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Hot answers tagged flaps

44

When flaps are retracted they do nothing, which is the whole point. The byproduct of lift is drag, a larger wing will create more lift, but more drag as well. More drag equals a slower cruising speed, or bigger engines to power past the drag along with higher fuel consumption. Flaps let airplanes cruise faster by getting out of the way.

25

Your concerns about heavy flaps are well founded. The designers try to get away with as few high-lift devices as they can afford to. But not fewer! If you observe the trend over the years, flaps became more complex with every new airliner generation, starting from simple split flaps in the 1930s to triple-slotted flaps on the Boeing 747 in the late Sixties. ...

25

Flaps out will reduce the ground run, but you're forgetting that they also increase drag. This is why you don't climb all the way to cruise altitude with flap extended. A 172 will climb better without flaps. With a take-off, you have to consider both the ground run and initial climb. After all, the take-off distance required is defined as the distance ...

22

Yes you must slow down to the white arc, or whatever your flap extension speed is for a given condition, regardless. If you are 10kts above the white arc and drop flaps anyway, it's not going to make the airplane come apart, and if you did it once, slap yourself on the wrist and don't do it again. It's putting stress on the flap attachments beyond what ...

18

Because there is a maximum deployment speed for things like flaps, gear extension (and sometimes retraction). Exceeding these speeds and using those devices can cause damage to control surfaces or other equipment. The speed check is there so that when the PF calls for flaps, the PM remembers to check the speed before performing the action.

13

Climb to cruise burns fuel. Adding additional drag burns fuel. Adding retractable mechanisms adds weight that burns fuel. More drag, even at higher cruise altitudes, requires larger engines for the same cruise speed. Larger engines burn more fuel (despite increases in modern engine fuel efficiency). Retracting high-lift, high drag devices reduces fuel burn ...

11

A flap increases airfoil camber, and can be on the leading edge or trailing edge. The Krueger Flap is a Leading Edge Flap, the actual generic term. The Krueger dude developed the LE flap used on some airliners so his name is attached. A slot increases stalling AOA, without necessarily increasing camber, as in the fixed slots used on a lot of light ...

11

For an aircraft designed for cruising efficiency it is important to have as little trim drag as possible. See ATR 72 link: The wing may appear unusually small, but it is made to produce the needed lift at cruising speed at its most efficient Angle of Attack, where lift to drag ratio is highest. If the wing produced too much lift for level flight at its ...

11

The questioner seems to have noted that the basic wing with flaps retracted provides a high ratio of L/D (or Cl/Cd). Where L denotes lift, Cl denotes lift coefficient, D denotes drag, etc. We can certainly scale up the basic unflapped wing to provide as low a landing speed as we wish, although landing will be tricky due to the flat glide path. Flaps help ...

10

It depends upon what the manufacturer recommends on the form of the AFM in cockpit placards. Certain aircraft do allow extension of the flaps outside the white arc for certain flap settings. For example the Cessna 182T is placarded for 10° flaps at or below 140 KIAS, 20° flaps at or below 120 KIAS and 30° flaps at or below Vfe of 100 KIAS, despite the fact ...

9

An Aileron is used to control the roll of an aircraft. Ailerons are found on the trailing edge of the wing, typically closer to the wing tip. Ailerons will move in opposite directions to each other, as one goes up, the other goes down. Flaps are used to increase the amount of lift that a wing produces by increasing the camber and surface area of the wing. ...

9

One function of common inner span flaps that's not often discussed is stall management. Not only does some flap lower the stall speed, but it ensures the wing root stalls while the tips are still flying; this prevents an incipient stall from turning into a low altitude stall-spin if a wind gust or unplanned maneuver pushes the aircraft from "controlled ...

8

In addition to the previous answers, you could argue that yes: provided you had a long enough runway you could theoretically perform a takeoff run that accelerates you to a speed which is sufficient for taking off and remain airborne with no flaps (and for this exercise let's assume an A320 has a flaps-up speed of 210 knots, give or take), but you'd be ...

8

Aside from the decreased takeoff speeds, there are a couple reasons why typical Part 25 aircraft do not allow flapless takeoff: There is usually a sweet spot at lower flap settings that generate the best climb gradient at V2, and it's usually not with flap retracted. It is typical to see several takeoff flap settings that cater to best climb and best field. ...

6

For a leading edge high-lift device to be called a slat, it has to have a slot behind it. Otherwise, it is a leading edge flap (or, if it's of a specific design, a Krueger flap). Because: By definition, the word slat means a thin, narrow strip. Its etymological roots lay in Middle English word slate, first recorded use in the aforementioned meaning dates ...

