V2 cut
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Mr. Tullamarine,
As usual you're spot on.
Of the three primary constant horizontal flight path states(among many variations), you could trim to with an engine inoperative:
Zero Side Slip: Lowest drag but no way to reliably trim to this state without a yaw string or differential pressure yaw detector.
Zero Wheel: Slightly higher drag than zero side slip but with a positive indication you are there.
Wings level: Highest drag of the three.
For takeoff climbout, zero wheel is the preferred training technique since it's easy to tell when you're there.
As usual you're spot on.
Of the three primary constant horizontal flight path states(among many variations), you could trim to with an engine inoperative:
Zero Side Slip: Lowest drag but no way to reliably trim to this state without a yaw string or differential pressure yaw detector.
Zero Wheel: Slightly higher drag than zero side slip but with a positive indication you are there.
Wings level: Highest drag of the three.
For takeoff climbout, zero wheel is the preferred training technique since it's easy to tell when you're there.
OAG, for "zero wheel" you do not specifiy the bank angle. Remember that lateral control input generates a rolling moment (either to generate a roll rate or to oppose another rolling moment, for instance that caused by sideslip due to lateral static stability) and does not directly generate a bank angle. I agree with what you say about using a rudder input that results in zero wheel, but you also need 5 deg of bank towards the live engine as this will always result in less sideslip (and hence less drag) than wings level. Note that all FAR 25 and JAR 25 asymmetric performance certification allows this bank angle. Therefore, if wings level you may not get the minimum scheduled performance climb gradients.
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Could I ask for directions to any authoritative source which suggests that one needs 5 degrees bank for optimum climb ?
FAR 25 and AC25-7A (which is, by far, the more useful document) only talk of 5 degree bank in respect of Vmca determination .. where this is a maximum bank limitation to prevent unduly innovative flight testing by manufacturers.
On the presumption that most, and possibly all, certifications are based on 5 degree Vmca determinations, it is a good idea to be very bank sensitive with a failure under critical conditions at low speed.
Due to the sensitivity of "real" Vmca to bank angle and especially with a swept-wing jet, a failure (or better still a good birdstrike or rotor seizure model) during the takeoff rotation flare at low weight and minimum speed schedule presents the most critical handling case for the line pilot. In these circumstances, (unless the sim training sequence progresses to more critical situations sensibly in line with improving pilot manipulative capability) it is not at all uncommon to see pilots in the sim lose the aircraft in a Vmca departure at speeds well above the published Vmca due to poor bank angle control ... generally takes a few goes for the new pilot to accept that he/she must control bank, where necessary, very aggressively if the aircraft is not to be lost.
For this reason, many of my training failures are done during the latter stages of the rotation flare (which, I suggest, is considerably more difficult and demanding for the pilot than a steady V2 cut due to the dynamic nature of the total manoeuvre) .. working up (down/back?) to critical speed/CG failures ... makes for rather vocal (one gets to learn all the impolite expletives in any given language) and sweaty pilots .. especially when one then requires them to backtrack the opposite end localiser as well as handle the failure .. but the end result is that the garden variety V1 cut becomes a bit of a yawn .... and can be flown with an extremely high level of precision. I always find it very satisfying when the training exercise progression can be guessed just right so that the pilot, while under a reasonably uniform high workload and stress level, improves dramatically without having the spare capacity to realise the fact and then one can release the tension with a comment along the lines of "that's about it, guys ... it doesn't get any harder than that .. coffee break time".
Looking at climb data against bank angle, it is typical to find that the best performance is at a bank angle somewhere (relating to zero slip) between wings level and 5 degrees into the operating side .. typically we talk of around 2-3 degrees as being a good compromise. Often the performance is similar for wings level and 5 degrees (ie similar slip, but in opposite directions).
More interestingly, AC25-7A suggests that the certification intention is to fly OEI climbs wings level (unless that results in full rudder and a small bank is necessary to maintain heading).
I can't find any reference to 5 degree bank being relevant to, or necessary for, the OEI continued performance climb case (other than where Vmca might be near-limiting).
Perhaps some from the TP community who have specialised in OEI climb tests might care to comment ..... ? ... especially if they are able to provide de-identified test data ...
FAR 25 and AC25-7A (which is, by far, the more useful document) only talk of 5 degree bank in respect of Vmca determination .. where this is a maximum bank limitation to prevent unduly innovative flight testing by manufacturers.
On the presumption that most, and possibly all, certifications are based on 5 degree Vmca determinations, it is a good idea to be very bank sensitive with a failure under critical conditions at low speed.
