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I should preface that I'm by no means an aviation person. I'm just in a aircraft knowledge obsession phase and daydreaming about designing my own ultralight (will never happen).

The idea would be to simplify and lighten a small aircraft using the flaps as spoilers. As a practical example, the same handle could be used in one movement to get from flaps raised just before touchdown to spoiler raised just after it, making it fast and intuitive.

Basically you would have on a single axis :

high lift + high drag <-> normal lift + low drag <-> low lift + high drag

Is that possible? I guess not because I couldn't find anything like that, but why?

I name them flapoilers.

flapoilers?

The Fairey-Youngman flaps seem to do that but all I could find as explanation is "so that the aircraft could be dived vertically without needing excessive trim changes" and I'm not sure how to understand that.

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    $\begingroup$ Welcome to Stack Exchange! I think this is a very interesting question. $\endgroup$ – Timber Swett Aug 2 at 12:50
  • $\begingroup$ Thank you for the welcome! This forum has tons of really great questions and information, it's a great source of brain food. $\endgroup$ – Adel Aug 2 at 12:57
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    $\begingroup$ Related: Could flaps replace spoilers by deflecting more than 90°? $\endgroup$ – ymb1 Aug 2 at 13:05
  • $\begingroup$ "simplify and lighten": the latter will certainly be true when combining functions, the former (probably) not. Recently came across an article by one of Airbus' heads of R&D, detailing their/his vision on multifunctional wing movables. Interesting read: issuu.com/maurits11/docs/00_magazine_/10. $\endgroup$ – Bram Aug 2 at 13:29
  • $\begingroup$ Pretty sure this is done on some model gliders but I don't have my copy of Simon's book handy atm. $\endgroup$ – AEhere Aug 2 at 13:36
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One reason is that any device you want to use as a lift dumper needs to be able to be instantly retracted and this is really difficult to do with a flap. On an airliner when the lift dumpers come up, if you slam the thrust back up to TO, they immediately come back down. A flap system with its slow moving drive line can't do this, and it's enough that it has to be retracted from landing to takeoff setting for a balked landing like that.

Plus, even in a normal landing, you would be landing with the flaps at the landing setting, and when you touch down they would need 10-20 seconds a typical drive system would need to move up past 0 to a fully up position. You'd be stopped by then, and deciding to take off again on the rollout is out of the question.

So you can see that any system like this would require flaps that can move up and down rapidly like ailerons. A really difficult engineering problem.

You might do this on a small airplane with manual flaps operated by a lever, but now you have to cater to twice the movement range as regular flaps, and you'd lose the mechanical leverage you'd need for manual flaps to work unless you made the lever move twice as far (by say having it move in a 180 degree arc - but now the lever handle is in the back seat).

Lots of gliders use flaps - without any spoilers - and they can in most cases be "reflexed" up a small amount, but this feature is done only to unload the trailing edge region for high speed running which has an effect similar to reducing wing area and pitching moment to reduce both induced drag and trim drag.

For approach control and landing, they actually do the opposite of what you would think; you drop the flaps down to near 90 degrees when you want to come down steeply and for the landing roll. Not everybody likes that kind of system because you have the same problem - you can't bring them up and down quickly like spoilers so you can't work the flap lever like a throttle on approach the way you normally do with regular spoilers/dive brakes, and they require different flying techniques, on which a pilot used to spoilers needs to be carefully briefed to avoid trouble.

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  • $\begingroup$ I was thinking for small planes using levers yes. So it's doable as long as the movement range is carefully designed? The technique of "flaps raised before touchdown and flaps down and spoiler up for hard brake" seem to be used by STOL bush plane flyers. They often don't have spoilers though... $\endgroup$ – Adel Aug 2 at 13:23
  • $\begingroup$ Sure if you had simple plain flaps on a light airplane it would be a simple matter to set the "up" stop at say 20 deg reflexed up if you could set up the required travel range in the lever. But I'm pretty sure you wouldn't find them all that useful in the overall scheme of things, which is why you don't see them very much. $\endgroup$ – John K Aug 2 at 15:00
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What is created by deflecting a flap (or aileron) up is a reflexed airfoil, which, at higher angle of attack actually might create LESS drag and contribute a lower pitching up tendency. This design is used on flying wings, while others prefer to have pitch control duties handled by a separate tail.

