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How raked wingtips reduce induce drag?

Mon Mar 18, 2019 4:56 pm

Hi all, I understand that both winglets and raked wingtips are for the same function (from what I have read) - to reduced the amount of induced drag. I understand the principles behind winglets, however I am uncertain how raked wingtips actually achieve this?

Could anyone please explain the aerodynamics behind it. Thanks
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Re: How raked wingtips reduce induce drag?

Mon Mar 18, 2019 10:12 pm

Murphy is an optimist
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Re: How raked wingtips reduce induce drag?

Tue Mar 19, 2019 1:45 pm

Let me try to reactivate my memory: Raked wingtips increase the aspect ratio of a wing, and the higher the aspect ratio, the lower the drag (see gliders have aspect ratios of 50+, whereas commercial jets are around 10-20). The most efficient wing has a huge wingspan and very short chord, or the zero-drag wing has an unlimited wingspan :smile: Raked wingtips follow this principle, while they still produce lift.

'Sharklets' (or whatever they are called) also reduce the induced drag, however they do not produce lift. As a benefit, they do not increase the wingspan which is favourable at small airports.

So in sum both designs have their advantages and disadvantages.
Please feel free to correct me, its been over 15 years since my uni degree, so things may have changed :embarrassed2:

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Re: How raked wingtips reduce induce drag?

Tue Mar 19, 2019 8:11 pm
any wingtip device increase lift by decreasing parasite airflow from lower to upper wing part
different types of provide different advantages and disadvantages. some of them provide advantage in one configuration and disadvantage in another - for example, on climb vs cruise.

raked wingtip reduce less drag, but also provide less load on wing frame. principle the same - reduce parasite airflow by placing "baffler" in between.

ultimate wingtip - double scimitar or something similar - provide more "calculated" aspect ratio, more lift, more direct drug, more weight and more load on structure, and used at planes where wingspan is a limit - 737 and A380

if you dont limit in wingspan and have enough frame strength, you take a very little benefit from wingtip device, so 787, SSJ and MC-21 dont have it.

also, here a discussion about P-8 raked wingtip

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