Due to the sensitivity of "real" Vmca to bank angle and especially with a swept-wing jet, a failure (or better still a good birdstrike or rotor seizure model) during the takeoff rotation flare at low weight and minimum speed schedule presents the most critical handling case for the line pilot. In these circumstances, (unless the sim training sequence progresses to more critical situations sensibly in line with improving pilot manipulative capability) it is not at all uncommon to see pilots in the sim lose the aircraft in a Vmca departure at speeds well above the published Vmca due to poor bank angle control ... generally takes a few goes for the new pilot to accept that he/she must control bank, where necessary, very aggressively if the aircraft is not to be lost.
For this reason, many of my training failures are done during the latter stages of the rotation flare (which, I suggest, is considerably more difficult and demanding for the pilot than a steady V2 cut due to the dynamic nature of the total manoeuvre) .. working up (down/back?) to critical speed/CG failures ... makes for rather vocal (one gets to learn all the impolite expletives in any given language) and sweaty pilots .. especially when one then requires them to backtrack the opposite end localiser as well as handle the failure .. but the end result is that the garden variety V1 cut becomes a bit of a yawn .... and can be flown with an extremely high level of precision. I always find it very satisfying when the training exercise progression can be guessed just right so that the pilot, while under a reasonably uniform high workload and stress level, improves dramatically without having the spare capacity to realise the fact and then one can release the tension with a comment along the lines of "that's about it, guys ... it doesn't get any harder than that .. coffee break time".
Looking at climb data against bank angle, it is typical to find that the best performance is at a bank angle somewhere (relating to zero slip) between wings level and 5 degrees into the operating side .. typically we talk of around 2-3 degrees as being a good compromise. Often the performance is similar for wings level and 5 degrees (ie similar slip, but in opposite directions).
More interestingly, AC25-7A suggests that the certification intention is to fly OEI climbs wings level (unless that results in full rudder and a small bank is necessary to maintain heading).
I can't find any reference to 5 degree bank being relevant to, or necessary for, the OEI continued performance climb case (other than where Vmca might be near-limiting).
Perhaps some from the TP community who have specialised in OEI climb tests might care to comment ..... ? ... especially if they are able to provide de-identified test data ...
Last edited by john_tullamarine; 5th Jan 2003 at 02:45.
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Zero sideslip
John: During the development of Concorde, it was felt that side-slip would be a critical factor in intake control, and so a sideslip (beta) vane was fitted and had an input to the engine intake control units. As happened many times in other areas, during subsequent flight-testing the intakes were found to be far more robust than any other previous supersonic design and the beta-input to the EICUs was disconnected.
The happy byproduct of this is a side-slip meter fitted underneath the HSI. Engine-out takeoff and climbout is taught with zero sideslip - the pointer on the instrument is zeroed using rudder in the conventional way and it helps to achieve this by remembering this amounts to slightly less rudder than would be needed for zero-ball and a residual bank of 2 or 3 degrees. All 3 axes can then be trimmed out and best possible climb performance is achieved. Useful for 3-engines, very important for 2.
In practice it is no more effort to fly zero SS with small residual bank than zero ball with no bank - just slightly different datums which are no more difficult to trim for. The delta wing results in almost no roll/yaw couple and what little there is is elegantly looked after by the active fly-by-wire flying controls. It wasn't just the cruise speed that was years ahead of its time........
I don't know if the situation is different in terms of bank angle required because of the slender delta configuration, but I would guess 2-3 degrees of bank (zero SS) would be about right for most types? A side-slip meter (bit of string on the windscreen) should be fitted to all multi-engine transports......
The happy byproduct of this is a side-slip meter fitted underneath the HSI. Engine-out takeoff and climbout is taught with zero sideslip - the pointer on the instrument is zeroed using rudder in the conventional way and it helps to achieve this by remembering this amounts to slightly less rudder than would be needed for zero-ball and a residual bank of 2 or 3 degrees. All 3 axes can then be trimmed out and best possible climb performance is achieved. Useful for 3-engines, very important for 2.
In practice it is no more effort to fly zero SS with small residual bank than zero ball with no bank - just slightly different datums which are no more difficult to trim for. The delta wing results in almost no roll/yaw couple and what little there is is elegantly looked after by the active fly-by-wire flying controls. It wasn't just the cruise speed that was years ahead of its time........
