Pilot People/Flap Questions +

[legalwife]

So I am kind of fascinated with those wing flaps that come up on landing. There are alot of wires and things under there in the wings. Sat close by this week-end and wished I knew more. Well, common sense - I guess - would tell you the flaps come up for the air stuff that I never really understood in school. Are all those wires just to make that happen? Maybe they are for the engines, but they weren't really near there. Hmmm... Can you explain in layman's terms?

 

Also, why do some planes have the wings that tip/fold up at the end? Is that just for decoration or does that do something for some of the planes?

 

And last of all, I heard a hissing sound a couple of times - shortly after take off and then later when over ocean. I am wondering, yes, but I want to know what is that? Like we are releasing something. :eek:

 

Thanks for answering my questions. It would be so neat to sit by a pilot so I could say why and what and what was that and so on. It would have to be a good tolerant friend, huh... :) I am NOT a nervous flyer. I love it. I just wish I knew more about it. It is always amazing to me.

[wcook]

Not a pilot, just a guy who can't resist a cheap joke and is willing to share a tiny bit of knowledge to justify it.

 

The bent-up tips of wings increase the plans fuel efficiency by keeping the air smoother and reducing drag. Here's the Wikipedia article, which is fairly readable.

 

http://en.wikipedia.org/wiki/Winglets

 

It would be so neat to sit by a pilot

 

Ever seen a grown ... (must resist cheap joke.)

[Gardyloo]

Under the skin the wing assemblies are very, very complicated. The parts of the wing that you see rise on landing are usually the "speed brakes" - which, like movable parts of the leading (front) edge and the trailing (rear) edges, are used to control how smoothly or not the air passes over/under the wing. The speed brakes simply add wind resistance which helps the plane slow down. Most of the work on slowing is done by reversing the direction of the jet engines' thrust (this is the very loud roar you hear from the engines when you land) as well as the ordinary brakes on the wheels.

 

But the wings also hold controls for in-flight stability, controls for flaps and ailerons that allow the plane to turn, fuel tanks and fuel lines, power and control cables for the engines, and numerous other things. When you get your glimpse below the surface (when the speed brakes come up) you're only seeing a fraction of all the bits and pieces contained inside the wing.

 

The "winglets" at the end of the wings help reduce the turbulence caused by the wing as it goes through the air. That makes the plane more "slippery" as it flies, which results in less fuel being required by the engines to maintain the plane's speed. You'd be amazed how something as innocent as the winglets can make such a huge difference in the amount of fuel a plane needs over the course of a year.

 

There are a lot of hissing and gassy noises in airplanes. Usually they have to do with the cabin air/temperature/pressure mechanisms, but you'd have to be a bit more specific. The air vents (next to the lights) over your head also hiss a lot (and usually blow cold air onto you when you don't want it.)

[Sargent_Schultz]

Depending on deployment could be speedbrakes or spoilers.

[FlyerTalker]

If you look at THIS ARTICLE, I think you will see a photo (2nd one down) of what you were describing. If so, those are the spoilers that come up on landing. There are also "flaps" and "slats" that get deployed on both takeoff and landing to increase lift and reduce the stall speed of the aircraft. Simple details on flaps in THIS ARTICLE.

 

There is much more to the whole subject...the 727 had a wing that was described at times as "coming apart". It had multiple leading and trailing edge devices due to the lack of wing-mounted engines. Thus, it could operate out of relatively short runways.

[CruiserBruce]

There are a lot of hissing and gassy noises in airplanes.

 

My tongue is bleeding, I am biting it so hard!:D

[kenish]

Legalwife- Great topic, I wish more people shared your curiosity. An airliner is probably the most complex and technologically advanced machine that most people will encounter. (Your car has 15-20 thousand parts and an airliner has 10-25 million parts!) I'm a private pilot but what keeps a Cessna and a 747 in the air is pretty much the same.

 

The links Flyer Talker provided are great; just ignore the equations unless you're into that. Almost all aircraft have flaps on the trailing edge of the wing. Since a wing makes less lift as a plane goes slower, the wing area has to be increased to make enough lift at slow speed. You will see the flaps out at takeoff and before landing but "clean" at high speed. Making lift also makes drag (air resistance) so flaps are good at low speed but a liability at faster speeds, like a boat dragging anchor.

 

Airliners have slats at the leading edge (front) of the wing that have the same purpose as flaps.

