Adjusting Your V1 ?
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Adjusting Your V1 ?
If my Beech 1900 TKOF data card states that for a particular day I can takeoff at a weight of 7000 kg with say a v1/vr of 120 but my actual BRW is 6000 kg and the v1/vr is 100, would it be safer to use the 120 which allows that litle bit longer for the decision to reject the takeoff ?
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I assume you are talking safer in terms of aircraft performance.
The worst case scenaro should be looked at, one engine inoperative, the climb gradients required to be met are the same for both weights.
The V1 speed is like a gate where with one engine inoperative, and the energy the aircraft has at the time it can successfully meet its climb gradient requirements.
Assuming you are talking about a runway that has a ASDR limit at 7000 kg. At a lower weight V1 is less, and the point you rotate is closer to the start of the takeoff roll. The climb gradient performance is based upon the point you lift off from the runway, so the aircraft may have and additional altitude by the time it pass the rotation point for the 120 knots. More ground clearance is better in my view.
Increasing your V1 in a 1900 is only really useful in conditions where microbursts, turbulance, ice formation is expected. You are far safer to delay your takeoff and not enter the conditions as the two engine climb performace may not exceed the conditions encounted.
The worst case scenaro should be looked at, one engine inoperative, the climb gradients required to be met are the same for both weights.
The V1 speed is like a gate where with one engine inoperative, and the energy the aircraft has at the time it can successfully meet its climb gradient requirements.
Assuming you are talking about a runway that has a ASDR limit at 7000 kg. At a lower weight V1 is less, and the point you rotate is closer to the start of the takeoff roll. The climb gradient performance is based upon the point you lift off from the runway, so the aircraft may have and additional altitude by the time it pass the rotation point for the 120 knots. More ground clearance is better in my view.
Increasing your V1 in a 1900 is only really useful in conditions where microbursts, turbulance, ice formation is expected. You are far safer to delay your takeoff and not enter the conditions as the two engine climb performace may not exceed the conditions encounted.
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Thanx Zeke, but I hope I dont sound to novice - but If the 7000 kg was ASDR limited for example and was at a BRW of 6000 kg with the above V1/VR speeds, I thought I would be buying myself more time to reject a takeoff at the higher V1/VR.
I know I can "successfully" have an RTO at 7000 kg but I am at 6000 kg using 7000 kg speeds. Does that make sense to you ?
Cheers for your help.
I know I can "successfully" have an RTO at 7000 kg but I am at 6000 kg using 7000 kg speeds. Does that make sense to you ?
Cheers for your help.
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The V'speeds for the 7000 wt,meet the legal cert' requirements-you have an addittional higher V2,if conditions warrant it.You may like a 'lower'V1' if the runway was wet/limiting(it's not limiting as you can go with 7k).It's the same with the 'bigger' boys! On the 320 the 'original'speeds for V1 were rediculousely 'low'(119K),with the [email protected] 'different'Co's aligned the V1's closer to the V2's(it still met the AsDA,for the weight),and was closer to the V2 in the 'encouraged'Go Case!!
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Indeed, your take off charts/regulated take off graphs (or whatever your aircraft type calls them) will probably give you a mid-range V1 for whatever weight you are using. In reality, you have a range of V1s to use - providing you are not field length limited (i.e Vstop=Vgo). You may have some sort of procedure for calculating this range from the quick graph/tables. If you have, the choice of which you use is yours.
The mid V1 gives you a safety margin either side of Vgo and Vstop. The high or low V1 gives you less margin for error, but gives you the choice of taking your emergency airborne or not.
In a small turboprop aircraft, you will probably prefer to stop and deal with the problem on the ground. But in a max weight 747 after an engine failure, you may prefer to get the aircraft airborne on three (which it is perfectly capable of doing providing the failure happened past Vgo) and deal with the problem in the air, rather than deal with possible brake fires and an evacuation of 450 frightened people after a high speed abort.
It's a captaincy decision!.
[This message has been edited by Dan Winterland (edited 21 June 2001).]
[This message has been edited by Dan Winterland (edited 21 June 2001).]
The mid V1 gives you a safety margin either side of Vgo and Vstop. The high or low V1 gives you less margin for error, but gives you the choice of taking your emergency airborne or not.
In a small turboprop aircraft, you will probably prefer to stop and deal with the problem on the ground. But in a max weight 747 after an engine failure, you may prefer to get the aircraft airborne on three (which it is perfectly capable of doing providing the failure happened past Vgo) and deal with the problem in the air, rather than deal with possible brake fires and an evacuation of 450 frightened people after a high speed abort.
It's a captaincy decision!.