Conceptually, "flapoilers" are a good idea, but aerodynamics requires spoilers to be placed further forward on the upper wing surface to be effective.

There for, they are usually a separate control surface from flaps, although a "clamshell" arrangement is seen as a speed brake. Model gliders, as AEhere mentioned, put both ailerons up and (closer to fuselage) flaps down in the "crow" configuration to achieve spot landings in competition.

But keep spoilers in mind as the (old and new B-52) makes very effective use of them as "spoilerons" to bank and turn the aircraft.

But, with exception of some gliders, most aircraft want to land at as low an airspeed with as much drag as possible. This favors the flap.

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For radio- controlled gliders, it is common to deflect both (outboard) ailerons upward while also deflecting both (inboard) flaps downward. This combination is called "crow", and it makes lots of drag to allow for a steeper glide path for easier landings, with no increase in stall speed.

Something similar would surely be possible with some full-scale aircraft, though as other answers have noted, there may be some engineering challenges.

Actually what you are trying to do is INCREASE the stall speed when the surface is deployed. (So after the wheels touch, the flaps suddenly snap to the raised-upward position.) My point is just that in the R.C. world it is possible for a control surface to be fast-moving AND to hold position in the face of heavy aerodynamic loading, so there must be SOME way scale this up. Whether that would ever be considered an optimal or good approach, is another matter.

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  • $\begingroup$ ( I now see some other answers have specifically mentioned crow) $\endgroup$ – quiet flyer Aug 2 at 19:15
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Current designs do not support that. In planes with Fowler style flaps for example, the flaps extend down and back on a curved track. The top back of the wing extends over the top of the flap when retracted to make a smooth surface. The track would have to be redesigned to allow the flap to go up.

I have not felt the need for spoilers in my 4-seat plane. Any big altitude losses, generally when coming in too high on final, can be accomplished by side slipping the plane - lots of right rudder while banking left with the ailerons for example. Makes the plane nice and draggy to enhance vertical descent rate.

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The concept you're sketching would reduce effective camber and increase pressure on upper wing surface (both of which is desired in a spoiler). It would however also produce a "nose up" moment while moving into position, relatively strongly so just before the flow on the underside of the flap separates -- and that's not really desirable. The classic spoiler sits further forward and starts separating flow the moment it starts being deployed. Because it sits further forward, a larger portion of the flow on the upper surface is affected, and because usually the flap is deployed (downwards) at the same time, that makes two surfaces which will create significant drag, but not a lot of pitching moment.

...oh, and if you used the flaps as spoilers, you couldn't use them as flaps at the same time :) Except if you're flying a B2, which I believe has split flaps/ailerons, so they can move one half up and one half down -- but that's mainly due to the particular flight mechanics of a "flying wing" configuration with no tailplane, and is both less effective and less efficient than Fowler flap plus spoiler.

That said: If memory serves right, then the Airbus A350 actually can in fact move its flaps up a little from neutral position, and also move its spoilers down a bit, too. The latter is to adjust the gap between the main element and the flap, depending on flight condition, and the former to support the ailerons, adjust span-wise loading and to adjust the effective wing camber for different phases of the flight (since the aircraft becomes lighter while burning fuel, so the lift requirement changes).

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  • $\begingroup$ That makes sense, didn't thought about the nose up moment. $\endgroup$ – Adel Aug 4 at 19:58
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Probably not since spoilers are located further up the wing (leading edge) to "spoil the air" that is moving faster over the top of the wing rather than after it falls off the back of the wing hitting the air from underneath. None the less, the idea sounds logical. My glider has spoilers do to the huge amount lift the wings produce and can send you rising past 15K feet before you know it and needing O2!! The spoilers are a separate lever and lift the flaps that are centered over the middle area of the wings and give equal "spoiling" allowing the aircraft to slow down evenly without tipping the nose up or down like control surfaces on the trailing edges do.

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Why upwards? They don’t dump much lift at the back of the wing. They do increase drag and reduce wing area a bit, like when deflected fully downwards, where they are much closer to after touchdown.

Re the design in Peter Kãmpf’s answer

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