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Effect of Retrofitted Winglets on 767 Handling

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Effect of Retrofitted Winglets on 767 Handling

Old 16th Oct 2012, 04:10
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fish Effect of Retrofitted Winglets on 767 Handling

I recently posted the same thread on Airliners.net, so apologies if anyone's reading this twice, but I wanted to get the largest possible amount of opinions.


I'm on an internship (for my final year thesis) at an MRO doing a study of blended winglets, in particular, those installed onto the 767-300ER.

I am interested to hear some views from current Flight Crew on any effects the installation of winglets has on the handling characteristics of the plane.
I have already spoken to a UA test pilot who was recently performing the post-mod test flight on one of their a/c and he suggested that there is little noticeable difference to the way the a/c handles following winglet installation. He did however admit that he wasn't the best person for me to ask as he does not exclusively fly the 767s.

I'm thinking that by adding these devices - they're really quite substantial on the 767-300 - there could be an increase to the dihedral effect of the wing adding some extra roll damping?

As the effective aspect ratio is increased, the Mean Aerodynamic Chord is perhaps shifted towards the tips slightly? Combining that with the presumed aftwards shift of the longitudinal centre of gravity due to the winglet's weight, are there any performance implications upon take-off/landing which are at all noticeable?

As pointed out to me, no further type-rating is required for pilots to fly these modified 767, but I just find it slightly difficult to believe that these devices go completely unnoticed from the controls. I'm certainly not a pilot so any views from current flight crew would be welcome!
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Old 16th Oct 2012, 10:07
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Old 16th Oct 2012, 10:42
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I know you asked about the 767 in particular but for some comparison I fly the 737-800. I certainly couldn't notice any difference in handling before and after perhaps apart from taking slightly more time to decelerate but it is a slippy aircraft anyway.
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Old 16th Oct 2012, 11:24
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Don't think I'm good enough to spot any real handling differences, except that if you do a normal flare you float for ages. They seem to need less flare/a flatter landing attitude.
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Old 16th Oct 2012, 13:18
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Less drag. Tougher to deaccelerate, more inclined to float in ground effect.

Shallower descent profile. If you have an unmodified FMC(no 'W' next to a/c type) you'll get fast("drag required").
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Old 16th Oct 2012, 13:33
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I believe aircraft with winglets are approved for 2 or 3kts less crosswind limit due to the extra surface area perpendicular to the wind.
That seems rather unlikely, seeing as the surface area of even the largest winglet is really minuscule compared to the (lateral) surface area of the fuselage. Even if they did make a difference then that would only affect gust limits, as a steady crosswind will have the same effect on any aircraft, regardless of shape or even size.

Last edited by Dg800; 16th Oct 2012 at 13:33.
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Old 16th Oct 2012, 14:35
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Our landing crosswind limit is the same for 737s with winglets and those without (40kts on dry and wet). Take off crosswind limit however is different as the NG with winglets is only demonstrated to 34kts and in my company that is now a fixed limit including any gusts whereas aircraft without limit have a take off crosswind limit of 36kts. So there is a difference of 2kts for take off, none for landing in my outfit.
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Old 17th Oct 2012, 02:32
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Thumbs up

OK, these replies are useful. I realise the effect will be minimal but I'm just looking for anything which will add depth to my report. Any further comments are always welcome!
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Old 17th Oct 2012, 06:25
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40kts is a fair old crosswind Denti.
My outfit has a 33kt crosswind limit dry for both takeoff and landing, and 25kts wet. (737-800)
I would be interested to hear if a 40kt limit is common from other -800 pilots.
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Old 17th Oct 2012, 07:55
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Actually, it is kinda new to us, we used to have a common take off and landing crosswind limit, but it got changed around a year ago into different ones for landing and take off. Remember though that those limits are including gusts, not steady wind and are applicable to narrow runway operation as well. A 25 kts crosswind limit on a wet runway is fairly low though considering that the autoland crosswind limit is 25kts as well (doesn't matter if wet or dry). Only single engine autoland crosswind limit is lower at 20kts.
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Old 17th Oct 2012, 08:35
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Hi Fergus,

Our fleet of 767 300s has both winglet and non-winglet aircraft and we regularly fly both. We use them for both long-haul and short-haul. The only differences I've noticed on normal revenue flights are the winglet aircraft are more slippery. If you need engine anti-ice in the descent its almost certain you'll also need speedbrake with a winglet jet. The fuel economy on long sectors is also better with winglets, less so on short sectors, probably due to the extra weight of the winglets not being offset by the lower drag on a short flight.

The fine differences in roll stability and cross wind landing behaviour are not noticeable in line flying. They probably exist but you'd need to do a test programme between identical jets apart from the winglets to find out. The biggest differences in practice are between flying a heavy jet (180000Kg) or a light one (100000Kg). Landing, we have the option of F25 or F30 landings (Company prefer F25 unless good reason for F30) which make more difference in handling than winglets or non-winglets. There is no difference in cross wind limits and I haven't noticed any difference in behaviour. Not to say there isn't any but to notice it you'd need to land a winglet jet, then land a non-winglet on the same runway with the same conditions. That obviously never happens in normal line operations.

Sorry that doesn't help your thesis much but best of luck.

Last edited by Beakor; 17th Oct 2012 at 08:37.
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Old 18th Oct 2012, 04:17
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Thanks for the informative reply, Breakor. Excuse my ignorance, but what is the relation between requiring anti-ice and needing to apply speed-brake? [Air temp is low, so air is more dense therefore more lift which needs to be ditched by deploying air-brake? ]

This does help my thesis in that I can state with confidence that the winglets don't significantly affect a/c handling. Until now I've been unable to find any reports on this particular subject.