[This message has been edited by Dan Winterland (edited 21 June 2001).]
[This message has been edited by Dan Winterland (edited 21 June 2001).]
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Some additional thoughts, presuming a reasonably limiting runway -
(a) if there is no difficulty with the aircraft's handling, then using the higher weight figures ought not to create a problem. From an accel stop point of view, the actual distances should be better at the lighter weight, providing some useful pad.
Desirable considerations-
(i) dry runway at an airport with a difficult escape path and lots of nasty terrain - one might prefer to stop.
(ii) at the higher V2 the aircraft's actual OEI climb gradient should be better than at the lower V2 (in the nature of an overspeed V2 takeoff) - useful if the obstructions are late second segment, but less so if they are early second segment.
(b) the lower weight figures would be desirable if the runway is wet and/or the overrun is nasty.
(c) one ought not to mix the lower V1 with the higher Vr/V2 unless you have additional data to make sure that the OEI TODR doesn't push out too far.
Safer ? ... if we accept that safety is the inverse of risk, then it comes down to a more global assessment of what is most likely to kill you soonest.
(a) if there is no difficulty with the aircraft's handling, then using the higher weight figures ought not to create a problem. From an accel stop point of view, the actual distances should be better at the lighter weight, providing some useful pad.
Desirable considerations-
(i) dry runway at an airport with a difficult escape path and lots of nasty terrain - one might prefer to stop.
(ii) at the higher V2 the aircraft's actual OEI climb gradient should be better than at the lower V2 (in the nature of an overspeed V2 takeoff) - useful if the obstructions are late second segment, but less so if they are early second segment.
(b) the lower weight figures would be desirable if the runway is wet and/or the overrun is nasty.
(c) one ought not to mix the lower V1 with the higher Vr/V2 unless you have additional data to make sure that the OEI TODR doesn't push out too far.
Safer ? ... if we accept that safety is the inverse of risk, then it comes down to a more global assessment of what is most likely to kill you soonest.
Guest
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Natas,
I presume that the fact you are quoting single figures for V1/Vr means that there is effectively no real V1: the aircraft will be airborne (Vr) before achieving the real V1?
If so, there should be no significant downside to using the higher figures other than you might enter the RTO at a higher energy level than necessary. Once airborne, everything should be enhanced - you will still be airborne before the lift-off point for the limiting weight and all of your speeds will be higher, thus improving your climb performance in all segments and achieving all segment end points before you otherwise would at the higher weight.
However, you need to know what the real V1 speeds are - there is no point in unnecessarily creating a limiting situation.
------------------
Stay Alive,
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I presume that the fact you are quoting single figures for V1/Vr means that there is effectively no real V1: the aircraft will be airborne (Vr) before achieving the real V1?
If so, there should be no significant downside to using the higher figures other than you might enter the RTO at a higher energy level than necessary. Once airborne, everything should be enhanced - you will still be airborne before the lift-off point for the limiting weight and all of your speeds will be higher, thus improving your climb performance in all segments and achieving all segment end points before you otherwise would at the higher weight.
However, you need to know what the real V1 speeds are - there is no point in unnecessarily creating a limiting situation.
------------------
Stay Alive,
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4dogs,
V1/Vr=1.00 is not at all unusual and is just as valid a V1 as a lower ratio (as permitted in the AFM) ... nothing "unreal" about the higher V1.
Your comment regarding being airborne before reaching the "real" V1 is, I suggest, not quite on the mark - the aircraft will be airborne sometime after passing Vr, regardless of whether V1/Vr=1.00 or 0.90 or whatever.
In the case of a longer runway with a smaller aircraft of course the operation might practicably be terminated from a speed in excess of the scheduled V1 or, for that matter the scheduled Vr on a very long runway, but this is not addressed for all the usual reasons ...
Normally V1/Vr is pushed to 1.00 in a case where the first segment performance is a nuisance and/or to address the case of close in first or second segment obstacles.
So far as enhancing the airborne phase goes, perhaps you might expand on your thoughts here as the comments confuse me somewhat....? In my limited view of the world, the after rotation performance relates principally to V2.
V1/Vr=1.00 is not at all unusual and is just as valid a V1 as a lower ratio (as permitted in the AFM) ... nothing "unreal" about the higher V1.
Your comment regarding being airborne before reaching the "real" V1 is, I suggest, not quite on the mark - the aircraft will be airborne sometime after passing Vr, regardless of whether V1/Vr=1.00 or 0.90 or whatever.
In the case of a longer runway with a smaller aircraft of course the operation might practicably be terminated from a speed in excess of the scheduled V1 or, for that matter the scheduled Vr on a very long runway, but this is not addressed for all the usual reasons ...
