Lift on aircraft wing
Discussion
GliderRider said:
Mave said:
all the lift generated comes via pressure on the wing (neglecting fuselage effects). If you increase angle of attack, then you increase the pressure differential (at a constant speed and altitude)
At anything greater than a horizontal thrust line, some lift is coming from the thrust generated by the engine. In a sustained completely vertical climb, if we exclude anything from kinetic energy, then all the lift is from the aeroplane's propeller or jet thrust. 
GliderRider said:
Mave said:
all the lift generated comes via pressure on the wing (neglecting fuselage effects). If you increase angle of attack, then you increase the pressure differential (at a constant speed and altitude)
At anything greater than a horizontal thrust line, some lift is coming from the thrust generated by the engine. In a sustained completely vertical climb, if we exclude anything from kinetic energy, then all the lift is from the aeroplane's propeller or jet thrust. 
Mave said:
...there's nothing special about zero degrees that says you get lift via a different phenomena to when you've got extra angrier of attack.
It's special in as much as a symmetrical aerofoil at zero degrees angry of attack* in free air won't produce any lift, either positive or negative.Conversely, there are aerofoil profiles that do generate substantial lift at zero degrees angry of attack, so there's clearly something going on beyond mere planar deflection of the air.
Truth is, it's a combination of Bernoulli decreasing the pressure above the wing, and planar deflection increasing it below. You can have a wing that generates some lift with one, without the other, but to achieve anything like an efficient aerofoil you need to use a combination of both.
* I'm going to adopt this phrase going forward, I think: it makes perfect sense that if you're attacking something, you must be angry, right?
Still no treadmill...lol but it did help me formulate the question a bit better
what was trying to ask (hopefully) is this situation
There is say a Cessna 172 and is anchored down at its home base
A VERY strong wind picks up and if blowing along the length of the aircraft
the pressure under this Cessnas wing is still 14psi( or whatever it is called now , (i am very old school)
The pressure above the swing is less, therefore the wind ( pressure difference) can lift the aircraft off the ground with no forward momentum Substitute plane going forward at 80kts in still air is the same? as a wing blowing at 80kts over the wings of a stationary aircraft
Therefore in my addled mind wings are designed to have an area ,that when travelling forward, should have enough pressure difference (upward push) t the aircraft e.g hypothetical plane weighs say 2000lb pressure difference is, to make the maths easy, 0,5psi
If the sing area is more that 4000sqi in, on paper that is enough to keep it airborne or at least glide .without going down like a brick, assuming the pilot knows what he should be doing.
do fflaps, both leading edge and rear add anything to increasing the differential.
Having sat just behind the wing of a 747, there isnt much 'solid' material left on the wing, it seems all flap
Thst for being patient and all the answers
Does that make sense
what was trying to ask (hopefully) is this situation
There is say a Cessna 172 and is anchored down at its home base
A VERY strong wind picks up and if blowing along the length of the aircraft
the pressure under this Cessnas wing is still 14psi( or whatever it is called now , (i am very old school)
The pressure above the swing is less, therefore the wind ( pressure difference) can lift the aircraft off the ground with no forward momentum Substitute plane going forward at 80kts in still air is the same? as a wing blowing at 80kts over the wings of a stationary aircraft
Therefore in my addled mind wings are designed to have an area ,that when travelling forward, should have enough pressure difference (upward push) t the aircraft e.g hypothetical plane weighs say 2000lb pressure difference is, to make the maths easy, 0,5psi
If the sing area is more that 4000sqi in, on paper that is enough to keep it airborne or at least glide .without going down like a brick, assuming the pilot knows what he should be doing.
do fflaps, both leading edge and rear add anything to increasing the differential.
Having sat just behind the wing of a 747, there isnt much 'solid' material left on the wing, it seems all flap
Thst for being patient and all the answers
Does that make sense
80kts through the air is exactly the same as 80kts wind over a stationary aircraft. I used to fly gliders and on a windy day doing the control check (putting each control to max deflection to make sure everything's working) it was quite normal for the tail to lift off the ground. and the person hanging on to the wing tip ( 2 wheels on the centerline and someone hangs on to the wing to keep you level for takeoff) needs to put some effort in to hold on when you check the ailerons.
