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Aileron Rigging Of 767-300ER With Retrofit Winglet  
User currently offlineJaggySnake From United Kingdom, joined Oct 2012, 6 posts, RR: 0
Posted (1 year 8 months 11 hours ago) and read 4612 times:

Hey,

As part of the installation process of retrofit APB blended wingets on 767-300ER aircraft, the outer ailerons are rigged upwards by one degree.

An idea I have as to the possible reason for this is to increase the lift at the outer wing thus alleviating some of the load and improving the lift distribution.

Is this correct, or does anyone know the real reason?

Thanks

17 replies: All unread, jump to last
 
User currently onlineMax Q From United States of America, joined May 2001, 4511 posts, RR: 18
Reply 1, posted (1 year 8 months 4 hours ago) and read 4466 times:

Why would that increase the lift ?


Rigging both outboard Ailerons up slightly would decrease the lift on the outer wing.


This would help unload that section.


Maybe that is what you meant ?



The best contribution to safety is a competent Pilot.
User currently offlineT prop From United States of America, joined Apr 2001, 1029 posts, RR: 1
Reply 2, posted (1 year 7 months 4 weeks 1 day 23 hours ago) and read 4373 times:

To lower drag.

I know a guy who tried this on his own little Piper, he had heard about it and wanted to try it. He said the airplane picked up 2 knots with the same power settings. BTW, what the guy did is NOT an approved procedure.


User currently offlineStarlionblue From Greenland, joined Feb 2004, 17038 posts, RR: 66
Reply 3, posted (1 year 7 months 4 weeks 1 day 23 hours ago) and read 4370 times:

Quoting T prop (Reply 2):
I know a guy who tried this on his own little Piper, he had heard about it and wanted to try it. He said the airplane picked up 2 knots with the same power settings. BTW, what the guy did is NOT an approved procedure.

Wow that's clever. Remind me never to fly with him...



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlinerwessel From United States of America, joined Jan 2007, 2351 posts, RR: 2
Reply 4, posted (1 year 7 months 4 weeks 1 day 22 hours ago) and read 4360 times:
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Quoting T prop (Reply 2):
I know a guy who tried this on his own little Piper, he had heard about it and wanted to try it. He said the airplane picked up 2 knots with the same power settings. BTW, what the guy did is NOT an approved procedure.

On many sailplanes with flaps you can set to flaps to a small negative setting (-5 degrees is common) to reduce drag at higher speeds. It can also help aileron effectiveness at the beginning of the takeoff run or end of the rollout (where you’re trying to keep the wingtips out of the grass) where the negative setting effectively reduces the incidence of the wingtip and you get non-separated flow past the ailerons* a bit sooner. Although if you do that, you need to drop the flaps to the takeoff position** early during the takeoff ground roll, which is why it’s often not a recommended procedure. That being said it was pretty much required on some of the early super-span ships like the Nimbus 1 and 2.


*on most gliders the ailerons move with the flaps

**zero degrees on most gliders


User currently offlineJaggySnake From United Kingdom, joined Oct 2012, 6 posts, RR: 0
Reply 5, posted (1 year 7 months 4 weeks 1 day 17 hours ago) and read 4322 times:

Quoting Max Q (Reply 1):

Yeah.. I wasn't really thinking straight.    So less lift is generated at the outer wings, why would this be an advantage? Less lift means less induced drag but I can't see any other reason why any other component of drag would be reduced.

Thanks for the replies, it's interesting to hear that this is often done on other a/c.

On the 767, do you think the aileron rigging is necessarily part of the winglet installation, or is it just a general drag reduction improvement which is convenient to carry out during the winglet mod?


User currently offlineStarlionblue From Greenland, joined Feb 2004, 17038 posts, RR: 66
Reply 6, posted (1 year 7 months 4 weeks 1 day 17 hours ago) and read 4321 times:

Quoting JaggySnake (Reply 5):
Yeah.. I wasn't really thinking straight.    So less lift is generated at the outer wings, why would this be an advantage? Less lift means less induced drag but I can't see any other reason why any other component of drag would be reduced.

Unless I'm mistaken, the aileron means more stress on the outer wing. Since the wing wasn't designed for this originally the winglet retrofit might mean you need less stress on the outer wing.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlinejetmech From Australia, joined Mar 2006, 2699 posts, RR: 53
Reply 7, posted (1 year 7 months 4 weeks 23 hours ago) and read 4134 times:

Quoting Max Q (Reply 1):
This would help unload that section.
Quoting JaggySnake (Reply 5):
Quoting Starlionblue (Reply 6):
Unless I'm mistaken, the aileron means more stress on the outer wing. Since the wing wasn't designed for this originally the winglet retrofit might mean you need less stress on the outer wing.

The re-rigging of the ailerons for structural and aerodynamic reasons both make sense to me.

Winglets and raked wingtips physically add span to the wing. From my intuitive point of view, this allows the aerodynamicist to do one of, or a combination of two things;

(1) Run slightly less lift coefficient at any span-wise station for a given overall lift force.
(2) Provide a greater span near the wing tip in order to "taper" off the lift distribution.

