Better not hiccup....

[Golfer]

Why do most modern airplanes have winglets?

[Mongoose]

Why do most modern airplanes have winglets?

  As the wing cuts through the air, the air at the tip of the wing will curl over the wingtip and on to the top of the wing.  This creates some drag.  It also creates a vortex coming off the wingtip, which trails behind the plane.  The winglet guides the air up and away from the tip of the wing, and diminishes the effect.

Wikipedia is not an authoritative source, but this page does explain it well, and has good illustrations: 

http://en.wikipedia.org/wiki/Wingtip_device

[Golfer]

The question is for earl regarding this post:

Vortices's are created by the Wing Tips, primarily by the shape of the wing tip. Some aircraft produce more vortices's than others and the heavy the aircraft, the more pronounced vortices's are present. The vortices's are what creates the "wake" turbulence and have been responsible for several accidents. Vortices's are no problem on landing, if you plan your touch down beyond where the aircraft in front of you touched down. It is best practice to wait on takeoff for a couple or 3 minutes to give the vortices's time  to dissipate or the wind move them to the side of the runway prior to you taking off. In FAA tests of vortices's, they settle behind the generating aircraft and as long as you climb above the aircraft in front of you, you shouldn't encounter any problem. Don't let ATC rush you into to taking off, until you are satisfied that wake turbulence will be no problem to you.
Vortices's per sae do not produce any drag, that is created by the shape of the wing itself. Any wing which produces lift, also produces drag, but again, the shape of the wing will dictate how much drag is created.
For example, in this game, the B-17G has a "Hersey Bar" type wing, which is designed to create a lot of lift, but it also creates a lot of drag, hence the reason for slow speed of the aircraft in all flight realms. In the other end of the spectrum, look at the LA-7 wing, which is designed for speed and because of the shape does not produce much drag.

[earl1937]

The question is for earl regarding this post:

Not being a trained aeronautical engineer, I have to rely on the experts to evaluate the affective's of winglets and Horner tips. Southwest Airlines claims to be able to save 10 million galleons of jet fuel over a 5 year period because of the installation  of "winglets" on their Boeing 737's. That seems to be the biggest advantage to them, as well as better low speed handling because of increased air flow over the aileron area and in proves lift over the whole wing. A French scientist named Burnelli, I think his name is spelled correctly, is credit with the discovery of the "venture" effect of compressing air over an area, increasing speed and there fore, a low pressure area, (lift). The Burnelli effect has had a huge influence on wing design and has certainly had a huge impact on a number of designs.
The Burnelli effect even had an effect on carburetor design, with a venture being the center piece of float type carburetors, which were first used in early aircraft, such as the Spit 1, which we have here in this game. That is the main reason for carburetor heat in internal combustion engines, as the increased airflow down through the carburetor produces increased airflow through the throat of the carburetor, but also produces a rapid drop in atmospheric pressure, which results in a rapid decrease in temperature, creating "ice" in the carburetor and choking off the air flow through the carburetor.
The U.S Air Force for years have studied their Boeing KC-135's and other aircraft with the winglet's installed and have concluded that they contribute to fuel range and a causal increase in lift to drag ratio.
There is a lot more to this subject and I would be the last one to rely on for the last word in winglets. I have never flown anything with winglets, although a club I used to instruct in, had a Cessna 210 with Horner tips.

[colmbo]

ET I have the utmost respect for you and your aviation experience.  I have to wonder if maybe we're arguing semantics.  However you're making some errors in this discussion about ground effect.  I don't say this because I think so, but because all the teaching I've had over the years, everything I've read over the years and the FAA don't agree with you about this.  Ground effect is "only a theory" as much as lift, weight, thrust and drag are "only a theory".

You and I can agree to disagree and move on.  <S>


For anyone who wants to read more about ground effect here is a link to a PDF taken from the FAA Pilots Handbook of Aeronautical Knowledge.  Scroll down to page 4-9 for the discussion on ground effect which starts with:

It is possible to fly an aircraft just clear of the ground (or water) at a slightly slower airspeed than that required to sustain level flight at higher altitudes. This is the result of a phenomenon better known of than understood even by some experienced pilots.  When an aircraft in flight comes within several feet of the surface, ground or water, a change occurs in the three- dimensional flow pattern around the aircraft because the vertical component of the airflow around the wing is restricted by the surface. This alters the wing’s upwash, downwash, and wingtip vortices. [Figure 4-13] Ground effect, then, is due to the interference of the ground (or water) surface with the airflow patterns about the aircraft in flight.

 

[earl1937]

ET I have the utmost respect for you and your aviation experience.  I have to wonder if maybe we're arguing semantics.  However you're making some errors in this discussion about ground effect.  I don't say this because I think so, but because all the teaching I've had over the years, everything I've read over the years and the FAA don't agree with you about this.  Ground effect is "only a theory" as much as lift, weight, thrust and drag are "only a theory".

You and I can agree to disagree and move on.  <S>


For anyone who wants to read more about ground effect here is a link to a PDF taken from the FAA Pilots Handbook of Aeronautical Knowledge.  Scroll down to page 4-9 for the discussion on ground effect which starts with:

 

No problem sir! This forum would be a dull place to visit if we all agreed on everything! I  the FAA for describing as best it can about the "phenomenon" known as ground effect, but, remember, these are the same folks who said that it was no longer necessary to teach primary students, "spin recovery tech's", nor was it necessary to make airliner cockpit doors inaccessible so passengers could not enter the cockpit area if not authorized and we both know the results of those two decisions. If you don't mind, I will cont' to keep "ground effect" in the same category as UFO's, Big Foot, high wing producing more lift than the low wing, which turns the a/c and last, but not least, Reptileman in Fla. They say a alligator and a good looking blonde headed woman had a relationship and there are blonde headed, dark eyed men walking around in the Everglades. I guess that is another thing on my bucket list which will be one of those things I will miss!
AT any rate, when you review their comments, the FAA, notice they don't say anything about grass, just water and pavement! In my view, if it really worked, the effect would be the same on all three surfaces.  You know all aviation aircraft started out on grass and then progressed to paved runways. Funny how this subject was never mentioned prior to paved runways!