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756/767 Pilot Strategies For Winglet Fuel Savings  
User currently offlinelrgt From United States of America, joined Jul 2004, 710 posts, RR: 0
Posted (2 years 5 months 1 week 4 days 20 hours ago) and read 4776 times:

When flying with winglets, I know that pilots should use a lower throttle setting on climb (than if aircraft didn't have wiglets) to reduce fuel burn. Generally, winglets only save money on cruse, and that if climb speed isn't slowed, the fuel burn will actually increase with winglets (they'll still produce notable savings with an inefficient/fast-climb due to savings on cruise on a longer flight).

How else do winglets change the dynamics of efficient flying?

Do they work better or worse in a headwind? Would the opposite be true in a tailwind?

Are there strategies that work well with winglets, involving changing throttle settings or altitude mid-cruise, or something else? (i.e. reducing throttle to, say, drop 200 feet over 5 minutes, and let speed sink to from M0.80 to M0.76, then restore throttle to go up 200ft over 10 minutes maintaining M0.76, let speed increase back to M0.80 over next 5 minutes, and repeat?) Or, is it best to set at M0.8 and leave alone, no matter tailwind/0-wind/headwind.

Is the most efficient cruise angle of attack changed by winglets?

I'm curious to hear what math-wiz 757/767 pilots have determined after experience flying the type with winglets.


Don't bring up the NW DC9's unless you have to!
18 replies: All unread, jump to last
 
User currently offlineflyhossd From United States of America, joined Nov 2009, 890 posts, RR: 2
Reply 1, posted (2 years 5 months 1 week 4 days 18 hours ago) and read 4706 times:

At my former carrier, it was determined that it was more fuel efficient to NOT climb at reduced power. That is, it was claimed that it was better to get to altitude quicker.

From my perspective, the winglets allowed the aircraft to get to a higher - more efficient - altitude sooner.

Our "bean-counters" looked for a return on investment of a year of less - including the winglet installation I believe. If that was the case, then the winglets really are a nice improvement.

Take all of this with a grain of salt, they're just my observations. I was just a "line-slug" and wasn't involved in any of the number-crunching.



My statements do not represent my former employer or my current employer and are my opinions only.
User currently offlinerendezvous From New Zealand, joined May 2001, 516 posts, RR: 0
Reply 2, posted (2 years 5 months 1 week 4 days 12 hours ago) and read 4590 times:

Derated climb thrust is primarily for reducing wear and tear on the engines - letting them run at a lower power setting gives you lower temperatures internally which means they last longer.

User currently offlineQFA380 From Australia, joined Jul 2005, 2075 posts, RR: 1
Reply 3, posted (2 years 5 months 1 week 4 days 7 hours ago) and read 4496 times:

Quoting rendezvous (Reply 2):

Slightly off topic but how does this work? Do components have to be replaced after a certain amount of time or during a certain check or just when they break? That would seem a little unsafe to wait until the engine components are just about to break before replacing them and possibly more costly if the plane needs to be taken out of service to have it done rather than during a prescheduled check.

Or is the wear constantly monitored and can it can be accurately predicted when it will need to be replaced based on current rates of wear?


User currently offlineSchorschNG From Germany, joined Sep 2010, 500 posts, RR: 0
Reply 4, posted (2 years 5 months 1 week 4 days 7 hours ago) and read 4489 times:

Depending on the particular engine, flying prolonged times at Max Climb may reduce engine life. Other engines may accept that. Especially the de-rated CFM56 on the smaller single aisles have plenty of reserves, usually never touch their true TET limit.
As for the climb: winglets reduce the drag at higher lift coefficients. That is, the wing becomes more efficient when he has to work hard. Winglets do not yield much advantage when the wing is only lightly loaded. Now, when flying faster the dynamic pressure increases and the actual coefficient [Lift / (Wing Area * Dynamic Pressure)] decreases. Each wing has its optimum lift coefficient, where lift over drag is maximized. In Airbus speak this called Green Dot speed.
The winglet reduces this speed, allowing to cruise more efficient at lower speeds.
However, most aircraft (from pure fuel burn perspective) go best when climb is achieved the fastest and steepest. This is not because the climb is very fuel efficient then, but the early cruise makes up for the few additional kg of fuel burned in the climb.

And that is where engine life kicks in: if the engine suffers from prolonged usage at Max Climb, the cash operating cost may be reduced by actually burning some additional fuel but saving on the maintenance.



