RogerS
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Dibs-h":31hgfy8y said:
But it isn't!
How does an aircraft's wing work?
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But it isn't!
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RogerS":2szbrj69 said:
OK Einstien? Wot is it then??? :mrgreen:
mailee
Established Member
Yeah, c'mon Roger tell us your theory. :?
mailee
Established Member
Yeah, c'mon Roger tell us your theory. :?
Wing Angle of attack relates to lift only while the airflow remains laminar, as the AofA increases and flow separates (becomes turbulent) wing begines to stall and lift reduces. To recover from the flow separation there are several options go faster, reduce AofA or change wing profile (flaps). Pressure difference still has some indirect influence, you will have seen water vapour forming above the wing on a fast jet in humid air also same effect on an F1 cars rear wing but upside down. What is for sure is the behaviour of wing dynamics is different between low speed flight, high speed (transonic) supersonic and hypersonic.
RogerS
Established Member
What newt says !
Dibs-h
Established Member
RogerS":2g1wevtc said:
Rog
Sorry mate, have to disagree. I studied Mech Eng at Uni and Fluid Dynamics in particular and having an interest in R\C planes, you can be assured I made sure I studied this one matter at least. How a wing generates lift is explained by Bernoulli's theory.
Here's the quote -
"In fluid dynamics, air is actually considered to be, and typically modeled as, a fluid. When modeling fluid movement, a scientist named Bernoulli discovered that a faster moving fluid has exerts less pressure than a slower moving fluid."
The exact page along with a Professor's (Cambridge Uni) explanation,
http://sciencebasedlife.wordpress.com/2 ... rate-lift/
Newt - the pressure differential has a direct bearing on Lift generation, not an indirect one.
Dibs
Dibs-h":l44cwo5v said:
Dibs what I should have said is that pressure difference has a secondary effect depending on type of aero foil and speed. I think the reason why the classical theory is being questioned is that there are significant differences in behaviour when you compare low subsonic with supersonic. No dispute with faster air producing lower pressure, just that it is not the only parameter involving lift.
RogerS
Established Member
Dibs-h":345jvnwo said:
So does a wing with a symmetrical cross-section work? :?
Dibs-h
Established Member
RogerS":11o2f30d said:
A symmetrical aerofoil produces equal lift on both sides - so no net lift. For useful lift - there must be a positive angle of attack, in which case there is net lift.
Bernoulli's theory isn't the one size fits all - Newtons 1st and 3rd laws also apply.
Dibs
p.s. Rog - this might be useful, http://www.grc.nasa.gov/WWW/k-12/airplane/short.html section labelled lift. The following is interesting too - http://www.grc.nasa.gov/WWW/k-12/airplane/bernnew.html
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"So does a wing with a symmetrical cross-section work? "
It did on this
I used to live just down the road from a retired navigator on Lightnings. Very interesting bloke!!
It did on this
I used to live just down the road from a retired navigator on Lightnings. Very interesting bloke!!
AES
Established Member
No it didn't Jonzjob - the Lightning (no Marks of that aeroplane - it's a Mk 6 in your pic) did NOT have a symmetrical wing section!
The only full-size aeroplanes which do have "more or less" symmetrical wing sections are the specilaist aerobatic contest machines like the Yak, Extra, etc.
And BTW, sorry to spoil your fun but no Lightnings ever carried a Navigator - not in the RAF, the RSAF (Saudi Arabia), or the Kuwaiti Air Force. And the Thunder Bay Lightnings in South Africa (now grounded following a very unfortunate fatal accident) also never carried Navs. There were only 2 marks with 2 seats, the T4 and the T5. As the designation suggests, they were 2 seat trainers - all the rest were single seaters. I used to work on them for my sins!
I thought this thread started out as fun, and in the first page or so it was (I certainly got a laugh out of some of the posts anyway), but now there's been so much "serious tosh" posted that - being a boring old realist - I feel it necessary to dispell some myths.
