Wing tips up vs. Wing tips down

SixPapaCharlie

SixPapaCharlie

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Whats the different reasons?

Lately everything seems to be getting winglets added to it.
I see a lot of older planes with wingtops that bend down significantly.

I think I get the winglets especially on large Jets and I see now they are even adding split tips.

But what do they do differently?

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This one can't decide
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one is more (questionable) effective for slow flight....the other is for the cruise configuration (DA42).
 
STOL kit. Keeps the airflow under the wing instead of having a certain percentage be lost off the wing tips because of the perpendicular flow between the upper and lower airflow improving effeciency at lower speeds.

Wing tips on top try to solve the drag induced by the vortices coming off the trailing edge of the tip improving efficiency at higher speeds.
 
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Yeah, STOL kits. Ours droop but not that much. Looks like one of the newer kits that don't change as much stuff as our Robertson kit did.

In addition to droop tips, we have leading edge cuffs (pretty mild ones), stall fences on top of the wing, and the big change, ailerons that are interconnected with the flaps which make our entire wing one big flap to a certain point and then they ease back up so they're only slightly extended downward at full flap travel.
 
I had the droop tips on the Skytrasher.
 

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Boeing has it figured out with the new 737MAX winglets. I like the look better than the API winglets. Funny how Airbus has just started using sharklets and that makes them years behind what API did for boeing.
 
CC268 said:
The engineering behind these scimitar winglets is amazing...Aviation Partners designs these.
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These have always looked ugly to me. The 737 Max wiglets look so much better IMO.
 
They look cool, and everyone knows that looking cool = more flying magic.

Sent from my SM-G930T using Tapatalk
 
Most of the redbull air race planes are getting them. They must be doing something!
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The scimitar winglets (or any winglet for that matter) increase the effective aspect ratio and interrupt wing tip vortices which subsequently increases fuel efficiency. It also increases lift at the wing tip which can reduce takeoff distance, etc. They can also change handling characteristics quite drastically, which is probably why you see some of the Red Bull air planes experimenting with them. I had a friend in school who was doing some CFD analysis on it...pretty cool stuff but I am no expert on it - just picked up a few things along the way.

A good friend of mine is a Captain for Southwest airlines and he said they do have to be careful with those scimitar winglets in a stiff crosswind - he said they are limited to "wing low" crosswind corrections. So no low knife edge passes in the 737 unfortunately.
 
SixPapaCharlie said:
So, what do these do?
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Dissipate pressure flow back over the top of the wing, which reduces weight and makes the plane more fuel efficient because it's not working as hard to stay airborne. I suppose theoretically there's less wake turbulence too. Cool stuff.
 
CC268 said:
A good friend of mine is a Captain for Southwest airlines and he said they do have to be careful with those scimitar winglets in a stiff crosswind - he said they are limited to "wing low" crosswind corrections. So no low knife edge passes in the 737 unfortunately.
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There is 8'6" clearance with them vs about 11' without them. It changes the max crosswind component by about 4 knots if I recall correctly.

In a year and a half of flying the airplane, I have not come close to dragging a wingtip. Yes, it may be a bit of an issue, but it is pretty rare.
 
Greg Bockelman said:
There is 8'6" clearance with them vs about 11' without them. It changes the max crosswind component by about 4 knots if I recall correctly.

In a year and a half of flying the airplane, I have not come close to dragging a wingtip. Yes, it may be a bit of an issue, but it is pretty rare.
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Yea I didn't mean to say it was a big issue just repeating what my friend said.
 
Cessna aerodynamicist and test pilot Bill Thompson wrote that the company experimented with drooped wingtips in the late 1950s, based on British research from the 1930s to improve spiral stability. The concept involved something called "conical camber geometry". The Model 182 prototype was the test bed.

"The apex of our imaginary cone was a specific distance ahead of the wing tip's leading edge, and the base of the cone was at the wing tip's trailing edge. Thus the complex curvature of the tip was a portion of this imaginary cone. In response to yawing and rolling motions, air loads on the tips were supposed to oppose those motions. We found only a marginal benefit, even with very large drooped wing tips. To be effective, they had to extend about two feet below the wing, and this, of course, was unacceptable in blocked visibility and general appearance."​

Though the engineers abandoned the idea, the marketing department thought that slightly-drooped tips, aerodynamic benefit or no, looked cool. Thus "Conical-Camber wingtips" appeared on the original Model 210 for the 1960 model year.

