You’ve probably stuck your hand out the window of a moving vehicle in the summertime — pivoted it up and down, changing the angle at which the oncoming wind bends around it. If you tilt it up ever so slightly, your hand goes up.It turns out that y our hand can be a pretty good approximation of an airplane wing. Out the window of a moving car, your hand is at once a wing, an aileron, a spoiler and a flap. (And if you stretch out your fingers, maybe even a slat.) The primary and secondary control surfaces on the wing of a modern commercial jet, an Airbus A320 (Image from the YouTube video below, modified by author.)Airplane wings are a majestic and highly complex piece of engineering. Quite simply, they’re almost alive.
Mar 03, 2000 Flaps are one of the most ingenious parts of the plane, and to most people, how they work is an utter mystery. The problem lies in that from the cabin, you can't really see what is really going on with the flaps when extended.
On the Boeing 787, computer systems control the wing’s components to adjust to flight conditions — gusts, wind shear, turbulence, even being slightly too high for landing, and more — and all of this independent of the pilot inputs. You’ll sometimes see those wing parts move quickly, sometimes with near-imperceptible adjustments — and on landing, those movements may happen very frequently.This article explores some of the components of an airplane wing that you’ll see when you look out the passenger window.Two experts helped me demystify how the components work together. Dean Plumb is British Airways’ Chief Technical Pilot, with more than 30 years of flying experience.
He’s got 10 years in the Royal Air Force flying C-130 Hercules transports, followed by 20 years at BA, including time on the Boeing 787 Dreamliner. Chip Kiehn, Director of Sales and Marketing for Aviation Partners Boeing, which makes and installs a part of the wing called a winglet, has spent close to 20 years at this Boeing joint-venture project. (Winglets are those curved ends jutting up from the end of the wing on many planes, including current models of the Boeing 737 and Airbus A320.) Ailerons: The Little WingAilerons — a commercial aircraft has two — control the movement of the aircraft on its longitudinal axis, causing it to roll left to right. Aileron is French for “little wing” — and that’s exactly what they are. “Like the wing, the aileron is tear-shaped when viewed from the side and has the thinnest edge at the back,” Plumb explained.
“Andthe aileron is surprisingly large when seen close-up.” Aileron deflected down on a Gulf Air Airbus A330-200. (Photo by: aviation-images.com/UIG via Getty Images)The ailerons are located on the outside trailing edge of the wing. To spot the ailerons, you’ll have to look closely.
On a passenger aircraft, ailerons move ever so slightly from the passenger’s perspective. Indeed, when your aircraft is banking in a turn, you may notice that the aileron returns to its flush-with-the-wing position, yet the aircraft continues to bank. It does this because of centripetal force holding it in a turn.When the control column is shifted to the right by a pilot (or by the autopilot more often than not), the aileron on the right wing is then raised while the aileron on the opposite wing drops down.
(They move opposite each other.) The act of raising the aileron on the right wing reduces the lift on the right wing — and when wings have a reduction in lift, they drop. Here, the right wing dips down in a controlled turn to the right. A NASA animation showing aileron deflection and roll about the longitudinal axis of the aircraft.“The ailerons are helped by spoilers on the wing which can reduce lift very slightly, aiding the turn,” said Plumb. Spoilers and Airbrakes: Decrease Lift, PrimarilyAs the name suggest, spoilers spoil something.
Here, they ruin the lift produced by the wing, much the same way an aileron does. So what’s the point? Spoilers allow the plane to lose lift and descend in a controllable way.“The spoilers act by making the wing less efficient, in a controlled way,” said Plumb.
“This is a great way of reducing unwanted airspeed as you slow down ready for the approach to land. It also allows the aircraft to descend at a quicker but comfortable rate if you have a lot of altitude to lose.
You don’t always need to use the spoilers in this way but it is very common and allows you to quickly match the speed of other aircraft ahead and behind you who are all in the same stream of aircraft coming into land.”There are often two sets of spoilers on airplane wings. The set close to the fuselage is called ground spoilers or airbrakes. “The ground spoilers are the exact same panels that are used as speed brakes in flight, except that on the ground they are allowed to deflect fully up and maximize the ‘lift dumping’ effect,” Plumb said. The Boeing 737 wing from a 1986 Boeing Maintenance Manual, modified by author.Plumb explained that the pilots pre-arm the system during descent to automatically activate when the wheels touch down.“A lot of people assume the spoilers work by acting as an airbrake, but in fact 80 percent of their contribution to stopping the aircraft is by stopping the wing from producing lift, and this forces the full weight of the aircraft onto the main wheels, thus making the wheel brakes much more efficient,” Plumb explained.