Apart from the above specialist machines there are no aeroplanes that I can think of off hand which have truly symmetrical wing sections - close to it in parts (most airliners and other commercial aircraft) but not truly symmetrical. How do they fly? As someone said a page or two back, it all comes down to Bernouli a physicst (an Italian Swiss I think) who discovered that any fluid in a confined area (e.g. a pipe) will be forced to slow down when entering a constriction (e.g. a venturi). That slowing down creates an increase in pressure and that increase is directly proportional to the speed reduction. This works for all fluids and by definition, air is a fluid - but unlike other fluids (e.g. oil, water, etc) air is compressible. That's what makes aeroplane aerodynamics so ivery nteresting, especially when dealing with modern swept-wing aeroplanes like airliners.
A wing section is, in effect, just a venturi turned "upside down" (i.e. the top of the venturi becomes the bottom of the wing and the bottom becomes the top of the wing) so it's a "venturi in reverse".
As Steve Maskery said a page or two back, aeroplanes with symmetrical or near symmetrical wings ALWAYS have the centre line of the wing rigged at a positive angle of incidence (i.e. the Leading Edge of the wing is set a couple of degrees nose up).
How the aeroplane maintains level flight in those conditions is a function of the trim setting which has the effect of either increasing or reducing that angle of incidence. On modern aeroplanes this is done by changing the angle of incidence of the tailplane (or in American, the horizontal stabilzer), and/or by means of adjustable tabs on the trailing edge of the tailplane. On modern commercial aircraft the tailplane also has realatively small "flaps" at the back of the tailplane and these are called elevators. These are what makes the aeroplane climb and dive (when "Capt Speaking" or the Autopilot pulls or pushes on the control column).
Ailerons are smallish tabs on the trailing edge of the wings and when one goes up the other goes down. The upgoing aileron reduces the amount of lift being produced on that wing (and the down-going aileron increases the lift) so that there's an imbalance between the lift produced by each wing, resulting in the aeroplane rolling towards the wing with less lift. That continues until the forces are balanced out again - i.e. the pilot/Autopilot removes the roll input and/or the aeroplane becomes stabilised at the required angle of bank. The upgoing aileron is always moved to a lesser angle than the down-going aileron and in addition, the basic angle of incidence ofthe wing is "washed out" as you move along the wing towards the wingtip. This is to prevent/reduce the tendency to tip-stall - i.e. what was laminar flow over the wing becomes broken up because the inner wing is going slower than the outer wing. Think of all those Hollywood musicals with the long lines of high-kicking dancing girls - the one on the uinside of the line virtually prances on the spot while the one on the outside iof the line is going like stink. It's just like on your models Jonzjob.
Many aircraft have their ailerons set to "droop"by a few degrees when landing and this reduces the runway length required (i.e. it increases the amount of lift produced by the wing) although the ailerons do continue their up and down roll role (sorry!) but set around their new drooped datum. Commercial aeroplanes I can think of with such features include the Pilatus Porter, the Airbus A320 (if I remember correctly - I did that Course a long while back!) and definitely the MD-11. There are certainly others.
On some aircraft there are more than one aileron on each wing, located fairly well inboard and a second one right out near the wingtips. And some aircraft don't have any ailerons on the outboard on the wingtip at all - the Airbus A310 springs to mind.
Flaps are of two basic types. Those on the Trailing Edge of the wings normally move outwards first (i.e. along the wing section centre line) and only then do they "droop" to certain pre-set angles. The purpose is to increase the lift from the wing first be increasing its area and then by increasing its camber (curvature).
There are also usually "flaps" on the Leading Edge of the wings (normally called "Slats") and they are almost always coupled to the Flaps control. They also increase the camber of the wing, again to increase the amount of lift produced. The only aircraft I can think of off hand which had separate Slats and Flaps controls was the Hawker Siddeley Trident and that "peculiar" feature led to a well-known fatal accident on Take-off at Heathrow when "Capt Speaking" neglected to lower the LE Slats.
