How does an aircraft's wing work?

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Well I am certainly learning some stuff here. I had always assumed a torpedo motor was powered by compressed air! I had no idea they actually used an internal combustion engine. Now i see about the starters on modern jet engines, thanks. I had heard of the cartridge starters before but assumed they were just used on marine Diesel engines and prop powered aeroplanes. Interesting here innit? :D
 
Sorry about the delay folks, but AES has now got himself organised and got the promised piccies. I’ve compressed them all for web viewing (hence the “ … -C” in each title). I hope they’ll be clear to see OK here.

A310-1-C
A310-1-C.JPG


This is the first shot of an Airbus A310 undergoing heavy maintenance. For info this particular aeroplane is/was operated by Air India after having started its life newly built for Swissair. The A310 is the 2nd “Scarebus” that Airbus produced (after the original A300) and this “stretched” model, the -300, seats roughly 220 in 2 or 3 classes over a medium range (e.g. Zurich to the Middle East). I took this pic because it clearly shows the LE Slats that I was talking about before. Here they’re fully deployed (“drooped”). If I remember correctly (it’s quite a few years since I had anything to do with A310s) they go down in 3 steps, ending up with 10 degrees down as shown here. The funny little vaguely triangle-shaped curved surface right up against the fuselage at the wing root is called a Kruger flap, and like the rest of the LE Slats, it increases the curvature (“camber”) of the front of the wing. BTW, I see that in my absence you’ve been discussing various types of gas turbine, so it may interest you to know that the “big hole” below the wing is where the No. 1 engine goes (it’s away in the shop for overhaul). The big outer round bit that’s left hanging from the pylon is the back end of the bypass duct, i.e. the rear of the engine nacelle. The “small hole” in the middle shows where the back end of the core of the engine, including its jet pipe, will fit. Big difference between the diameter of the fan at the front of the engine and the engine core at the centre isn’t there? This aircraft has Pratt & Whitney JT9D high-bypass ratio engines of about 50,000 lbs thrust each. There is of course another engine on the RH wing (otherwise the aeroplane would only go round & round in circles! ;-)

A310-2-C
A310-2-C.JPG


View of the same aeroplane from above & behind. First, the inboard TE Flap has been removed and is sitting on a pair of cradles on the floor. More on that in a mo. The next “flap” hanging down but still fitted to the aeroplane is the Inboard Aileron. This provides roll control throughout all flight phases. Being a bit of a “barn door” surface it’s “hydraulically geared” so that up & down movements are quite large at low speeds (say up to about 220 mph) but are then much restricted above that speed. Next, on the upper surface of the wings there are 5 oblong “empty spaces”. These are the “Speed Brake/Spoiler” panels. They’re more or less flat panels, each powered by a hydraulic actuator. On landing, once the on-ground sensor says the aeroplane is firmly on the ground and the wheel-spin sensor confirms that they are turning at above about 140 mph, all 5 will be automatically raised to their max, about 60 degrees. This is “Spoiler” (or “lift-dumping”) mode. During high-speed flight (above about 220 mph) the 3 most outboard spoilers become “assistant ailerons” and are raised (by progressively smaller amounts as we move out along the wing towards the tip) to assist the “proper” (Inboard) aileron with roll control. The angle that these are raised to varies with the speed and their individual position along the wing. The outboard 4 of those 5 panels can also be raised to various angles (as signalled by the pilot) to act as Speed Brakes, for example during descent, when it may be necessary to slow down quickly to obey ATC instructions, or to quickly get below the max allowable Flaps lowering speed.
The pic does not show it (the wing tip is hidden under the balcony I was standing on) but believe me, this aeroplane has no Outboard Aileron out near the wing tip. Someone will no doubt ask me why, and being a smart a**e I will answer “ ’cos it makes the wing more efficient”; but when someone then asks “how’s that then?” I’ll have to reply that I’m not an aerodynamicist and don’t really understand it all. But the A310 is not the only aeroplane without Ailerons in the usual place (on/near the wing tip) but it’s one of the few that I know anything at all about.
The other apparently one big surface hanging down at an angle from the TE of the wing is the rest of the TE Flaps. More on those in pic A310-3-C.

