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Do they realy reduce drag or improve performance? If so, how? enter image description here enter image description here enter image description here

Federico
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The main effect of the ranked wingtips is not improving the glider performance but change handling characteristics during thermaling. Such wing tip changes the stall pattern of the inboard wing during the circling in a thermal. They are optional.

Pros:

  • Whit this wingtip installed, you should be able to climb better in weaker thermal. Due to a change in the wing stall pattern and bigger area.
  • Glider should have a higher glide ratio at a lower speed. Thanks to the higher aspect ratio. See. this answer https://aviation.stackexchange.com/a/8797/54674

Cons:

  • Such wing tips adversely affect roll rate. Especially if you need to quickly change your bank angle in "wild thermals".

  • In theory, they should decrease your glide performance characteristics in high sped flight.

It is always a pilot choice. Glider looks much better with them ;)

Robert Kulhanek
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Parasitic drag is caused by the tip vortices that spill off the wingtips. With a rectangular wing with no washout, the pressure difference between the upper and lower surfaces will be more or less constant across the entire wing and so the vortices will be large. With a tapered wing and washout towards the tips, most lift is generated near the root and so there’s less pressure difference near the tips and hence the vortices are smaller. Adding the raked sections in the photo will help a little more but it’s hard to say whether it will make a measurable difference. It would certainly be better than abruptly terminating the wing at the last batten.

Frog
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    intresting observation , that parastic drag is cused by vortices,usually people think that vortices cause induced drag(which is again wrong).. –  Jan 23 '21 at 22:04
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    The vortices are just the faster core of a larger flow field circulating around the tip and are better thought of as just efficiency losses from "leakage". The extensions make the core of the flow field small/weaker, but the larger flow field is still there. There is probably a difference in computer modelling and in a wind tunnel, but to measure it in the real world would be pretty difficult. Best way to test it would be to fly it with one tip removed, if one has the nerve. Steve Wittman. crazy racing pilot he was, once tested the triangular wing tip extensions for the Tailwind that way. – John K Jan 23 '21 at 22:26
  • I’ve seen crazier experiments carried out. However, this would likely indicate a change in drag rather than overall efficiency. While the two are closely related they aren’t inseparable. – Frog Jan 23 '21 at 23:36
  • @frog can you explain how do you mean that parastic drag cuased by vortices? –  Jan 24 '21 at 07:35
  • @EBV821, can you explain what you mean that vortices cause neither parasitic nor induced drag? – Michael Hall Jan 24 '21 at 15:49
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    @MichaelHall Wing tip vortices are behind wing,so they dont cause any of drag..Vortices are manifestation of lift creation.There is only two real sources of drag: fricition(tangential) and pressure(normal)..Induced drag is component of pressure drag parallel to airflow, caused by tilted wing at given AoA minus zero lift drag..How vortices increase parastic drag? –  Jan 24 '21 at 16:23
  • I get it, cause/effect reversion in the wording. Thanks. – Michael Hall Jan 24 '21 at 16:27
  • It’s fair to say that the vortices themselves don’t cause drag, but the fact that the air is spilling between the upper and lower surfaces means that energy is being lost/wasted and that energy results in the vortex. Ultimately of course, the thing that is creating the drag is the fact that the wing is being pushed through the air, although that’s possibly not the best way to think of it. – Frog Jan 25 '21 at 05:03
  • @Frog, main reason for the vortex is that the air is accelerated downwards in the middle and not accelerated anywhere outside the span. That creates a low pressure region at the top of the wake and high pressure region on the bottom and these also equalize to the sides, creating the rotating motion, but most of that happens well behind the wing. The flow around the tips themselves only contributes a tiny fraction. – Jan Hudec Jan 27 '21 at 09:50
  • @Jan Hudec the vortices are the flow of air round the wingtips. In the big picture the air movement is a torus, albeit a highly distorted one in normal circumstances - all the air that is pushed downwards must eventually equalise. This is unavoidable, but losses are worse where air moves at high speed such as in vortices. – Frog Jan 28 '21 at 19:33
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    @Frog, yes, the air movement is a distorted torus that sharply bends at the wing-tips. But that's not what comes in most people's mind when you mention flow around the wing tips, so while it is not wrong, it is misleading. – Jan Hudec Jan 29 '21 at 16:03