A subset of [tag:fluid-dynamics] concerning primarily forces such as lift and drag generated on bodies as they move through gasses or as gasses move through the body (typically air).

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669 views

Does it make sense to open one window all the way when the other window is much smaller?

I can't wrap my head around this idea because I don't know much about air flows. Say we have this imaginary apartment with two windows, one of which is two times smaller than the other: Will the ...
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1answer
66 views

Why Don't Birds Stall?

I often hear about planes stalling when they lose lift due to low airspeed/too high angle of attack. Why don't birds stall? Does it have to do with the structure of their wings and their flexibility, ...
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5answers
4k views

Why isn't jumping from a high altitude fatal?

After seeing this answer claiming that displacing matter "In a very short time", "no matter whether the matter is solid, liquid, or gas" (even though he concludes that falling from a high altitude is ...
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6answers
4k views

Why is jumping into water from high altitude fatal?

If I jump from an airplane straight positioned upright into the ocean, why is it the same as jumping straight on the ground? Water is a liquid as opposed to the ground, so I would expect that by ...
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2answers
64 views

Does the wing-propeller plane or jet-plane struggle up at the high altitudes because of low pressure?

We all know that wing-propeller planes rely on air to create a thrust. They suck the air in and push them back hard that it's opposite reaction pushes the plane (Newton's law). Does that mean ...
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2answers
364 views

Toy helicopters at very high altitude

Because air is thin up there, toy helicopters usually have a maximum operational altitude. If the toy brought up by a real aircraft, higher than its intended maximum altitude, would it be able to ...
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2answers
41 views

Stratospheric ship

Let's assume that we build a giant steel hull in a shape of cube with open top (2km long edge) and lift it to the top of stratosphere and then pump air out of it. Would it float on the outer layer of ...
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1answer
40 views

Aerodynamics and thermodynamic [closed]

Why can we refer an object as being aerodynamic but we can't refer an object as being thermodynamic, and if an object is thermodynamic what does it even means?
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3answers
110 views

How do birds generate thrust?

I have been watching this video carefully and I want to know how the wings of birds generate thrust. This is because the wings are more or less flapping up and down --- generating the lift. But I do ...
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2answers
45 views

What would be the minimal size of an aerial vehicle capable of sustained suspersonic flight? [closed]

I wonder, what's the smallest possible size for a UAV capable of sustained supersonic flight at the current technology level? Let's say 10 minutes of flight at 1.1 M.
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0answers
33 views

Modal analysis with aerodynamic damping

I'm using modal decomposition to predict the steady state response of a beam structure to harmonic loading. The structure itself is very lightly damped, but we know from experiments that the ...
3
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1answer
57 views

Mathematically impossible for a vortex line to have loose ends?

Could someone show the math behind it? Source : "A vortex is a bunch of air circulating around itself. The axis around which the air is rotating is called a vortex line. It is mathematically ...
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0answers
33 views

Why does air circulate on an airfoil — The Kutta Condition

Why does the air circulate on a flowing airfoil, thus giving rise to increased velocity (circulation + relative airspeed) above the wing and hence decreased pressure.
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2answers
54 views

Turbofan: Efficiency wrt. the bypass ratio: “a lot of slow air > a little faster air”?

Reading / viewing up on how jet engines work, this video explains at the 9:02 mark that, for turbofan engines, ".. it is more aerodynamically efficient to have a lot of air moving relatively slowly ...
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1answer
46 views

Airfoil theory — Why does air travel faster above? [duplicate]

I do not understand, why the air above the airfoil travels faster than the air below it? The air above has to travel faster than the air below so that both streams meet simultaneously at the ...
3
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0answers
62 views

Why do some (older) wind generators have more than three blades?

Based on my personal observations, newer windmills seem to have three blades while older ones tend to have four or even more. This question has excellent discussion on my three is an optimal number. ...
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0answers
25 views

Compute an aerodynamic shape [closed]

I'm interested in building a Fairing for a recumbent bicycle. A fairing is just a rigid curved surface (usually plastic or fiberglass) that surrounds the bike in order to reduce wind drag. Apparently ...
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0answers
17 views

What factors determine how long airplane condensation stays in the air?