Normally V1/Vr is pushed to 1.00 in a case where the first segment performance is a nuisance and/or to address the case of close in first or second segment obstacles.
So far as enhancing the airborne phase goes, perhaps you might expand on your thoughts here as the comments confuse me somewhat....? In my limited view of the world, the after rotation performance relates principally to V2.
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JT,
Ah, my usual lack of precision in paraphrasing my thoughts brings me undone.
My understanding was that many turboprop aeroplanes such as the B1900 are most often much more limited by the continued takeoff requirements then they are by the RTO case and thus V1/Vr=1.0 simply because ratios of greater than 1 are somewhat redundant. My presumption (presented to be disputed, if appropriate) was that the actual V1 was generally greater than Vr. I had no intention to suggest that 1.0 could not be a real ratio, merely that it often is not.
Should that be the case, then my logic was simply that the performance planning for obstacle avoidance would be conducted for the most limiting case and, all things such as tyre speed limits and brake energy limits being equal, operating the aircraft to the higher speeds of the limiting weight would not compromise obstacle clearance. Moreover, given that V2 is the first and lowest speed at which the certification gradient requirements can be satisfactorily met, operating to the speeds for the higher weight would enhance the performance in all segments because the climb speeds are closer to optimum for the lower weight and the acceleration segment will be shorter because there should be greater excess power to accelerate less mass than the planning envisaged.
Your reference to when Vlof is achieved is not disputed, I was merely trying to indicate that the take-off would be initiated at Vr and thus before reaching a V1 significantly higher than Vr. There is no satisfactory way of second guessing the RTO once you have initiated rotation.
In turn, I was confused by your usage of "V1/Vr is pushed to 1.00" - from what real ratio??
As for your last comment, I thought I was safe in assuming that I didn't have to specify that we rotate in order to achieve V2 and that thereafter my comments related to the second and later segment speeds as appropriate. Apart from that, I am unsure about which bits I stuffed up as you read them.
------------------
Stay Alive,
[email protected]
Ah, my usual lack of precision in paraphrasing my thoughts brings me undone.
My understanding was that many turboprop aeroplanes such as the B1900 are most often much more limited by the continued takeoff requirements then they are by the RTO case and thus V1/Vr=1.0 simply because ratios of greater than 1 are somewhat redundant. My presumption (presented to be disputed, if appropriate) was that the actual V1 was generally greater than Vr. I had no intention to suggest that 1.0 could not be a real ratio, merely that it often is not.
Should that be the case, then my logic was simply that the performance planning for obstacle avoidance would be conducted for the most limiting case and, all things such as tyre speed limits and brake energy limits being equal, operating the aircraft to the higher speeds of the limiting weight would not compromise obstacle clearance. Moreover, given that V2 is the first and lowest speed at which the certification gradient requirements can be satisfactorily met, operating to the speeds for the higher weight would enhance the performance in all segments because the climb speeds are closer to optimum for the lower weight and the acceleration segment will be shorter because there should be greater excess power to accelerate less mass than the planning envisaged.
Your reference to when Vlof is achieved is not disputed, I was merely trying to indicate that the take-off would be initiated at Vr and thus before reaching a V1 significantly higher than Vr. There is no satisfactory way of second guessing the RTO once you have initiated rotation.
In turn, I was confused by your usage of "V1/Vr is pushed to 1.00" - from what real ratio??
As for your last comment, I thought I was safe in assuming that I didn't have to specify that we rotate in order to achieve V2 and that thereafter my comments related to the second and later segment speeds as appropriate. Apart from that, I am unsure about which bits I stuffed up as you read them.
------------------
Stay Alive,
[email protected]
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Pass, friend.
References to V1/Vr ratios depend on the AFM presentation. Whether one uses this terminology or V1 as a separate number is immaterial.
The upper end is 1.00 (ie V1 = Vr) and the lower generally Vmcg limited or for any other reasons which may fall out of the certification analyses.
Reference to "pushing" the ratio up is my slack terminology. In general, the higher V1 helps out for closer in obstacles, and the lower V1 for shorter runways especially with declared clearway and no significant obstacle problems ... Depending on the particular aerodrome circumstances, there will be some usable range of ratios and you pick whichever suits your particular agenda.
I wouldn't necessarily agree that turboprops have a greater problem. Due to the larger V2/VCL split with the jets, the third segment is often a big hassle. On the props the small speed increment makes the escape procedure design a bit easier.
Using RTOW V2 instead of the minimum speed for the actual weight makes good sense up to, say, V2min plus 20-30 knots as the climb gradient will be improved and the obstacle clearances have been based on the higher weight data. One caveat, though, is that any turning escape paths may be turn radius critical, so one needs to know what the operations engineering strategy was .. and this ought to be clearly stated in the procedure.