 

The panels on top of the wing are spoilers. You may recall from science class that a wing makes lift by accelerating air over the top curved surface of the wing. The spoilers interrupt (spoil) the smooth flow of air and greatly reduce lift. They flip up on landing to stop the wing from making lift and firmly plant the aircraft on the runway. (Very important on wet runways to get maximum braking). You may see the spoilers come up a little on descent. It allows the plane lose altitude quickly while keeping speed under control.

 

Wings leave a turbulent wake that spirals off the wingtips, similar to the wake of a boat. It's wasted energy, and the upturned tips (winglets) turn some of the wake into lift. A longer wing would have the same effect but there are structural issues and the airplane may not fit into some gates at airports. Winglets only have an advantage during high speed cruise. At low speeds they just increase weight, drag, and fuel consumption. So you will not see winglets on planes that fly short routes. (For example the defunct Aloha Airlines had inter-island 737s with no winglets while the Hawaii-Mainland aircraft had them).

 

Keep on asking questions...even though I really understand aicraft as a pilot and an engineer it's still magical to me!

[scottbee]

So I am kind of fascinated with those wing flaps that come up on landing. There are alot of wires and things under there in the wings. Sat close by this week-end and wished I knew more. Well, common sense - I guess - would tell you the flaps come up for the air stuff that I never really understood in school. Are all those wires just to make that happen? Maybe they are for the engines, but they weren't really near there. Hmmm... Can you explain in layman's terms?

 

Also, why do some planes have the wings that tip/fold up at the end? Is that just for decoration or does that do something for some of the planes?

 

And last of all, I heard a hissing sound a couple of times - shortly after take off and then later when over ocean. I am wondering, yes, but I want to know what is that? Like we are releasing something. :eek:

 

Thanks for answering my questions. It would be so neat to sit by a pilot so I could say why and what and what was that and so on. It would have to be a good tolerant friend, huh... :) I am NOT a nervous flyer. I love it. I just wish I knew more about it. It is always amazing to me.

 

Wow, I'm going to try and fill in some of the missing pieces that explain what/why all these bits are.

 

• Ailerons: hooked up to work in opposite direction from the equivilant one on the other wing; this is connected to the control stick/column/wheel and in order to make the plane bank (roll); one goes up - forcing the wing down; and the other down - forcing the wing up.
  
• Flaps: extend out and down from the back of the wing. Also a lot of aircraft have leading edge slats/droops which go out and down from the front. The aim is to make the wing bigger and 'curvier' (for lack of a better term). A curvier wing generates more lift at slower speed than the normal wing shape, but causes extra drag at high speed; so flaps/slats down for landing and up during cruise (the extra speed at cruise results in enough extra lift to not need them). Generally about ½ flaps for take-off and full flaps for landing; and the difference it makes is quite astounding. No flap stall speed (where the wing stops generating lift) is about 200+kts whereas most commercial jetliners land at 135ish with the flaps down.
  
• Spoilers: pop straight up at right angles from the wing about 1/2-2/3 of the way back; generally after landing, but you might see them used in initial decent too. Used to remove lift from the wing (obvious after landing); and used in decent so you can lose altitude quickly without having to point the nose down (which picks up forward speed).
  

All clear as mud now?

 

 

 

• 
  
• Spoilers
  

[Sargent_Schultz]

Am I the only engineer on this board who actually has experience designing primary flight controls?

 

Travel agents and similar need not apply. :p

[scottbee]

Am I the only engineer on this board who actually has experience designing primary flight controls?

 

Travel agents and similar need not apply. :p

 

Perhaps, perhaps not. But you're the only poster that didn't make an attempt at answering the OP's question.

[scottbee]

So I am kind of fascinated with those wing flaps that come up on landing. There are alot of wires and things under there in the wings. Sat close by this week-end and wished I knew more. Well, common sense - I guess - would tell you the flaps come up for the air stuff that I never really understood in school. Are all those wires just to make that happen? Maybe they are for the engines, but they weren't really near there. Hmmm... Can you explain in layman's terms?

 

Also, why do some planes have the wings that tip/fold up at the end? Is that just for decoration or does that do something for some of the planes?

