, can pick the brains of the SME folk .. and we have a few of those in capital letters. Consider that, for near 50 years, now, I have fondly believed that nil slip was the end of it for min drag. Score one to my education from PPRuNe.
I am being quite serious in this comment. By the ends of our careers, most have acquired sufficient skill etc. to be considered SMEs in this or that. The brighter folk manage half a dozen disciplines. None of us knows it all .. learning continues until the Grim Reaper cuts our run short.
use of TOGA with low weights and speeds. Vilas said the regulatory performance is met with flex.
Of course one can push up to TOGA. But flex will (must) meet all the requirements as that is a necessary prerequisite for the flex setting.
Caveat is that the handling patting-the-head-while-rubbing-the-tummy can get out of hand very quickly. If one is of a mind to increase above flex .. then, please, do it slowly so that the leg can keep pace with the hand and engine response .. that's what the FCTM words "require precise handling" mean. Really, though, unless there is a good reason to do so, why not just leave things as they are and concentrate on flying the thing ? Very much worth the training value to do it for fun, either in the sim or aircraft (the latter at a safe height, etc). If you don't get a feeling that you are hanging onto the tail of the tiger ....
Long while ago now but I was heavily involved with a fatal investigation where they probably would all have survived had the crew left the operating throttle where it was ... pushed it up, yaw, roll, crash, burn, majority died.
OG, I was hoping that you might wade in, good sir. Have located your references and they will keep me busy for a while .. I can well see why you might have remembered the AGARD event ... guess I'll have to swot up on supersonic predictions as well ...
Interestingly, I think that the majority of FT folks probably adopt the nil slip idea as min drag. Vessbot, it appears I was a bit behind the intimate bits of the detail .. mea culpa and thanks.
This is getting as silly as it usually does.
Well, yes, and no. The main value of Tech Log to PPRuNe folk is that dummies, such as I, can pick the brains of the SME folk .. and we have a few of those in capital letters. Consider that, for near 50 years, now, I have fondly believed that nil slip was the end of it for min drag. Score one to my education from PPRuNe.
I am being quite serious in this comment. By the ends of our careers, most have acquired sufficient skill etc. to be considered SMEs in this or that. The brighter folk manage half a dozen disciplines. None of us knows it all .. learning continues until the Grim Reaper cuts our run short.
use of TOGA with low weights and speeds. Vilas said the regulatory performance is met with flex.
Of course one can push up to TOGA. But flex will (must) meet all the requirements as that is a necessary prerequisite for the flex setting.
Caveat is that the handling patting-the-head-while-rubbing-the-tummy can get out of hand very quickly. If one is of a mind to increase above flex .. then, please, do it slowly so that the leg can keep pace with the hand and engine response .. that's what the FCTM words "require precise handling" mean. Really, though, unless there is a good reason to do so, why not just leave things as they are and concentrate on flying the thing ? Very much worth the training value to do it for fun, either in the sim or aircraft (the latter at a safe height, etc). If you don't get a feeling that you are hanging onto the tail of the tiger ....
Long while ago now but I was heavily involved with a fatal investigation where they probably would all have survived had the crew left the operating throttle where it was ... pushed it up, yaw, roll, crash, burn, majority died.
