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Questions tagged [lift]

The force on a body moving through a fluid that opposes the force of gravity.

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Angle of attack and lift: is there a model?

The relation between the angle of attack $\alpha$ of an airplane's wing and the lift $F$ generated by it is quite complex. If I treat air particles as tennis balls hitting the wing at the front, then ...
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31 views

What is the lift coefficient of human body?

Assuming we can change angle of attack by changing our hands orientation what is the maximum aerodynamic lift coefficient of human body?
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27 views

At what wind speed will a ceiling fan 10 feet above my desk move a sheet of paper? [on hold]

We sell fans. An engineer asked this question. He wants to buy a fan large enough to cool without being so large it blows paperwork off his desk. Q: At what wind speed will a ceiling fan 10 feet ...
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Is it possible to substitute wind speed for the speed of an aircraft in the lift equation $L = \frac12 dv^2sCL$

As in, how would you calculate the amount of lift an aircraft experiences, if for example the plane itself was stationary in a wind tunnel but is subject to high wind speeds and as a result ...
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32 views

Would a puddle of spill milk on the elevator floor float when I cut the cable?

Imagine I pour some milk inside the elevator and then I cut the cable to allow the elevator to free fall, does it immediately float or only when the elevator speed has reached 9.81m/s/s? Oh and assume ...
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3answers
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Please explain airflows above and below aerofoils for a layman

I have read about the lift of aerofoils a lot recently and just want a few things cleared up. When incoming airflow hits a typical cambered aerofoil and diverges into "top" and "bottom" airflows, why ...
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Is Bernoulli's equation the correct explanation of a curved soccer ball? [duplicate]

I saw a lot of materials supposing that the Bernoulli's equation explains the curvature of a soccer ball: since the ball is spinning, two sides of the ball would experience different velocities, and ...
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27 views

Drag of flat plate at any orientation in 3D

I am trying to calculate the force vector on a flat plate caused by wind, when that plate is not perpendicular to the wind. Imagine a sailboat, and assume that its sail is a rectangular flat plate. ...
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62 views

Thrust needed from an engine to reach orbit

Assume you had an airplane with magical engines that didn't need fuel, air or power, to operate. What thrust to ground weight ratio would the airplane need to reach orbit? By ground weight I mean mass ...
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1answer
33 views

Does the weight on a car's wheels decrease with increasing speeds? [duplicate]

Ignoring the reduction in fuel weight as it burns, does the weight on a car's wheels decrease with increasing speeds? If so, by how much and is there a fomula for calculating that? At what speeds ...
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56 views

Confusion with the $\lambda$ in this experiment

I am still having trouble seeing why on this manual for experiment ideas, that they say the $\lambda$ is constant. My question is, how do we find this value of lambda or why can it be kept constant? ...
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Inverted flight [duplicate]

I've read the answers provided but I'm still confused that if an aerofoil is designed so that air flows faster over the upper surface for the purpose of providing lower pressure and hence lift why in ...
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34 views

But how exactly do you calculate the Joukowsky Airfoil, within a minimal margin of error?

After reading a fair bit of theory around the uses of conformal mapping to solve for the forces of lift acting on a wing, or a 2D cross section of the wing, in relation to the angle of attack. However ...
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1answer
32 views

How to obtain the $dC_d/dC_l^2$ value from the drag polar of an airfoil?

I'm currently trying to do an initial design for a propeller. In order to do this I'm trying to use Xrotor. Xrotor allows the user to enter certain information about both the propeller geometry, ...
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3answers
113 views

A drone, or any lifting vehicle, enclosed in a container. Will it lift along with the container? [duplicate]

Consider a drone, or any lifting vehicle, enclosed in a container. Will it lift along with the container? Suppose I place a small drone in a large container of negligible weight and place them in ...
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2answers
55 views

Is lift force proportional to size?