Flaps: Increase LiftThat first machine-like whirring noise you hear as your aircraft descends for landing is the sound of the flaps deploying. Flaps are both lift and drag devices. Deploying flaps allows the pilot to descend and maintain lift at a much slower speed on approach. At the same time, deploying flaps provides drag, which slows the aircraft. On most jetliners today, there are inboard flaps and outboard flaps, with the inboard flaps being closest to the fuselage.
They are deployed in degrees, as the aircraft descends for landing. These components are huge. A man washing the wing trailing-edge flaps of a Boeing 747-400. (Photo by: aviation-images.com/UIG via Getty Images).The flaps are raised and lowered via aircraft hydraulics inside the torpedo-shaped bodies under the wing, called track fairings. These also serve a dual purpose of improving aerodynamic flow under the wing. Flaperons: To Assist with RollAs the name suggests, a flaperon is a device that is both an aileron and flap.
They operate more like ailerons than flaps; they can adjust quickly up and down like an aileron, especially compared to flaps (which deploy ploddingly). Flaperons are found on larger twin jets such as the Boeing 777, Airbus A350 and Dreamliners. Flaperons will deploy during a turn when control inputs are performed. For a right turn, for example, the right wing’s aileron will raise ever so slightly, decreasing lift on the wing, whereas the flaperon will extend ever so slightly to counteract a portion of that loss of lift in a controlled manner. This all done by the airplane’s computers without additional input from the pilot. Spoilerons: A MisnomerA spoileron is a spoiler that also acts similar to an aileron — and these days they all do. It is not a separate component but a term used to describe the function of spoilers on many modern commercial aircraft.
Spoilers automatically, and without pilot input, in tandem with the aileron, as Plumb described above, to aid in the roll along the longitudinal axis. You won’t find “spoileron” in official documentation from Boeing or Airbus. Slats: Like Flaps, but on the Other Side of the Wing Wing leading edge slats deployed showing the extension mechanism on an Asiana Airlines Boeing 747-400. (Photo by: aviation-images.com/UIG via Getty Images)Slats extend outwards from the leading edge of the wing. Their main purpose is to allow the plane to fly at a higher angle compared to the relative wind; slats act to shift the oncoming air over the top surface of the wing. This allows the wing to maintain lift at a lower speed, such as when landing.
You don’t get to see the slats in operation from underneath, as a passenger.“The modern wing can pull the slats and flaps in so that it is the perfect shape for high speed, high altitude flying where the engines are most efficient,” Plumb said. “However, when aircraft come in to land we want the wing to produce maximum lift at much slower speeds so, much like a soaring eagle coming in to land, the slats at the front of the wing and the flaps at the back extend to create a much bigger surface area and produce more lift.”“Slats are incredibly important on jet aircraft with swept-back wings, which are ideal for high-speed flight but need enhancement to provide enough lift for low-speed flight.” What About Up and Down? A Quick Word About ElevatorsThe angle of the aircraft relative to the wind (and generally the horizon) is controlled by the elevators, but those aren’t found on the wing; they are part of the tail. “Pull back on the stick, the houses get smaller. Push forward, and the houses get bigger,” pilots like to say. As a passenger, you can’t see the elevators; they’re placed on the trailing edge of the horizontal stabilizer, i.e.
The tail of the aircraft. Putting It All Together“All of these flight controls work together to get the perfect wing shape for efficient flight. This is highly complex to coordinate but is made possible by modern flight control computers and means the wing is constantly adapting to conditions in a way that is not dissimilar to the way a bird flexes and adapts the shape of its wings,” said Plumb.You can see this in action with the video below, where an aircraft departs on its takeoff roll. Look for the flap-like flaperons moving quite a bit, as well as the spoilers acting in tandem to spoil lift and help stabilize the aircraft automatically. Winglets: Increase Lift and Reduce DragMost modern jets have winglets — those upward-sloped pieces on the ends of wings, often sporting advertising for the airline (Southwest.com!).
They serve an important purpose for efficiency. Chip Kiehn explained why. A Boeing 737-700 with “split scimitar” winglets.
(Photo by Alberto Riva/TPG)“Vortices of air are produced on wingtips due to the pressure differences between the upper and lower wing surfaces, which cause excess drag,” said Kiehn. “Wingtip devices are generally designed to disrupt those vortices in such a way that reduce overall air drag and increase overall wing lift.”“On new wing designs, designers have clean-slates when considering wing tip shapes and can incorporate the necessary efficiency at the onset,” Kiehn said. “As technology improves, so too does wingbox design.