My understanding is that the turbulence formed by the flight of an airplane has low-pressure zones with low temperatures that cause water molecules to condense to form a fog. My question is about the ...
2
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2answers
113 views

Why does a flat clover-like shape fall slower when it is rotating?

The plastic flat clover-like shape pictured below falls noticeably slower when it is rotating fast. I wonder why. Its three edges are flat, so I don't think that the rotation makes it act like a ...
0
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1answer
2k views

Relation between pressure, velocity and area

In a nozzle, the exit velocity increases as per continuity equation $Av=const$ as given by Bernoulli equation (incompressible fluid). Pressure is inversely proportional to velocity, so we have lower ...
0
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1answer
92 views

Quadrotor dynamical equations on center of propeller

I work on a quadrotor project. It is commonly wide dynamical model according to the center of quadrotor. However, I need quadrotor dynamic equations on center of one of the propellers. It seems very ...
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4answers
242 views

Is it possible to sky dive without a parachute and land safely?

Let's assume an averaged sized man (1.8 meters height 80 kg) who's sky-diving from a 5000 m height. Let's also assume he's using tight clothes and no parachute. The idea is: Is it possible for him ...
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1answer
250 views

Nose cone design for minimal drag

What formula defines a curve for a nose cone with the minimal possible drag? The nose cone is attached to a cylinder (assume it goes on forever). The volume of the nose cone is not relevant. The ...
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2answers
95 views

Spontaneous motion in a wind tunnel

Suppose that a hollow truncated cone is placed in a wind tunnel with a steady wind speed $V$. The cone is placed in such a way that it's base of area $A_1$ faces the wind (rather than the other side ...
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1answer
31 views

Velocity in the lift equation

What exactly is the nature of the velocity in the lift equation? I have read that it is the velocity of the aircraft, and I think I have read that it is the relative velocity of the air to the ...
0
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1answer
96 views

Exactly how much lift is needed to overcome the weight of an average person?

I am designing a "glider" of sorts, and I have some basic questions about the physics involved to get me started. How much lift is required to overcome the weight of an average person, say 150 pounds? ...
4
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3answers
397 views

Number of blades in a helicopter rotor

I was wondering how it is possible to determine what is the optimal number of blades in a helicopter rotor. I think that the length of the blade is involved as a longer blades would have to spin ...
15
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1answer
350 views

Causes of hexagonal shape of Saturn's jet stream

NASA has just shown a more detailed picture of the hexagonal vortex/storm on Saturn: http://www.ibtimes.com/nasa-releases-images-saturns-hexagon-mega-storm-may-have-been-swirling-centuries-1496218 ...
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2answers
153 views

The criteria for potential flow theory

I am learning aerodynamics. In this course a potential flow is denoted that a flow in which the rotation is zero everywhere. But the book told me that we can add vortex into a flow field, and we can ...
3
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1answer
289 views

What exactly is the 'lift' of a sailboat as explained by Bernoulli principle

I have heard that when a sailboat is sailing aginst the wing, it operates on the principle of 'lift'. I did not understand very well the explanation based on Bernoulli principle. My question is, when ...
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1answer
266 views

Difference resultant aerodynamics force on an airfoil and a flat plate

From basic airfoil theory the following free body diagram can be determined for a two dimensional asymmetric airfoil: Here the direction of the resultant force is governed by the geometry of the ...
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3answers
229 views

How to end up with Newtons in the calculation of the lift force

In another StackExchange Physics question, @Rego had found the following equation to calculate the lift force generated by a simple rectangular blade. $$F = \omega^2 L^2 l\rho\sin^2\phi$$ in ...
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2answers
169 views

How can you calculate air resistances at different speeds?

I've read that at 50mph air resistance to an average car is the equivalent of driving through water and at 80mph it's the equivalent of driving through oil. I can't find any references online to ...
2
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1answer
205 views

Why does mini quadcopter doesn't maintain altitude?