I'm trying to calculate lift force of a particular object I'm working with. However, I can't find much information on how much force is required for an object to stay in flight though. My questions ...
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1answer
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Principle of Lifting of an Aircraft [duplicate]

While using the Bernoulli's equation to deduce the upthrust on an aircraft , a statement is always made that The air particles going above th wing have to cover a greater distance in same time than ...
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3answers
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Would it generate a lift if wind is circulating inside a nearly closed tube?

For a setup like the below image, would there be a lift generated to the tube, due to bernoulli effect?
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1answer
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How fast do the aerodynamic forces on a surface build up?

I`m currently working on my thesis in the field of active car aerodynamics. In order to design a controller to move parts of the cars body I need to know how fast the drag and downforce acting on this ...
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1answer
78 views

How do frogs and fish rain? [closed]

I saw a documentary about the rain of frogs and fish in certain areas due to water sprouts sucking them up and causing rain of frogs and fish (pretty large ones) hundreds of miles away. But how is it ...
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1answer
100 views

Energy consumption from acceleration

I have an interesting problem. I have a machine which has to lift 35 kg (this is the total mass of the object and the lifting arm). The lifting is done by a servo motor. Now I want to calculate the ...
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1answer
70 views

Why is the polar diagram of an airplane depended on weight?

Can anybody answer this question? Although aviation-related, it is in fact a fluid mechanics problem: https://aviation.stackexchange.com/questions/54192/why-is-polar-curve-of-a-glider-dependent-on-...
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4answers
137 views

Effect of tailwind on aircraft speed

I have been spending some time in analyzing the impact of tailwind on the ground speed of the aircraft. My analysis is based around the following equation : VAW = VAG - VWG ; where VAW is the velocity ...
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Could the energy (voltage) required by a ionocraft style EHD thruster be decreased through combining multiple small ionocraft?

I saw a lot of ionocraft designs are focused on building them as big as possible to increase the amount of air the ionized air could push down. This got me thinking. Since one big problem facing ...
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4answers
542 views

What causes the air speed difference above and below the wing of a plane?

I am studying about the lift generated by a fluid flowing on a surface. In the case of an airfoil I have seen that there are various ways to explain it, you can use for example: the third law of ...
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1answer
43 views

Aerodynamics of wet versus dry sail

I recently read in a history book that sailing ships that really needed to go fast would pour water on their sails because "wet sails capture the wind better than dry sails." Why might this be? Does ...
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3answers
315 views

How does the lift force of an airplane work? [duplicate]

At first I thought that the lift force of an airplane wing came from the buoyant force of the air. Thus we can calculate it's lift force using $$ F_b={\rho}gV$$ However, that does not seem to be ...
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1answer
227 views

Boundary Layer Physics and Bernoulli Principle

I was taught that the relative velocity of all fluid particles directly in contact with the boundary in a fluid flow is zero. In other words, that the relative velocity of fluid particles in the ...
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2answers
85 views

Flow over Airplane Wings

I recently read this from Wikipedia in an article discussing lift. A fluid flowing over the surface of a body exerts a force on it. It makes no difference whether the fluid is flowing past a ...
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1answer
39 views

Flow through pipe while being lifted from water [closed]

The setting is as follows. A hollow pipe (flooded) with radius R-pipe is being lifted from below the water surface (totally submerged) to above the water surface with a speed of v1. The pipe is closed ...
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91 views

Why the paper plate is sucked?

In the diagram below, A is a disk and C is a pipe, the A and C combination is a nozzle, B is a board. As long as B is close enough to A, with the air from the D, B will be sucked and will not fall ...
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What is a simple, effective, and physically consistent explanation of Bernoulli's principle (in the context of airfoil lift)? [duplicate]

I am not here to continue any debate about what really allows airplanes to fly. Rather, what I am looking for is an informed, thoughtful, illuminating and self-contained explanation of Bernoulli's ...
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1answer
239 views

Determining tension and free body diagrams for a three-stage linear slide

I'm trying to compute the torque and current requirements on a motor powering a three-stage linear slide. I have included a diagram of the system below: The first stage (right-most) is fixed to the ...
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2answers
89 views

Why do boats carry cargo above water?