Aviation Partners Boeing winglets are designed as an improvement on older wingbox technology. Our split-scimitar design is a further improvement on our Blended Winglet technology, providing the 737-NG as much as 2.2% additional reduction in fuel consumption over the original blended winglets. ”To see this whole dance in action, watch this video of a Lufthansa Airbus A320 — featuring blended winglets — aircraft descending to landing; you’ll see the ailerons move just a tiny bit, the flaps deploy, spoilers to slow the aircraft and ground spoilers deploy just after touchdown.
This particularly aircraft does not have flaperons. “The wing of a bird is a clue to future developments in wing design as some rather futuristic designs already imagine the whole wing morphing subtly, rather than just the flaps and slats moving,” Plumb said. “So next time you see a soaring eagle, pay attention to how the wing changes shape depending on whether it needs high or low speed; you may well be looking at the inspiration for the next generation of aircraft wings.”Mike Arnot is the founder of, a New York-based travel brand, and a private pilot.Featured image of a Boeing 747 wing by JT Genter/TPG. Advertiser DisclosureMany of the credit card offers that appear on the website are from credit card companies from which ThePointsGuy.com receives compensation. This compensation may impact how and where products appear on this site (including, for example, the order in which they appear). This site does not include all credit card companies or all available credit card offers.
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Please don't just answer by saying 'it changes angle of attack'. If you say that then you may need to explain me the AOA. Ok we say that AOA is the angle between the relative wind and chord line of the wing and that's the concept we have learned mechanically.For me the AOA an imaginary angle doesn't seem to be affected by changes under the wing at trailing edge. Because once the streamline hits the airfoil then the air flows on upper and lower area just from stagnation point. And this split flap neither increase the wing area nor changes the curveture to delay the separation of airflow.
Then how this split flap can increase lift apart from increasing drang while brings no changes to surface area or curveture of the wing? You have hit upon an observation asked by many, and answered by few!Three aircraft I have flown were equipped with split flaps (Cessna 310/340, DC-3). Each of these aircraft specified the use of the first flap setting for takeoff, when I presume additional low speed lift, but not drag, is desired. My (non-engineer) observation is that there was a small increase in lift with these flap settings, which was probably accompanied by undesired drag. This lift was probably mostly the result of making the best of the ground effect cushion, and moving the center of pressure aft a little so extreme nose high attitudes were not required to rotate the aircraft.Split flaps are mechanically the easiest of all flap systems, and are very good for creating drag, which the older, simpler aircraft needed. Like many things in aircraft developement, a better way (plain or fowler flaps) was found.
Since then, you really have not seen new aircraft designs come out with split flaps in the recent decades.Pilot DAR. Wizofoz, maybe I had too much to drink at dinner tonight. From my limited knowledge of aerodynamics, I thought:the 'chord' is the straight line between the leading and trailing edges of an aerofoil, while the 'camber line' is the average of the cambers of the top and bottom surfaces of the aerofoilthe angle between the longitudinal axis of the fuselage and the chord is the 'angle of incidence' and is distinguished from the 'angle of attack' which is the angle between the chord and the relative airflow meeting the aerofoil. Despite dated textbooks mentioning that lift is developed predominately from a low pressure region on top of the wing; it's not. The reality is that an aircraft's lift is developed as an opposite reaction to the wing moving air down in accordance with Newton's 3rd Law.
The low pressure is part of the process of getting air to move down. (Air is forced away from a region and creates a vacuum in its place.) Look at it this way and it might be a little easier to understand. Deploying split flaps at a given speed results in more air being pushed down, therefore more lift (and drag), resulting in the pilot either lowering the nose or reducing speed, or both, to maintain the flight path.I'm sure someone will disagree and someone else will elaborate.
Reverse,A quick Google shows that you are correct wrt the definition of chordline. It then makes split-flaps a little complex in that, when deployed, the wing now effectivley has two trailing edges, and therefore two chord-lines!As too your second point, that is basically what I said. An increase in incidence (which is basically what deploying a flap does) leads to an increase in A of A For a given attitude.mavis- You fink correctley- we're just working out WHY cl changes.Lowdown- to dicuss whether the pressure differential between upper and lower surface or the reaction to down-wash is the major contributor to lift is a bit like chicken V egg- one automatically leads to the other. I don't dis-agree, but hope I have elaborated!! Wiz, you may have commented while I was in the process of editing one of my numerous rewrites so that my comment made sense. I just remember how it was taught to me and I could never understand how air simply speeding up over the top surface of the wing created enough low pressure to lift an aircraft. Many of the diagrams at the time showed air in parallel paths moving aside to make way for a wing and then getting restored to order once the wing had passed.