Also, your 2nd paragraph is definitely useful in demonstrating how countless different conditions and parameter mean that no one landing or flight is directly comparable to another.

Last edited by Jaggy_Snake; 18th Oct 2012 at 04:21.
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Old 18th Oct 2012, 06:53
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Excuse my ignorance, but what is the relation between requiring anti-ice and needing to apply speed-brake? [Air temp is low, so air is more dense therefore more lift which needs to be ditched by deploying air-brake? ]
Anti ice on the 767 requires bleed air, this means a higher idle setting which means more residual thrust....
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Old 18th Oct 2012, 07:02
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Originally Posted by Jaggy_Snake
Excuse my ignorance, but what is the relation between requiring anti-ice and needing to apply speed-brake?
Most jet airliners use bleed air from the engines for deicing which means you need to carry extra power in icing conditions & the reduced drag of the winglet-fitted airframes means you are more likely to need to deploy a little speedbrake to offset the extra power.
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Old 19th Oct 2012, 10:35
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I flew B737-700 before and after installation of winglets. I never detected the slightest difference in any handling, and they were quite large- 2 metres, I believe. Some of my colleagues claimed they did detect a difference, but I think it was more in their imagination. I also flew B747s early models without winglets, and the -400 with. Again no difference you can notice. We used to occasionally fly the -400 with a winglet removed- absolutely no difference. It's like filling your car with standard or super petrol- absolutely no detectable difference so take the cheaper one! Though there's always smart ones who claim they can feel the difference!
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Old 31st May 2013, 14:34
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alot of info for you

Go check out APB (aviation partners Boeing) website, they are the division of boeing that created the winglets and they have a ton of info about them. Im a mechanic working for Delta Airlines installing winglets currently on the UPS fleet. I know UPS also has a winglet line in hong kong currently installing on the other half of their fleet. You should try to get a tour to check out the install, its impressive! Good luck with your theisis
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Old 5th Jun 2013, 11:00
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Jaggy, some thoughts from a flight test specialist:

the winglets are nearer vertical than horizontal, so their contribution to lateral stability will be tiny. They will shift the lateral position of the centre of pressure outboard slightly, but the shift will be very small - think how much wing area is inboard compard to outboard, and also remember the CL distribution along the wing span favours the inboard part of the wing also, so changes to the tips do very little to the lift distribution as a whole.

Longitudinal CG change will be negligible compared to other factors such as fuel, cargo and passenger distribution in the aircraft.

The winglets main function is to extract some energy fom the tip vortex that would otherwise be lost, and convert it to a small forward thrust force. They also slightly increase the wing efficiency factor, thus reducing induced drag and increasing the L/D ratio. This gives increased range and less fuel burn for a given sector, which saves operators a lot of money, as I am sure you know! This also will affect climb and descent peformance, and potentially takeoff and landing performance, hence the need for a different performance database in the FMS for some aircraft types when winglets are fitted.

As for changes to cross-wind limits, it may be that the flight manual limits are simply that which has been demonstrated by the test team, thus they can gaurantee the aircraft's handling characteristics will remain safe and within certification limits.

Aerodynamically it is hard to see why crosswind limits should be different with/without winglets, unless they are affecting directional stability, which could be possible given their size and orientation. If they make the aircraft slightly more directionally stable, then it would be harder to kick off the drift for a crosswind landing, hence the slight reduction in the crosswind limit.

Hope this helps.
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Old 5th Jun 2013, 12:41
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Hi WF,

I thought winglets worked by reducing the drag of the wingtip vortex, and this is how they improve efficiency?

Do they really produce thrust from the vortices as well? Can you explain how? I am not having a go, I am genuinely curious.

I would imagine that the increased vertical area of the winglets would affect crosswind performance - they are large vertical surfaces which would generate more sideways force from the crosswind than an aircraft without them?
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Old 6th Jun 2013, 05:58
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I fly both winglet and non-winglet 300er versions and don't have much to add to what's been said already, except that the winglet machines look really sexy!!
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Old 6th Jun 2013, 11:58
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Winglets and Vortices

Uplinker,

as I understand it, tip vortices take a lot of energy from the aircraft because previously still air becomes rapidly spinning air. That increase in Kinetic energy has to come from somewhere, and ultimately it manifests itself as induced drag. Force * velocity = power = energy per second, so the induced drag force * TAS gives you an idea of the rate of energy transfer from the aircraft to the air. This energy transfer creates the vortices, the upwash ahead of the leading edge and outside the wing tips, and the downwash behind the wing.

The vortices are caused by high pressure air beneath the wing forcing its way around the wingtips to try and fill the low pressure area above the wing. This causes airflow towards the wingtips from underneath, and away from the wingtips on the top of the wing. Adding this span-wise velocity component with the velocity of the air coming towards the wing and you get tip vortices.

Winglets exploit the vortices by taking the flow from the top and fuselage-facing parts of the vortex and using it just like a normal wing uses the relative airflow - i.e to generate a lift force. However, for a winglet this force acts mostly horizontally towards the fuselage but also has a forward facing component. This "thrust" component cancels out some of the induced drag force, resulting in lower overall induced drag and thus could be argued to be a form of energy recovery from the vortices. The resulting vortices are therefore smaller and less energetic and the downwash is thus reduced. These changes are small, but enough to lead to significant fuel savings in the long run.


Regarding directional stability - yes, I suspect winglets have sufficient area in the vertical plane to cause a non-trivial sideforce at high sideslip angles. As this will be acting behind the aircraft CG it will cause a small increase in directional stability, which in turn could lead to a slightly lower crosswind limit for takeoff and landing to ensure directional control can be retained.

Hope this clarifies things a bit!

Last edited by WeekendFlyer; 11th Jun 2013 at 08:02. Reason: Spelling!
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