From a structural standpoint, passengers are the worst possible payload. [Michael Chun-Yung Niu]
User currently offlinemusang From United Kingdom, joined Apr 2001, 864 posts, RR: 7
Reply 5, posted (2 years 5 months 1 week 4 days 5 hours ago) and read 4462 times:

Quoting QFA380 (Reply 3):

Or is the wear constantly monitored and can it can be accurately predicted when it will need to be replaced based on current rates of wear?

The wear is constantly monitored. Relationships between various engine parameters allow analysis e.g. how much fuel goes in compared to the resultant turbine or exhaust temperatures and the rotational speed of the turbine/fan etc.

The wear on the engine rises disproportionately as temperature increases, and I believe (I'm only a pilot) that the heat in the turbine section is the critical issue. E.g. using fan speed as a rough measure of thrust, increasing the engine from 86% N1 (the fan speed) to 87% wll cause much less wear than an increase from say, 90% to 91%. Generally, launching from the full length of the runway rather than an intersection allows the use of less thrust, so prolongs engine life. The relationship between high/low thrust/speed in the climb is complicated, and our bean counters think low thrust and moderate speed are the best combo, balancing fuel consumption with engine wear.

Quoting lrgt (Thread starter):
When flying with winglets, I know that pilots should use a lower throttle setting on climb (than if aircraft didn't have wiglets) to reduce fuel burn. Generally, winglets only save money on cruse, and that if climb speed isn't slowed, the fuel burn will actually increase with winglets (they'll still produce notable savings with an inefficient/fast-climb due to savings on cruise on a longer flight).

How much throttle (or thrust) pilots will use on take-off or climb, or indeed cruise, is computer calculated for each flight, taking many variables into consideration. Pilot just enters the weight, temperature, wind, runway, pressure etc. etc. and the appropriate thrust settings are presented by the Flight Management Computer and fed to the autothrust system, varying with altitude during the climb. Its transparent to the pilots, they wouldn't be conciously using less thrust because they have winglets. It just happens.

In very general terms, if you installed winglets without telling the FMC that the aircraft had them, so it calculated the same old thrust settings as before, the aircraft would take off after a slightly shorter run, climb at a higher rate, find that it needed a lower thrust setting for the same cruise speed, and have a bit of trouble descending from the (wrongly) predicted Top of Descent point (because for a given calculated descent speed, the wing is now producing slightly more lift than the FMC knows about. The correct TOD for the winglets should have been earlier).

So the pilots will not have to do much, if anything, different, as the FMC will calculate thrust according to the speed requirement (fuel economy because you're on schedule, high speed 'cos you're late, low speed to avoid arriving before the airport opens in the morning etc.). An alert pilot may notice a lower fuel burn rate for a given mach number, but weight, flight level (i.e. temperature/pressure), centre of gravity and head/tail winds will all have been automatically compensated for so in my case I'm sure it would be the accounts department who would see the effects before I did, in terms of reduced overall fuel consumption. Or the engine analysers, who would notice longer engine life between overhauls due to the lower operating temperatures as the engines have an easier life running a little cooler.

Regards - musang


User currently offlineMax Q From United States of America, joined May 2001, 4525 posts, RR: 18
Reply 6, posted (2 years 5 months 1 week 4 days 4 hours ago) and read 4451 times:

Quoting flyhossd (Reply 1):


At my former carrier, it was determined that it was more fuel efficient to NOT climb at reduced power. That is, it was claimed that it was better to get to altitude quicker.

From my perspective, the winglets allowed the aircraft to get to a higher - more efficient - altitude sooner.

Absolutely, the quicker you get to altitude the sooner you will be burning less fuel.



The best contribution to safety is a competent Pilot.
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 79
Reply 7, posted (2 years 5 months 1 week 3 days 23 hours ago) and read 4387 times:

Quoting musang (Reply 5):

The wear on the engine rises disproportionately as temperature increases, and I believe (I'm only a pilot) that the heat in the turbine section is the critical issue.

Specifically, the turbine inlet temperature (the temperature at the back of the combustor). This is the hottest portion of the engine gas path (the igniter is hotter but that's contained). Material wear is extremely non-linear with temperature, especially in modern engines where the turbine inlet temperature can be well above the melting temperature of the turbine and turbine nozzle materials. This means that they're hypersensitive to the performance of the cooling system and protective coatings.

Tom.