It wasn't until much, much later when I was 'educated' that the air is moved downwards. It makes it a lot easier to understand many things about how the wing works. Rho.Vsq.S it's the Cl bit that changes (I fink)try L=Cl (1/2rhoVsq)Slodown is just abusing bernoulli i have video proof of bernoulli in action over a wing. And i don't think it should be explained as the 'low pressure lifting the wing', (at a very basic level) more that the higher px is trying to move to the low px area, but the wing is in the way - that conveniently explains spanwise flow nicely toohere's what i reckon:the average chord will change with split flap, but angle of attack should remain the same, just at a lower IAS, for the same nose attitude as the higher IAS.
No different than extending 'simple' flap really. We could go into circulation theory as well if you like but we won't complicate things. Simply put Lowdown is spot on. It is Newton's third law in action.
For every action there is an equal and opposite reaction.Bernoulli's principal is simply a way of quantifying the amount of air displaced by the wing according to Newtons Third law. For a 2000kg aircraft to fly straight and level 2000kg's of air must be displaced at any one time for the aircraft to remain flying level. Therefore they are both correct.However according to CASA all you need to know is Bernoulli’s theorem so don't go getting confused by all the rest of the (correct) theories.
I believe CASA exams still state that two particles of air that split at the front of the wing meet again at the trailing edge? (May not be anymore, but it was when I did my theory). What a load of hogwash!
But again don't worry about it, as the theory works regardless of the fact it is wrong.As stated in other posts a Split flap increases the amount of air displaced and thus increases lift (does stuff all to the airflow over the top of the wing). It does also increase drag so you need to overcome this to maintain speed (more power) or you can reduce speed and get the 2000kgs of lift and thus stay straight and level. Think about it this way, all an increase in AoA is doing is presenting more of the bottom of a wing to the airflow, therefore it displaces more air down thus creating more lift. You can also increase lift by increasing speed iaw L=0.5(rho)V^2 S Cl. Increasing speed again works with Newton as during whatever period of time, the amount of are displaced increases with speed.
Again Bernoulli's equation simply quantifies this.There are other factors that we can go into but you don't need to worry about them unless you are enjoying the fun of studying for an Aeronautical Engineering degree.So there you have it, a rather verbose explanation, but just remember that whatever theory you adopt they are in fact all correct (except for the two particle theory - an abuse of Bernoulli's work and Bernoulli never ever said that). However they do all simply come back to Newtons Third LawQEDAny questions please fire away.
I love this Sh.t!!! (yes I am a sadistic Aero Eng.)CheersCBEdited to add, The top shape of the wing is largely irrelevant. Essentially all the top of an aerofoil is good for is reducing the drag. A flat plate will produce lift (but a massive amount of drag), thus to ensure that our C172 flies with 150HP we have an aerofil shape that controls the airflow across the top of the wing reducing drag so we don't have to fit a merlin to a 172 (although that would make it sound better!). That should put the cat amongst the purist's.
I'd like to disagree with that for the 310, I don't think there's anything in the book about using flaps for take offThough I have not flown the 310 in 25 years, and no longer have the flight manual, I do recall flaps 15 for a short or soft field takeoff was a normal procedure in the flight manual. A review of information I can find through Google seems to confirm that. I agree that flaps zero is the procedure for normal takeoffs, but I did many at flaps 15 out of shorter paved and grass runways, and would not have done them if the flight manual had not so instructed.It did seem to shorten the ground roll. I always did wonder why, and just credited pushing a bubble of air ahead of the flaps, and thus getting good ground effect.Pilot DAR.
Split flaps, interesting! More drag than any other attachment.
Was described once to me that the wing has good enough aerodynamic qualities for the entire envelope so the need for only split flaps. 402 and 402B have split flaps as well. 404 went to fowlers. This goes the same for me as trying to explain how those barn door Kruger Flaps actually increase lift???? Swinging forward from under the leading edge???
Dropping vertically down??? Wouldn't that kill any smooth flow? Does the turbulent air behind the flap, both Split and Kruger, form a boundary that acts like an airfoil shape?