Flap retraction
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V2+20 clean is my final segment climb speed and configuration.
I can climb at that for as long as I like.
However, I can also accelerate to my enroute climb speed and achieve a better climb rate though not necessarily a better gradient because of the increased forward speed. If there are no obstacles we should climb at Venr because of the increased climb rate.
Recap. These are all the same - retract the flaps on schedule and you can't go wrong.
If we have an engine failure at V1 up to V2+20 - can't retract the flaps because we can't accelerate and climb. So climb to 1500 feet, reduce pitch to level flight and retract the flaps accelerating through V2+20. Keep accelerating to Venr, climb away.
If we manage to get to V2+20 with both engines running we can now retract the flaps WITHOUT a level segment or pitching to accelerate.
So if we have an engine failure V2+20 up to Venr we're clean now (or in the middle of reconfiguring to clean). Keep the constant pitch and gently allow the speed to reduce back to V2+20. Its important not to pitch up because again the drag will increase (from the elevator) so just let the speed bleed back naturally. You are still well above the pitch for V2+20 clean so you'll still be trading speed for extra height and therefore definitely above the required gradient. The speed will bleed back to V2+20 and you pitch to maintain that. At 1500 feet (the platform we've all agreed on for a level acceleration) you can lower the pitch to accelerate to Venr and when you get there, climb away. There are conditions on this which you already do calculations for (I'm sure). Far out obstacles may require you to stay at your final segment climb gradient so you may have to do that but you're still in a much better position than the guys who left the flap selected as you don't have to pitch level and accelerate to get rid of the flap.
Engine failure after Venr up to cruise climb speed. Gently slow down to Venr because that gives you (roughly) the best climb clean OEI.
This is what isn't explained during perf lessons. It is, however, what the manufacturer thinks you're going to do. It leaves you in all cases after V2+20 with an aircraft thats climbing better and easier to fly than leaving the flap down past the flap retraction speed. It means you do the same thing whether all engines keep running or one fails ie:-
Take off, Retract the flap at V2+20, if you need a level acceleration platform to achieve flap retraction and a Venr climb use 1500 feet (subject to normal perf constraints)
its the same plan for every take off whether an engine fails or not.
Spandex (cool name) asked what maneuvering limitations we have at V2+20 clean. I can retract the flaps at 1.25Vs which is V2+4 when light and V2+7 when max weight and that will give the same maneuvering protection as flap 20 and V2 so there's already improved maneuvering margin but I'll look up the limits in the manual tomorrow.
I can climb at that for as long as I like.
However, I can also accelerate to my enroute climb speed and achieve a better climb rate though not necessarily a better gradient because of the increased forward speed. If there are no obstacles we should climb at Venr because of the increased climb rate.
Recap. These are all the same - retract the flaps on schedule and you can't go wrong.
If we have an engine failure at V1 up to V2+20 - can't retract the flaps because we can't accelerate and climb. So climb to 1500 feet, reduce pitch to level flight and retract the flaps accelerating through V2+20. Keep accelerating to Venr, climb away.
If we manage to get to V2+20 with both engines running we can now retract the flaps WITHOUT a level segment or pitching to accelerate.
So if we have an engine failure V2+20 up to Venr we're clean now (or in the middle of reconfiguring to clean). Keep the constant pitch and gently allow the speed to reduce back to V2+20. Its important not to pitch up because again the drag will increase (from the elevator) so just let the speed bleed back naturally. You are still well above the pitch for V2+20 clean so you'll still be trading speed for extra height and therefore definitely above the required gradient. The speed will bleed back to V2+20 and you pitch to maintain that. At 1500 feet (the platform we've all agreed on for a level acceleration) you can lower the pitch to accelerate to Venr and when you get there, climb away. There are conditions on this which you already do calculations for (I'm sure). Far out obstacles may require you to stay at your final segment climb gradient so you may have to do that but you're still in a much better position than the guys who left the flap selected as you don't have to pitch level and accelerate to get rid of the flap.
Engine failure after Venr up to cruise climb speed. Gently slow down to Venr because that gives you (roughly) the best climb clean OEI.