User currently offlineSchorschNG From Germany, joined Sep 2010, 500 posts, RR: 0
Reply 8, posted (2 years 5 months 1 week 2 days 22 hours ago) and read 4164 times:

Quoting Max Q (Reply 6):

Absolutely, the quicker you get to altitude the sooner you will be burning less fuel.

But fuel is only one thing.
I think the cost optimum depends on the type on engine, and I could think that the engines of the B757/767 are less forgiving and long-living than the current CFM56-5/7. Just a guess though.



From a structural standpoint, passengers are the worst possible payload. [Michael Chun-Yung Niu]
User currently offlinelrgt From United States of America, joined Jul 2004, 710 posts, RR: 0
Reply 9, posted (2 years 5 months 1 week 1 day 22 hours ago) and read 3914 times:

Quoting musang (Reply 5):
How much throttle (or thrust) pilots will use on take-off or climb, or indeed cruise, is computer calculated for each flight, taking many variables into consideration. Pilot just enters the weight, temperature, wind, runway, pressure etc. etc. and the appropriate thrust settings are presented by the Flight Management Computer and fed to the autothrust system, varying with altitude during the climb. Its transparent to the pilots, they wouldn't be conciously using less thrust because they have winglets. It just happens.

In very general terms, if you installed winglets without telling the FMC that the aircraft had them, so it calculated the same old thrust settings as before, the aircraft would take off after a slightly shorter run, climb at a higher rate, find that it needed a lower thrust setting for the same cruise speed, and have a bit of trouble descending from the (wrongly) predicted Top of Descent point (because for a given calculated descent speed, the wing is now producing slightly more lift than the FMC knows about. The correct TOD for the winglets should have been earlier).

This concerns me a little from a safety perspective that pilots perhaps are perhaps not receiving enough training on differences with winglets... since the "computer handles all the changes... GENERALLY"

1. When autopilot is turned off, do the pilots really understand the differences with the winglets? (particularly at small carriers that perhaps have weak differences training for winglets on 752/763 types.

2. MOST importantly... do the pilots understand the effect winglets have on landing, which is necessary to slow the a/c down in time and not to overshoot the runway. So far, I've not heard of an incident with this happening with a 752WL or 763WL, but I still see it as a huge concern.

On landing, while not a fuel saving strategy, don't pilots need to keep the nose gear high-off the pavement longer on landing, since winglets make it harder to stop an airplane with a certain (flat/near-flat) angle of attack? Don't procedures need to be done to keep the angle-of-attack high for as long as possible, even with the rear wheels already on the ground? (in order for distance of runway used to stop to remain the same versus a non-wingleted 752/763).

Even if a pilot is well trained on this, a safety issue could still come up when that pilot flies wingleted and non-wingleted aircraft of the same type, and can easily forget that he has winglets, or what to do differently. Thankfully most airlines have been quick about deploying them across their fleet in a matter of months (save Delta's 763's, which are still not all done, and smaller operators with mixed fleets).

Not to pick on DL, but if a DL pilot flying a 76P with winglets (76P's can be non-ER, but all have ETOPS I believe, and are getting winglets before 76Q's) into OGG is used to flying 76Q's (mostly non-wingleted, but otherwise the same 767-300 aircraft), could he not have a little trouble stopping in time at OGG if he forgets about the WL's?



Don't bring up the NW DC9's unless you have to!
User currently offlinemandala499 From Indonesia, joined Aug 2001, 6872 posts, RR: 75
Reply 10, posted (2 years 5 months 1 week 1 day 22 hours ago) and read 3886 times:

Quoting lrgt (Reply 9):
2. MOST importantly... do the pilots understand the effect winglets have on landing, which is necessary to slow the a/c down in time and not to overshoot the runway. So far, I've not heard of an incident with this happening with a 752WL or 763WL, but I still see it as a huge concern.

Land positively, check spoilers up and derotate promptly, let the spoilers and wheelbrakes do the work. Keeping nose up for long = not enough weight on wheels = ineffective braking. Use autobrakes for immediate brake action as soon as aircraft is on the ground, no delays caused by delays in stepping on the brakes... all standard methods really...

Once your nose is down, spoilers up... winglet or not... makes little difference.

Make sure you're dispatched with the correct fuel burn for the correct landing weight, using the correct landing distance tables (winglets or non winglets)... dispatch landing distance tables are factored so you'd only need 2/3 of the distance if nothing goes wrong.