The ultimate aim being the provision of an elliptical lift distribution across the span which in turn, results in the minimum induced drag. For either option, the lift distribution at the outboard aileron would be less than that of the original wing, hence the re-rigging of the ailerons to produce less lift at that span-wise location.

Regards, JetMech



JetMech split the back of his pants. He can feel the wind in his hair.
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 79
Reply 8, posted (1 year 7 months 3 weeks 6 days 22 hours ago) and read 3931 times:

Quoting JaggySnake (Thread starter):
An idea I have as to the possible reason for this is to increase the lift at the outer wing thus alleviating some of the load and improving the lift distribution.

The winglet alters the flow around the airplane. I suspect they're just re-aligning the aileron to the most advantageous neutral position given the new flowfield.

Quoting JaggySnake (Reply 5):
So less lift is generated at the outer wings, why would this be an advantage? Less lift means less induced drag but I can't see any other reason why any other component of drag would be reduced.

If less lift is generated outboard, more must be generated inboard. Moving lift inboard is generally good since the wing structure is stronger there and it's farther from the wingtips so the induced drag isn't as bad.

Quoting jetmech (Reply 7):
The ultimate aim being the provision of an elliptical lift distribution across the span which in turn, results in the minimum induced drag.

Very few aircraft run an elliptical lift distribution, or even want to, because even though it gives you the minimum induced drag *for that lift*, it forces you to design a heavier wing, forcing you to generate more total lift, which causes more induced drag, which eats the gain you initially got by having a good lift distribution. Swept-wing transonic airliners are a lot closer to triangular lift distribution than elliptic.

Tom.


User currently offlineJaggySnake From United Kingdom, joined Oct 2012, 6 posts, RR: 0
Reply 9, posted (1 year 7 months 3 weeks 6 days 11 hours ago) and read 3854 times:

Quoting tdscanuck (Reply 8):
Quoting JaggySnake (Reply 5):
So less lift is generated at the outer wings, why would this be an advantage? Less lift means less induced drag but I can't see any other reason why any other component of drag would be reduced.

If less lift is generated outboard, more must be generated inboard. Moving lift inboard is generally good since the wing structure is stronger there and it's farther from the wingtips so the induced drag isn't as bad.


Right, but reducing lift on the outboard isn't going to produce any more lift over the rest of the wing. Unless the aeroelastics are changed to such an extent that alters the lift distribution. And no other aerodynamic changes are made other than adding a few vortex generators to the slats.


User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 79
Reply 10, posted (1 year 7 months 3 weeks 6 days 5 hours ago) and read 3791 times:

Quoting JaggySnake (Reply 9):
Right, but reducing lift on the outboard isn't going to produce any more lift over the rest of the wing.

Not inherently, no. But if you lower the outboard lift you're going to have to fly at higher AoA, which will raise lift all along the wing, until you're back up to lift=weight. Lowering outboard lift will increase inboard lift for the same flight condition.

Tom.


User currently offlineBE77 From Canada, joined Nov 2007, 455 posts, RR: 0
Reply 11, posted (1 year 7 months 3 weeks 4 days 14 hours ago) and read 3619 times:

Here's a list of considerations that may apply"
- the winglet makes the wing more efficient (which is why it is there).
- most wings have a lot more lift potential than what is required for cruise
- most wings have an incidence angle / angle of attack (AOA) that is a compromise between slow and cruise flight
- many ailerons can be set to negative settings for decreaded lift / increase cruise performance
- many ailerons get 'drooped' with flaps for additional lift at low speed

If you add all these up, it could be something along the lines of:
Adding the winglets increased the wing performance. The new performance at low speeds was enough to provide more than the required performance at those speeds (so now the AOA compromise is skewed more to the slow speed end).
Since the wing would now generate more lift than needed at cruise, would would have to trim the nose down a bit more than designed, and so now you might be creating induced drag because the fuselage is no longer aligned with the airflow. In the A380 I believe that they actually changed the AOA / wing incidence angle between the wing and fuselage for newer line numbers after they got real performance data.
Since changeing the relative angle of the wing to the fuselage is challenging(!) for an airliner already built, and it might be overkill anyway for the effects of a winglet, look for other ways to manage wing lift.
Dialing in a little negative aileron is a tried and true (and easy) way to decrease cruise lift (and drag) if you found some extra from somewhere else.

The guy in the Piper is certainly playing test pilot, but the 2 knots are probably real, and it would probably be barely noticeable looking at the ailerons (and might possibly be within service limits anyway - depends on how much he moved it and what the specs are for his model). He should probably pay a little more attention to low speed manuevers - but depending on what Piper it is there might be 10 other things that affect the performance more than aileron pitch - CG, current state of the horizontal stab, trueness of the airframe, hangar rash, and so on. (For model of piper I'm hoping it was a Cherokee or derivative - if it's a Malibu or something then he's an idiot, not a test pilot, and needs to read about all the aerodynamic things that can go wrong fast with no warning at higher speeds).
Minor 'real world' differences like this are a real part of the reason why no two airplanes of any model (Cub through to A380) fly exactly the same. It doesn't mean you should mess with things of course, but, a lot of these things get out of trim naturally, which is why they get checked inspected, and why there is a tolerance set.



