Winglets, horizontal stabilizerlets and vertical stabilizerlets?

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You will find that winglets are normally fitted as a retrofit to older wing designs. Most 'clean sheet' designs within the last half a decade have found new and more efficient ways to achieve the same effect.

Winglets are designed to move the origin of the vortices created during high lift flight. Of course, these vortices are created at all times during flight, although during cruise for example, the pressure difference between under and above the wing is less by virtue of the lesser lift required.

During high lift areas, the increase in pressure difference causes more extreme vortices to be created, which in turn reduce the effectiveness of the aerofoil at the end of the wing. Depending on the size of the aircraft, the speed, the aerofoil shape, the angle of attack etc etc, this can render up to approximately 20% of the wingspan effectively useless.

By adding winglets, these vortices are moved to the tip of the winglet, up and away from the end of the 'effective' wing. The winglets also act to increase the wing span, and thus the usable area, which makes more a higher aspect ratio wing, and thus more efficiency at low speeds. This can all be proved through simple mathematics from the standard lift equations.

You will notice that I have mentioned the term 'high lift' quite frequently. Herein lies the reason why some manufacturers choose not utilise winglets for certain aircraft. The winglets are most effective at high lift, and therefore during take off, climb, late descent, approach and landing. If the aircraft spends a large percentage of it's flight profile in these stages, as a short haul aircraft does, the winglets may make sense as a retrofit or during initial design (small aircraft, small wingspan, raked wingtips are not viable for numerous reasons).

For, however, a long haul aircraft which spends a large amount of time in cruise configuration, the extra drag and wait caused by winglets renders the efficiency gained during climb etc lesser. This is why some manufacturers do not use winglets on long haul aircraft, and newer designs are utilising raked wingtips. The way raked wingtips work is somewhat similar, but the explanation and discussion is enough for an entire thread in itself.

To answer as to why there are no winglets on tail surfaces, this is due to the fact that the lift caused by the tailplane is very small for most aspects of flight, and the increased drag and other aerodynamic considerations far outweigh any potential benefits. There are no vertical stabiliserets for the simple reason that the vertical stabiliser does not cause any lift, and therefore carries no pressure differential to cause vortices (Rudder inputs excluded, obviously).

I hope this helps understanding, PMs and discussion always welcome.

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