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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How is the kinetic energy of the wind transferred onto a lift based wind turbine?

The rotor blades of a lift based wind turbine are shaped like airfoils, so the wind flowing around them creates a lift force which in turn moves them around. From a thermodynamic viewpoint and like ...
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3answers
2k views

How do eagles fly slowly for a long time?

Eagles fly slowly for a long time. Many other species fly faster and move their wings faster. But eagles keep their wings steady, and move only their tail. How do they move slowly in the air, ...
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2answers
378 views

Why ballasted gliders fly faster

The fact: Gliders have ballast tanks that can be filled with water. The addition of ballast increases weight, and this allows the glider to fly at faster airspeeds while maintaining the same glide ...
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1answer
49 views

Why don't we build helicopter based space shuttles?

As seen in this video: the principle of the helicopter does work in space. So we could make a helicopter based space shuttle! It would be easier to navigate with it than with propulsors.
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1answer
29 views

Control surface effect

If we know the Center of Mass and the Center of Lift, and the position and rotation of some control surface, how can we calculate what control surface must be operated to change our path? lets say we ...
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4answers
266 views

Why is paper (or any tailless) airplane pitch stable?

To clarify my question further I'll use a practical example. Here is the simplest paper plane design I could think of - it is a rectangular thick drawing paper with a weight attached at the middle of ...
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6answers
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Turning an Airplane. What actually causes the circular motion in a banked (roll) turn?

Basically I'm wondering if this is correct. Which essentially says that you need a torque to get the nose of the craft to turn and that this is provided by the rear tail surfaces. After trying to ...
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0answers
33 views

What is the role of Tail section of a fixed-wing aircraft? [migrated]

In a standard fixed-wing aircraft, say cessena, What is the role of tail section, i.e. Rudder and Elevators?
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1answer
236 views

Why are the backs of airplanes curved?

I get the front part, but why is the back curved too? I do not see a problem with the back being flat.
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1answer
43 views

How does a hovercraft hover, if it has low pressure underneath it?

I've read a few different explanations of how hovercrafts hover, and they all mention a low-pressure cushion of air. This confuses me though: If there is low pressure under the hovercraft, why doesn't ...
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1answer
35 views

Reynolds number of airfoil in a pipe

As part of a physics high school paper I am writing, I need to build a wind tunnel. As part of my calculations, it appears that Reynolds number is very relevant in aerodynamics (specifically for ...
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2answers
50 views

Do rotating non-circular projectiles also experience Magnus lift?

The Magnus effect has been studied on spherical projectiles such as golf balls, tennis balls, and soccer balls. The backspin of a golf ball leads to Magnus lift that opposes gravity, thus allowing the ...
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2answers
753 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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4answers
77 views

In aircraft design why are light materials preferred to heavy ones?

Especially given the relative cost between (say) steel and carbon composites. After all, I assume most fuel is consumed overcoming drag not accelerating mass. Once an aircraft reaches cruising speed ...
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1answer
21 views

Speed of pressurized gas escaping into vacuum

Does speed of pressurized gas escaping through a narrow nozzle into vacuum depend on the pressure? I've asked a question on Space.SE regarding utilizing gas at extreme pressures for propulsion. My ...
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2answers
158 views

Counter rotating propellers: better in same column or staggered?

In an octo-copter design, is it better to put four pairs of counter-rotating props over each other so that each pair works in a column together? Or will you get more power or efficiency from ...
2
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2answers
40 views

Force on pilot ejecting at supersonic speeds?

Using the Rayleigh drag equation, and approximations for the air density, drag and frontal area of the pilot, and mass, at around 300 m/s (subsonic) a pilot might experience deceleration forces of ...
2
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1answer
53 views

Calculating wind force and drag force on a falling object

I'm trying to numerically integrate the motion of an object (say, a falling vertical cylinder). Here, there's a drag force: the wind "acting" on the body (presumably adding horizontal velocity) and ...
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0answers
136 views

Equation derivation for skipping rocks

oWhy can rocks skip over water? For instance, if you conduct an experiment where you drop both rocks from the same height, but give one considerable acceleration in the x direction, one will fall in ...
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0answers
34 views

Ratio between power of chaotic and regular airflow

Turbulent field is created as a result of an impact of an airjet on an edge (the flow velocity is high enough). The field of velocities have a regular and a chaotic component. What I need is to ...
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3answers
147 views

Disconnected aileron/surface deflection in terms of speed?

Would a disconnected surface, especially aileron, deflect upwards as you slow down due to increased alpha? I figure out it is more likely to deflect upwards as you increase your airspeed, thus having ...
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2answers
46 views

Does air density influence a football player's ability to “bend” the ball?

Whilst reading an article on nasa.gov, there was a claim that I found interesting: At higher altitudes, the density r is lower producing a larger radius of curvature and a straighter path. The ...
144
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9answers
22k views

What really allows airplanes to fly?

What aerodynamic effects actually contribute to producing the lift on an airplane? I know there's a common belief that lift comes from the Bernoulli effect, where air moving over the wings is at ...
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6answers
45k 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 ...
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0answers
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How big is the power loss of a downwind wind turbine due to turbulence created by an upwind turbine?

When a horizontal axis wind turbine is placed downwind of another horizontal axis wind turbine (distance between the two is minimal), then the downwind wind turbine has a lower power output because of ...
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1answer
20 views

Explain an experiment: airstream between two hinged curved surfaces

Please, see the following video (the experiment starts at 3:40 and ends at 3:55): https://www.youtube.com/watch?v=7pB6q_bH35s&feature=youtu.be&t=216 The basic idea: given 2 curved surfaces ...
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1answer
33 views

How are shock waves related to sound, and are there equations describing its density, size, and pressure?