Aircraft generally make use of this by taking off in to wind, and in the case of aircraft carriers steaming in to wind at full speed to get 30kts or more headwind.
Flaps and slats on the wing effectively increase it's camber, to generate more lift at the expense of more drag. As an added complication for takeoff and landing there's also ground effect, imagine the air being displaced downwards bouncing back of the ground and then pushing back on the aircraft
Aircraft generally make use of this by taking off in to wind, and in the case of aircraft carriers steaming in to wind at full speed to get 30kts or more headwind.
Flaps and slats on the wing effectively increase it's camber, to generate more lift at the expense of more drag. As an added complication for takeoff and landing there's also ground effect, imagine the air being displaced downwards bouncing back of the ground and then pushing back on the aircraft
Edited by RizzoTheRat on Thursday 23 March 08:05
silverfoxcc said:
Still no treadmill...lol but it did help me formulate the question a bit better
what was trying to ask (hopefully) is this situation
There is say a Cessna 172 and is anchored down at its home base
A VERY strong wind picks up and if blowing along the length of the aircraft
the pressure under this Cessnas wing is still 14psi( or whatever it is called now , (i am very old school)
The pressure above the swing is less, therefore the wind ( pressure difference) can lift the aircraft off the ground with no forward momentum Substitute plane going forward at 80kts in still air is the same? as a wing blowing at 80kts over the wings of a stationary aircraft
Therefore in my addled mind wings are designed to have an area ,that when travelling forward, should have enough pressure difference (upward push) t the aircraft e.g hypothetical plane weighs say 2000lb pressure difference is, to make the maths easy, 0,5psi
If the sing area is more that 4000sqi in, on paper that is enough to keep it airborne or at least glide .without going down like a brick, assuming the pilot knows what he should be doing.
do fflaps, both leading edge and rear add anything to increasing the differential.
Having sat just behind the wing of a 747, there isnt much 'solid' material left on the wing, it seems all flap
Thst for being patient and all the answers
Does that make sense
Not just small aircraft:what was trying to ask (hopefully) is this situation
There is say a Cessna 172 and is anchored down at its home base
A VERY strong wind picks up and if blowing along the length of the aircraft
the pressure under this Cessnas wing is still 14psi( or whatever it is called now , (i am very old school)
The pressure above the swing is less, therefore the wind ( pressure difference) can lift the aircraft off the ground with no forward momentum Substitute plane going forward at 80kts in still air is the same? as a wing blowing at 80kts over the wings of a stationary aircraft
Therefore in my addled mind wings are designed to have an area ,that when travelling forward, should have enough pressure difference (upward push) t the aircraft e.g hypothetical plane weighs say 2000lb pressure difference is, to make the maths easy, 0,5psi
If the sing area is more that 4000sqi in, on paper that is enough to keep it airborne or at least glide .without going down like a brick, assuming the pilot knows what he should be doing.
do fflaps, both leading edge and rear add anything to increasing the differential.
Having sat just behind the wing of a 747, there isnt much 'solid' material left on the wing, it seems all flap
Thst for being patient and all the answers
Does that make sense
https://www.youtube.com/watch?v=cHhZwvdRR5c
So, in the first couple of posts, how does that relate to wind speed over the wing?
Clearly a 0kts there is no lift, and at (say) 100kts there is enough to lift the weight of the aircraft off the ground, is "wing loading" at a rated/given airflow? Does it increase, exponentially, linearly, or in a diminishing way? The aircraft I was on yesterday was cruising at 700kph, but was still flying at 400kph just before landing. Was it generating more lift at cruising speed and less at slower speeds?
Clearly a 0kts there is no lift, and at (say) 100kts there is enough to lift the weight of the aircraft off the ground, is "wing loading" at a rated/given airflow? Does it increase, exponentially, linearly, or in a diminishing way? The aircraft I was on yesterday was cruising at 700kph, but was still flying at 400kph just before landing. Was it generating more lift at cruising speed and less at slower speeds?
