Questions tagged [flaps]

Surfaces that extend from the wings to increase lift, allowing flight at slower speeds (such as for takeoff and landing).

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20
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3answers
27k views

Why and when to use flaps?

On a commercial airliner, what is the purpose of the flaps? I understand that depending on which direction they move in, they can be used to decrease airspeed, but I don't know when flaps are used. ...
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3answers
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How does the particular piece of flap behind an engine on a B777 work?

On several B77 photos, I notice that flaps just behind the engines are not always coordinated with the others flaps. On this photo flaps are extended but not behind the engine whereas on this photo ...
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2answers
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Why didn't the Concorde have flaps or slats?

It's well known that the Concorde had no flaps or slats. The lack of high-lift devices considerably reduced lift at low speeds, requiring the Concorde to take off and land at higher speeds and angles ...
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2answers
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How do the uninterrupted and interrupted flaps compare?

(wikimedia.org) Airbus A350. There aren't many wide-bodies out there. Whether it's Douglas, Boeing, or Ilyushin, they all have the high-speed aileron interrupting the flaps. Whereas Airbus uses ...
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14answers
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Is it considered good or bad practice to raise the flaps right after touchdown?

This question is about light, tricycle, single engine aircraft. I have made it a habit to raise the flaps right after touchdown (when the nosewheel is on the ground). My instructor used to do that ...
18
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3answers
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Why do slats deploy first?

I know on the 737, the leading edge slats deploy at the first flap setting, and the trailing edge flaps deploy after that at higher flaps settings. Why do the slats deploy before the trailing edge ...
25
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4answers
5k views

Why are heavy flaps better than just a bigger wing?

Flaps increase lift during landing and T/O. But when retracted, they do nothing. The space needed to stow the common fowler flaps can't be used for anything else - fuel or structure. Extended flaps ...
3
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2answers
862 views

Why is the critical AoA of most flaps 40° when most airfoils stall at 15°?

A plain flap deflected 40 degrees is largely stalled (...) Flaps stall at 40° according to an answer on Quora, why is this so when typical airfoils stall at 15°?
19
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2answers
53k views

What is the difference between flaps and slats?

I have heard pilots talk about flaps and slats, seemingly interchangeably. Is there a difference between a flap and a slat or they are the same thing?
18
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3answers
8k views

Can a super land without flaps/spoilers?

Can the Airbus A380 or Boeing 787 land safely without flaps/slats/spoilers or thrust reversers?
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2answers
4k views

Do negative flaps increase glide ratio?

If I understand correctly, gliders uses negative flaps while crossing between 2 thermals, but I don't understand why. For me: positive flaps decrease sink rate but increase drag and thus worsen glide ...
11
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3answers
9k views

How does the slotted flap work?

Slotted flap is an improved version of the plain flap, generating more lift (a fact I don't challenge). However the principle is air passing between the wing and the flap. Source This seems ...
21
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5answers
36k views

Should full flaps be deployed on takeoff?

Are full flaps ever used on takeoff? One flying book I read strongly discouraged anything more than quarter flaps on most planes due to the amount of drag produced. I was just wondering if there are ...
11
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5answers
3k views

What is the point of making one control surface play the part of multiple control surfaces?

For example, flaperons (flaps + ailerons) and elevons (elevator + ailerons), are all individual control surfaces but play the roles of two different control surfaces. What is the point of making a ...
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7answers
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Is it possible to takeoff without flaps extended?

related questions: landing wihtout flaps takeoff with full flaps My question focus on passengers jets (goes from Embraer E-jet family to Airbus A380). I don't know why pilots would attempt to ...
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1answer
298 views

Why is subsonic lift at 25% of chord? [duplicate]

I pretty much understand the way a wing works and the different ways of explaining it, what I don´t understand is why the lift on a subsonic wing manifest itself at the 25% chord.... The 50% chord ...
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5answers
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Why are flaps retracted when an aircraft is parked on ground?

I found this question. One of the answer tell the flaps are generally retracted after landing. I assume this mean flaps are retracted when the airplane is on the ground between flights. Flaps are ...
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2answers
9k views

Why does stall speed decrease when flaps are deployed?