This is what isn't explained during perf lessons. It is, however, what the manufacturer thinks you're going to do. It leaves you in all cases after V2+20 with an aircraft thats climbing better and easier to fly than leaving the flap down past the flap retraction speed. It means you do the same thing whether all engines keep running or one fails ie:-
Take off, Retract the flap at V2+20, if you need a level acceleration platform to achieve flap retraction and a Venr climb use 1500 feet (subject to normal perf constraints)
its the same plan for every take off whether an engine fails or not.
Spandex (cool name) asked what maneuvering limitations we have at V2+20 clean. I can retract the flaps at 1.25Vs which is V2+4 when light and V2+7 when max weight and that will give the same maneuvering protection as flap 20 and V2 so there's already improved maneuvering margin but I'll look up the limits in the manual tomorrow.
Last edited by tommoutrie; 1st Dec 2012 at 22:42.
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am I nuts to suggest that we can do what the men that build the plane say and raise the flaps at V2+x
Re accelerating at 400 or 1500 feet - a history lesson:
1500 feet is an arbitrary number that marks the change from the takeoff phase to the enroute phase in terms of required obstacle clearance. It's the lowest height where you're likely to meet the enroute requirement of 1000' above obstacles.
Early jets couldn't climb at all with flap down OEI at max continuous; and because of their poor climb and acceleration even at takeoff thrust with water injection, they could only make it to 400' before having to level off and start accelerating to be clean before their 5 minutes ran out. I understand that the 400' figure was a battle between manufacturers and regulators; manufacturers wanted lower and were told "no".
Later, we get jets like your 601 that can get straight to 1500 (just); this allows them to take more weight in a scenario with distant obstacles below 1500 by delaying acceleration until you are above them.
More modern still a/c (604/5) can get higher still - and we have graphs in the manual for extended second segment climb. So we quite often are climbing above 1500' before accelerating if it is required for obstacle clearance. Zurich RW28, for example, AA is 3410', which is 2020' above the runway.
So the answer to your question is that we use 1500 normally because at 95% of airports we are clear of obstacles and are only interested in rate of climb, not angle.
Your logic for your profile appears to work for the 601, but only because it is a special case on two counts;
1) that the flap retraction minimum speed and the final segment climb speed are the same - on most aircraft there is still acceleration required. Of course, if you adopt my logic this problem goes away, because you leave the flaps down until you have reached Vfs
2) because the final segment gradient is always better than the 2nd segment. There are plenty of aircraft where this is not the case, because the reduction in thrust from TO to MCT reduces the performance by more than the gain of getting the flaps up.
And on aircraft like the Hawker with flaps up performance data, if you've looked up the appropriate clean V2 then you could use that in case of an engine failure after flap retraction but below AA; But that comes back to introducing too many variables to expect the average pilot to cope with.
BizJet, the point I meant to make (but didn't type) was that if I was struggling to clear an obstacle I wouldn't give a fcuk about noise.
This may mean we can develop a more appropriate noise technique for business jets that we can actually fly!
Enjoy the rest of the weekend.
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Hello Biz
I just need to deal with a couple of points that you've made because you're trying to make the 601 a special case. The final segment climb is not the same as the enroute segment climb and I'm not sure what type you fly but I strongly suspect the same will be true for your type. What do you fly? I'll have a look at the manual to see if its any different to the 601 in this respect.
Anyway
1) that the flap retraction minimum speed and the final segment climb speed are the same - on most aircraft there is still acceleration required. Of course, if you adopt my logic this problem goes away, because you leave the flaps down until you have reached Vfs
No acceleration will be needed for the final segment climb on any aircraft. An acceleration will be needed for the enroute climb. Leaving the flap down until you reach Vfs is gash because you are climbing against unnecessary drag. In the event of an engine failure you will ALWAYS be below the path you would be on had you taken the flaps up at the flap retraction speed.
2) because the final segment gradient is always better than the 2nd segment. There are plenty of aircraft where this is not the case, because the reduction in thrust from TO to MCT reduces the performance by more than the gain of getting the flaps up.
Which aircraft? Not adversarial, just interested. Its true for all the aircraft I have manuals for. Can you let me know which ones its not true for? Also, don't forget that in the event of a failure once you have cleaned up you still have max thrust (in the Challenger the APR would still trigger) so you will substantially outperform the published figures. By not cleaning up you are throwing away this advantage and I just don't get the logic behind doing that.
I'm busy downloading figures for a 605 and will look at the Global tomorrow because I'm in work and have the manuals available.