A310-3-C

View of the same aeroplane from above & behind. First, the inboard TE Flap has been removed and is sitting on a pair of cradles on the floor. More on that in a mo. The next “flap” hanging down but still fitted to the aeroplane is the Inboard Aileron. This provides roll control throughout all flight phases. Being a bit of a “barn door” surface it’s “hydraulically geared” so that up & down movements are quite large at low speeds (say up to about 220 mph) but are then much restricted above that speed. Next, on the upper surface of the wings there are 5 oblong “empty spaces”. These are the “Speed Brake/Spoiler” panels. They’re more or less flat panels, each powered by a hydraulic actuator. On landing, once the on-ground sensor says the aeroplane is firmly on the ground and the wheel-spin sensor confirms that they are turning at above about 140 mph, all 5 will be automatically raised to their max, about 60 degrees. This is “Spoiler” (or “lift-dumping”) mode. During high-speed flight (above about 220 mph) the 3 most outboard spoilers become “assistant ailerons” and are raised (by progressively smaller amounts as we move out along the wing towards the tip) to assist the “proper” (Inboard) aileron with roll control. The angle that these are raised to varies with the speed and their individual position along the wing. The outboard 4 of those 5 panels can also be raised to various angles (as signalled by the pilot) to act as Speed Brakes, for example during descent, when it may be necessary to slow down quickly to obey ATC instructions, or to quickly get below the max allowable Flaps lowering speed.
The pic does not show it (the wing tip is hidden under the balcony I was standing on) but believe me, this aeroplane has no Outboard Aileron out near the wing tip. Someone will no doubt ask me why, and being a smart a**e I will answer “ ’cos it makes the wing more efficient”; but when someone then asks “how’s that then?” I’ll have to reply that I’m not an aerodynamicist and don’t really understand it all. But the A310 is not the only aeroplane without Ailerons in the usual place (on/near the wing tip) but it’s one of the few that I know anything at all about.
The other apparently one big surface hanging down at an angle from the TE of the wing is the rest of the TE Flaps. More on those in pic A310-3-C.

See "Part 2"
 

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View of the same aeroplane from above & behind. First, the inboard TE Flap has been removed and is sitting on a pair of cradles on the floor. More on that in a mo. The next “flap” hanging down but still fitted to the aeroplane is the Inboard Aileron. This provides roll control throughout all flight phases. Being a bit of a “barn door” surface it’s “hydraulically geared” so that up & down movements are quite large at low speeds (say up to about 220 mph) but are then much restricted above that speed. Next, on the upper surface of the wings there are 5 oblong “empty spaces”. These are the “Speed Brake/Spoiler” panels. They’re more or less flat panels, each powered by a hydraulic actuator. On landing, once the on-ground sensor says the aeroplane is firmly on the ground and the wheel-spin sensor confirms that they are turning at above about 140 mph, all 5 will be automatically raised to their max, about 60 degrees. This is “Spoiler” (or “lift-dumping”) mode. During high-speed flight (above about 220 mph) the 3 most outboard spoilers become “assistant ailerons” and are raised (by progressively smaller amounts as we move out along the wing towards the tip) to assist the “proper” (Inboard) aileron with roll control. The angle that these are raised to varies with the speed and their individual position along the wing. The outboard 4 of those 5 panels can also be raised to various angles (as signalled by the pilot) to act as Speed Brakes, for example during descent, when it may be necessary to slow down quickly to obey ATC instructions, or to quickly get below the max allowable Flaps lowering speed.
The pic does not show it (the wing tip is hidden under the balcony I was standing on) but believe me, this aeroplane has no Outboard Aileron out near the wing tip. Someone will no doubt ask me why, and being a smart a**e I will answer “ ’cos it makes the wing more efficient”; but when someone then asks “how’s that then?” I’ll have to reply that I’m not an aerodynamicist and don’t really understand it all. But the A310 is not the only aeroplane without Ailerons in the usual place (on/near the wing tip) but it’s one of the few that I know anything at all about.
The other apparently one big surface hanging down at an angle from the TE of the wing is the rest of the TE Flaps. More on those in pic A310-3-C.

A310-3-C

A310-3-C.JPG


Here’s a picture of the removed Inboard TE Flap. Notice that it’s actually 2 separate (but joined) surfaces. There’s the highly cambered “LE Slat” belonging to this Flap segment that you can (hopefully) just see against the forward Main Landing Gear wheel. Notice also the “wavy” TE of this flap segment. This is partly due to the change of Dihedral (upward angling of the wings to aid stability) but is also a function of the fact that as said in my last post, the wing at the root (where it joins the fuselage) is set at a positive angle of incidence (i.e. nose up) but as we move out along the wing to the tip that angle of incidence is progressively “washed out” until at the tip it will be, typically MINUS a degree or so (nose down). As said before, this is to prevent/reduce “tip stalling” (i.e. the wing tip on the inside of a turn will otherwise tend to stall before the rest of the wing does). Not good for stability and control, let alone pax comfort!