I've been told that deploying the flaps on approach enables the following: Potentially steeper approach Slows down the plane Lower stall speed It's the last one that confuses me. Given the equation ...
2
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1answer
565 views

Does the flap settings for the best lift/drag ratio change with speed on the Diamond DA20-A?

As I've recently started time building in DA20, I've noticed the AFM suggests flaps at T/O for a glide. Being very intrigued by this I run across this post. Although I appreciate Peter's reply that ...
13
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1answer
3k views

What is the meaning of flap detent names (e.g., 10 degrees)?

When I extend my flaps to 10 degrees, what exactly is the 10 degrees measuring? Is this referring to the angle of the flap blades themselves, the new angle of the wing chord, the change in the new ...
8
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1answer
1k views

When should I use the global Reynolds number and when the local Reynolds number?

I know that for the wing, the Reynolds number is based on the MAC. This makes sense to me, as the boundary layer develops along the length of the wing. However, what kind of Reynolds number needs to ...
138
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9answers
103k views

Is this plane landing or departing?

I have a picture of Air Force One I took fairly up close several years ago. Unfortunately, I don't remember if that was on arrival or departure. Is there anything visible in the airplane's ...
11
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3answers
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What is the point of having lots of different flaps settings?

This question is about the number of flaps settings on different airliners. One can notice that this varies greatly between models and manufacturers. On a Cessna 172, you usually only have 4 or 5 ...
10
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2answers
6k views

Why do similar Airbus and Boeing aircraft use different flap and slat mechanisms?

Why do most Boeing aircraft and their corresponding Airbus counterparts have different flaps and slats mechanisms (747 and A380, 737 and A320)? I'm assuming a lot of these mechanisms are patented. For ...
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1answer
4k views

How do flap track guides work?

I am planning to build a large-scale LEGO airlier with most parts functional. Doing a little looking at pictures and research I see that commercial airliners have an underwing body that houses the ...
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1answer
5k views

Is the A320 family allowed to take off with the flaps retracted?

Is it legal for the A320 family (A318, A319, A320 and A321) to take off without flaps? An answer to this question states that the A300 can take off without flaps. On the other hand, the 737 family of ...
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2answers
2k views

What are the flaps on the exhaust of military airplanes for?

I have been looking over some pictures of military airplanes, and I noticed that some of the more modern air planes have flaps on the exhaust I was wondering if anyone knew what the purpose of the ...
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1answer
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How is the area of flaps determined?

While may be possible to look up the dimensions of high lift devices in an aicraft's documentation, there is no information on what the underlying design choices are. Using Wikipedia, I found out ...
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1answer
652 views

Why does the DHC-6 pitch down when the flaps are retracted, rather than up?

Air Moorea Flight 1121 crashed because one of its elevator cables broke immediately after the pilot retracted the flaps, but before he could trim out the resulting pitch-down moment - to quote the ...
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2answers
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Is an Airbus A319 allowed to fly with a missing flap track fairing?

During a recent flight from Copenhagen to Milan in an Airbus A319, one of the flap track fairings were missing from the wing. I saw this during takeoff, and notified a flight attendent as soon as the "...
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8answers
23k views

If flaps are used on takeoff, when should they be retracted?

If a pilot uses a notch of flaps on takeoff, when do they get retracted? At that time, what changes (i.e. climb rate, speed, pitch)? NOTE: I have purposefully not specified the type of airplane.
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3answers
8k views

Why did Cessna get rid of manual flaps in their 172?

At the club I fly at, there is an older Cessna 172 that has a manual "Johnson Bar" that is used to put the flaps down. In the newer 152, and I believe the rest of the planes (I have yet to fly them), ...
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2answers
8k views

What are the benefits of using Krueger Flaps?

I mean why using Krueger flaps in some aircraft instead of using slats all over the leading edge?
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1answer
2k views

Why is deploying speed brakes not recommended with the flaps extended?

