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I am designing a wing for a Vertical Takeoff and Landing aircraft. I am trying to choose a wingtip winglet for my aircraft. One of the option is a aft-swept wingtip winglet. However, this structure would cause the horizontal loading of my wing to increase, according to my lecture notes. I am wondering whether this effect could strengthen my wing?

Here is a picture of my aircraft, the red crossed component is a rotation mechanism for my wings enter image description here

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  • $\begingroup$ Rotate the wing? why? just duct the engine thrust... Check out the Hawker Harrier. $\endgroup$
    – Solar Mike
    Mar 10, 2021 at 7:22
  • $\begingroup$ A drawing will help people understand the particular implementation you have in mind. Also there is certain ambiguities in your question. E.g. this structure will cause the horizontal loading. I suspect you refer to the wingtip winglet (which is also not entirely clear), but I what I am unclear about is the horizonal loading increase. When do you expect it? When the wing is rotated 90 degrees, or when the wind is at 0 (flight mode)? $\endgroup$
    – NMech ♦
    Mar 10, 2021 at 10:17
  • $\begingroup$ By rotating the wing, no thrust would be wasted to overcome the drag brought by having the wing surface perpendicular to the flight path during VTOL. Also, engine thrust ducts are kinda complex for civilian aircrafts. Also, I got the "increase in horizontal loading" from my lecture notes, which should be talking about level flight--when the wing is parallel to the flight path $\endgroup$
    – user39178
    Mar 10, 2021 at 15:54
  • $\begingroup$ Learn about aerodynamic stall. Then think of a different idea which might work. $\endgroup$
    – alephzero
    Mar 10, 2021 at 22:43
  • $\begingroup$ @user39178, I removed the rotation details from your question as they were not relevant to your primary question. The winglet will not stiffen the wing regardless of a round beam in the middle or not. $\endgroup$
    – ericnutsch
    Mar 13, 2021 at 7:11

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The image below is from the wiki winglet page shows the wingtip vortices with and without wiglets. It is producing lift to oppose wingtip vortices and as a result adds a horizonal force component (Think Newton equal and opposite).

enter image description here

Obviously the results of this force are highly geometry dependent, as winglet could be up, down, or both. In the case of the photo, the upward winglet is pushing air outward and consequently has a resultant force oriented towards the aircraft. This creates a load and a moment that must be structurally supported by the wing and root of the wing; just as if it were a cantilever light pole opposing gravity. This moment is in addition to the much greater lift forces on the wing that are more or less operating in the same direction. Basically there is more load, so you need to build the wing stronger to accommodate it. Putting it into perspective though, a properly designed winglet will have a very small force (say less than 5%) relative to the lift of the wing.

The wing will not stiffen because of the winglet or this force. Excluding the geometric complexities of a tapering wing, it will somewhat follow the cantilever beam deflection equation where the deflection is proportional to load.

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