Not sure what speed/attitude/angle the wing loading quoted will relate to, but al those things will impact the amount of lift generated. If the aircraft cruises at say 500kts and 35000 feet, it will likely be optimised for conditions, ie the wings will be set up to generate lift equal to the mass when the fuselage is horizonatal so producing minimum drag. At lower speeds you can increase the amount of lift by increasing the angle of attack of the aircraft (pitch the nose up), or increase the effective camber of the wings (flats and slats), both of these come with a drag penalty though.
Aircraft have a trim control to tweak this, so for example of something like a small Cessna there'll be a little wheel that moves trim tabs to make the aircraft fly straight and level if you take your hands off. If you increase the speed you change the lift and need to fly at a slightly different angle, so might need a bit of forward pressure on the stick to maintain altitude, so you spin to wheel to add a bit of nose down and trim the aircraft.
I'm guessing it's all automatic on airlines though.
Aircraft have a trim control to tweak this, so for example of something like a small Cessna there'll be a little wheel that moves trim tabs to make the aircraft fly straight and level if you take your hands off. If you increase the speed you change the lift and need to fly at a slightly different angle, so might need a bit of forward pressure on the stick to maintain altitude, so you spin to wheel to add a bit of nose down and trim the aircraft.
I'm guessing it's all automatic on airlines though.
Condi said:
So, in the first couple of posts, how does that relate to wind speed over the wing?
Clearly a 0kts there is no lift, and at (say) 100kts there is enough to lift the weight of the aircraft off the ground, is "wing loading" at a rated/given airflow? Does it increase, exponentially, linearly, or in a diminishing way? The aircraft I was on yesterday was cruising at 700kph, but was still flying at 400kph just before landing. Was it generating more lift at cruising speed and less at slower speeds?
A simple way to look at it - in straight and level flight, lift has to equal weight.Clearly a 0kts there is no lift, and at (say) 100kts there is enough to lift the weight of the aircraft off the ground, is "wing loading" at a rated/given airflow? Does it increase, exponentially, linearly, or in a diminishing way? The aircraft I was on yesterday was cruising at 700kph, but was still flying at 400kph just before landing. Was it generating more lift at cruising speed and less at slower speeds?
Lift is proportional to lift coefficient, air density, speed squared (and wing area).
As an approximation, for a given wing, there's a single straight ish line which defines the relationship between angle of attack and lift coefficient (this changes with flaps etc though)
So as you change speed or altitude you need to change the angle (or anger!) ?? of attack to vary lift coefficient, to keep lift balanced against weight.
Wing loading of the type quoted is normally a nominal wing loading for clean 1g flight - the wing loading can increase or decrease depending on how much lift you need.
Edited by Mave on Thursday 23 March 11:42
Back when I was hang gliding, I went to a gathering at Weston super Mare. Those of us new to sand dune flying would lug our wings up to the tallest part of the dune and do a conventional launch to soar the ridge. The local fliers would just lay in prone beneath their gliders on the sand ahead of the dune, facing into the 20+mph wind. Then when the person on the nose released the nose wires, the pilot would pitch the glider up. It would then rear up into the air, heading backwards over the dune. Just as the glider was about to pass over the top of the dune, the pilot would haul him or herself forward over the base bar for extra speed, stop the rearward trajectory and start soaring conventionally.
This is a clear explanation of the incorrect lift theories as well as the current accepted correct theory.
Incorrect and correct aerofoil theories
TLDR: It is the centripedal force exerted on the aerofoil by the airflow around it that generates lift. The effective camber, which is derived from the combination of any camber the aerofoil section itself has and its angle of attack. Either can be zero, but not both, if lift is to be created.
Any theories that purely concern air being deflected downwards would be unable to explain how the Kasperwing ultralight (pictured below) with its full span reflexed wing section or autogyros with non-pitching aerofoil rotor blades work.
This is a clear explanation of the incorrect lift theories as well as the current accepted correct theory.
Incorrect and correct aerofoil theories
TLDR: It is the centripedal force exerted on the aerofoil by the airflow around it that generates lift. The effective camber, which is derived from the combination of any camber the aerofoil section itself has and its angle of attack. Either can be zero, but not both, if lift is to be created.
Any theories that purely concern air being deflected downwards would be unable to explain how the Kasperwing ultralight (pictured below) with its full span reflexed wing section or autogyros with non-pitching aerofoil rotor blades work.
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