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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125
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6answers
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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 ...
36
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3answers
2k views

What is going on in front of and behind a fan?

Why is it that when you drop paper behind a fan, it drops, and is not blown/sucked into the fan, whereas if you drop paper in front of a fan, it is blown away?
29
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6answers
8k 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 ...
27
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13answers
2k views

What does a wing do that an engine can't?

This isn't a question of how a wing works -- vortex flow, Bernoulli's principle, all of that jazz. Instead, it's a question of why we need a wing at all. A wing produces lift, but why is that ...
21
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2answers
10k views

How can airplanes fly upside down?

I've read many times, including here on this very site that the commonly known explanation of flight is wrong, and that airplanes can fly because the shape of their wings deflects air down. This makes ...
20
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1answer
502 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 ...
15
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5answers
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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 ...
14
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2answers
3k 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 ...
13
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4answers
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Why is exhaling more forceful than inhaling?

By blowing at pencil, a piece of paper, or another object up to fifty centimeters away, I can cause it to move away from me significantly. But I can't move an object toward myself by inhaling sharply ...
13
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4answers
1k views

Helicopter in an Elevator

You buy one of those remote control toy helicopters. You bring it into an elevator. The elevator goes up. Does the helicopter hit the floor or does the floor of the elevator push the air up into the ...
12
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3answers
3k views

Does a wing in a potential flow have lift?

I have a hard time understanding whether or not a wing placed in a potential flow, assuming there is no viscosity and no friction with the wing, will produce a lift. I've seen several contradictory ...
12
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5answers
829 views

Is flying really easier on smaller scales?

In the book Playing with Planets, the author makes the following argument, pertinent to flying robots of the future: As it is, an important law of physics says that smaller organisms fly much more ...
12
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3answers
5k views

What causes an aircraft to roll when rudder is applied

When continuous rudder is applied in a typical light aircraft during straight and level flight at "normal" flying speeds and altitudes, the primary effect is that the aircraft will yaw to the left - ...
12
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1answer
4k views

Did Felix Baumgartner produce a sonic boom during his jump?

I really got to thinking about this. The speed of sound is measured at 761.2 MPH at sea level. But how does this number change as air density decreases? The lack of air density is what allowed his ...
12
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1answer
845 views

Do modern Formula One cars produce enough down-force to drive upside-down?

For example, if they were driving at top speed through a long tunnel, could they transition to and stay on the ceiling?
12
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4answers
1k views

How to sail downwind faster than the wind?

Recently a group set a record for sailing a wind-powered land vehicle directly down wind, and a speed faster than wind speed. Wikipedia has a page talking about it, but it doesn't explain exactly how ...
10
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1answer
2k views

Why exactly does a boomerang return back to the thrower?

I was always intrigued by the phenomena that govern the returning back of a boomerang to the thrower. Even if it is dependent on various factors such as velocity, aerodynamics, wind resistance and ...
10
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8answers
22k views

Why does the air flow faster over the top of an airfoil?

I understand the common explanation of lift, which describes the airflow over the top of the wing as moving faster than the air below the wing. However, I don't quite understand why the air moves ...
10
votes
2answers
511 views

Energy from man-made tornadoes

Peter Thiel just paid $300,000 to Canadian inventor Louis Michaud who is working to construct useful "man-made tornadoes" or "atmospheric vortex engines" which could be components of future power ...
9
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2answers
1k 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 ...
9
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2answers
779 views

Why do co-rotating vortices coalesce, but not counter-rotating ones?

In studying the aerodynamics of modern aircraft equipped with high-lift devices, I have discovered that quite a number of distinct trailing vortices are present in the immediate wake of an airplane in ...
8
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2answers
1k views

How much more efficient is a road bike than a mountain bike? [closed]

What would be a good estimate on the difference of efficiency between a road bike and a mountain bike? A number of links cite all the usual reasons: thinner tires, better aerodynamics... But I'm ...
8
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2answers
3k views

What is the optimal design for a paper airplane? (Or, at least, how can you approach it?)

Having only really known two designs for paper airplanes since my days as a child, one which flies about eight feet and another which flies about ten feet, I have always wondered how people manage to ...
8
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1answer
400 views

NASCAR drafting at Daytona

This year, the racetrack at Daytona has been repaved. The track was always faster than other tracks NASCAR raced at and several cars in a "train" were faster than single cars or smaller trains. This ...
7
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2answers
1k views

Could some design of a propeller be used in both air and water?