When losing situational awareness, pray Cumulus Granitus isn't nearby !
User currently offlinelrgt From United States of America, joined Jul 2004, 710 posts, RR: 0
Reply 11, posted (2 years 5 months 1 week 1 day 19 hours ago) and read 3833 times:

Quoting mandala499 (Reply 10):
Land positively, check spoilers up and derotate promptly, let the spoilers and wheelbrakes do the work. Keeping nose up for long = not enough weight on wheels = ineffective braking. Use autobrakes for immediate brake action as soon as aircraft is on the ground, no delays caused by delays in stepping on the brakes... all standard methods really...

Once your nose is down, spoilers up... winglet or not... makes little difference.

Make sure you're dispatched with the correct fuel burn for the correct landing weight, using the correct landing distance tables (winglets or non winglets)... dispatch landing distance tables are factored so you'd only need 2/3 of the distance if nothing goes wrong.

I've still heard you should keep the nose SLIGHTLY off the ground longer with WL aircraft. This is one of the things the A330 auto-land does automatically I've also heard, but the pilots need to do it manually on 757/767.

I would assume that manually keeping the nose ever so slightly off the ground while maintaining enough friction-breaking is difficult, and could mean a slower stop if there's not enough weight on the main gear.

But I'm not a pilot, and the DL pilot telling me this perhaps was wrong.



Don't bring up the NW DC9's unless you have to!
User currently offlinepilotpip From United States of America, joined Sep 2003, 3150 posts, RR: 10
Reply 12, posted (2 years 5 months 1 week 1 day 19 hours ago) and read 3813 times:

The criteria set forth within an airline's SOP for landing, winglets or not, is the same. While their may be some differences in handling, I believe the 757 has a lower max crosswind component when equipped with winglets, this doesn't change what we have to do to make a safe landing within standards. A proper touchdown within the touchdown zone, prompt lowering of the nose to maintain directional control and steady braking for deceleration are all the same regardless of how the aircraft is equipped.


DMI
User currently offlinemandala499 From Indonesia, joined Aug 2001, 6872 posts, RR: 75
Reply 13, posted (2 years 5 months 1 week 1 day 17 hours ago) and read 3793 times:

Quoting lrgt (Reply 11):
I've still heard you should keep the nose SLIGHTLY off the ground longer with WL aircraft. This is one of the things the A330 auto-land does automatically I've also heard, but the pilots need to do it manually on 757/767.

On the 320/330/340, once you're on the ground, the trim unloads itself (less aircraft nose up position down to neutral) to assist in derotation.
On 320/330/340, on flare mode, the aircraft itself induces a nosedown command, this is to simulate a need to flare by pulling on the stick.
On 320/330/340, on autoland, the aircraft flares automatically (and you should idle the throttles when called for), and aircraft derotates. But, if you don't watch out, sometimes, yes, your nose can come banging down and do a nose bounce... but that's being picky   

On wingleted aircraft, it weathervanes a bit more than non-wingletted aircraft. So in crosswind landings, why keep your nose up, with reduced visibility, and rely on the rudder only? Get the nose down, better visibility of the ground, and steer using the pedals at the high speed regime with the rudder AND the nosewheel (coupled).

Quoting lrgt (Reply 11):
But I'm not a pilot, and the DL pilot telling me this perhaps was wrong.

I'd like to see the DL guys keep the nose up on those gusty stormy crosswind conditions at Narita... (especially at the shorter one!    ). You might end up with a tailscrape instead!

Being a pilot ain't easy (although enjoyable), but careful... some pilots love to make it look a heck of a lot harder than it actually is, to non pilots... it's err... an ego-boost (probably born out of ADD) for some!   

Mandala499



When losing situational awareness, pray Cumulus Granitus isn't nearby !
User currently offlinePGNCS From United States of America, joined Apr 2007, 2825 posts, RR: 45
Reply 14, posted (2 years 5 months 1 week 1 day 14 hours ago) and read 3745 times:

Quoting lrgt (Reply 9):
This concerns me a little from a safety perspective that pilots perhaps are perhaps not receiving enough training on differences with winglets... since the "computer handles all the changes... GENERALLY"

Based on what?

Quoting lrgt (Reply 9):
MOST importantly... do the pilots understand the effect winglets have on landing, which is necessary to slow the a/c down in time and not to overshoot the runway. So far, I've not heard of an incident with this happening with a 752WL or 763WL, but I still see it as a huge concern.