I have a mini quadcopter controlled by remote controller. I have set the motors (e.g 50% thrust) it will remain at altitude at 10 cm~ but once I increase to 80% and then follow by decrease to 50% I ...
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1answer
77 views

Motion of elevating airplane

I wonder how the motion of an airplane which will not try stop to elevate should look like. Of course, at some point the plane will no longer be able to go to higher altitudes but is it going to stay ...
2
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1answer
116 views

How can electrostatic forces provide lift to the gossamer spider?

I was reading this article entitled "“Ballooning” Spiders Use Electrostatic Forces To Generate Lift". What I would like to know is how can a electrostatically charged object generate lift within the ...
3
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1answer
335 views

What is the physics behind Roger Federer's & Rafael Nadal's iconic shots

Two Iconic players of Tennis, Roger Federer & Rafael Nadal, with two iconic shots. One with a top spin forehand & other with a slice backhand. I want to understand the physics of these two ...
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0answers
125 views

Efficiency estimation for small-scale (~15cm) propellers

First up, apologies if this isn't quite the place for this; Aerospace is still in Area 51 so there doesn't seem to be a better place for it. If it helps, feel free to give theoretical answers and I'll ...
2
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0answers
130 views

What is wrong with this downforce calculcation?

I tried calculating the downforce of a spoiler I need for a robot. I used this formula. $$F = \frac{1}{2}Ac_a\rho v^2$$ Where $\rho$ is air density, $v$ is the speed of my robot, $c_a$ is the lift ...
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1answer
304 views

Book recommendations for fluid dynamics self study [closed]

I have my bachelors degree in engineering science: computer science, option electrotechnic. I have a good understanding of basic mechanics and dynamics, calculus (differential equations). The books ...
2
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1answer
197 views

In a turning plane, will the vector of combined centrifugal plus gravity force experienced by passengers be perpendicular to the floor?

In a turning plane, will the vector of combined centrifugal plus gravity force experienced by passengers be perpendicular to the floor? In other words, will the passengers experience the feeling of ...
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0answers
122 views

Calculating rotor torque out of mass center

Suppose I have an engine with propeller. I know there is aerodynamic force pushing the propeller opposite direction the engine is turning it. One component of this force is creating lift, but second ...
0
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2answers
211 views

Aerodynamics drag of hollow cylinder vs solid cylinder of the same cross area?

I wonder how a hollow cylinder at the same cross area perform vs a solid one, i.e the hollow cylinder has larger radius? I guess they have a similar drag, is that true?
4
votes
1answer
124 views

Ducted or open fluid flow, which is best for aerodynamics and lift

I'm designing a copter and trying to decide if the propellers should be ducted or open axial flow. I've read some theory on ducted and open air flow but I can't find any where that compares the two. I ...
12
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2answers
2k views

Why can't supersonic planes “just fly higher” to go faster while maintaining cost?

First post to this site, and I've got at most a high school background in physics - I really appreciate any answer, but I may not be able to follow you if you're too advanced. I suppose this goes for ...
4
votes
1answer
252 views

Why do wind power plants have just 3 blades? [duplicate]

Why do wind power plants have just 3 blades? It seems that adding more blades would increase the area that interacts with the wind and gather more energy. (Image from Wikipedia.)
0
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1answer
135 views

Equal Transit Time Fallacy [duplicate]

I learned, in grade school, that lift was generated via the particles on either side of the wing having to reach the other end at the same time. Looking back, that indeed has no physicality to it. So ...
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2answers
416 views

Are the hypotheses of the Bernoulli equation satisfied for a bird or airplane wing at low Mach number?

A previous question by David Zaslavsky was a request for a broad, "how things work" type of explanation of the lift of an airfoil. The answers given there are enlightening, but don't address a more ...
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1answer
347 views

Enginering question about F1 car

In formula F1 car, air coming infront of the car goes up with very high velocity as a result pressure difference is created which is very high from Bernoulli theorem.. The F1 car is very light so ...
5
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0answers
369 views

Why is it hard to breathe when cycling against the wind?

Sometimes when I bicycle against hard wind, I find it difficult to breathe. Others I have discussed it with have also noticed this effect. A possible related phenomenon that I heard from an ...