That's a pretty old aeroplane and I can't think of any of the more modern types which have such separate controls. For example the Boeing 737 project which I'm working on now has TE Flaps position 2 degrees (which also lowers the LE Slats by 1 degree); Flaps 5 degrees (Slats 2 degrees); Flaps 15 degrees (no more LE Slat movement); Flaps 25 degrees; and finally, Flaps 40 degrees. To continue with that example, these clever bits give a wing which is capable of flying about 160 pax, their bags and all the fuel needed for say a 1,800 miles journey at probably 500 mph in cruise. But at the same time that wing will lift the same load off the ground (and lower it back down again) at take-off and landing speeds of about 160 mph.
If anyone wants to know more about the basic principles of venturis (which is what we're talking about here) then I recommend a visit to the site of Mathias Wandel at http://woodgears.ca/index.html.
Look up his experiments on various aspects of venturis (inc a video dealing with all sorts of interesting stuff including spray guns, flame-trowers, and sucking up dust). Nothing on wings, but as said, exactly the same principles apply. And the video should help you to visualise some of the stuff I've been spouting here.
Last but not least, anyone want to try this very simple experiment? Take an ordinary piece of paper (A4 will be fine), hold the paper at the 2 corners of the narrow side. Raise your hands (with the paper) up to your lips (the paper will of course be drooping downwards) and then blow gently over the top surface of the paper. The harder you blow the more the paper will raise up until it's almost sticking out from your mouth horizontally (but still with a curvature ("camber"). And NOT a puff of your blown air went underneath the paper!
One last point to the poster talking about Piper Cubs earlier (LOVELY little aeroplane ;-) ). It's a 2 not a 4 seater, and I very much doubt you could get it to fly at the speeds you quoted (and if you did you'd tear the wings off it!). About 90 mph flat out is more like it.
Sorry if I'm just a boring old spoil-sport - IMHO what started off as a fun post just got silly with many just plain wrong "facts", hence the realism injection.
With respect to all
AES
The only full-size aeroplanes which do have "more or less" symmetrical wing sections are the specilaist aerobatic contest machines like the Yak, Extra, etc.
And BTW, sorry to spoil your fun but no Lightnings ever carried a Navigator - not in the RAF, the RSAF (Saudi Arabia), or the Kuwaiti Air Force. And the Thunder Bay Lightnings in South Africa (now grounded following a very unfortunate fatal accident) also never carried Navs. There were only 2 marks with 2 seats, the T4 and the T5. As the designation suggests, they were 2 seat trainers - all the rest were single seaters. I used to work on them for my sins!
I thought this thread started out as fun, and in the first page or so it was (I certainly got a laugh out of some of the posts anyway), but now there's been so much "serious tosh" posted that - being a boring old realist - I feel it necessary to dispell some myths.
Apart from the above specialist machines there are no aeroplanes that I can think of off hand which have truly symmetrical wing sections - close to it in parts (most airliners and other commercial aircraft) but not truly symmetrical. How do they fly? As someone said a page or two back, it all comes down to Bernouli a physicst (an Italian Swiss I think) who discovered that any fluid in a confined area (e.g. a pipe) will be forced to slow down when entering a constriction (e.g. a venturi). That slowing down creates an increase in pressure and that increase is directly proportional to the speed reduction. This works for all fluids and by definition, air is a fluid - but unlike other fluids (e.g. oil, water, etc) air is compressible. That's what makes aeroplane aerodynamics so ivery nteresting, especially when dealing with modern swept-wing aeroplanes like airliners.
A wing section is, in effect, just a venturi turned "upside down" (i.e. the top of the venturi becomes the bottom of the wing and the bottom becomes the top of the wing) so it's a "venturi in reverse".
As Steve Maskery said a page or two back, aeroplanes with symmetrical or near symmetrical wings ALWAYS have the centre line of the wing rigged at a positive angle of incidence (i.e. the Leading Edge of the wing is set a couple of degrees nose up).
How the aeroplane maintains level flight in those conditions is a function of the trim setting which has the effect of either increasing or reducing that angle of incidence. On modern aeroplanes this is done by changing the angle of incidence of the tailplane (or in American, the horizontal stabilzer), and/or by means of adjustable tabs on the trailing edge of the tailplane. On modern commercial aircraft the tailplane also has realatively small "flaps" at the back of the tailplane and these are called elevators. These are what makes the aeroplane climb and dive (when "Capt Speaking" or the Autopilot pulls or pushes on the control column).