I read this in the normal procedures section of the A320 FCOM. Why is it so? When the speed brakes are deployed, extending the flaps beyond FLAPS 1 may induce a slight roll movement, and in calm ...
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4answers
555 views

Why do flaps retract?

Why do flaps retract? I know, it might seem obvious at first, because of drag, but instead of retracting the flaps, can't they just make the flaps flexible enough to get into a reduced drag position, ...
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6answers
8k views

Why retract flaps at go-around?

As I understand the procedure for go-around it includes retracting the flaps. Why is this? The decision to make a go-around must sometimes be made quickly, under stressful conditions, like in bad ...
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2answers
4k views

Do flaps have a maximum speed limit but spoilers don't? Why?

This related question on Aviation SE describes how in most aircraft spoilers (flight spoiler mode not ground spoilers) are deploy-able at any speed But flaps on the other hand mostly have a V_FE above ...
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2answers
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Why were the 747SP's trailing-edge flaps so much different than those of the -100/-200?

I read several decades ago about how the 747SP's trailing edge flaps were substantially redesigned from those of the "original" 747-100/-200s. The images on the 747SP Wikipedia page clearly show what ...
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3answers
4k views

To flap or not to flap?

I am learning to fly an Ikarus-C42. The instructor I have recommends to all students that they land without flaps, because it is less to think about and because it gives you more airspeed, thus less ...
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2answers
2k views

Do modern airliners have a flaps warning indication?

Years ago I was on a flight from San Francisco to Los Angeles, a 737 if I remember rightly, and was sitting just behind the wings and could not help noticing the flaps were partly extended for the ...
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4answers
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Why not always take off with 10 degree flaps in a Cessna 172?

10 degree flaps increase our lift, reduce stall speed, reduce ground roll. Seems like all advantages with no disadvantages. So why does the Cessna 172 POH say normal take off is 0-10 degree flaps? Why ...
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2answers
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Do auto-flaps exist?

Slats can be extended automatically depending on dynamic air pressure. Fly-by-wire systems provide flight envelop protection when flaps/slats are extended but I cannot find any reference of fly-by-...
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6answers
3k views

What would happen if flaps are extended beyond 40 degrees?

The angle of flaps is limited to a specific value. It's around 30° to 40° on most aircraft what I've seen. Source But what happens when they get extended even further? 50°, 80°, 90°, ... Let's also ...
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2answers
2k views

Is it right to extend flaps only in the white arc?

If the cruise speed is >80kts on the downwind leg but I can only extend flaps in the white arc, am I right in saying I need to get to the white arc, even if I'm on - for example - 100kts? For ...
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3answers
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Why doesn't extending the flaps on a B-2 send it into an uncontrollable dive?

The Northrop-Grumman B-2, a tailless-flying-delta-wing aircraft, has a set of flaps along its trailing edge, as seen (for instance) in this cutaway diagram: (Image from Funker530.) But tailless ...
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2answers
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What is the flap extension schedule on approach for an airliner?

I understand that there are probably no set altitudes and speeds for flaps extensions, but can someone with insight provide a general guide for speeds, altitude and flaps for an ILS approach in good ...
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1answer
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Why and how do flaps increase the curvature of the wing?

Why or how do flaps increase the curvature of the wing? Do they alter the curvature of the upper surface of the wing?
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2answers
940 views

How does the flap configuration affect the tailstrike limit on the A320 aircraft family?

The configuration that provides the maximum FLEX temperature varies with the runway length. On short runways, CONF 3 usually provides the highest FLEX temperature, and the tail clearance at lift off ...
5
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1answer
909 views

What are the aerodynamic differences between the different types of slotted flaps?

How do the different types of slotted flaps (Single, double, and triple as well as a non-slotted one just for comparison) differ aerodynamically? I read in Joe Sutter's book 747 that a double-slotted ...
5
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1answer
2k views

Why don't aircraft use gimbaled engines instead of flaps? [duplicate]

Why do aircraft use flaps rather than vectoring the engine or angling the engine? Elon Musk said he would gimbal the engine like a rocket with the aim of reducing total weight of the aircraft and ...