Tower, Affirmitive, gear is down and welded
User currently offlineJaggySnake From United Kingdom, joined Oct 2012, 6 posts, RR: 0
Reply 12, posted (1 year 7 months 3 weeks 3 days 18 hours ago) and read 3539 times:

Great answer, BE77. Thanks for the contribution

User currently offlineT prop From United States of America, joined Apr 2001, 1029 posts, RR: 1
Reply 13, posted (1 year 7 months 3 weeks 2 days 23 hours ago) and read 3433 times:

Quoting BE77 (Reply 11):
(For model of piper I'm hoping it was a Cherokee or derivative - if it's a Malibu or something then he's an idiot, not a test pilot, and needs to read about all the aerodynamic things that can go wrong fast with no warning at higher speeds).

Yes, it was an older model PA-28...


User currently offlineSFOMB67 From United States of America, joined Dec 2005, 417 posts, RR: 0
Reply 14, posted (1 year 7 months 3 weeks 2 days 22 hours ago) and read 3420 times:

Wouldn't rigging neutral up one degree result in one degree less aileron up travel and add one degree down travel? Generally the actuators have a set amount of travel, unless they replace the actuators.


Not as easy as originally perceived
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 79
Reply 15, posted (1 year 7 months 3 weeks 2 days 10 hours ago) and read 3338 times:

Quoting SFOMB67 (Reply 14):
Wouldn't rigging neutral up one degree result in one degree less aileron up travel and add one degree down travel?

It depends on how you change the rigging and how much of the envelope you're using. If you just change the cable rig to move the actuator neutral point then yes, you'd bias the total envelope up by one degree. However, that would only matter if the flight controls are capable of commanding full actuator throw and I strongly suspect that isn't the case (it's generally bad to run actuators into their end stops).

You could also do it by altering the relationship between the aileron and actuator, then the actuator still has the same range of motion as before.

Tom.


User currently offlinejetmech From Australia, joined Mar 2006, 2699 posts, RR: 53
Reply 16, posted (1 year 7 months 2 weeks 6 days ago) and read 3117 times:

Quoting tdscanuck (Reply 8):
Very few aircraft run an elliptical lift distribution, or even want to, because even though it gives you the minimum induced drag *for that lift*

Certainly, and I did overlook this aspect.

Quoting tdscanuck (Reply 8):
Swept-wing transonic airliners are a lot closer to triangular lift distribution than elliptic.

Interesting. So, no matter the specific lift distribution used, what would the primary purpose be for winglets or extended (raked) wingtips?

My intuitive thoughts are that the extra span allows one to more gradually "taper" off the lift distribution towards the wingtip region. This would then have the effect of reducing the spanwise components of flow near the tip region, and hence reduce the intensity of the wing tip vortices, which appears to be the dominant source of vorticity shed off the wing as a whole.

I suppose the other way tip devices could reduce the induced drag is by allowing one to run a reduced lift coefficient along the entire span of the wing. This may then reduce the intensity of the vortex sheet as a whole, instead of just concentrating on the tip region.

Regards, JetMech



JetMech split the back of his pants. He can feel the wind in his hair.
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 79
Reply 17, posted (1 year 7 months 2 weeks 5 days 23 hours ago) and read 3110 times:

Quoting jetmech (Reply 16):
So, no matter the specific lift distribution used, what would the primary purpose be for winglets or extended (raked) wingtips?

Reduce induced drag. It makes the wing act like it has a higher aspect ratio than it actually does. Mathmatically, you can think of it as pushing e (Oswald's Efficiency Factor) higher (http://en.wikipedia.org/wiki/Oswald_efficiency_number).

Quoting jetmech (Reply 16):
My intuitive thoughts are that the extra span allows one to more gradually "taper" off the lift distribution towards the wingtip region. This would then have the effect of reducing the spanwise components of flow near the tip region, and hence reduce the intensity of the wing tip vortices, which appears to be the dominant source of vorticity shed off the wing as a whole.

Vorticity comes off the entire wing trailing edge as a vortex sheet. The strength depends on both the spanwise direction and the amount of lift at that location (i.e. the lift distribution). Reduction of the vortices at the tip isn't that effective...this is why flat fences like the A320/330/340 or MD-11 or 747-400 aren't nearly as effective as larger winglets or braked tips.

Quoting jetmech (Reply 16):
I suppose the other way tip devices could reduce the induced drag is by allowing one to run a reduced lift coefficient along the entire span of the wing. This may then reduce the intensity of the vortex sheet as a whole, instead of just concentrating on the tip region.

This is basically what happens, although the chain of causation goes in a different direction. The effect is more on C_Di than on C_L. The winglet reduces the strength of the shed vorticity by distributing the same lift across a longer trailing edge, which reduces the downwash at all points on the wing, which reduces the angle that the lift vector tips back. Since that angle is typically small, the effect on lift is also small (though not zero). The effect on drag is more pronounced.

Tom.


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