A310-4-C
A310-4-C.JPG


See Part 3
 

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his shows the Port Tailplane (Horizontal Stabiliser in American-speak). It’s one half of the “little wing at the back” that I spouted about in the previous post. There are 3 interesting things about this (and 2 apply to most other high speed aeroplanes):
1st, it is only slightly cambered (but almost flat) along the top surface (I have another photo in a minute showing the underside of a Tailplane). This means that compared to the wing itself, the Tailplane is mounted upside-down – i.e. - the most cambered surface is on the BOTTOM, not the top of the “wing”. This means that if our experiment with blowing on the bit of paper is correct (anybody tried it?) such Tailplanes are actually “sucking downwards” (if you’ll excuse the expression) rather than lifting upwards.
The 2nd thing is that again like most high speed aeroplanes, the angle of incidence of the taiplane can be adjusted by the pilot (or Autopilot). The Tailplane pivots as a complete unit around an “axle” positioned roughly opposite the highest points of those 2 “lozenge-shaped” grey bits you can see on the fuselage above and below the Tailplane. Thus the amount of “down-suck” can be adjusted to suit all phases of flight. Basically at high speeds we want the balance point – Centre of Gravity – of the whole aircraft to be very much rearwards – perhaps 70% of the chord (the front to back measurement of the “big” wing). But at low speeds like landing we want the C of G to be pretty far forward to assist stability. This is because one of the interesting things about high speed flight is that the nearer we get to the speed of sound (supersonic), then the further “naturally forwards” – becomes the C of G – i.e. the aeroplane tends to become more and more nose heavy. It’s not too clear in this picture but you may be able to see the 1 degree graduations marked on the fuselage at the Tailplane’s root to show the Tailplane’s range of movement. I have another photo to show in a minute which shows this rather more clearly (this time on an A319, but it’s pretty similar).
The 3rd interesting thing about this Tailplane (and quite a few others too) is that this is a “wet” Tailplane – i.e. it has a fuel tank within the aerofoil sections, just like the “big” wings. On the same lines as Concorde (which I believe was the first aircraft to have this feature), as speeds increase the fuel in the “Main” (Wing and Centre Section) tanks can be pumped aft to the Tailplane tanks. Otherwise the Tailplane would need to be set at an excessive nose down angle at high speed, increasing drag and therefore fuel burn. The Tailplane tanks also provide a “convenient” place to store more fuel, thus allowing the aeroplane to fly further. This aft and forwards pumping of fuel is reckoned (by Airbus) to reduce cruise speed drag, and therefore fuel burn, by about 1.5%. Unlike Concorde I believe, the movement of fuel is computer-controlled (though may be manually overridden).
Finally, at the very TE of the Tailplane we see the Elevator (just above the aircraft tug). There’s another exactly the same on the other side. As discussed in the last post, these are responsible for making the aeroplane climb or dive according to pilot (or Autopilot) inputs. Note that (like the Britannia others have already mentioned) all the control surfaces on modern aircraft are hydraulically powered, so when the any such aeroplane is at rest the surfaces will take up all sorts of strange angles. Very off-putting to those not knowing about such things.

A319-1-C

A319-1-C.JPG


As said for the last picture, the under surface of the Tailplane is much more steeply cambered than its upper surface. As noted above, this happens to be an A319 (a somewhat smaller aeroplane than previous A310) but just about all high speed aeroplanes that I’ve ever seen have this same basic feature. This photo also clearly shows the angular graduations on the fuselage much more clearly than the previous photo, and the available range of movement is between +4 (nose up) and -12 (nose down) degrees on this particular type - the last 2 down positions are not normally used. This aeroplane doesn’t have the wet fin feature of the previous A310 but I still think this clearly illustrates what happens to the C of G as we get nearer and nearer to the speed of sound.
The angle of the Tailplane is set before Take-off, either manually by the pilot or more often, by the Flight Guidance Computer. It’s set according to the total weight and C of G position of the aeroplane, plus the wind (speed and direction), temperature and air density. During flight the FGC sends signals to the Autopilot to automatically move the Tailplane angle as speeds increase and decrease.