How exactly does one model a shock wave? I've done a lot of searching and have failed to find any equations where we're able to relate things such as its pressure, density, temperature etc. I've ...
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1answer
55 views

The demise of the Tacoma Narrows bridge was casused by aeroelastic flutter. But isn't that just a special case of resonance?

Much of the research I've done on the Tacoma Narrows bridge disaster of 1940 attribute the collapse of the bridge due to aeroelastic flutter - not strucural resonance. But isn't aeroelastic flutter ...
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1answer
131 views

Is Magnus effect a corollary of Bernoulli principle?

Magnus effect is commonly explained using Bernoulli principle. However, taking the lift on a rotating cylinder as an example, the velocity difference is caused by the extra work done by the rotating ...
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1answer
43 views

Boundary Layer in aerofoil

I want to know how the top and bottom boundary layer interact at the trailing edge of an aerofoil (zero angle of attack) and what happens to the boundary layer after a small distance from the trailing ...
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1answer
54 views

Why does a propeller suck in air from the front?

A rotating but fixed propeller sucks in air from the front. What is the cause for this acceleration of air particles? Since propeller blades act like rotating wings, my best guess is that the blades ...
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4answers
73 views

How can a petrol car require less fuel at 55mph than a lower speed at the same rpm?

It seems to be widely accepted that somewhere around 55mph is the most economical speed to drive in a conventional petrol car. Recently I ordered an EV, and learned that (with the exception of at ...
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1answer
74 views

How to obtain this equation for skipping stones over water?

I think I have a decent conceptual understanding of the forces at work when stones are skipped over water. My question pertains to the equation found in this [source][1]. Reproduced in Latex this ...
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3answers
379 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?
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2answers
353 views

Aerodynamics of two objects closely following each other

On bicycles.se a question came up about whether one cyclist drafting another causes the lead cyclist to be slowed down. A contributor suggested that the opposite might be the case, that the leading ...
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1answer
43 views

How to calculate the actual drag force on a wing?

I want to calculate the actual drag force that a NACA 63-412 wing would experience at a given planform area and relative wind speed. Airfoiltools gives a drag coefficient of 0.01676 for the optimal ...
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0answers
13 views

The torque produced in the rotor blades of an axial flow turbine

I want to ask about the torque experienced by a axial flow turbine, and how the torque is related to the ange of attack, or pitch angle of the turbine blades. (I'm new to technical terms, please ...
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2answers
65 views

How do you calculate/estimate hypersonic leading edge and skin temperatures?

At lower speeds (below Mach 5-ish), stagnation temperature (TAT) is a very accurate proxy for skin temperature. But at mid/high hypersonic speeds (especially in the thin upper atmosphere where mass ...
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2answers
50 views

Pressure-Velocity relation at a point in a flow

How can we relate pressure and velocity at the same point in a fluid flow? Why does pressure decrease with increase in velocity?
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0answers
31 views

Mass flow rate and force on moving disk

If I understood correctly, the force $F$ related to a given mass flow rate $\dot{m}$ through orifice area $A$ (or, say, on a disk of area $A$) is given by Newton's 2nd law of motion - assuming a ...
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1answer
186 views

Why does deflating baloon spurting through the air make circular motion? [duplicate]

When you inflate a balloon and then let it go again, it will fly through the air in an unpredictable motion. My kids (1 and 3 year old) love watching this. At some point my oldest asked how it worked ...
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1answer
124 views

Helicopter, Tricopter, Quadccopter - what's really happening here? Are there generalized advantages on a small scale?

There have been, it seems, a proliferation of quad-copters commercially available. Amazon seriously tried to use them for deliveries. (Search Drone on their website.) The NFL uses one for cameras. ...
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0answers
25 views

In momentum theory, what happens if atmospheric velocity is larger than outflow velocity?

I am currently reading up on aerodynamics, essentially the actuator disk concept and momentum theory as it is described in e.g. Basic Helicopter Aerodynamics by Seddon and Newman. There they assume ...
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1answer
70 views

Why dosen't my boomerang return [closed]

My boomerang I built will only turn just a bit back towards me, but that's it, but why? Is it my design, I incorporated the recommended dimensions from the website I used, such as an 107 degree ...
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3answers
1k 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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1answer
29 views

Airfoils contradict the law of the lever?

The law of the lever says that "the less force you use, the more distance you have". It is often exemplified by referring to simple machines, but it should apply to all technical systems. But I do not ...
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3answers
924 views

Why does an airplane need to climb during a takeoff even if it is in emergency situation?

Right after take-off (which means an airplane already exceeded V1) it is recommended that an airplane keeps climbing even when emergency occurs. Beside worries of crashing into houses and buildings by ...
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1answer
48 views

Why does a parachute open up faster on Mars than on Earth? [closed]

I recently heard that a parachute opens up much faster on Mars than on Earth. Why is that the case? More specifically, during a NASA Edge TV program, one of the scientists working on parachute tests ...
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0answers
21 views

how much air pressure can be varied (in dapa) when an empty syringe's plunger is pulled in and out?

I'm new to the forums so please guide me appropriately if this is the wrong place to ask this question. When the syringe plunger is puller out ,a negative pressure is created at the nozzle....Isn't ...
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1answer
1k views

How fast does water fall in the middle of a very very thick waterfall?

Let me create a very artificial experimental set up. Take a bathtub the size of Delaware and suspend it a mile above the ground. Fill it with water (though I'm not sure to what depth - and it might ...