Lift on aircraft wing
Discussion
Putting this in very basic terms ,,and that there may well be plus and minus in the answers with regarding various wing shapes the question is
As i understand it the shape of a wing makes the air pressure passing over it less than the pressure under the wing. so if there is a figure of say 14 psi under the wing, what would be it above?
As i understand it the shape of a wing makes the air pressure passing over it less than the pressure under the wing. so if there is a figure of say 14 psi under the wing, what would be it above?
Depends on wing loading (mass of aircraft divided by wing area, usually given in pounds per square foot)
Divide by 144 to convert to psi
for example wing loading of a Spitfire is 28 pounds per square foot.
28/144 = 0.19psi
so 13.81psi above the wing
Boeing 737 wing loading 104 pounds per square foot
104/144 = 0.72psi
so 13.28psi above the wing
Divide by 144 to convert to psi
for example wing loading of a Spitfire is 28 pounds per square foot.
28/144 = 0.19psi
so 13.81psi above the wing
Boeing 737 wing loading 104 pounds per square foot
104/144 = 0.72psi
so 13.28psi above the wing
silverfoxcc said:
Putting this in very basic terms ,,and that there may well be plus and minus in the answers with regarding various wing shapes the question is
As i understand it the shape of a wing makes the air pressure passing over it less than the pressure under the wing. so if there is a figure of say 14 psi under the wing, what would be it above?
It's usually less than one psi of pressure difference between the upper and lower wing surface - often barely any difference at all on light aircraft with relatively big wings. Divide the wing loading (weight carried divided by wing area) in pounds/square foot by 144 and you get the theoretical pressure difference. As i understand it the shape of a wing makes the air pressure passing over it less than the pressure under the wing. so if there is a figure of say 14 psi under the wing, what would be it above?
So for a Boeing 787 it's about 0.85psi (14psi under the wing, 13.15psi above). For an F-35A fighter it's 0.74psi, and for a Cessna 172 it's a hair under 0.1psi. For a modern sailplane it's 0.06psi.
But through the magic of physics, a small pressure over a big area can do a lot of work.
If you crunch the numbers - a fully laden Boeing 787 is generating 496,699 pounds-force via the pressure differential on its wing surfaces. But weighs over 502,000lbs. The Cessna is also just short of being able to lift its gross weight via wing pressure force alone. The difference comes from the lift generated by the wing's angle of attack; the wing is angled down from its leading edge and deflects air downwards.
These numbers are in the weird world of 'accurate but theoretical' - for any given specific flight condition the exact balance between lift generated by the Bernoulli principle and lift generated by angle of attack will be different, and of course the application of things like flaps, slats, droops etc. will change it further.
RizzoTheRat said:
lufbramatt said:
<good stuff>
From the name and content, are you a Loughborough Trans Tech grad?
My job involves lots of poring over old drawings of aircraft and although I don't design ones that actually fly it helps to understand a bit about how they work.
I did originally want to go into aero engineering but struggled with A-level maths so took a slightly different course.
lufbramatt said:
Loughborough Industrial Design
My job involves lots of poring over old drawings of aircraft and although I don't design ones that actually fly it helps to understand a bit about how they work.
I did originally want to go into aero engineering but struggled with A-level maths so took a slightly different course.
My first degree was industrial design... Ah the joy of Magic Markers, pastels, and lighter fluid. My job involves lots of poring over old drawings of aircraft and although I don't design ones that actually fly it helps to understand a bit about how they work.
I did originally want to go into aero engineering but struggled with A-level maths so took a slightly different course.
lufbramatt said:
Loughborough Industrial Design
My job involves lots of poring over old drawings of aircraft and although I don't design ones that actually fly it helps to understand a bit about how they work.
I did originally want to go into aero engineering but struggled with A-level maths so took a slightly different course.
Have you appeared in that telly programme yet?My job involves lots of poring over old drawings of aircraft and although I don't design ones that actually fly it helps to understand a bit about how they work.
I did originally want to go into aero engineering but struggled with A-level maths so took a slightly different course.
Yertis said:
lufbramatt said:
Loughborough Industrial Design
My job involves lots of poring over old drawings of aircraft and although I don't design ones that actually fly it helps to understand a bit about how they work.
I did originally want to go into aero engineering but struggled with A-level maths so took a slightly different course.
Have you appeared in that telly programme yet?My job involves lots of poring over old drawings of aircraft and although I don't design ones that actually fly it helps to understand a bit about how they work.
I did originally want to go into aero engineering but struggled with A-level maths so took a slightly different course.
LimaDelta said:
Mave said:
48k said:
"Bernoulli's principle is not how wings generate lift" can of worms being opened in 3... 2....
LimaDelta said:
Mave said:
48k said:
"Bernoulli's principle is not how wings generate lift" can of worms being opened in 3... 2....
Edited by Mave on Tuesday 21st March 18:32
2xChevrons said:
If you crunch the numbers - a fully laden Boeing 787 is generating 496,699 pounds-force via the pressure differential on its wing surfaces. But weighs over 502,000lbs. The Cessna is also just short of being able to lift its gross weight via wing pressure force alone. The difference comes from the lift generated by the wing's angle of attack; the wing is angled down from its leading edge and deflects air downwards.
