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The early history of aviation is full of crazy designs, so please allow me this one:

A span wise narrow gap in the wing halfway between the leading edge and the trailing edge.

The door to the gap would be aerodynamically balanced, it would open at slow speeds. The gap cross section would be nozzle shaped to accelerate the air from underneath the wing to the top side. Lowering its pressure.

At the wing root and tip there will be no gap.

The idea is similar to slotted flaps and slats, but with the aim of energizing the aft portion of the wing. Thereby combining slats and flaps into one. Would it work?

In other words, it would split the wing into two smaller wings.

I expect the answer to be no, but would love to know why.

Edit: edges below are meant to be curved.

enter image description here

(Original Image)

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    $\begingroup$ So it would be used in the same situations that slats would be used? $\endgroup$
    – SMS von der Tann
    Oct 20, 2016 at 17:24
  • $\begingroup$ Are you sure the drag from the "nozzle" wouldn't completely overwhelm any advantages? $\endgroup$
    – Ron Beyer
    Oct 20, 2016 at 17:25
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    $\begingroup$ I've got a better crazy idea. We know most lift is created on the leading part of the wing. How about cutting off the trailing half altogether? ;) $\endgroup$
    – Zeus
    Oct 20, 2016 at 23:27

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This might be a bit late but the short answer is, again, no.

Check NACA report 427 and Experimental investigation of a Handley Page 44f wing. Slots at locations other than the vicinity of the leading edge are shown to be rather useless.

In addition, there seems to be no correlation between the "rounding" of the channel inlet and a better performance. The latter is solely my deduction since I co-authored the HP44F experiment.

The increase in lift due to slots is mainly due to a fresh boundary layer on the trailing element, a transfer of turbulent kinetic energy from the leading element wake into the trailing element boundary layer, and separation suppression due to the lower pressure recovery requirements on the trailing element.

If the slot is located too far aft., separation has already occurred, in which case there is hardly any kinetic energy to be transferred and the attached flow on the trailing element is unable to provide any substantial benefit.

enter image description here
NACA report 427

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  • $\begingroup$ Thanks for that graph! Yes, all of the slots produced a higher lift coefficient and a higher stall AOA than the unslotted (+) wing (with rounded edges). Now look a a slow soaring (eagle/vulture) wing tip. NACA report 427 validates nature! But keep in mind the drag penalty. Albatrosses do not use slots because they work at the more efficient lower AOA, where lift to drag ratio is highest. But the massive airliner needing to come in slow, yes, and check out Fowler flaps. $\endgroup$
    – Robert DiGiovanni
    Mar 26, 2019 at 20:13
  • $\begingroup$ @PeterKämpf: What gliders do, contour breaks, data on varying location, each answer provides great insight – but this late one I really didn't see until today for some reason, it deserved some attention that's all :) $\endgroup$
    – user14897
    Mar 27, 2019 at 0:15
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No, it will not work in the way you plotted it.

First, the corners of the duct should be nicely rounded. With the sharp corners you will get a lot of vorticity, but little lift increase. Actually, lift will drop and drag will go up.

Next, a gap works best when connected with a contour break, such as that of a slat or a flap. If you round the corners and add a hinge in order to deflect the rear part of the airfoil, then yes, the gap will help to delay flow separation.

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    $\begingroup$ Thanks Peter, I meant the edges to be rounded of course. And of course sliding the wing is a nightmare compared to just sliding out the flaps, I see your point. $\endgroup$
    – user14897
    Oct 20, 2016 at 18:33
  • $\begingroup$ Turns out it's [kind of] been done in the 20s. I came across it from here. $\endgroup$
    – user14897
    Mar 24, 2019 at 14:37
  • $\begingroup$ @ymb1: Thank you for sharing this find! It shows a step on Sir Handley Page's way towards the slat, and indeed the slot of Fig. 4 is quite a bit ahead of the one in the question. Of course, better rounding of the edges lead to better results eventually. I had contact in the Nineties with an Iranian living in Berlin at the time who claimed that this kind of slot would improve lift/drag, and I tried to verify it with MSES. The results were less than spectacular. $\endgroup$
    – Peter Kämpf
    Mar 24, 2019 at 22:34
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It works but your description is not so clear about the real size of the gap.

Gliders sometimes have little holes along the wing on the upper side where air from beneath is provided to them by a little duct.

The reason is to keep the linear air flow straight a little longer at low speeds.

an example

I have not found a live picture. For this I'll have to visit the DG300 of my flying club.

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    $\begingroup$ Just added one. Maybe I can take a photo some day. $\endgroup$
    – Aviator
    Oct 20, 2016 at 18:14
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    $\begingroup$ The little holes are for tripping the transition of the boundary layer. If you ask a new question I will explain how they work and why they are better than other means of tripping the boundary layer. $\endgroup$
    – Peter Kämpf
    Oct 20, 2016 at 18:16
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    $\begingroup$ @PeterKämpf I obliged. :) $\endgroup$
    – user14897
    Oct 20, 2016 at 19:28

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