Hot answers tagged aerodynamics
45
A short summary of the paper mentioned in another answer and another good site.
Basically planes fly because they push enough air downwards and receive an upwards lift thanks to Newton's third law.
They do so in a variety of manners, but the most significant contributions are:
The angle of attack of the wings, which uses drag to push the air down. This ...
27
From Stick and Rudder by Wolfgang Langewiesche, page 9, published 1944:
The main fact of all heavier-than-air
flight is this: the wing keeps the
airplane up by pushing the air down.
It shoves the air down with its bottom
surface, and it pulls the air down
with its top surface; the latter
action is the more important. But the
really ...
24
Since you asked for an explanation appropriate to an non-specialized audience, maybe this will do: "A Physical Description of Flight; Revisited" by David Anderson & Scott Eberhardt. It is a revision of the earlier "A Physical Description of Flight" (HTML version).
15
Upside-down or right side up, flight works the same way. As you stated, the wing deflects air downward. When inverted, the pilot simply controls the the pitch of the aircraft to keep the nose up, thus giving the wings sufficient angle of attack to deflect air downwards.
Most airplanes are designed with some positive angle of attack "built-in," meaning that ...
13
Fundamentally, a boomerang has two arms that spin. One arm spins in the same direction of flight and the other spins away from the direction of flight. For this reason, there's a tilt force on the boomerang.
Now, since the boomerang is spinning it has angular momentum. Therefore the tilt force generates precession which is pretty much what makes the ...
12
I think the reason is that when you are blowing on an object, you are making lots of air particles collide with it perpendicularly in one direction thus transferring a lot of momentum to the object. When you are sucking air in, the only force that's acting on the object is by the air particles that rush in to fill up the gap that you just created. These ...
12
Sonic boom refers to the explosive sound caused by the shock wave from an object traveling faster than the velocity of sound. Yes, It's actually spoken out as breaking the sound barrier.
Felix jumped from an altitude of 39,044 km (which is 128,097 ft.) and reached a peak speed of 833 mph. Yes, He did produce the Sonic boom. Most likely, we use the term ...
11
Apparently that is possible.
From http://en.wikipedia.org/wiki/Formula_One_car:
Indycars, for example, produce downforce equal to their weight (that is, a downforce:weight ratio of 1:1) at 190 km/h (118 mph), while an F1 car achieves the same at 125 to 130 km/h (78 to 81 mph), and at 190 km/h (118 mph) the ratio is roughly 2:1.
From ...
10
The first question you need to ask is: does an irrotational, inviscid, incompressible fluid really exist?
The answer is no (well, yes, sort of, if you consider super-fluids). The irrotational, inviscid, incompressible fluid is a mathematical creation to make the solution of the governing equations simpler.
Lift cannot exist without viscosity! That's is ...
9
The air in an elevator does tend to move with the elevator, because it has relatively little inertia. However, thinking about the problem in these terms seems, to me, misleading. The simplest way to think about this is to consider the acceleration of the elevator as and addition to the normal acceleration due to gravity.
In this light, it would be as if the ...
9
Although this is an engineering question it's one that I've had great interest in the specific values myself. Wikipedia does an alright job with the question.
Looking a little bit deeper into it, this seems to be ripped from some Oak Ridge National Lab report, which as been taken down, but is still on the wayback machine. In fact, a lot of the Wikipedia ...
9
The primary factor that determines the ability of an aircraft to takeoff is having a speed exceeding that of the liftoff speed: that is the minimum (air) speed of the aircraft to generate sufficient lift by its wings to counteract the gravitational pull from the earth.
Large passenger planes at takeoff often change the wing configuration (lowers flaps etc) ...
9
Your assumption that there is a significant pressure differential due to fluid dynamics is correct. The assumption that it is a lifting force is not. An airplane generates lift because it has been engineered with lift in mind. An F1 car actually generates a powerful down force to push it against the track, allowing it to get better traction than it ...
8
Colin's answer is right. Let me see if I can clarify a little bit.
First, forget that old Bernoulli explanation.
It's not wrong, but it confuses everybody.
If you create a simple symmetrical teardrop-shaped airfoil, and place it in a wind stream, then the air will flow past it, and it you turn it at an angle to the wind, it will deflect the wind stream, ...
7
Insect flight is different than bird flight. With insects, the rapidly moving wings, which do a figure 8 sort of motion, generates a vortex tube over the wings. This vortex by Bernoulli principle has less pressure, which permits the larger air pressure underneath to lift the animal up. If one is trying to understand insect flight according to the mechanics ...
