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I've noticed that winglets are very rare on small aircraft. I wonder why this is the case. Wouldn't they have the same advantages, especially because they travel at low speed? Or is it just a wrong impression I got and they aren't that rare?

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4 Answers 4

up vote 18 down vote accepted

I've talked to a couple of aerodynamicists, and for small aircraft when you run the numbers the improvement offered by winglets is often less than the drag penalty caused by their weight (which also reduces allowable payload). For larger aircraft that fly long distances, the proportion of the aircraft's weight that is due to the winglets is much smaller than it is for small aircraft, so they don't have this problem and that makes winglets a viable strategy.

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Seems to be the more pressing argument against it so I changed the accepted question. Sorry Jan Hudec... –  André Stannek May 19 at 14:49
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As others have pointed out winglets don't make much aerodynamic sense for small aircraft.

The point of a winglet is basically to deflect the wingtip vortex away from the lift-producing part of the wing, granting an increase in effective wing span without the added form drag of actually making the wing longer.

The winglet itself creates some form drag though, and it adds weight. On most small aircraft the potential improvement in wing efficiency doesn't exceed the weight and form drag that result from adding the winglet.


What you will find on many small aircraft are Hoerner-style wingtips (either installed at the factory or added later through a STC modification). At lower speeds these have aerodynamic benefits similar to winglets, but without the additional form drag, and usually little or no added weight.

Hoerner Wingtip Diagram Hoerner Wingtip Photo

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So if Hoerner-style wingtips offer similar benefits to winglets without the drag/weight, then why aren't they used on larger aircraft? –  Lnafziger May 19 at 16:16
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Because winglets can provide more benefit on longer range aircraft than these wingtips, and there are other options as well (see 777 or 787). Things can be different in the upper Mach numbers. –  fooot May 19 at 16:20
    
Pretty much what @fooot said -- at higher speeds and with larger wings the wingtip vortex would be comparatively larger, and would still "spill over" onto the lifting surface with Hoerner tips (they would be an improvement over a "plain" rounded wingtip, but winglets are a further improvement over the Hoerner-style tip). There's a crossing point where the winglet becomes more efficient than the Hoerner-style tip, but where that is depends on aircraft/airfoil design, expected cruise speeds, etc. –  voretaq7 May 19 at 16:42
    
I get that, but it isn't clear in your answer (so you may want to clarify it a bit.) :-) –  Lnafziger May 19 at 18:33
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Many small aircraft designs are rather old and winglets were not common on airliners either when they were certified. For airliners that fly 8 or more hours a day saving a few percent on fuel quickly pays off the additional development and certification, so winglets were adopted quickly there. But typical general aviation aircraft does not fly anywhere close to that and the few that fly more and would be worth upgrading (and their owners have money for upgrade) are not enough to make the design and manufacture profitable.

Note, that winglets did find their way to gliders, especially competition ones, as the little benefit is more noticeable there. They also do appear on some newer designs, most notably the Diamond ones (DA20, DA40, DA42).

The situation is very similar to why we don't see more aircraft diesel engines. They are more efficient, use cheaper fuel and are somewhat cheaper to maintain, but the certification is so complicated that there are only few modifications available.

Also most GA aircraft are not really very efficient to begin with. The DA20-A1 claims glide ratio 14:1 and that is way better than most competitors. Compare with airliners where 18:1 is nothing special (was claimed by A320 some 30 years ago). So winglets are not going to help as much.

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The chief designer of DA comes from a glider background and knows winglets in and out. On the other hand, more conservative designers do not embrace winglets openly. When Rutan's Starship design was forced upon the engineers at Beech, the winglets were a major source of their many complaints, which mostly turned out to be correct, btw. –  Peter Kämpf May 19 at 11:59
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First, winglets look fancy but will not help that much in drag reduction. They were pushed less by engineers than by marketing, Boeing's in particular. They help a litte in ideal conditions, but in sideslip or at high speed they can quickly increase drag.

Then, most small aircraft are designs from a pre-winglet era. Adding them means to invalidate the type certificate, unless someone takes the initiative to re-certify the aircraft with winglets. I guess nobody has seen this as a profitable endeavor so far.

Gliders benefit from winglets because in competitions they are grouped in classes. Membership of some classes is defined by wingspan. Gliders get better with increasing wingspan, so if regulations limit the lateral extension, the way out is to extend the wings upwards. If there is no such artificial limit, it will in most cases be better to expand the wing in spanwise direction.

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+1 for the second paragraph. Would accept your answer too if I could but Jan Hudec wins this one for beeing a little more extensive. –  André Stannek May 19 at 9:03
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