I don't know if the situation is different in terms of bank angle required because of the slender delta configuration, but I would guess 2-3 degrees of bank (zero SS) would be about right for most types? A side-slip meter (bit of string on the windscreen) should be fitted to all multi-engine transports......
Do a Hover - it avoids G
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Surely the easiest way to settle beer type bets about which control should be put in first is to move nothing and just watch what happens for the first second or two after an engine is chopped (you are in a sim after all) If the nose slice very clearly happens first then the thing surely needs rudder first and if it mainly rolls then it needs aileron. I suspect the vast majority will need rudder first. To need aileron first the design has probably got too much rolling moment due to sideslip to be certificated.
When it comes to keeping drag (from sideslip and resultant control deflections) to a minimum after control is regained my guess is it will not be too obvious whether you have got it just right and it could be very type dependant.
When it comes to keeping drag (from sideslip and resultant control deflections) to a minimum after control is regained my guess is it will not be too obvious whether you have got it just right and it could be very type dependant.
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NW1 and JF sum up the problem nicely ... one needs an idea of where the goalpost is .. and then does one's best to get there using whatever tools are available .... and whatever techniques are reliable and repeatable.
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Lomcevak,
I don't need to specify a bank to fly "Wheel Zero". For trim at this condition, you put enough rudder in so the airplane is tracking straight (not turning) with the wheel centered (zero lateral control input if the wheel has an offset).
The nose won't be pointing in the direction of the ground track since this isn't the "Zero Sideslip" case.
Bank angle will be whatever it needs to be to match the airplane configuration and will vary with flap setting, thrust to weight ratio and V2.
Bank angle will be less than 5 deg. since that is all that is allowed for Vmca and V2 is greater than Vmca, making the rudder more effective.
I don't need to specify a bank to fly "Wheel Zero". For trim at this condition, you put enough rudder in so the airplane is tracking straight (not turning) with the wheel centered (zero lateral control input if the wheel has an offset).
The nose won't be pointing in the direction of the ground track since this isn't the "Zero Sideslip" case.
Bank angle will be whatever it needs to be to match the airplane configuration and will vary with flap setting, thrust to weight ratio and V2.
Bank angle will be less than 5 deg. since that is all that is allowed for Vmca and V2 is greater than Vmca, making the rudder more effective.
OAG,
My mistake; I realised after I posted that bank angle becomes defined using the technique but did not have time to edit it. One point to consider using the "zero wheel" techniqus is that it works well for jet aircraft with swept wings whereby most of the rolling moment under asymmetric power is as a result of sideslip and static lateral stability. However, in twin (or 4-engined!) propeller aircraft, an engine failure results in a significant loss of lift over the wing that has the failed engine, due to the loss of propwash, thus giving a strong rolling moment. Combine this with the fact that static lateral stability will probably be less than on a jet airliner (straight wing vs. swept wing) and the use of rudder to achieve zero wheel in a prop aircraft may result in a large sideslip angle as you are using the rudder to generate sideslip and thus create a rolling moment to oppose the lateral lift asymmetry. It would be interesting to get the views of some twin turbo-prop operators on the "zero wheel" technique.
The 5 deg bank angle question is an interesting one, and the precise AoB to achieve stabilised flight for a given sideslip angle is mainly a function of the sideforce characteristics of the aircraft (if not at zero sideslip) and the lateral aerodynamic force produced by the rudder. I suspect that 5 deg is generally considered as most aircraft have bank angle markers on the AI at 0 and 10 deg and 5 is then relatively easy to judge; 2-3 deg would not be so easy to judge. Using too much bank (10 deg) would give a significant reduction in the vertical component of lift, necessitating an increase in AoA and hence drag to maintain stabilised flight. The extra drag would then degrade climb performance so this would be inefficient and counter-productive.
One final thought on this thread is that the theory of flight under asymmetric power, with respect to rudder and lateral control inputs, leads to an optimum solution that will give the best controllability and performance for virtually all aircraft. However, this theoretical solution may be difficult to fly, and for any specific type there may be a procedure that is easier to teach and to fly that still gives adequate performance and controllability. Hence the differences in techniques discussed by the various respondents in this thread. Remember, fly what works in your aircraft but accept that this may not work for other types and you may need to learn and practise different techniques.