7
The common explanation given is that it flows faster over the top of the wing because the top is more curved than the bottom of the wing. However, I understand why you would find this explanation unsatisfactory.
To start with, I think we need to identify the point at which the flow separates. Looking at Wikipedia, I'll post two images:
The argument ...
7
In reality, it is possible to "(almost) freeze time" and examine such phenomena, through the use of high speed photography. The fact that no clear photographs of "bullet trails" are readily found is a good indicator that such phenomena are not readily produced or observed. That said, there are two effects I can think of that could in principle lead to ...
6
I would just like to add something here.
These answers are great but I might have another answer.
At first it was indeed a mystery how these insects were capable of flying, but thanks to high speed recordings they found something which investigators didn't concider. The wing motion has a sort of dubble lift feature.
By twisting her wings over at the end of ...
6
In general, the forward thruswt is achieved by tilting the entire helicopter forward. This converts some of the lift produced by the main rotor into a forward component of force. The same is true for turns.
Yes, the swashplate may be used to create a thrust imbalance; but this imbalance does not provide any horizontal forces. It merely creates a force ...
5
This story may have originated with August Magnan and André Sainte-Laguë. In the forward to his book Le vol des insectes, August Magnan wrote
Tout d'abord poussé par ce qui se fait en
aviation, j'ai appliqué aux
insectes les lois de la résistance de l'air, et je suis arrivé avec M.
Sainte-Laguë a cette conclusion que
leur vol est impossible.
...
5
An engineering answer:
Note that it's not just about water vs air. It depends on a lot of things: the density & compressibility of the fluid, and tradeoffs between torque, efficiency, cost, materials, maintenance needs, fouling hazards, and so on. Below is a water turbine blade, the SeaGen, that's not much different from a wind turbine blade, because ...
5
You've seen biplanes.
Almost anything can fly if it has enough area, an angle of attack, and is nose-heavy.
I've seen a model airplane in the shape of Snoopy's doghouse!
It flew just fine.
If you're wondering why nose-heavy it's this.
Look at a normal plane with a main wing and a tail. It's nose heavy.
The main wing holds the weight by lifting up.
The tail ...
5
You're correct, the ice block will not turn automatically. It will require a torque. In aviation this is basically what is called coordinating a turn. With an airplane, if the pilot does not provide the necessary coordinating torque via rudder/elevator inputs, the torque will be generated automatically via the weathervane effect, which tends to align the ...
5
My apologies, I won't be reading your entire question.
But still I will provide an answer. Why is that? Because flight does not require any of the things you talk about.
You could build an airplane that would fly with no "airfoil" shapes. You could build an airplane that would fly with completely flat rectangular wings made out of plywood. The ...
5
Seems to me your question contains two physics questions which depend on the definition of "easier". Certainly in an atmosphere it is easier to balance gravity the larger the ratio of surface to weight due to the viscosity of the medium.
On the other hand this does not make "easier" the maneuverability of the system in energy demands. So you are asking ...
5
As I understand it, there are two versions of this idea. The first is kind of interesting and might work - the idea is that you heat the air at the bottom using a power station, and allow the vortex to carry the air into the upper troposphere. The vortex acts like a chimney, drawing the hot air out of the unit, causing a pressure difference that allows you ...
5
There's quite a few factors at play here, and granted, it's been a while since my last flight dynamics class :)
After a few iterations with the other answerers below, here is a (still not yet complete) list of reasons the effect will occur:
While yawing, the left and right wings will have slightly different speeds. This difference in wing speed causes ...
5
Rody and Mike almost got it right. :)
Most aircraft are designed with swept wings. That is the primary mechanism that gives the roll effect to an airplane that may only receive a yaw input. if you look at this picture:
You can see that both wings have a backwards sweep to them. Now, if you introduce a yaw to the aircraft, one wing will extend out ...
5
I would guess you've heard that an airplane in a spin or some other critical state can dive to build up speed, then when it pulls out of the dive the increased speed increases the lift and can allow the pilot to regain control. You are presumably asking if the same idea can be used for a falling person.
The problem is that an aircraft wing is carefully ...
5
It is just easier, i.e. less expensive, to build and maintain them that way. There exist alternative designs that are more efficient but also more difficult (= more expensive) to build, put up and maintain. You can check those out via this link.
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