[This message has been edited by john_tullamarine (edited 30 June 2001).]
References to V1/Vr ratios depend on the AFM presentation. Whether one uses this terminology or V1 as a separate number is immaterial.
The upper end is 1.00 (ie V1 = Vr) and the lower generally Vmcg limited or for any other reasons which may fall out of the certification analyses.
Reference to "pushing" the ratio up is my slack terminology. In general, the higher V1 helps out for closer in obstacles, and the lower V1 for shorter runways especially with declared clearway and no significant obstacle problems ... Depending on the particular aerodrome circumstances, there will be some usable range of ratios and you pick whichever suits your particular agenda.
I wouldn't necessarily agree that turboprops have a greater problem. Due to the larger V2/VCL split with the jets, the third segment is often a big hassle. On the props the small speed increment makes the escape procedure design a bit easier.
Using RTOW V2 instead of the minimum speed for the actual weight makes good sense up to, say, V2min plus 20-30 knots as the climb gradient will be improved and the obstacle clearances have been based on the higher weight data. One caveat, though, is that any turning escape paths may be turn radius critical, so one needs to know what the operations engineering strategy was .. and this ought to be clearly stated in the procedure.
[This message has been edited by john_tullamarine (edited 30 June 2001).]
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V1 can never exceed VR by definition, the theoretical V1 for you max regulated take off weight can be higher, but that means V1 = VR.
John, I don't quite understand you reasoning regarding a higher V1 helping with close in obstacles. Do you mean that if you elect to stay on the ground, you are less likely to be scared by the obstacle if you lose an engine? V1 selection will have no effect on the climb.
Selecting a higher V2 is an option on some big jets, this allows a better climb angle due to being closer to VIMD. I don't think this applies to turboprops though.
John, I don't quite understand you reasoning regarding a higher V1 helping with close in obstacles. Do you mean that if you elect to stay on the ground, you are less likely to be scared by the obstacle if you lose an engine? V1 selection will have no effect on the climb.
Selecting a higher V2 is an option on some big jets, this allows a better climb angle due to being closer to VIMD. I don't think this applies to turboprops though.
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Dan,
..higher V1 helping with close in obstacles?
Actually, I rather like your reasoning .... the reasoning is geometric - for the same weight and V2, lower V1 results in longer TODR, higher V1 in a shorter value. This all presupposes a failure, of course, and is normally limiting.
If a close-in obstacle is the limiting factor for this takeoff, then a higher V1 will improve the calculated obstacle clearance and maximize the RTOW, assuming that some other consideration doesn't become limiting in the process.
The question of overspeed V2 takeoffs needs to be looked at from two viewpoints. If the AFM provides data to account for this procedure on a longer runway, then RTOW credit can be taken for the improved climb gradient availability. However, regardless of that, if the aircraft happens to be a few knots above V2 when the failure has been sorted out, it is preferable to hang onto the higher speed for the same reason.
I don't know if I have any specific data for props but I would expect that the same results apply. I vaguely recall one turboprop with provision for overspeed calculations but the memory is too dim to bring the specifics to mind.
..higher V1 helping with close in obstacles?
Actually, I rather like your reasoning .... the reasoning is geometric - for the same weight and V2, lower V1 results in longer TODR, higher V1 in a shorter value. This all presupposes a failure, of course, and is normally limiting.
If a close-in obstacle is the limiting factor for this takeoff, then a higher V1 will improve the calculated obstacle clearance and maximize the RTOW, assuming that some other consideration doesn't become limiting in the process.
The question of overspeed V2 takeoffs needs to be looked at from two viewpoints. If the AFM provides data to account for this procedure on a longer runway, then RTOW credit can be taken for the improved climb gradient availability. However, regardless of that, if the aircraft happens to be a few knots above V2 when the failure has been sorted out, it is preferable to hang onto the higher speed for the same reason.
I don't know if I have any specific data for props but I would expect that the same results apply. I vaguely recall one turboprop with provision for overspeed calculations but the memory is too dim to bring the specifics to mind.
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Dan,
By selecting a higher V1 you are using an unbalanced field, the distance required to accelerate with a failed engine from the higher V1 to VR / V2 is shorter than if you were using a Balanced field V1. Therefore you still have the same climb gradient at V2, but the start datum for the climb is not at the end of the runway.
Try to have a look at some Airbus takeoff charts, they love doing this.
Mutt.