My mistake; I realised after I posted that bank angle becomes defined using the technique but did not have time to edit it. One point to consider using the "zero wheel" techniqus is that it works well for jet aircraft with swept wings whereby most of the rolling moment under asymmetric power is as a result of sideslip and static lateral stability. However, in twin (or 4-engined!) propeller aircraft, an engine failure results in a significant loss of lift over the wing that has the failed engine, due to the loss of propwash, thus giving a strong rolling moment. Combine this with the fact that static lateral stability will probably be less than on a jet airliner (straight wing vs. swept wing) and the use of rudder to achieve zero wheel in a prop aircraft may result in a large sideslip angle as you are using the rudder to generate sideslip and thus create a rolling moment to oppose the lateral lift asymmetry. It would be interesting to get the views of some twin turbo-prop operators on the "zero wheel" technique.
The 5 deg bank angle question is an interesting one, and the precise AoB to achieve stabilised flight for a given sideslip angle is mainly a function of the sideforce characteristics of the aircraft (if not at zero sideslip) and the lateral aerodynamic force produced by the rudder. I suspect that 5 deg is generally considered as most aircraft have bank angle markers on the AI at 0 and 10 deg and 5 is then relatively easy to judge; 2-3 deg would not be so easy to judge. Using too much bank (10 deg) would give a significant reduction in the vertical component of lift, necessitating an increase in AoA and hence drag to maintain stabilised flight. The extra drag would then degrade climb performance so this would be inefficient and counter-productive.
One final thought on this thread is that the theory of flight under asymmetric power, with respect to rudder and lateral control inputs, leads to an optimum solution that will give the best controllability and performance for virtually all aircraft. However, this theoretical solution may be difficult to fly, and for any specific type there may be a procedure that is easier to teach and to fly that still gives adequate performance and controllability. Hence the differences in techniques discussed by the various respondents in this thread. Remember, fly what works in your aircraft but accept that this may not work for other types and you may need to learn and practise different techniques.
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John Farley
It is unarguable (on boeing types) that in the situation that you described, rudder would be the control input that is required. After all, any roll observed during an engine failure is only a product of the yaw generated by the assymetric thrust condition. That is the theory.
The practice however is far different. We are not, or at least should not, be training guys to recognise and deal with sim failures. We should be giving them the tools they need to deal with a failure in the real case.
There are two major issues with recognition of engine failures and application of the correct technique. Firstly, as has been previously pointed out, if the incorrect rudder is applied, the aircraft will become unrecoverable in a matter of seconds. Secondly when operating on the line (i.e not in the state of heightened alertness for Eng failures as you are in the sim), the first indication of an engine failure airborne is usually the roll associated with the yaw. The problem being that in the real world, many other things cause roll as well, like gusty wind conditions, wake turbulence etc. As the AA crew discovered in New York, rudder is not the best course of action to deal with every wing drop. This, I believe, is why Boeing advocate initially aileron, followed closely by rudder. The natural reaction by any transport category pilot when noticing a roll, should be to correct initially aileron. When it becomes apparent (as it will almost immediately) that the roll has been caused by an engine failure, then apply the appropriate rudder to stop the yaw. Stopping the yaw is the primary objective. Not necessarily to level the yoke, it just so happens that a level yoke is a big, easy to use, and obvious indicator of when you have got approximately the correct amount of rudder.
I hope i have got this almost right as i am giving a brief on it soon!
It is unarguable (on boeing types) that in the situation that you described, rudder would be the control input that is required. After all, any roll observed during an engine failure is only a product of the yaw generated by the assymetric thrust condition. That is the theory.
The practice however is far different. We are not, or at least should not, be training guys to recognise and deal with sim failures. We should be giving them the tools they need to deal with a failure in the real case.
There are two major issues with recognition of engine failures and application of the correct technique. Firstly, as has been previously pointed out, if the incorrect rudder is applied, the aircraft will become unrecoverable in a matter of seconds. Secondly when operating on the line (i.e not in the state of heightened alertness for Eng failures as you are in the sim), the first indication of an engine failure airborne is usually the roll associated with the yaw. The problem being that in the real world, many other things cause roll as well, like gusty wind conditions, wake turbulence etc. As the AA crew discovered in New York, rudder is not the best course of action to deal with every wing drop. This, I believe, is why Boeing advocate initially aileron, followed closely by rudder. The natural reaction by any transport category pilot when noticing a roll, should be to correct initially aileron. When it becomes apparent (as it will almost immediately) that the roll has been caused by an engine failure, then apply the appropriate rudder to stop the yaw. Stopping the yaw is the primary objective. Not necessarily to level the yoke, it just so happens that a level yoke is a big, easy to use, and obvious indicator of when you have got approximately the correct amount of rudder.
I hope i have got this almost right as i am giving a brief on it soon!