 

And last of all, I heard a hissing sound a couple of times - shortly after take off and then later when over ocean. I am wondering, yes, but I want to know what is that? Like we are releasing something. :eek:

 

Thanks for answering my questions. It would be so neat to sit by a pilot so I could say why and what and what was that and so on. It would have to be a good tolerant friend, huh... :) I am NOT a nervous flyer. I love it. I just wish I knew more about it. It is always amazing to me.

 

Wingtips;

sorry didn't address this in my first answer. As the air comes off the end of the wing, part of it spirals around and hits the top of the wing canceling out some of the lip. The wingtip acts as a 'fence' to prevent some of this from happening, and hence you lose less lift from wingtip vortices (which of course means more lift, more efficiency). See the diagram below to see what happens w/o a wingtip

 

 

Another way to solve this (777, 767-400) is to use a raked wingtip, where the sweep of the wing increases dramatically near the end, such that the air flipping back on top does so behind the bulk of the wing; like this

[FlyerTalker]

Am I the only engineer on this board who actually has experience designing primary flight controls?

Not an engineer, but does folding up the wingtips and cutting out ailerons, on a paper glider, count?:confused: :D

[kenish]

Interesting aside on winglets- Most 747-400s have them but they are actually an option. Japan Air Lines and All Nippon have a fleet of short haul 747-400s used on domestic flights (Boeing calls them -400D for "domestic"). They carry 550+ passengers with all-economy seating and fewer galleys and lavatories. Since flights are 30-90 minutes flying time, this recipe works. However lots of landings and takeoffs require beefed up landing gear and other structure. Also it's hard service on the plane so there's a point where it becomes economically better to convert the plane to longhaul routes.

 

Boeing designed the 400D with this in mind and the extra structure is removed since it's unnecessary for 1-2 flights per day instead of 20. Also the winglets are added since they will provide a benefit on long flights (see my previous post). Of course the airline removes a lot of seats and adds galleys and lavs so they are a conventional 3-class cabin.

[Globaliser]

The parts of the wing that you see rise on landing are usually the "speed brakes" - which, like movable parts of the leading (front) edge and the trailing (rear) edges, are used to control how smoothly or not the air passes over/under the wing. The speed brakes simply add wind resistance which helps the plane slow down. Most of the work on slowing is done by reversing the direction of the jet engines' thrust (this is the very loud roar you hear from the engines when you land) as well as the ordinary brakes on the wheels.

The panels on top of the wing are spoilers. You may recall from science class that a wing makes lift by accelerating air over the top curved surface of the wing. The spoilers interrupt (spoil) the smooth flow of air and greatly reduce lift. They flip up on landing to stop the wing from making lift and firmly plant the aircraft on the runway. (Very important on wet runways to get maximum braking). You may see the spoilers come up a little on descent. It allows the plane lose altitude quickly while keeping speed under control.

Just so that there's no confusion over this: The spoilers do both of these jobs. When they're extended they add to drag through wind resistance, tending to slow the aircraft; and they also reduce the lift produced by the wing.

 

Both of these effects are important to managing the aircraft's speed and helping it to stop.

 

If the spoilers are used in flight, they're usually extended part way for the drag they produce - so they're basically being used as speed brakes to keep the speed under control during descent. Otherwise the aircraft would speed up as it descends - just like a car tends to speed up as it goes downhill, and for the same reason.

 

When the aircraft touches down, the spoilers are fully extended. At this position, they also do a good job of destroying the lift produced by the wing. The reason this is important is that the effectiveness of the wheel brakes is dependent on how much weight is placed on the wheels: the more weight that is on the wheels, the more braking can be applied through the wheels before they start skidding (and once a wheel starts skidding, the braking produced through that wheel drops dramatically - just as in a car). So full extension of the spoilers lets the wheel brakes do the best possible job, as well as the spoilers acting as aerodynamic brakes themselves.

 

On many aircraft, wheel braking is actually the primary method of slowing the aircraft on landing. Although reverse thrust is noisy and dramatic - all those moving parts! - it's often a relatively small contributor to overall braking. Use of the thrust reversers is actually more important for high speed rejected takeoffs, where every bit of margin counts. But on landing, modern routine on many aircraft is to select only reverse idle, and to let the wheelbrakes do the main job; the main advantage of having selected reverse idle is so that you can call on full reverse quickly if you need to later in the landing roll. Modern carbonfibre brakes are actually happiest, and tend to give the longest life, if used like this; and the engines are also happier in the long term if not asked for a short burst of high power on every landing roll.