By selecting a higher V1 you are using an unbalanced field, the distance required to accelerate with a failed engine from the higher V1 to VR / V2 is shorter than if you were using a Balanced field V1. Therefore you still have the same climb gradient at V2, but the start datum for the climb is not at the end of the runway.
Try to have a look at some Airbus takeoff charts, they love doing this.
Mutt.
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One of the interesting things which is coming through to me from these discussions is the apparent view held by most that BFL is A GOOD THING ... and it may be, if the aim is a quick, but reasonable, calculation.
Most of time, though, you can tweak a few more kilos out of an unbalanced calculation. Hence I tend to keep forgetting about the BFL case.
Most of time, though, you can tweak a few more kilos out of an unbalanced calculation. Hence I tend to keep forgetting about the BFL case.
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JT,
BFL is easy because dumb pilots can see on a Jeppeson chart how long the black bit of the runway is - all that RESA/Stopway/clearway is confusing. From the manufacturers' perspective, data presentation is simplified dramatically and therefore it is soooo much cheaper!
We always work unbalanced because reality rarely is balanced. We actually throw away most of our payload in our take-off splay conservatism (based on realistic radii of turn, based in turn on practical buffers on placarded operating speeds), hence we maximise the runway weights (although we have long applied practical line-up allowances!!)
However, I must say that I was drawn to a little curiousity about your attitude to maximising payload through use of the clearway given your passion about runway buffers. Two bob one way??
------------------
Stay Alive,
[email protected]
BFL is easy because dumb pilots can see on a Jeppeson chart how long the black bit of the runway is - all that RESA/Stopway/clearway is confusing. From the manufacturers' perspective, data presentation is simplified dramatically and therefore it is soooo much cheaper!
We always work unbalanced because reality rarely is balanced. We actually throw away most of our payload in our take-off splay conservatism (based on realistic radii of turn, based in turn on practical buffers on placarded operating speeds), hence we maximise the runway weights (although we have long applied practical line-up allowances!!)
However, I must say that I was drawn to a little curiousity about your attitude to maximising payload through use of the clearway given your passion about runway buffers. Two bob one way??
------------------
Stay Alive,
[email protected]
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4Dogs,
A contradiction ?
Not really.
First I don't think that it is sensible to get the pilot to do the ops engineer's job - he has neither the time nor the data.
My attitude is that the ops engineer's job is to screw the best weight out of the runway considering all relevant matters, including company commercial and risk policies. You mention escape paths - this is a matter in which I have considerable experience and, I suspect, it is not always addressed as well as it ought to be by all operators.
The problem which I see often is that the pilot is somewhat ill-informed by his system as to the details which went into the sums. If he were to have these, and adequate knowledge about the various matters, then he is better placed to make assessments as to what is, or is not, reasonable to lift, from a given runway under given conditions. That is, the pilot ought to be empowered, within sensible bounds, to invoke a risk related buffer when such is appropriate.
Clearly, it is a balance between commercial reality, risk, and a bit for mum and the kids .... and the Chief Pilot might want to discuss the Commander's decision over tea and bikkies if it is a bit too much on the conservative side.
My interest in this forum is to see stimulated discussion from a pilot's viewpoint on these, sometimes grey, areas with a view to pilots gaining increased awareness of some of the problems. This, I think, is better than the blinkered rote approach seen in many pilots.
With knowledge comes realistic approaches to, and solutions in respect of, such matters....
[This message has been edited by john_tullamarine (edited 03 July 2001).]
A contradiction ?
Not really.
First I don't think that it is sensible to get the pilot to do the ops engineer's job - he has neither the time nor the data.
My attitude is that the ops engineer's job is to screw the best weight out of the runway considering all relevant matters, including company commercial and risk policies. You mention escape paths - this is a matter in which I have considerable experience and, I suspect, it is not always addressed as well as it ought to be by all operators.
The problem which I see often is that the pilot is somewhat ill-informed by his system as to the details which went into the sums. If he were to have these, and adequate knowledge about the various matters, then he is better placed to make assessments as to what is, or is not, reasonable to lift, from a given runway under given conditions. That is, the pilot ought to be empowered, within sensible bounds, to invoke a risk related buffer when such is appropriate.
Clearly, it is a balance between commercial reality, risk, and a bit for mum and the kids .... and the Chief Pilot might want to discuss the Commander's decision over tea and bikkies if it is a bit too much on the conservative side.
My interest in this forum is to see stimulated discussion from a pilot's viewpoint on these, sometimes grey, areas with a view to pilots gaining increased awareness of some of the problems. This, I think, is better than the blinkered rote approach seen in many pilots.
With knowledge comes realistic approaches to, and solutions in respect of, such matters....
[This message has been edited by john_tullamarine (edited 03 July 2001).]