Ailerons are smallish tabs on the trailing edge of the wings and when one goes up the other goes down. The upgoing aileron reduces the amount of lift being produced on that wing (and the down-going aileron increases the lift) so that there's an imbalance between the lift produced by each wing, resulting in the aeroplane rolling towards the wing with less lift. That continues until the forces are balanced out again - i.e. the pilot/Autopilot removes the roll input and/or the aeroplane becomes stabilised at the required angle of bank. The upgoing aileron is always moved to a lesser angle than the down-going aileron and in addition, the basic angle of incidence ofthe wing is "washed out" as you move along the wing towards the wingtip. This is to prevent/reduce the tendency to tip-stall - i.e. what was laminar flow over the wing becomes broken up because the inner wing is going slower than the outer wing. Think of all those Hollywood musicals with the long lines of high-kicking dancing girls - the one on the uinside of the line virtually prances on the spot while the one on the outside iof the line is going like stink. It's just like on your models Jonzjob.
Many aircraft have their ailerons set to "droop"by a few degrees when landing and this reduces the runway length required (i.e. it increases the amount of lift produced by the wing) although the ailerons do continue their up and down roll role (sorry!) but set around their new drooped datum. Commercial aeroplanes I can think of with such features include the Pilatus Porter, the Airbus A320 (if I remember correctly - I did that Course a long while back!) and definitely the MD-11. There are certainly others.
On some aircraft there are more than one aileron on each wing, located fairly well inboard and a second one right out near the wingtips. And some aircraft don't have any ailerons on the outboard on the wingtip at all - the Airbus A310 springs to mind.
Flaps are of two basic types. Those on the Trailing Edge of the wings normally move outwards first (i.e. along the wing section centre line) and only then do they "droop" to certain pre-set angles. The purpose is to increase the lift from the wing first be increasing its area and then by increasing its camber (curvature).
There are also usually "flaps" on the Leading Edge of the wings (normally called "Slats") and they are almost always coupled to the Flaps control. They also increase the camber of the wing, again to increase the amount of lift produced. The only aircraft I can think of off hand which had separate Slats and Flaps controls was the Hawker Siddeley Trident and that "peculiar" feature led to a well-known fatal accident on Take-off at Heathrow when "Capt Speaking" neglected to lower the LE Slats.
That's a pretty old aeroplane and I can't think of any of the more modern types which have such separate controls. For example the Boeing 737 project which I'm working on now has TE Flaps position 2 degrees (which also lowers the LE Slats by 1 degree); Flaps 5 degrees (Slats 2 degrees); Flaps 15 degrees (no more LE Slat movement); Flaps 25 degrees; and finally, Flaps 40 degrees. To continue with that example, these clever bits give a wing which is capable of flying about 160 pax, their bags and all the fuel needed for say a 1,800 miles journey at probably 500 mph in cruise. But at the same time that wing will lift the same load off the ground (and lower it back down again) at take-off and landing speeds of about 160 mph.
If anyone wants to know more about the basic principles of venturis (which is what we're talking about here) then I recommend a visit to the site of Mathias Wandel at http://woodgears.ca/index.html.
Look up his experiments on various aspects of venturis (inc a video dealing with all sorts of interesting stuff including spray guns, flame-trowers, and sucking up dust). Nothing on wings, but as said, exactly the same principles apply. And the video should help you to visualise some of the stuff I've been spouting here.
Last but not least, anyone want to try this very simple experiment? Take an ordinary piece of paper (A4 will be fine), hold the paper at the 2 corners of the narrow side. Raise your hands (with the paper) up to your lips (the paper will of course be drooping downwards) and then blow gently over the top surface of the paper. The harder you blow the more the paper will raise up until it's almost sticking out from your mouth horizontally (but still with a curvature ("camber"). And NOT a puff of your blown air went underneath the paper!
One last point to the poster talking about Piper Cubs earlier (LOVELY little aeroplane ;-) ). It's a 2 not a 4 seater, and I very much doubt you could get it to fly at the speeds you quoted (and if you did you'd tear the wings off it!). About 90 mph flat out is more like it.
