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Winglets are used to reduce induced drag on the main wings of an aircraft as per explanations on wikipedia. Since they are very effective I was wondering why they are not installed also on horizontal stabilizers. For sure there must be some sort of induced drag being generated on horizontal stabilizers too as they are cutting through the air just as the main wings do. So why aren't there any sort of "minified" winglets available as an aftermarket installation (or, at least, I haven't ever seen some myself)?

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Induced drag is caused by the pressure difference over and under the wing meeting at the tip generating a vortex, not by "cutting through the air" (that's straight up drag, not the 'induced' kind) –  falstro Apr 15 at 10:01
    
Or in other words, induced drag is induced by producing lift. –  Jan Hudec Apr 15 at 19:34

3 Answers 3

up vote 9 down vote accepted

Horizontal stabilizers don't generate as much pressure difference as the wings- Generally the deflections are very small in flight, and there's so much other drag during landing when they are intensively used that they are probably the least of your problems. The stabilizer winglets on their own when there's no pressure difference would simply result in drag, whereas the main winglets are constantly effective while flying.

Furthermore, the weight and trouble of adding little winglets to the horizontal stabilizers with larger actuators and hinges for example would probably outweigh the very slight aerodynamic benefit that might be gained. I could also imagine that since the airflow over latter part of the wing is pretty complex and varied, getting a good solution would be difficult.

As @Federico points out, the DA42 has them, but that's a composite airframe rather than the metal construction you seem in most Cessnas for instance, where you have to be more conservative in construction.

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So why aren't there any sort of "minified" winglets available as an aftermarket installation?

Actually the DA42 has them enter image description here

and in the MPP version they are even more pronounced enter image description here

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i'm not sure these are the pressure difference purpose like classic winglets. IMHO just from appearance it looks like the DA42 has a very short rudder, so these might be for stability purposes :) –  MikeFoxtrot Apr 15 at 11:16
    
@Manfred actually pilots I have spoken to report that these worsen the stability, not improve it. –  Federico Apr 15 at 11:17

The induced drag from wingtip vortexes is mostly on lift generating surfaces, horizontal stabilizers don't generate that much lift.

That said there is a twintail design with double vertical stabilizer at the ends of the horizontal one; but that is not for reducing vortexes but for improving rudder response.

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