Propellers in water are smaller in diameter. They also move more slowly. On the other hand, aircraft propellers are larger in diameter, have narrower blades and operate at very high speeds. An ...
7
votes
2answers
216 views

How should I throttle my rocket to reach highest altitude? [closed]

"Real world" problem. Suppose we want to launch a rocket equipped with an engine which can be throttled as we prefer. Suppose also that the amount of fuel burnt per time is directly proportional ...
7
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1answer
110 views

Why Are Normal Shock Waves Unstable in a Converging Channel?

While learning about shock waves in an introductory Gas Dynamics course, it was revealed that normal shocks are unstable if formed in a converging channel. Even if the local conditions ostensibly ...
7
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0answers
135 views

Could the phenomenon of vortex bursting be exploited to reduce wake turbulence?

One of the classic stories in the annals of aerospace engineering is the development (and subsequent redesign) of the F-18 and its Leading Edge Extensions (LEX) due to fatigue problems, problems that ...
6
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5answers
1k views

Why do blades of windturbine propellers as comp. to propellers of ships cover very different areas?

This is a thought I asked myself often, but never did real efforts to get an answer. Barsmonsters question about number of fans of a wind turbine made me think of it again Why do blades of aircraft ...
6
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4answers
3k views

Why is 55-60 MPH optimal for gas mileage of a passenger car?

My driver's education teacher back in high school said 55 MPH is optimal for gas mileage of a passenger car. Just last week, I read an article in a magazine saying 60 MPH is optimal. These numbers are ...
6
votes
1answer
869 views

What is a Physically Accurate Explanation for the Kutta Condition?

Countless arguments between highly intelligent people have been waged (on this very site in fact) as to exactly how lift can be explained in an experimentally and mathematically rigorous way. Taking ...
6
votes
1answer
393 views

Why aren't airplanes like golf balls?

Ok this is a silly question but here it goes Although it is good to have a laminar flow of the air around the object for low drag but the laminar flow is prone the phenomena called separation (sounds ...
6
votes
1answer
731 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 ...
6
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2answers
76 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 ...
5
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2answers
2k views

how does a helicopter get forward thrust?

Just passed a helicopter on my way to work. We have read in some detail how an airplane gets forward thrust and lift by deflecting air. How does a helicopter with horizontal fans achieve that ?
5
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5answers
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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 ...
5
votes
3answers
682 views

Benefits of rear spoiler in cars

What would be the benefits of rear spoilers in cars, like this one:
5
votes
2answers
295 views

How does train back draft work

Quoting platforms and stations : Fast trains can create a vacuum called a ‘back draft’ that can blow you over or suck you under a train. How does that work ? I thought that the volume of air ...
5
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4answers
3k views

Why do aircraft inner wings lose lift when turning?

first question here, so please be gentle! I'm reading an entry-level engineering course book and am currently up to discussion of aircraft design. There's one particular statement that is unclear to ...
5
votes
2answers
339 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 ...
5
votes
1answer
295 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.)
5
votes
1answer
152 views

Aircraft nose-up glide

In the pilot's introductory book "Stick and Rudder" it claims that a nose-up glide is possible. It doesn't state how, why or when. It implies it's possible to do and maintain a constant forward ...
5
votes
1answer
300 views

Why does your car lurch toward an oncoming truck as it passes you?

I notice that the larger the truck the greater the magnitude of the lurch. Can anyone give a physical explanation to this?
5
votes
1answer
1k views

Paper plane between two fans - is this possible?

The setup: two fans facing each other, distance around 1m. Both are turned on. In between them, place a simple paper plane and according to this video, it will fly. ...
5
votes
3answers
83 views

Why do tropical cyclones not tear themselves apart?

A tropical cyclone is the generic term for a hurricane, typhoon, or tropical storm. Tropical cyclones derive their energy from evaporation of water at the ocean surface which ultimately recondenses ...
5
votes
3answers
3k 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 ...
4
votes
5answers
3k views

Is it really impossible for Bumblebees to fly?

According to some source or other (I forget which now) it is theoretically impossible for bumblebees to fly by virtue of their size/bulk/aerodynamic properties. Is this old adage apocraphyal or true? ...
4
votes
2answers
1k views

What is the optimal weight for a golf ball?

I am 32 now, and have forgotten the basic physics formulas we used in school. I am sitting with a question that is bugging me. If I had to hit two golf balls of different weight with the same force, ...
4
votes
3answers
796 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 ...
4
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3answers
2k views

How is the Joukowsky Transform used to calculate the Flow of an Airfoil?

As I read in The Road to Reality by Roger Penrose, the Joukowsky transform $$w(z) = \frac12\left( z + \frac1z \right)$$ after Nikolai Zhukovsky (transcribed in several versions from Никола́й Его́рович ...