I just need to deal with a couple of points that you've made because you're trying to make the 601 a special case. The final segment climb is not the same as the enroute segment climb and I'm not sure what type you fly but I strongly suspect the same will be true for your type. What do you fly? I'll have a look at the manual to see if its any different to the 601 in this respect.
Anyway
1) that the flap retraction minimum speed and the final segment climb speed are the same - on most aircraft there is still acceleration required. Of course, if you adopt my logic this problem goes away, because you leave the flaps down until you have reached Vfs
No acceleration will be needed for the final segment climb on any aircraft. An acceleration will be needed for the enroute climb. Leaving the flap down until you reach Vfs is gash because you are climbing against unnecessary drag. In the event of an engine failure you will ALWAYS be below the path you would be on had you taken the flaps up at the flap retraction speed.
2) because the final segment gradient is always better than the 2nd segment. There are plenty of aircraft where this is not the case, because the reduction in thrust from TO to MCT reduces the performance by more than the gain of getting the flaps up.
Which aircraft? Not adversarial, just interested. Its true for all the aircraft I have manuals for. Can you let me know which ones its not true for? Also, don't forget that in the event of a failure once you have cleaned up you still have max thrust (in the Challenger the APR would still trigger) so you will substantially outperform the published figures. By not cleaning up you are throwing away this advantage and I just don't get the logic behind doing that.
I'm busy downloading figures for a 605 and will look at the Global tomorrow because I'm in work and have the manuals available.
Last edited by tommoutrie; 2nd Dec 2012 at 20:39.
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And on aircraft like the Hawker with flaps up performance data, if you've looked up the appropriate clean V2 then you could use that in case of an engine failure after flap retraction....
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So, you are saying...
That the test pilots, aerodynamic engineers, and PhDs that built the plane could not figure this out and publish the data? Or is it possible that maybe your wrong?
AWACS
AWACS
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not sure what the intention of that post was but I think the engineers etc know exactly what they are doing and they do publish the data. I don't think we read it properly and many of us don't understand it.
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Which aircraft?
2nd Segment at Flaps 7, V2, A/I off, T/O Thrust (limited to 10 min in OEI):
Sea Level / 15°= 6,3% with 30300 lbs (MTOM), 9,2% at 26000 lbs
5000 ft / 5° = 6,4% / 9,3%
10000ft / -5° = 5,2%/7,9%
Enroute Climb (Flaps 0, MCT, A/I off, at Venr = 180KIAS)
SL/ 15° = 5,7 / 7, 6 (-0,6 / -1,6, -> less than 2nd segment)
5000ft / 5° = 5,6 / 7,4 (-0,8 / -1,9 -> less than 2nd segment)
10000ft / -5 ° = 4,6 / 6,4 (-0,6 / -1,5 -> less than 2nd segment)
JFI: T/O Thrust vs. MCT, A/I off
SL: 96,0 / 94,8
5000ft: 100,0 / 98,6
10000ft: 102,5 / 102,3
Last edited by His dudeness; 3rd Dec 2012 at 15:38.
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can't compare it to the enroute segment - groundspeed is too high. Don't you have final segment climb gradients (as opposed to the enroute segments)? If you have a manual that allows flap retraction at V2+x you should have a final segment gradient table that gives you the gradient at that speed.
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No, Njet, Niente, Nada....
All there is is first segment, second segment and enroute.
What is there though is a distance table from reference zero (35ft) to end third segment (acceleration V2 to Venr)
All there is is first segment, second segment and enroute.
What is there though is a distance table from reference zero (35ft) to end third segment (acceleration V2 to Venr)
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Leaving the flap down until you reach Vfs is gash because you are climbing against unnecessary drag.
Profile 1
- complies with all regulations
- allows the handling pilot to concentrate on accurate speed and flight path control without interruption for the first 30 seconds after liftoff
- in the event of an engine failure requires the same profile all the way from liftoff to clear of obstacles, and the only difference from the all engines profile is the speed
Profile 2
- does not comply with at least two regulations
- requires configuration changes involving large attitude/trim adjustments almost immediately after liftoff
- in the event of an engine failure requires different profiles depending on where you are in the initial climb
and you think the first one is gash??!! You have seriously lost the plot there, I'm afraid.