 

As you can imagine, this means that the wheel brakes absorb an enormous amount of energy during the process. That is transformed into heat, which has to be gradually dissipated into the atmosphere. If an aircraft performs a rejected takeoff at high speed, that makes the brakes do the hardest job they have to. Even if there is actually nothing wrong with the aircraft, you then have to wait for an hour or more before the brakes have cooled off sufficiently that another takeoff can be attempted.

Interesting aside on winglets- Most 747-400s have them but they are actually an option.

And they can be removed from any 744 that does have them. You sometimes see this when a winglet has been damaged in an incident. The aircraft can still be dispatched after the winglets have been removed, although the extra drag as a result means that there are payload and range limitations. But at least the aircraft can fly home under its own power, with most or all of its payload, and then get repaired at base.

[legalwife]

Wow.

 

I just can't thank you enough for all of your answers. How very interesting and explained so that I can understand it -well, I will print it out and re-read as I am not the most scientific minded but I got most of it. You all did great for me.

 

The hissing sound was shortly after take off and outside the plane when we were over the ocean.

 

Again, thank you so very, very much. I really enjoyed your explanations and bet others will as well.

[darth frosty]

I am an A&P airframe and powerplant mechanic. I had 60 flight hours before I ran out of money and life took over ;-)

 

But another great thing if your interested airplanes fly based on bernouli's principle: As velocity increases pressure decreases. As air flows over the curved top of a wing the pressure decreases because of the speed. Mean while the pressure underneath the wing increases pushing the wing upward. This causes the lifting force necesary for a plane to fly.

 

http://library.thinkquest.org/2819/bernoull.htm

 

A fun thing to do to see this in action as you are driving stick your hand out of the window and notice how the wind flows faster over the top of your hand and lifts it up.

[Bill S]

Sarge-I am far from being an engineer, but in my early days I was an Air Force pilot.

Just an interesting note on spoilers: one of the types of aircraft I flew was -G model B-52s, and they had no ailerons, just spoilers. Because the deployment of spoilers in a turn induced a slight nose-up moment, we had to put a little nose-down force in the yoke or trim, or if on auto-pilot, the stabilzer trim wheel would move down a bit at the start of a bank.

Great job by everyone who responded to OP's questions!

[Globaliser]

But another great thing if your interested airplanes fly based on bernouli's principle: As velocity increases pressure decreases. As air flows over the curved top of a wing the pressure decreases because of the speed. Mean while the pressure underneath the wing increases pushing the wing upward. This causes the lifting force necesary for a plane to fly.

 

...

 

A fun thing to do to see this in action as you are driving stick your hand out of the window and notice how the wind flows faster over the top of your hand and lifts it up.

There's also another component to this. If you look closely at an airliner's wing, it's angled up a bit - the leading edge (nearer the nose) appears higher than the trailing edge (the thin edge nearer the tail). And when airliners fly, most of them fly slightly nose up, making this wing angle more pronounced.

 

This helps to generate some lift, in addition to the Bernoulli effect. In simplistic terms, you can think of it as some of the air hitting the bottom surface of the wing and being deflected downwards, thus pushing the wing up. (You can also feel this effect if you stick your hand out of the car window.) Slightly more precisely, moving the wing through the air like this means that all of the air that's passed over the wing ends up slightly lower than it was before, with the effect that the wing that's caused it must end up slightly higher.

[scottbee]

Nope.

 

Wingtips are shoes.

 

Winglets are something else

 

Actually, a winglet is merely a type of wingtip that curves up, see also Hoerner wingtips, and various other shapes etc, generally in order to try and reduce drag.

 

Every aircraft has wingtips, it's the very end of the wing, and often contains usefly things like WINGTIP strobes or wingtip marker lights. Hopefully this Wikipedia article on wingtips will help clarify

[Sargent_Schultz]

Sarge-I am far from being an engineer, but in my early days I was an Air Force pilot.

 

Just an interesting note on spoilers: one of the types of aircraft I flew was -G model B-52s, and they had no ailerons, just spoilers. Because the deployment of spoilers in a turn induced a slight nose-up moment, we had to put a little nose-down force in the yoke or trim, or if on auto-pilot, the stabilzer trim wheel would move down a bit at the start of a bank.

 

Great job by everyone who responded to OP's questions!

 

Interesting...