Depending upon its angle of attack, a small amount of lift will be generated by the fuselage. Being pretty inefficient as a wing, fuselage lift would be minimal in the cruise as it would create unwanted drag.2xChevrons said:
It's usually less than one psi of pressure difference between the upper and lower wing surface - often barely any difference at all on light aircraft with relatively big wings. Divide the wing loading (weight carried divided by wing area) in pounds/square foot by 144 and you get the theoretical pressure difference.
So for a Boeing 787 it's about 0.85psi (14psi under the wing, 13.15psi above). For an F-35A fighter it's 0.74psi, and for a Cessna 172 it's a hair under 0.1psi. For a modern sailplane it's 0.06psi.
But through the magic of physics, a small pressure over a big area can do a lot of work.
If you crunch the numbers - a fully laden Boeing 787 is generating 496,699 pounds-force via the pressure differential on its wing surfaces. But weighs over 502,000lbs. The Cessna is also just short of being able to lift its gross weight via wing pressure force alone. The difference comes from the lift generated by the wing's angle of attack; the wing is angled down from its leading edge and deflects air downwards.
These numbers are in the weird world of 'accurate but theoretical' - for any given specific flight condition the exact balance between lift generated by the Bernoulli principle and lift generated by angle of attack will be different, and of course the application of things like flaps, slats, droops etc. will change it further.
The figures you quote don't make any sense to me without you stating the speed and angle of attack of the aircraft, do you mean at level cruising speed?So for a Boeing 787 it's about 0.85psi (14psi under the wing, 13.15psi above). For an F-35A fighter it's 0.74psi, and for a Cessna 172 it's a hair under 0.1psi. For a modern sailplane it's 0.06psi.
But through the magic of physics, a small pressure over a big area can do a lot of work.
If you crunch the numbers - a fully laden Boeing 787 is generating 496,699 pounds-force via the pressure differential on its wing surfaces. But weighs over 502,000lbs. The Cessna is also just short of being able to lift its gross weight via wing pressure force alone. The difference comes from the lift generated by the wing's angle of attack; the wing is angled down from its leading edge and deflects air downwards.
These numbers are in the weird world of 'accurate but theoretical' - for any given specific flight condition the exact balance between lift generated by the Bernoulli principle and lift generated by angle of attack will be different, and of course the application of things like flaps, slats, droops etc. will change it further.
The lift of the wings may be limited to those figures by trim to maintain level flight but the wing will be capable of providing much more lift, if that were not the case the aircraft would never get off the ground.
Wing lift rises in proportion to the square of the airspeed so the wing will have a much higher lift capacity than the mass of the aircraft at speeds higher than take off.
oakdale said:
2xChevrons said:
It's usually less than one psi of pressure difference between the upper and lower wing surface - often barely any difference at all on light aircraft with relatively big wings. Divide the wing loading (weight carried divided by wing area) in pounds/square foot by 144 and you get the theoretical pressure difference.
So for a Boeing 787 it's about 0.85psi (14psi under the wing, 13.15psi above). For an F-35A fighter it's 0.74psi, and for a Cessna 172 it's a hair under 0.1psi. For a modern sailplane it's 0.06psi.
But through the magic of physics, a small pressure over a big area can do a lot of work.
If you crunch the numbers - a fully laden Boeing 787 is generating 496,699 pounds-force via the pressure differential on its wing surfaces. But weighs over 502,000lbs. The Cessna is also just short of being able to lift its gross weight via wing pressure force alone. The difference comes from the lift generated by the wing's angle of attack; the wing is angled down from its leading edge and deflects air downwards.
These numbers are in the weird world of 'accurate but theoretical' - for any given specific flight condition the exact balance between lift generated by the Bernoulli principle and lift generated by angle of attack will be different, and of course the application of things like flaps, slats, droops etc. will change it further.
The figures you quote don't make any sense to me without you stating the speed and angle of attack of the aircraft, do you mean at level cruising speed?So for a Boeing 787 it's about 0.85psi (14psi under the wing, 13.15psi above). For an F-35A fighter it's 0.74psi, and for a Cessna 172 it's a hair under 0.1psi. For a modern sailplane it's 0.06psi.
But through the magic of physics, a small pressure over a big area can do a lot of work.
If you crunch the numbers - a fully laden Boeing 787 is generating 496,699 pounds-force via the pressure differential on its wing surfaces. But weighs over 502,000lbs. The Cessna is also just short of being able to lift its gross weight via wing pressure force alone. The difference comes from the lift generated by the wing's angle of attack; the wing is angled down from its leading edge and deflects air downwards.
These numbers are in the weird world of 'accurate but theoretical' - for any given specific flight condition the exact balance between lift generated by the Bernoulli principle and lift generated by angle of attack will be different, and of course the application of things like flaps, slats, droops etc. will change it further.
The lift of the wings may be limited to those figures by trim to maintain level flight but the wing will be capable of providing much more lift, if that were not the case the aircraft would never get off the ground.
Wing lift rises in proportion to the square of the airspeed so the wing will have a much higher lift capacity than the mass of the aircraft at speeds higher than take off.
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)
Angle of attack is just a reference, 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 just a way of setting how much lift you've got when the aircraft is on the runway.
So you've got just under 1g of lift on the take off run, then because you're slow you need a reasonable angle of attack to generate sufficient lift, and take off. Ignoring flaps, as you accelerate (so lift increases) but also climb (so lift decreases) you trim up and down the CL / alpha curve to keep 1g lift (ie 0.85ish psi in the example)
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. Gassing Station | Boats, Planes & Trains | Top of Page | What's New | My Stuff