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The style spread to other new models in the 200 series during the 1960s; and finally to the rest of the single-engine line in 1970. Thompson concluded,

"Although there were no measurable aerodynamic benefits, it didn't take long for sales people across the country to dream up some wild claims, and drooped wing tips have become a part of our aviation culture."​
 
There are two ways that wingtips are modified:

1: to generate more lift such as in a S.T.O.L. Kit. 2. to reduce drag and increase fuel efficiency such as in Winglets seen on airliners.
Both wingtip modification address the adverse effects of wingtip vortices. The fundamental situation is that a wing works best with high pressure on the bottom and low pressure on the top, and (without modifications) air sneaks out from underneath the wing and over to the top in a continual cycle which makes a spinning cyclone traveling from fore to aft on the wing.
Technique 1: STOL KIT stop any vortices from forming by creating a drooped wingtip. The drooped airfoil directs air opposite the direction of the vortice. The primary result isn't that air is trapped underneath, but that the lower-pressure air flowing over top the wing is not disrupted by wandering high pressure air. The primary disadvantage of a STOL Kit is that when there is not a high pressure difference between bottom and top wing surfaces (IE in cruise flight) the drooped wingtips are constantly deflecting air inward at the wingtip (opposing each other) and are simply generating worthless induced drag.

Technique 2: "WINGLET" GO WITH THE FLOW, and use the energy. The winglet method of dealing with wingtip vortices strikes a balance between stopping the vortex, and trying Using the spinning motion of the vortex to create thrust. Imagine yourself standing at the center of a tornado with two little wings strapped to your arms. Could you figure out a way to deflect the wings that would both propel you into the vortex as well as slow the vortex down a bit? (for those who understand turbine engines, think of the action of the "stators" inside) The action of the winglet is just like that of a stator, turning a vortex of air into forward thrust. The winglet mounted on the top of the "737 Scimitar" starts outward and ends closer to the fuselage. When as air rotates in that portion of the Vortex the relative wind is traveling from outward to inward. The winglet effectively has used up the vortice AND created forward vector of lift. The bottom Winglet of the Scimitar style 737 is in the bottom vortice which is travelling from inward to outward. Therefore the winglet is mounted (slightly back-set) with a slightly outward deflection. As is slows the vortice there it creates forward thrust there as well. ISN'T THAT COOL!!!!!

Do you like that explanation???
 
Obviously Boeing could not decide and now they face both up and down
 
SixPapaCharlie said:
Whats the different reasons?

Lately everything seems to be getting winglets added to it.
I see a lot of older planes with wingtops that bend down significantly.

I think I get the winglets especially on large Jets and I see now they are even adding split tips.

But what do they do differently?

14708-analternate-aviation-efficiency-theory-549970726_tmbcq-l-1.jpg


1358.jpg



This one can't decide
aurora-flight-sciences-da42-opa-0212a.jpg
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The elevator is often deflecting air the opposite direction as the wings when loaded in a normal configuration. This airplane is designed for Maximum efficiency and long range. Let me know what you think of my post at the bottom. ;-)
 
djw4fish said:
The elevator is often deflecting air the opposite direction as the wings when loaded in a normal configuration. This airplane is designed for Maximum efficiency and long range. Let me know what you think of my post at the bottom. ;-)
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Necroposting for your first two posts on the board. Bravo! ;)
 
I thought I heard a Boeing engineer once indicate that the winglets on the 747-400 were largely negligible and added more for aesthetic reasons

I trust they generally help, but I always sort of also saw them as putting flame stickers on cars

Look at birds, they have more of a 787 type wash out at the end of the wing, versus the super aggressive "FEAR THIS" junk you see on much of the fleet
 
Tantalum said:
I thought I heard a Boeing engineer once indicate that the winglets on the 747-400 were largely negligible and added more for aesthetic reasons
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I don't believe this is true at all. Even a 1% increase in efficiency is a massive improvement over the lifetime of the aircraft.

@djw4fish welcome to PoA. That was an excellent explanation, please stick around and introduce yourself :).
 
Mtns2Skies said:
I don't believe this is true at all.
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For sure there is some benefit, but I've seen this quoted in a couple places, I think I even saw some "chief" on documentary say that it jokingly, that it was a fantastic marketing element so passengers in the jetway would know they're getting on a new state of the art aircraft.. by 1988 the 747 has been flying for two decades, so wasn't exactly "knew" .. also, in the late 1980s and early 90s really no one else had winglets.. this gave the 747-400 some real sex appeal when it was seen taxing by, flying overhead, in brochures, etc.

You can dispatch them with missing winglets, someone with a POH can quote the fuel penalty and that proves there's indeed a gain from it.. but I do believe that the marketing folks at Boeing loved touting the winglet..

Now everyone has them..

If anyone does some Google sleuthing the whole wingtip device topic is obviously tantalizing to engineers, I mean, look at this monstrosity:
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Given the freedom from wingspan restrictions I bet you'll find that the raked tips, more like what birds have, offers the best solution to minimize tip vortices and its associated drag
 
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