This might be a really dumb question, but why do boats carry cargo above water? For example, I can pick up a rock under water that is too heavy to pick up on land. The water has an upward lift on ...
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1answer
90 views

What happens if a helicopter's propeller spins in reverse?

I know airplanes and helicopters fly thanks to the same principle, the Bernoulli Principle. The wings and blades are designed so that the air travels faster across the up side than it does on the ...
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2answers
373 views

Coaxial rotors and thrust

I'm only a HS physics student, so please bear with my lack of jargon. My question goes like this: In the scenario of two coaxial rotors spinning independently in two different directions, each with ...
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5answers
471 views

How does this cup-with-a-cylinder-inside puzzle work?

There is a desk-top puzzle making its way around my university, sold as "Newton's Gravity Defying Puzzle". It consists of a cup with a little cylinder that sits inside. Here are some pictures: The ...
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1answer
127 views

Why neglect gravity in Kutta-Joukowski theorem?

In an example I was asked to calculate the lift force using Bernoulli's equation $$u^2/2 \ + p/\rho +gz \ = \ constant$$ and show that its consistent with Kutta-Joukowski theorem, but seems like ...
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1answer
2k views

Why is a piece of paper lifted upward even when blown below?

According to Wikipedia, A correct explanation of why the paper rises would observe that the plume follows the curve of the paper and that a curved streamline will develop a pressure gradient ...
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78 views

How to calculate lift and drag of a non-standard aerodynamic body

It is my understanding that the standard method to calculate the lift and drag characteristics of an airfoil is to use formulae and existing data of its coefficients of lift ($C_l$) and drag ($C_d$). ...
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1answer
54 views

How many calories are burned by lifting 80 kilos once?

After some calculations i figured it was something like 192 kilocalories but it sounds a bit too much so im not sure if i did the right calculations. What i did was calculate the work and then convert ...
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What are the mathematics behind a disc being elevated by air flow?

I realize the question title is a little vague... I was at the Smithsonian air and space museum recently and they had a set-up showing a disc with an air pipe. The pipe is flowing air fairly ...
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2answers
308 views

Why does the wind speed increase when streamlines approach each other?

In my physics textbook, there's a chapter on fluids which discusses pressure, flow rate, continuity, and the Bernoulli effect. I understand why pressure gradients induce net force on a column of fluid ...
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2answers
1k views

Why does a rocket spin during launching

Why does a rocket spin during launching? https://www.youtube.com/watch?v=BuPY5l45UC8
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2answers
97 views

Lifting force applied to an object

The question is as following: Identical $K$, $L$ and $M$ containers have liquids with densities $d$, $2d$ and $3d$ respectively. A solid object with density $d$ is being dropped in all of ...
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1answer
434 views

Does the rotation of a frisbee have any noticeable effect on the frisbee lift?

If you throw a frisbee horizontally (with zero attack angle), the only uplifting force comes from the rim, which makes the air above the frisbee move faster and thus (Bernoulli) decreases the pressure ...
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1answer
5k views

Dimensional Analysis: How to choose the repeating variables?

The aerodynamic lift (force) $F$ that acts on an aircraft to support its weight when at cruise conditions depends on the following quantities: the speed of the aircraft relative to the air (the "air-...
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3answers
519 views

Downwash created by horseshoe vortex at zero travelling speed?

This is a simple aerodynamics question about the horse shoe vortex. As it seems, the trailing edges on the side cause the downwash on the wing of the plane. However, since the circulation is constant, ...
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1answer
120 views

Would this chambered cylinder be possible? [closed]

Could a flexible light weight chambered cylinder (looks similar to bamboo) was filled with helium and stood up to reach outside the atmosphere? Each chamber would have a different psi according to ...
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0answers
84 views

How to calculate the amount of psi needed to pull a 150lb object? [closed]

I am working on a project, and I wanted to know how to calculate the amount of psi I would need to apply to a wheel-like mechanism (Like in a pneumatic torque wrench) to be able to pull a 150lb object ...