You are making a huge issue out of a very minor one. I have flown the 757, 767-200, and 767-300ER all in one day without issue. The handling differences are vastly more pronounced between any 757 and any 767 than is induced by the presence of winglets. I am curious as to your assertion that this is a "huge concern" and your evidence that it has not been trained properly.

Quoting lrgt (Reply 9):
Even if a pilot is well trained on this, a safety issue could still come up when that pilot flies wingleted and non-wingleted aircraft of the same type, and can easily forget that he has winglets, or what to do differently.

See above.

Quoting lrgt (Reply 9):
Not to pick on DL, but if a DL pilot flying a 76P with winglets (76P's can be non-ER, but all have ETOPS I believe, and are getting winglets before 76Q's) into OGG is used to flying 76Q's (mostly non-wingleted, but otherwise the same 767-300 aircraft), could he not have a little trouble stopping in time at OGG if he forgets about the WL's?

Again, you have evidence of this problem from where?


User currently offlineMax Q From United States of America, joined May 2001, 4525 posts, RR: 18
Reply 15, posted (2 years 5 months 1 week 1 day 7 hours ago) and read 3663 times:

Quoting PGNCS (Reply 14):

You are making a huge issue out of a very minor one. I have flown the 757, 767-200, and 767-300ER all in one day without issue. The handling differences are vastly more pronounced between any 757 and any 767 than is induced by the presence of winglets. I am curious as to your assertion that this is a "huge concern" and your evidence that it has not been trained properly.

I could not agree more

Quoting PGNCS (Reply 14):
Again, you have evidence of this problem from where?

I was wondering the same thing !



The best contribution to safety is a competent Pilot.
User currently offlineJetlagged From United Kingdom, joined Jan 2005, 2556 posts, RR: 24
Reply 16, posted (2 years 5 months 1 week 23 hours ago) and read 3571 times:

Quoting musang (Reply 5):
In very general terms, if you installed winglets without telling the FMC that the aircraft had them, so it calculated the same old thrust settings as before, the aircraft would take off after a slightly shorter run, climb at a higher rate, find that it needed a lower thrust setting for the same cruise speed, and have a bit of trouble descending from the (wrongly) predicted Top of Descent point (because for a given calculated descent speed, the wing is now producing slightly more lift than the FMC knows about. The correct TOD for the winglets should have been earlier)

I don't think modifying the FMC performance data for winglets should or will have any effect on calculated engine thrust ratings. Anyway in the 767 and 757 these limits aren't computed by the FMC. What might be different with winglet data is the FMC performance models used to calculate climb, cruise and descent speeds and optimum altitudes. Obviously it will affect Cost Index calculations too. But essentially you could climb, cruise and descend at the same speeds, winglets on or off. The only difference would be the fuel burn.

The FMC (or TMS for 767/757) doesn't compute a thrust setting for cruise. It computes a cruise thrust limit of course, but the FMC computes the cruise Mach No and the autothrottle sets thrust to achieve it. The FMC needs to know the aircraft will burn less fuel at that speed than it would without winglets of course. As you say, it certainly needs to know the aircraft has less drag for the descent calculaitons.

Basically, by adding winglets you've changed lift and drag, not thrust limits.



The glass isn't half empty, or half full, it's twice as big as it needs to be.
User currently offlinemandala499 From Indonesia, joined Aug 2001, 6872 posts, RR: 75
Reply 17, posted (2 years 5 months 1 week 22 hours ago) and read 3549 times:

Quoting Jetlagged (Reply 16):
Obviously it will affect Cost Index calculations too. But essentially you could climb, cruise and descend at the same speeds, winglets on or off. The only difference would be the fuel burn.

Yes... the vertical trajectories have changed.
For the same weight and thrust setting you can now get up there faster... and stay higher... and need a bit longer to descend... result... lower burn.
ECON speed will be based on the CI... so it's the CI that may change, but that's a policy issue. right?



When losing situational awareness, pray Cumulus Granitus isn't nearby !
User currently offlineJetlagged From United Kingdom, joined Jan 2005, 2556 posts, RR: 24
Reply 18, posted (2 years 5 months 1 week 18 hours ago) and read 3483 times:

Quoting mandala499 (Reply 17):
ECON speed will be based on the CI... so it's the CI that may change, but that's a policy issue. right?

Yes you're right, my mistake. CI doesn't take account of fuel burn as such, just fuel cost.



The glass isn't half empty, or half full, it's twice as big as it needs to be.
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