Sorry if I'm just a boring old spoil-sport - IMHO what started off as a fun post just got silly with many just plain wrong "facts", hence the realism injection.
With respect to all
AES
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I could well stand corrected on the wing section of the Lightning, but my friend and neighbour WAS a nav on Lightnings. He was stationed at Farnborough for several years and it was when they were doing the speed trials on them.
His job was mainly to make sure that while they were doing the supresonic trials over Le Manche, the Channel, that they didn't overrun the coast. But he aslo had to guide the driver to the correct start point for the trials. At the speed they were traveling by the time the driver saw the coast they were going to cross it supersonic and the R.A.F. didn't like all the claims for broken glass.
Sorry, but I knew someone would bite :twisted: :twisted: :twisted:
He was also a nav on theShackelton that was used to test the Concord break chutes. They would stagger up to 30,000 feet, dive until the speed reached something around 300 mph plus and then deploy the chute! After a few seconds it ws jettisoned and by the finish of the tests the airframe was about a foot longer than when they started. Not one of his favorite jobs. I worked on Mk2 Phase 2 taildragger Shacks in Changi Singapore for a while. The last taildraggers in the R.A.F. Lovely aircraft!!
His job was mainly to make sure that while they were doing the supresonic trials over Le Manche, the Channel, that they didn't overrun the coast. But he aslo had to guide the driver to the correct start point for the trials. At the speed they were traveling by the time the driver saw the coast they were going to cross it supersonic and the R.A.F. didn't like all the claims for broken glass.
Sorry, but I knew someone would bite :twisted: :twisted: :twisted:
He was also a nav on theShackelton that was used to test the Concord break chutes. They would stagger up to 30,000 feet, dive until the speed reached something around 300 mph plus and then deploy the chute! After a few seconds it ws jettisoned and by the finish of the tests the airframe was about a foot longer than when they started. Not one of his favorite jobs. I worked on Mk2 Phase 2 taildragger Shacks in Changi Singapore for a while. The last taildraggers in the R.A.F. Lovely aircraft!!
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AES
Established Member
@newt
Agreed, Bernouli is only a part (but the main part) of the story. Aerodynamics is a BIG, but fascinating subject, especially if we start to talk about modern aeroplanes which can fly from, typically, about 150 mph up to 500-ish mph (about 0.9 the speed of sound).
As it happens I'm in an aircraft hangar in TRurkey right now and (amongst others) there's an Airbus A310 with various wing bits & pieces deployed and removed right outside my office window. IF anyone is interested I can post a couple of pix illustrating some the stuff I was spouting about yesterday - BUT ONLY anyone isinterested enough to request ;-)
AES
Agreed, Bernouli is only a part (but the main part) of the story. Aerodynamics is a BIG, but fascinating subject, especially if we start to talk about modern aeroplanes which can fly from, typically, about 150 mph up to 500-ish mph (about 0.9 the speed of sound).
As it happens I'm in an aircraft hangar in TRurkey right now and (amongst others) there's an Airbus A310 with various wing bits & pieces deployed and removed right outside my office window. IF anyone is interested I can post a couple of pix illustrating some the stuff I was spouting about yesterday - BUT ONLY anyone isinterested enough to request ;-)
AES
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I'm interested in seeing them A :mrgreen: :mrgreen:
AES
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OK Jonzjob, tomorrow.
AES
AES
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Ta very muchly.. I look forward to seeing them. The last aircraft I worked on were VC10s and Belfasts in the early 70s at Brize Norton for 5 years. The 10 is a lovely aircraft, but the Belslug was a real camel, designed by a comitte who knew nowt about aircraft!!
Jonzjob":z03mn89s said:
The super VC10 was and still is a brilliant aircraft having been fortunate to have flown many hours in both passenger and tanker variants. At one stage they were going to be re-engined and refurbished, and there was talk that Boeing wanted to buy up all the airframes, if true I can only assume to eliminate competition. The wing main spar did have to have some repairs carried out, but it was a very efficient design, I think the wing may have been super critical, although I am not sure. When they were first introduced it was the only jet that could operate hot / high in Africa.
