A 500 ton jumbo jet needs 472 square feet of perfect vacuum above its wings or equivalent. Isn't this true?

Question

Something that heavy needs a large pressure difference above and below its wings for support. Even railroad locomotives riding on steel rails are not that heavy. How is this accomplished? Can the Bernoulli Effect or Venturi Effect create a near perfect vacuum or even a half perfect vacuum above the wings? Is there a formula that provides the lift force? If not, why not? Does this formula apply to wind turbines to provide the blade driving force as well?

Something that heavy needs a large pressure difference above and below its wings for support. Even railroad locomotives riding on steel rails are not that heavy. How is this accomplished? Can the Bernoulli Effect or Venturi Effect create a near perfect vacuum or even a half perfect vacuum above the wings? Is there a formula that provides the lift force? If not, why not? Does this formula apply to wind turbines to provide the blade driving force as well?

To put it another way, isn't there a pressure increase beneath the wings as well as a pressure decrease above? Can Bernoulli work in reverse underneath? If not Bernoulli then what causes these large pressure changes? If vacuum above the wings is all there is, then as one person said, better be careful not to open the cabin doors when in flight!!!

Someone said the F16 fighter plane has tiny perforations in the upper wing surface that draw in air for additional lift. Hopefully those perforations don't ever get clogged up. How airplanes fly continues to be a mystery despite everything. Ever see an F16 or any other fighter jet up close? Heavy like a rock are the only words that come to mind.

The philosophical pragmatist William James once mentioned that answers to questions that are only "vague verbal accounts" of some phenomenon should be dismissed and that what is needed is the "particular go" of how it works. So no vote will be taken here and no best answer found. Don't anyone feel slighted since even experts seem to disagree about flight and the lift principle.

A best answer was chosen although a more concise reply would have helped me see that the great weight of large aircraft is nothing compared to the great weight of air itself - 500 tons of air is a volume block only 236 feet on a side, about the same as the wingspan of a jumbo jet. Tossing such airflow masses downwards easily creates large pressure differences on wing surfaces. Thanks to all who answered.

Answer 1

All planes are affected by 4 forces of flight. Thrust, drag, Lift & gravity. Airplane wings and other airfoils are designed to deflct the air so that although streamline flow is largely maintained, the streamlines are crowded together above the wing. Just as flow lines are crowded together in a pipe constriction where the velocity is high, so the crowdered streamlines above the wing indicate that the air speed is greater than below the wing. Hence the air pressure above the wing is less than below and there is thus a net upward force, which is called DYNAMIC LIFT. Actually, Bernoulli's princple is only one aspect of the lift on the wing. Wings are usually tilted slightly upward so that air striking the bottom surface is deflected downward; the change in momentum of the rebounding air molecules results in an additional upward force on the wing.


The thing about holes? That is called a LAMINAR FLOW WING.At a certain speed air flow becomes turbulant. This creates eddies or whirlpools around the wing surface. Air is sucked in by the holes by a vaccum and expeled out rhe tips or trailing edge. The vaccum stops the turbulance And brings back smooth air flow.


Here is the standard equation for calculating lift using a lift coefficient:L=Cl*1/2*(rho)*Vsquared*A

L = lift
Cl = lift coefficient
(rho) = air density
V = air velocity
A = wing area

As an example, let's calculate the lift of an airplane with a wingspan of 40 feet and a chord length of 4 feet (wing area = 160 sq. ft.), moving at a speed of 100 mph (161 kph) at sea level (that's 147 feet, or 45 meters, per second!). Let's assume that the wing has a constant cross-section using an NACA 1408 airfoil shape, and that the plane is flying so that the angle of attack of the wing is 4 degrees.

We know that:

* A = 160 square feet
* (rho) = 0.0023769 slugs / cubic foot (at sea level on a standard day)
* V = 147 feet per second
* Cl = 0.55 (lift coefficient for NACA 1408 airfoil at 4 degrees AOA)

So let's calculate the lift:

* Lift = 0.55 x .5 x .0023769 x 147 x 147 x 160
* Lift = 2,260 lbs

Answer 2

OK, im not sure how accurate this is, but a while back i saw a video of an F16 with 'special wings' each wing had thousands of tiny perforations with which to suck air through. The underside of the upper surface of the wing had a void where the air could travel and this void was linked directly (somehow) to the engine intake, the result was an artificial vacuum created above the wing to create extreme low pressure, it apparently gave the wing 'free lift' and improved the range and handling capabilities of the aircraft. I have since trawled the www looking for a decription of the principle but have drawn a blank. Hope this helps.

Answer 3

The actual wing area of a jumbo is well over ten times your figure. The velocity over various parts of the wing needs to be calculated and the Bernoulli equation applied to each area. The higher the velocity the lower the pressure, but it will never be a perfect vacuum. At high altitude of course the pressure is very much lower. There is also a lift effect due to the angle of incidence of the wing and this applies also in the wind turbine example you asked about.

Answer 4

There is no such thing as a perfect vacuum, my electrolux sucks !!

Joking aside, Robert is right, the low pressure above the wing is nowhere close to a perfect vacuum, not really possible unless we start getting into hypersonic flows I would imagine, but I only know my subsonic and transonic stuff so don't quote me on it. But yes the suction needs to at least equal the weight and then some if maneuvering is taken into account.

Answer 5

Paul- thats one of the reasons why the cabins are pressurized.

Question guy- you have the right concept, but how much lift (vacuum effect) that you need also depends on the geometry of the wing. As far as specific equations, I've only taken up to fluid mechanics so I would suggest buying an aeronuatical book to help you out. Good luck

Answer 6

Assuming the flight became over the open ocean,or throughout the time of barren land alongside with the desolate tract or Arctic areas,a Jumbo jet might want to cruise at one hundred ft,in theory. How the 'airplane might want to circumvent obstructions,or get over climate consequences alongside with wind shear earlier it crashed is yet another question. At this appropriate the gasoline intake might want to be extreme,gasoline scarcity on my own might want to ward off a flight of many hours.

Answer 7

With all the information that you and others have given you forget one thing.
You have to remember the square inches of displacement available. the force of lift you are talking about is a reaction to force exerted on one little bitty square in of of area multiplied by how many you got and how much force on each one of them. This is a very very huge amount it you do the math lol.

Answer 8

I don't think this is right. If it had the vacuum above the wings how could the passengers sitting inside the plane breathe?

Answer 9

i think you might light this website:
howstuffworks.com

Answer 10

i have no idea