You keep saying there's something wrong about leaving the flaps down for another 30 seconds because it causes drag. This on an aircraft that - if you have done your sums right - can clear all obstacles with the flap down on one engine, and on two is so embarrassingly overpowered that we can't fly a proper noise abatement profile. The flap drag allows us to fly a moderately sensible speed in the initial climb, allowing us to target a speed rather than just an attitude and makes a low level off much easier to handle. A benefit!
Which brings us to
In the event of an engine failure you will ALWAYS be below the path you would be on had you taken the flaps up at the flap retraction speed.
For the Challenger we can even quantify it. If you fly level at 200 kts clean you need +5 degrees pitch. If you select flap 20, you need to pitch down to 0 degrees to maintain level flight; or conversely if you maintained the attitude you would start climbing at 5 degrees - over 8%. That is a huge difference in the flight path.
His Dudeness has posted an aircraft where the final segment is less than the second. From memory all the 500 series Citations are the same, but I haven't got the figures to hand.
Between all those, I think we can say that your theory is well and truly debunked. As I said before, it is not a new idea; such profiles were used when aircraft struggled to climb with flap even on all engines, but modern (i.e. within the last 30 years!) thinking is to take advantage of the better performance from modern aircraft to simplify the handling and cut down on noise.
Last edited by BizJetJock; 4th Dec 2012 at 12:44. Reason: Spelling
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BJJ, I think the discussion itself is a good one and I´m not too sure that Toms theory is complete bollocks....
The discussion has changed and in the beginning we were talking about all engine performance and noise footprint...now we are at OEI performance...
By the way, IIRC is the difference net to gross gradient 0,8 on the 2nd (2 engines) and 1,1 on the enroute climb (too lazy to look it up right know), so the difference is almost neglicable and if we bear in mind that the enroute climb is in MCT and the 2nd is T/O thrust then his theory has its merits. (I havenßt got the numbers to crunch it or prove it)
Also Cessna has elected to stick to one Venr for all weights. I would guess that this speed would normally also change with weight. Most likely Cessna has found the difference to be so small that for the benefit of the average stupid flying the C680 (such guys like me) it sticks with just one speed....
Manufacturers like to save money time and hassle and tend to make just the necessary documentation and I think the legal implications especially in the US might be a contributing factor.
The real question for me stays the same: what do I do when one donk goes awol after the flaps are retracted, I´m somewhere between V2+10 and Venr and there is an obstacle I still have to make. (what gradient am I doing) Our CL / AFM doesn´t give guidance here and I admit it, I haven´t thought about this scenario before and certainly have not trained it with FSI.
I think it is a valid question, OTOH its not a scenario that happens often and to the best of my knowledge there has not been one accident where this had played a role...
Its not practical to stay at V2+10 with both engines and flaps til clear (I´d block the departures at 120-130 KIAS...)
The discussion has changed and in the beginning we were talking about all engine performance and noise footprint...now we are at OEI performance...
By the way, IIRC is the difference net to gross gradient 0,8 on the 2nd (2 engines) and 1,1 on the enroute climb (too lazy to look it up right know), so the difference is almost neglicable and if we bear in mind that the enroute climb is in MCT and the 2nd is T/O thrust then his theory has its merits. (I havenßt got the numbers to crunch it or prove it)
Also Cessna has elected to stick to one Venr for all weights. I would guess that this speed would normally also change with weight. Most likely Cessna has found the difference to be so small that for the benefit of the average stupid flying the C680 (such guys like me) it sticks with just one speed....
Manufacturers like to save money time and hassle and tend to make just the necessary documentation and I think the legal implications especially in the US might be a contributing factor.
The real question for me stays the same: what do I do when one donk goes awol after the flaps are retracted, I´m somewhere between V2+10 and Venr and there is an obstacle I still have to make. (what gradient am I doing) Our CL / AFM doesn´t give guidance here and I admit it, I haven´t thought about this scenario before and certainly have not trained it with FSI.
I think it is a valid question, OTOH its not a scenario that happens often and to the best of my knowledge there has not been one accident where this had played a role...
Its not practical to stay at V2+10 with both engines and flaps til clear (I´d block the departures at 120-130 KIAS...)
Last edited by His dudeness; 4th Dec 2012 at 08:54.
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The engine failure procedures are just one of the factors you need to take into account planning your all engines normal takeoff. Some people have got fixated a bit on that one aspect forgetting the rest.
No, it's not complete bollocks, just there are more ifs and buts involved than Tom is making out.