To be really “technical” we should also be talking about the “C of P” (Centre of Pressure), the “MAC” (Mean Aerodynamic Chord), and probably about “Winglets” too. But I think the above’s enough’s for now.

See Part 4
 

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B737-1-C & -2-C

B737-1-C.JPG


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Just to show I’m not (not reallyè) biased in favour of Airbus I’ve added a couple of pix of a different aeroplane type altogether – the Boeing B737. This is arguably the most successful commercial aeroplane (in terms of numbers produced and on order) since the famous Dakota/DC3 of WWII.
The first pic shows the TE flaps fully deployed (40 degrees) taken from behind the aeroplane. Note that unlike the earlier pic of the A310 Flap segment on the ground, this aeroplane has TWO separate surfaces in front of the “main” (i.e. the most rearward) Flaps. This has the effect of providing the Flaps with 2 separate “L-E Slats” of their own. These LE Slats enable the aerofoil sections of the Flaps themselves to operate at much higher angles of attack without stalling (i.e. the breakup of smooth airflow) over the Flaps. The Flaps would stall at much less than 40 degrees without these extra surfaces at the front - just like the functioning of the “real LE Slats” on the front of the wings.
The second view, from underneath, clearly shows how highly cambered these “high lift” surfaces really are. Nothing like symmetrical.


Well that’s about it from me for a while folks. I hope the above is interesting and not too much detail.

Just in closing, and NOT wanting to take a “jab” any anyone else posting on this thread - the poster early on in this thread who wrote that an aircraft’s wing cannot be compared with a boat’s sail will, I hope, now see that this statement is just not correct. The shape of an airliner’s wing (and of most other aeroplanes too) is “adapted” to optimise its efficiency during the various phases of flight. So just as sailing boat’s crew pull on ropes to change the shape of the sail, so the pilot (or Autopilot) changes the Flap and Slat positions – i.e. the shape of the aeroplane wing. And the EXACT equivalent of the sailing boat’s keel or centre-board is that big thing sticking up at the back of all aeroplanes – i.e. the Fin and Rudder (or ”Vertical Stabilizer” and Rudder in American speak). If any one doubts that Google for the 2 tragic accidents which amply demonstrate what happens if an aeroplane looses its Fin/Rudder. Not only will it not turn but it also becomes so unstable that it cannot stay airborne at all.

Krgds
AES
 

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Thank you for takinng the time AES! Great write up and photos.

I was always under the impression that as soon as you move a control surface you screw up the aeorfoil section so that could well be one reason for not having wing tip ailerons?

Justa slight correction about the Britannia. It doesn't have any power controls at all. The surfaces are moved by servo tabs on the trailing edge of each of them. The servo tabs are moved by 'torque tubes' each up to about 6 foot long and going through a small universal drive. They are about 1 /4" diameter and are so thin ally that you could actually crush them in your hand. The ailerons and elevators 'droop' until about 80 kts and the rudder flaps around until about 60 kts and has some kind of authority at about 90 kts so nose wheel steering is used till then. The only problem with those controls was that the elevator was so light it had to be fitted with a feel control or the driver could just pull too much movement. The idea is that the driver pulls up, the servo tab on the elevtor moves down, the elevator is pushed up, the tail goes down and the aircraft climbs, hopefully :mrgreen:

It was also the very first 'fly by wire' commercial passenger aircraft in that it had Ultra Throttle analog computer controls with no mechanical connection at all. If the Ultra failed there was a switch just behind each throttle lever to switxh that throttle to manual and behind that switch was another little center sprung toggle switch which became the throttle. The drivers didn't like that too much. No big butch lever to push/pull. It did mean that if he, there weren't any shes then as far as I know, tried to do something that was likely to do the engine a mischief it didn't happen.

One of the things on the VC10 is that each of the control surfaces are split into sections. Each section being individually controlled by its own hydraulic system. There aren't any mechanical connections from the stick to them. They work by changing the phase position in a 3ø transmitter and the receiver takes up the same position. Much easier to understand than to try to explain :? his does it better than I http://www.allaboutcircuits.com/vol_2/chpt_13/11.html . It made it a extreamly safe aircraft in that you could have dammage to or failure of a control surface and only part of it would fail, the others would still function. They could be pippers to set up though and it was part of my trade to do so!

The other thing about the original R.A.F.VC10s were that they had a 'wet' fin and as one clown found out, if you fuel that one first opr defuel it last it will sit up on its ass! http://www.vc10.net/History/incidents_a ... ber%201997
 

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