Why do some Jets have wing tips that slant upwards?

Answer 1

I assume you are talking about the dihedral or winglits.

I'll discuss both.

The Winglits are there because of the way the wing works. Low pressure exists above and high pressure below. This difference in pressure is always trying to equalize. When air flows from the bottom surface to the top, it forms a vortice, increasing drag. Wingtips help stop these vortices's and increase fuel efficiency. They also help minimize the formation of wake turbulence, which can be deadly to other aircraft.

The dihedral help increase stability on the longitudinal axis( from nose to tail). This occurs because when the plane starts to turn, the relative wind strikes the wing at an angle. Because it's angled upwards, the wing will tend to level off again.

Here is an example of a wingtip http://www.airliners.net/open.file/1252708/L/

and of a dihedral( you can notice the wings angle upwards)
http://www.airliners.net/open.file/1152973/L/

Also if it interests you, a downward angle is called an anahedral. It does the opposite of the dihedral. It increases the aircraft's response to a roll command, and because of this it's mainly found on fighters, like this one.
http://www.airliners.net/open.file/0740200/L/

Answer 2

Drewpie for best answer.

The dihedral of the wing increases roll stability, the same as raising the wing, which increases the metacentric hight (difference between center of gravity and center of lift).

I think the rest has been covered adequately.

As an aside, I like the swept tip solution, it's another way of keeping the low and high pressure areas separate but it doesn't require a fence, which is basically what the vertical winglets are. Since birds don't have winglets I suspect the swept tip is more efficient.

Answer 3

Blended Winglets, fuel saving is forecast at 6% on long haul. Short haul not so much, because proportionately there is less cruise time.
Given that the winglets give a jet a certain desirable appearance too, they are being fitted to Small commercial / private Jets. On these, the fuel saving is doubtful and the owner probably doesn't give a rats *** about a few dollars of fuel anyway. These retro fitted good looking ones are known as "Blinglets".

Answer 4

* Wingtips * are simply the ends of the wings and nothing more.

Wingtip devices (which is what I think you mean) come in many flavors:

*Winglets*
Blended winglets
Wingtip fence (airbuss others)
Raked wingtip
non-planner wingtips
Actuated wingtips (XB-70 compression lift)


Wingtip devices are generally used to increase the lift generated at the wingtip plus reduce the lift-induced drag caused by end vortices's thus improving lift-to-drag ratio. This increases fuel efficiency and performance. They also decrease wake-turbulence for aircraft flying behind them.

Winglets
Are the most common on newer aircraft and function very simply with a toed out angle to them. This toed out angle not only accomplishes all of the above general functions but also adds a thrust vector.

Charles: much respect to you but Dihedral is simply a description of an angle and not anything to do with the tips. Also it actually works because the lift vector becomes inefficient compared to the weight vector. Here is a descent explanation: http://en.wikipedia.org/wiki/Dihedral


More on the other types of wingtip devices:
http://www.answers.com/topic/wingtip-dev...

Answer 5

This is due to turbulence. the tip on the end of the wing deflect air from the edge of the wing tips if they where not there the the turbulence would affect the stability of the wing, this dos not go for every aeroplane.

Stability

Answer 6

To bleed off the wing tip vortices and keep the laminar air flow smooth and turbulence free.

Answer 7

To better disperse the vortexes that accumulate there the faster the plane goes. Vortexes make the wing less efficient

Answer 8

Pretty too huh?