6

Flaps retract in order to reduce wing area. This has several advantages when flying fast: The higher wing loading (weight per lift-producing area) reduces gust loads. When hit by a vertical gust, the angle of attack increases suddenly, and so does lift. If this happens at high speed (more precisely: At high dynamic pressure), the lift increase might ...

6

Some answers presume that raising flaps reduces lift. That is wrong.* All it does is to increase angle of attack, until the change in flap setting is so severe that the airplane stalls. Only then will the airplane lose lift. With a smaller flap setting, the pitch trim changes and the airplane pitches up a little to keep lift constant. If the (auto)pilot ...

5

Flaps 50 vs. Flaps 35 results in approximately a 5 knot reduction in approach speed in calm conditions. I routinely use flaps 50, depending on weight, runway, and conditions.

5

The MD-11 has one of the highest approach speeds, which is comparable to the 747-400 (Boeing), while having higher wing loading: 806 vs. 756 kg/m$^2$. In other words, the MD-11's wing is small, so flaps 50 is not an overkill. The standard MD-11 landing flaps are either 35 or 50 depending on the weight, altitude, available stopping distance, etc. Aircraft ...

5

Note that your plots show lift coefficient over angle of attack. This lift coefficient is referenced to a reference area which must be defined somehow. It is customary to use the projection of the clean wing area in the x-y plane for all flap settings in order to keep coefficients comparable. The lift curve slope increases because the real wing area ...

5

A slat is a retractable version of a device known as “leading edge slot”. It is basically a slot just behind the leading edge. When an airplane is flying slow, it will probably either be somewhat nose-up to maintain level flight, or be descending, or somewhere in between. In either case, the air strikes the wing at a higher angle than when the plane is ...

5

You did the right thing when asking a new question. Comments are poorly suited for the explanation of non-trivial issues. Now follow several links to older answers. They should help to explain a couple of things, such as: what flaps do to L/D. how thrust changes over speed for propeller aircraft. and how efficient propeller airplanes are in cruise. does ...

4

The plane is landing. the engines are running on low power setting, otherwise there would be considerable blurring visible below the rear fuselage because of the hot exhaust plumes. In this picture the blur behind the main gear is similar to that in front of the main gear, consisting of bokeh and motion blur. looking carefully you can actually see that the ...

4

And some older Mooneys have infinite flap settings depending on how much you pump them up... The reality is that there are no regulations on how many flap settings an airplane must have and on an airliner that may also have things like speed breaks or slats as well, flap settings may vary by design or simply by engineering choice. Flaps are used for ...

3

It is theoretically possible to do a flaps up take off if you have a long enough runway, but why would you want to? An airplane is designed to be most efficient in the air, so the sooner you get there, the better. The lift available to an aircraft is proportional to the area of the wings (and flaps increase that area), however, the drag those wings produce ...

3

Several other good answers, but one reason I haven't seen yet is pilot proficiency. You don't want pilots only practicing short-field takeoff and landing technique on actual short fields, which might be rare depending on 5he routes any given pilot happens to fly. If they use that technique on every takeoff and landing, though, then you know they'll always be ...

3

The aspect ratio of a wing is defined as: $$\text{AR} \equiv \frac{s^2}{A} ,$$ where $s$ is the wingspan and $A$ is the total wing area. Some types of flaps are not only increasing wing camber, but also the wing area: The Fowler, Fairey-Youngman and Gouge types of flap increase the wing area in addition to changing the camber. (Wikipedia) Since the ...

3

No, for several reasons What you want is to compensate for the additional lift from downward deflected flaps at the back of a flying wing with vectored thrust. As @Sean points out this will not bring a noticeable net benefit if the lengthwise location of both forces is similar. But that is not all. Besides the force equilibrium around the flying wing you ...

2

The airplane's reaction to full flap deflection depends strongly on how much of the wing chord is occupied by the flaps. "The Full Ninety" (degrees) was once a popular marketing phrase, alluding to the racy title of a movie then in wide release, bragging about how the airplane's manufacturer had finagled the linkages for that much deflection to increase ...

2

When flaps are extended beyond the standard 40 degrees the result depends on the design of the rest of the aircraft. Extreme deflection of large full span flaps has been used experimentally to attempt to create STOL/VTOL aircraft, such as the Ryan/Fairchild VZ3. Flaps here are at 90 degrees and have huge end plates to reduce losses. A turbine in the ...

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