Lift

[Hyperlite]

I'm doing a project for Calculus on F1 car aerodynamics, and my entry argument is a detailed explination of lift, as the basis of downforce.

So from what understand, normal lift (up) is created by the (1) diversion of air in a downward direction due to physical design of an object moving through a fluid, and (2) skin friction drag along the longer (top) edge of said object, aka the longest cord or edge length, being propelled downward. did i miss anything?

 

[Gibsons]

bernoulli?

 

[MrDudeMan]

you forgot that lift is a result of a difference in pressure regarding the top and bottom of the wing.

gibsons is right by telling you to look into bernoullis principle. it isnt a complete explanation, but its a damn good start.


the angle of the wing, looking at it from the side, is called the angle of attack. the bigger the angle produces more lift but also produces more drag. more air molecules hit the bottom of the wing with a proper airfoil and cause a net upward force, or lift.

 

[The Boston Dangler]

Most lift is generated by Bernoulli's principle. Every effort is made to speed up the airflow under the chassis, to maximize downforce with less angle of attack. Fortunately, F1 will be moving towards more mechanical grip and less aero.

 

[Hyperlite]

Originally posted by: Gibsons
bernoulli?

Students of physics and aerodynamics are taught that airplanes fly as a result of Bernoulli?s principle, which says that if air speeds up the pressure is lowered. Thus a wing generates lift because the air goes faster over the top creating a region of low pressure, and thus lift. This explanation usually satisfies the curious and few challenge the conclusions. Some may wonder why the air goes faster over the top of the wing and this is where the popular explanation of lift falls apart.

In order to explain why the air goes faster over the top of the wing, many have resorted to the geometric argument that the distance the air must travel is directly related to its speed. The usual claim is that when the air separates at the leading edge, the part that goes over the top must converge at the trailing edge with the part that goes under the bottom. This is the so-called "principle of equal transit times".

thats why i didn't include bernoulli. and why i shy away from the so called "popular explination. The airspeed over the top of the wing issue has been baffling me. i can't see to find anything that really explains why that happens.

 

[Pulsar]

You are right to shy away from that - "Lift" is a very touchy subject.

For instance, if you're going to argue that a wing shape creates "lift" and that the transit time of air over the top of the wing and the bottom is different, then go ahead and explain how an aircraft can fly upside down.

The "simplistic" explanations are FAR too simplistic. http://travel.howstuffworks.com/airplane6.htm

How stuff works explains a little bit about it.

 

[CycloWizard]

Originally posted by: Hyperlite
thats why i didn't include bernoulli. and why i shy away from the so called "popular explination. The airspeed over the top of the wing issue has been baffling me. i can't see to find anything that really explains why that happens.

If you really want to get into this, you need to look at boundary layers, which is probably well beyond your scope of knowledge if you're taking calculus (no offense - we were all there once 😛).

Essentially, pressure differences are the driving forces that result in velocity gradients. Thus, the explanation you quoted is looking at it in the wrong way. The region of low pressure is created, thus controlling the velocity, not the other way around. One thing that you might do, then, is to solve the Bernoulli equation for incompressible flow around a typical wing shape. You could then calculate the velocity based on the pressure field result. I don't think this should be overly difficult, and sounds like a very interesting project (at least to me, but I'm a big dork). The Bernoulli equation will tell you the pressure at any point along a streamline - basically a line traced by a molecule as it works its way around the wing. Solve this for a variety of cases (over the wing, under the wing at varying distances from the wing) and you're pretty much done.

 

[DrPizza]

Originally posted by: LsDPulsar
You are right to shy away from that - "Lift" is a very touchy subject.

For instance, if you're going to argue that a wing shape creates "lift" and that the transit time of air over the top of the wing and the bottom is different, then go ahead and explain how an aircraft can fly upside down.

The "simplistic" explanations are FAR too simplistic. http://travel.howstuffworks.com/airplane6.htm

How stuff works explains a little bit about it.

edit: never mind... I'm not positive it was correct - this is an area I'd personally need to research more.

 

[The Boston Dangler]

Originally posted by: LsDPulsar
You are right to shy away from that - "Lift" is a very touchy subject.

For instance, if you're going to argue that a wing shape creates "lift" and that the transit time of air over the top of the wing and the bottom is different, then go ahead and explain how an aircraft can fly upside down.

The "simplistic" explanations are FAR too simplistic. http://travel.howstuffworks.com/airplane6.htm

How stuff works explains a little bit about it.

Not many airplanes can fly upside down. Those that can are fighters and acrobatic stunt planes. Fighters can maintain altitude while upside-down with a very high angle of attack. Recently, thrust vectoring has added to the maneuverability of new jets. Stunt planes sometimes have a symmetrical profile, i.e. the top curve is the same as the bottom curve. This is for eliminating the upward bias, and enabling extreme maneuverability. These planes, too, generate lift through controlling the angle of attack.

It's worth noting, both of these aircraft types are, intentionally, extremely unstable.

Many planes, and some helos, can perform rolls. However, altitude will be lost. Often, pilots will be ascending while entering the maneuver, so upon exit, they are more or less level.


Bernoulli is in full effect. Nature abhors a vaccuum, whether it's a wing, a carbureter, or a perfume bottle.

 

[eLiu]

Originally posted by: CycloWizard

Originally posted by: Hyperlite
thats why i didn't include bernoulli. and why i shy away from the so called "popular explination. The airspeed over the top of the wing issue has been baffling me. i can't see to find anything that really explains why that happens.

If you really want to get into this, you need to look at boundary layers, which is probably well beyond your scope of knowledge if you're taking calculus (no offense - we were all there once 😛).

Essentially, pressure differences are the driving forces that result in velocity gradients. Thus, the explanation you quoted is looking at it in the wrong way. The region of low pressure is created, thus controlling the velocity, not the other way around. One thing that you might do, then, is to solve the Bernoulli equation for incompressible flow around a typical wing shape. You could then calculate the velocity based on the pressure field result. I don't think this should be overly difficult, and sounds like a very interesting project (at least to me, but I'm a big dork). The Bernoulli equation will tell you the pressure at any point along a streamline - basically a line traced by a molecule as it works its way around the wing. Solve this for a variety of cases (over the wing, under the wing at varying distances from the wing) and you're pretty much done.

Actually, the *pathline* is the line traced by an element of air as it moves through the flow. Think of it as a time-lapse photo of a spec of dust blowing in the wind. The path traced out is the pathline.

The streamline is the set of lines that are everywhere-tangent to the velocity field. Think of this as an instaneous photo of the velocity (vector) field.

In a steady, uniform flow, streamlines and pathlines are the same...but this is not true in general.