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Interesting reading this one!
Lomcevak,
To answer your question, in the Dash 8 sim (and I hope the aircraft is similar) you do start to roll and yaw quite quickly with a failure just after V1/Vr, requiring almost full rudder and about half control wheel deflection pretty much at the same time to track straight. I imagine the yawing sensation may be more obvious in a turboprop than a jet making the rudder input a pretty natural first reaction and that is what is taught. While at V2 the control inputs stay pretty steady and we try for ball centred and wings as level as possible. The checkies say the sim does climb out better with wings level ball centred rather than any bank toward good engine. And after all why complicate things too much when the Dash 8 climbs out OK like this.
More interesting in the box can be single engine go-rounds, especially if you have an AC failure as well (strange how that happens in the sim), which means you lose some roll spoilers as well and then you just go full rudder and full aileron and hope it almost goes straight.
At least Dash 8 pilots are always pretty current with hand flying the aircraft which probably also helps. If we don't do 10 landings a week for both captain and FO we have had a quiet week and we do sim every 3 months.
Lomcevak,
To answer your question, in the Dash 8 sim (and I hope the aircraft is similar) you do start to roll and yaw quite quickly with a failure just after V1/Vr, requiring almost full rudder and about half control wheel deflection pretty much at the same time to track straight. I imagine the yawing sensation may be more obvious in a turboprop than a jet making the rudder input a pretty natural first reaction and that is what is taught. While at V2 the control inputs stay pretty steady and we try for ball centred and wings as level as possible. The checkies say the sim does climb out better with wings level ball centred rather than any bank toward good engine. And after all why complicate things too much when the Dash 8 climbs out OK like this.
More interesting in the box can be single engine go-rounds, especially if you have an AC failure as well (strange how that happens in the sim), which means you lose some roll spoilers as well and then you just go full rudder and full aileron and hope it almost goes straight.
At least Dash 8 pilots are always pretty current with hand flying the aircraft which probably also helps. If we don't do 10 landings a week for both captain and FO we have had a quiet week and we do sim every 3 months.
Moderator
I think we all accept that a sim is only the deluxe version of MS FS with the $20m+ hardware upgrade .... and that it varies in fidelity according to how the software is tweaked.
If we play somewhere in routine-middle-of-the-envelope areas, then the fidelity tends to be good as it is subject to regular assessment and acceptance. Conversely, the more we move away, the more questionable might become the Type/model fidelity. This doesn't necessarily mean that the machine ceases to be useful ... it might just mean that the observations are generic rather than specific to the model alleged on the data plate and, at times, might be quite unrealistic ....
This was brought home to me some time ago when I was working with a particular sim which had a significant software upgrade affecting a particular primary control .. I had the opportunity to test the before and after versions with the installing software engineers (something about no-one else being interested in doing this at 3 am on a Sunday morning as I recall ..) and the differences in the envelope region affected were quite astounding ... the "before" characteristics were unrealistic .. the "after" very much like the reported flight article's behaviour.
I find it a little sad that so many people use the devices only for very routine, stereotypical training and proficiency checking .. the opportunity to give crews exposure to areas a little out of the ordinary (especially for building confidence in the more routine manipulative areas) is discounted ...
... and, of course ... we ARE trying to build skills which might prove to be of use for the flight article .. if one only wanted to play with the toy .. then the MS article is a lot cheaper ...
If we play somewhere in routine-middle-of-the-envelope areas, then the fidelity tends to be good as it is subject to regular assessment and acceptance. Conversely, the more we move away, the more questionable might become the Type/model fidelity. This doesn't necessarily mean that the machine ceases to be useful ... it might just mean that the observations are generic rather than specific to the model alleged on the data plate and, at times, might be quite unrealistic ....
This was brought home to me some time ago when I was working with a particular sim which had a significant software upgrade affecting a particular primary control .. I had the opportunity to test the before and after versions with the installing software engineers (something about no-one else being interested in doing this at 3 am on a Sunday morning as I recall ..) and the differences in the envelope region affected were quite astounding ... the "before" characteristics were unrealistic .. the "after" very much like the reported flight article's behaviour.
I find it a little sad that so many people use the devices only for very routine, stereotypical training and proficiency checking .. the opportunity to give crews exposure to areas a little out of the ordinary (especially for building confidence in the more routine manipulative areas) is discounted ...
... and, of course ... we ARE trying to build skills which might prove to be of use for the flight article .. if one only wanted to play with the toy .. then the MS article is a lot cheaper ...