 

Then there was United Flight 232 DC-10 that lost use of all flight control surfaces and only had the engines for control. They did crash land, but NASA decided to see if safe propulsion control was possible. We were one of the contractors that helped prove it could be done, but nobody was interested in paying for it commercially and it was never mandated. Intriguing concept, however.

[kenish]

Just an interesting note on spoilers: one of the types of aircraft I flew was -G model B-52s, and they had no ailerons, just spoilers. Because the deployment of spoilers in a turn induced a slight nose-up moment

 

Interesting...FYI, the B-52 was built by Boeing. Even on modern-day Boeings (and maybe other brands), at medium speeds (initial descent for example), the planes are banked by putting out a little spoiler on one wing- decreasing lift, and a little flap on the other wing- increasing lift. For example a left turn requires banking the plane to the left or a lot of Merlot will be spilled in First Class. So spoilers will be raised on the left wing making it go down, and flaps on the right wing making it go up. If you see spoilers coming up as the plane starts a turn that's why...once a turn is entered further bank isn't required so flaps/spoilers will retract.

 

Your comment on nose-up is also interesting. (Very technical here)...a wing creating lift has a nose-down twisting force called "section moment". Spoilers will decrease lift and the reduced section moment will cause the plane to nose-up. Didn't doubt your comment but had to think about why it's true.

 

OP- Several things that can cause a hissing sound outside the plane. In the first 5 minutes after takeoff, the flaps and slats are retracted. Air rushing through the gaps gets "squeeged" as the gap narrows and there is often a hissing sound with increasing pitch during the very last part of retraction (closest sound I can think of is a cappucino machine). Another source of hissing- on many aircraft the slats are powered by high-pressure air from the engines. When the slats are moving you may hear the air being vented through a control valve.

[spongerob]

Your comment on nose-up is also interesting. (Very technical here)...a wing creating lift has a nose-down twisting force called "section moment". Spoilers will decrease lift and the reduced section moment will cause the plane to nose-up. Didn't doubt your comment but had to think about why it's true.

Could it just be a case of adverse yaw? I learned to fly in a Schweizer 2-22. That glider had unbalanced ailerons (the downward deflection on one wing was equal to the upward deflection on the other) so the aileron moving down into the higher pressure air under the wing had more force acting on it. This created a turning moment opposite to the direction of bank. If the pilot didn't use enough rudder to compensate or just threw the stick to one side the result was a side slip opposite to the bank with an upward pitch.

[legalwife]

Well, you have also made my dad's day. I was telling him about this and he wanted me to bring him a copy. He is 86 and thoroughly enjoyed reading all of your comments.

 

I am NOT a dumb person, but you all sure sound smart!!! ;) Really!

 

Thanks again.

[Bill S]

Could it just be a case of adverse yaw? I learned to fly in a Schweizer 2-22. That glider had unbalanced ailerons (the downward deflection on one wing was equal to the upward deflection on the other) so the aileron moving down into the higher pressure air under the wing had more force acting on it. This created a turning moment opposite to the direction of bank. If the pilot didn't use enough rudder to compensate or just threw the stick to one side the result was a side slip opposite to the bank with an upward pitch.

 

Hi Spongerob-I had nothing to add to your observation, until I happened upon an article about spoilers in a recent aviation magazine.

I learned a couple of things, mainly that when aircraft have no ailerons and use spoilers exclusively for roll control, then the term to describe them is "spoilerons". The other thing was that according to the author, using spoilers "for roll control" usually results in less adverse yaw than ailerons. Wish I could explain that one!

In the B-52G we used our "spoilerons", not only for roll, but as airbrakes to increase rate of descent, and on landing roll to reduce speed (along with a drag chute). Also, during air-to-air refueling we raised them about 1/3 of full deployment to enhance responsiveness to slight roll inputs on the yoke.

It is a good article on spoiler basics. If you want to know where to find it, email me at the link below. I'm going to take a glider ride someday. Good stuff. :)

[spongerob]

Hey Bill, must have been fun to fly the BUFF. It's still amazes that something weighing close to half a million pounds fully loaded could take to the air.

 

We used our spoilers the same way when landing. In a glider you want to maintain constant airspeed on approach, which for us was our best L/D speed (most efficient exhange of altitude for distance) plus wind speed. We used our spoilers to control rate of descent. On the 2-22 the spoilers were small and not very effective but the 2-33 was a great improvement. The spoilers were longer and paired with dive brakes. You could really get down in a hurry with those.