Why do some aircraft have upturned wing tips?

Question

The F-4 Phantom Jet Fighter was the first one i ever saw with this but that was just at an angel.

Then several years ago the C-17 Globemaster III was on a video and its tips were straight up and down. (if i saw em correctly).

Since then ive seen a lot of this on some comercial planes and such.

What is the advantage to this?

Answer 1

They are called winglets, and they increase efficiency by reducing the size of the vortexes that for on the wingtips.

The pressure difference between the top and bottom of the wing create giant vortexes behind the wings, they can be several thousand feet long on a large aircraft, and they cause several turbulence and have to be avoided, especially by light aircraft.

The vortexes waste a massive amount of energy, and the winglets help reduce that. They usually save from 4-6% on fuel consumption, which adds up to tens of millions over the 75-100k hour life of most airlines, which burn thousands of gallons per hours. Even the fuel efficient 757 and 767 burn about 2500-4000 gallons per hour.

Answer 2

As the wind passes over the wing it tends to shoot of the sides (vapor trails) so the ppl who build the planes up turn the tips of the wings so that the air cant shoot off the side of the wing so fast, therefor increasing lift

Answer 3

Their Winglets and they provide better lift at takeoff, eventually saving fuel for the airline.

Answer 4

They are called wing-lets, and they give better stability on take of and landings because they prevent wake turbulence (The difference between high pressure on top of the wing and low pressure on the bottom of the wing) from meeting, thus calming the airflow turbulence.

Answer 5

The reason for vertical winglets is to reduce the wake turbulence that is generated by the difference of pressure over and under a wing. It also helps to decrease the stall speed. Some aircraft have upward winglets and some have it downward.

My Kitfox III homebuilt aircraft have them downward; so-called 'drooping winglets.' It is done to lower the stall speed and give a STOL (Short Take Off and Landing) characteristic to the aircraft. Mind you, the Kitfox owners who removed them didn't notice much of a difference. But I like them because:

1) in a crosswind it will prevent a gust to lift my windward wing. and,

2) If I loose control of my taildragger when landing and end in a ground loop, the winglets will protect my wings from hitting the ground. After all, they are only light moulded platic tips that can easily be replaced.

Answer 6

Normally the reason for winglets is to reduce induced drag (caused by vortices or whirling air mass over the outer wing).  Reduce the drag you, increase spanwise lift.  In most cases (it depends on the winglet type) the induced drag is reduced by increasing the vertical height of the lifting system (wing).  With more vertical height more lift is created at the wingtips, reducing drag and making the wing more efficient.  More efficiency...less thrust required, less thrust...more fuel savings.

You mention the F4 Phantom II.  Its upswept outer wing was to counteract severe unstable “dihedral” (upward angle of a wing) and lateral control problems at supersonic speeds.  At twice the speed of sound you want a very stable airplane.  The original wing had no dihedral at all.  The horizontal tail of the F4 has “anhedral” (downward angle).  Fuel savings wise the F4 was a fuel burning hog. The upsweep didn't help its fuel efficiency.  But when you're in a go-fast machine like that shootin' at stuff, who cares about fuel efficiency.

Answer 7

I build the c-17 for a living, but some commercial planes have "winglets" also.

The help fuel economy by helping break the vortex coming off the wing tip (ever see video where there is a swill coming off the wing tips?) reducing drag, and also increase wing area.

Answer 8

They break up wake turbulance

Answer 9

These are called winglets.

Trying not to go too technical but:

They increase the efficiency by reducing what is called Induced Drag.

As the air flows over the wing, the air is compressed and its velocity increases. This also causes the air to expend. The expanding air at the end of the wing "rolls over" the wing tip cause a vorticex flow. This vortex flow causes a phenomina called induced drag.

The winglet reduces the amount the expanding air on the top of the wing can "roll over" the wing tip hence reducing the amount of vortex flow. The reduction in vortex flow also causes a reduction in the Induced Drag making the flight more efficient.

This is a simplified version of what is going on. This technique is applicable to short range flights of around 3500 KM or less though. You will notice in long range aircraft the wintips are more racked and the short range aircraft have the "bent up" winglets.

Answer 10

The use of the winglets, are so that the aircraft can be more economic, it allows for the aircraft to fly longer distances, therefore saving fuel, and allows the aircraft to travel faster. The winglets are beneficial to the airline company as it saves more money, since the aircraft can travel longer distances.