The main problem is that rather than being a great leap forward as he is suggesting, it is a great leap backward. As I have said, the airline world went through this discussion and came up with the current procedures 30 years ago. You wouldn't think it would take so long for the corporate world to catch up.
No, it's not complete bollocks, just there are more ifs and buts involved than Tom is making out.
The main problem is that rather than being a great leap forward as he is suggesting, it is a great leap backward. As I have said, the airline world went through this discussion and came up with the current procedures 30 years ago. You wouldn't think it would take so long for the corporate world to catch up.
Last edited by BizJetJock; 4th Dec 2012 at 10:24. Reason: Spelling
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Where in the airlines do they go blasting though the flap retraction speed? Which airline has an all engines operating policy of exceeding the flap retraction speed by 40 or 50 knots before retracting the flap at a pre-determined height?
The airline world is entirely consistent with what I've posted right from the start of this thread. The flap retraction schedules in all airline are based on speeds. There may be "not below" heights and MFRA's but the retraction of the flap is based on the speed schedule. The heights do not come from legislation (for all the bleating the only post relating to height is FAR/JAR 25 and that relates to OEI at V1).
The argument that this hasn't caused an accident or been a factor in the business jet world so it isn't a problem concerns me. Firstly, I don't know whether that's true. Business jets generally have very good performance on one engine so even if a failure is handled very badly the aircraft will still tend to climb away so there isn't really enough data to argue the point (well, I dont have access to that data). But the argument regarding noise and extra fuel burn applies to every take off - why is this invalid?
I'm hoping to get a 680 manual later today and I'm interested to see what it actually says. If there's genuinely no data between flap retraction and the enroute climb speed that will be a very big surprise to me - I have never seen a manual like that!
The airline world is entirely consistent with what I've posted right from the start of this thread. The flap retraction schedules in all airline are based on speeds. There may be "not below" heights and MFRA's but the retraction of the flap is based on the speed schedule. The heights do not come from legislation (for all the bleating the only post relating to height is FAR/JAR 25 and that relates to OEI at V1).
The argument that this hasn't caused an accident or been a factor in the business jet world so it isn't a problem concerns me. Firstly, I don't know whether that's true. Business jets generally have very good performance on one engine so even if a failure is handled very badly the aircraft will still tend to climb away so there isn't really enough data to argue the point (well, I dont have access to that data). But the argument regarding noise and extra fuel burn applies to every take off - why is this invalid?
I'm hoping to get a 680 manual later today and I'm interested to see what it actually says. If there's genuinely no data between flap retraction and the enroute climb speed that will be a very big surprise to me - I have never seen a manual like that!
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At the risk of sounding like a stuck record 400 feet does come from regulation, just because it does not fit with your theory does not mean it is not true.
I have manuals that state that 400 feet is the minimum for flap retract from Bombardier and Dassault. Good fun this.
I have manuals that state that 400 feet is the minimum for flap retract from Bombardier and Dassault. Good fun this.
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Tom, the airlines are 99% of the time using reduced thrust for takeoffs - i.e. matching the thrust used to the weight/altitude/temperature so the problem does not arise. If you have a lightly loaded airliner where they have to use TOGA for takeoff (contaminated runway, antiskid inop, etc.) then you will find that on reaching their pitch limit they allow the speed to increase. On reaching their acceleration altitude if they find that they are already above the minimum flap retraction speed they can do it straight away.
This technique is available on the 601, although interestingly because so few people used it Bombardier decided it wasn't worth the time and cost to certificate for the 604/5.
You are actually the only person on here who seems to think that when people refer to a flap retraction height that they mean that there is no reference to speed. Therefore it would appear that the only problem is your lack of understanding. Knowing the training at both your operator and their third party training provider, I would lay the blame for that squarely with them initially, but the more you refuse to listen to the evidence put forward on here, the more it appears that you are the problem.
This technique is available on the 601, although interestingly because so few people used it Bombardier decided it wasn't worth the time and cost to certificate for the 604/5.
You are actually the only person on here who seems to think that when people refer to a flap retraction height that they mean that there is no reference to speed. Therefore it would appear that the only problem is your lack of understanding. Knowing the training at both your operator and their third party training provider, I would lay the blame for that squarely with them initially, but the more you refuse to listen to the evidence put forward on here, the more it appears that you are the problem.