Aerodynamic lift- A real problem

[Nerys]

Wow ok guys some basic aero here.

an ideal teardrop produces ZERO lift. "HALF" a tear drop can produce lift.

next just because TWO forces are in play does not automatically mean the forces are directly connected.

The DRAG created by the Aero Top when it produces lift is NOT directly linked to the drag you lose by adding the top.

TWO SEPERATE FORCES acting on the total equation.

When you add an aero cover you are HURTING your mpg by adding TWO kinds of drag.

Parasitic Drag via the extra surface area and drag induced by the work of generating lift. These are seperate unto themselves.

NOW the cover mathmatically does NOT reduce drag at all.

it STOPS YOUR TRUCK FROM MAKING THE DRAG it was making before. a SEPERATE drag force completely unrelated to the lift drag and parasitic drag.

In rocketry we call this "base drag" the "suck" you get off the back side of anything flat.

SO why does the cover work?

because the values are UNRELATED to each other and NON EQUAL.

the drag you STOP the truck from creating by adding the cover is far far larger than the drag you ADD when you introduce the cover.

so you see and overall amount of drag that is LOWER.

one did not cause the other. this is the mistake your making. LIFT NEVER EVER reduces drag. Period. Lift by definition is "work" work by definition will induce drag.

but you can TRADE WORK from one piece to another piece for a net desirable goal.

Like using a pulley to lift something heavy. your exerting the SAME EXACT amount of energy (in fact MORE energy because of the DRAG you introduce with the pulley) than a dead lift.

but the pulley lets you spend less energy over a LARGER time period (so net same energy)

So don't think of a boat tail as reducing drag. Think of it as STOPING the car from MAKING the drag in the first place. same with the aero cover same with making some lift etc..

Lift is a consequence not an objective.

[Christ]

No, sir. You're wrong. If you view a teardrop shape as half of itself mirrored, you will see that there is a change in pressure at the front, widest point, and tail. That means that any cross section of the tear drop shape does in fact create lift, but all sections acting together counteract the other sections.

The widest point of the teardrop shape represents the highest pressure area *not including the nose*, which, according to Bernoulli, represents the slowest moving area of the flow around the object. As the flow follows the profile of the shape back to a static point, it accelerates, so the pressure on the object lessens as the taper increases, allowing the previously compressed flow to re-expand to atmospheric conditions.

That being the case, the teardrop shape would create lift at every tangent of it's widest point. Simple fluid dynamics.

[Nerys]

there is no optimal CL for a desired CD.

there is an effective CL that is an undesired but necessary CONSEQUENCE of acquiring a CD.

you are also incorrect about ground effect.

tear drop is optimal. the smaller the profile the better.

OPTIMAL is zero drag. 1 dimensional live.

WE NEED to put "stuff" inside it so we have to COMPROMISE DRAG in order to accomodate out needs.

with that compromise on the table the tear drop becomes more ideal (unless you go supersonic then the tear drop is no longer the ideal. Interaction of shock waves etc.. something pointier becomes more ideal but thats not relevant for this discussion.

NOW we have a FURTHER consequence. we MUST have a flat bottom. Why? because we drive on a flat surface so inevitable the bottom of our structures will be flat!

now we are NO LONGER TEAR DROP we are now AIRFOIL. Not because we want to be but as a consequence of our compromises.

all those nice pictures you guys drew of car shapes over a tear drop. Not one of them was a tear drop. that overlay was an AIRFOIL. ie HALF a tear drop. (for an example of a car that is close to more ideal teardrop see the aptera)

another COMPROMISE because of how we wish to USE these shapes.

CL is NOT a desire NOT a want and NEVER GOOD. Period. CL in this case is a CONSEQUENCE of the compromises we had to make to make our machines function and be reasonable to operate and construct.

SO we "accept" some CL as a consequence of these decisions. but it is NOT GOOD and it is NOT HELPING. Its just unavoidable from a practical stand point.

Lift never reduces drag. Period. SHAPE reduces drag the shapes our compromises require us to use as a SIDE EFFECT generate lift UNRELATED to the drag.

[Nerys]

No sir you are wrong. by definition that is not lift that is simple a pressure gradient. I spent my early life designing and building model airplanes and took 3 years of AE. this is one area where I do have a small amount (and it is pretty small) of knowledge.

a tear drop has ZERO base drag designed properly. Drag is ZERO.

Parasitic drag however is non zero. IE surface drag and induced drag via the pressure gradient. drag does not equal drag. There are many forms sources and variations of drag.

a symmetrical object by definition can not generate lift. ITS SYMMETRICAL. you have to make it NON SYMMETRICAL to gain lift. with a symmetrical wing airplane we do this with INCIDENCE of the wing and angle of attack.

this is why a flat plate wing can fly why a paper plane can fly.

a base ball produces ZERO lift a golf ball produces ZERO lift. unless you SPIN them which uses parasitic drag to effect the pressure profile and generate lift but thats another subject all together. (think curve ball and "slicing")

this is where you guys are getting confused his is why you guys are unclear and this is why you are mistaken.

your not fully grasping what drag is and the fact that there are many UNRELATED forms of drag at play on our cars.

Parasitic Drag has nothing to do with Base drag etc.. etc...

you also do not understand how drag is effective and added up in the equation of overall drag.

you think an aero cover reduces drag. It does not. While the effect is reduced drag the cover did not reduce it. The cover stopped it from every being created to begin with by removing the blunt tail.

while it sounds semantic in discussion mathmatically its a night and day difference.

the produce of lift by the curved aero cover has ABSOLUTELY NOTHING to do with the reduction of drag by not letting it be formed by a blunt rear shape base drag.

they are UNRELATED.

[cfg83]

Frank Lee -

Amazing Kitty! It must be going viral, my wife showed it to me last week.

CarloSW2

[Christ]

There is still gross lift at any tangent of the teardrop shape. The opposing tangent counteracts it, but that doesn't mean it doesn't exist.

It's like saying that because you're putting 5 lbs of pressure in two opposing directions, you're not putting any pressure anywhere. That's exactly what you've said here.

[Nerys]

yes it does. LIFT is one way pressure change when you really boil it down. without the ONE WAY its by DEFINITION not lift.

the other half canceling out the pressure change effect IS WHAT MAKES IT NOT LIFT.

I did not say your not pushing any pressure anywhere. I just said the pressure you do have is NOT CALLED LIFT. Its just pressure. LIFT is a special kind of pressure.

your trying to say pressure and lift are the same thing. THEY ARE NOT.

[Christ]

Originally Posted by Isaac Newton

For every action there is an equal, and opposite reaction.

According to Newton's Third Law, it is.

If there is to be lift, there is also to be a change above the object being lifted. That change must be equalized below the object, meaning that higher pressure under an object, or lower pressure over an object, will create lift. Lift, in essence, is generated by a change in pressure... that would make pressure equivalent to lift, since they change linearly with each other, they can be transposed.

The above being the concrete case in physics, a force can only be counteracted by an equivalent force of opposing direction. This is to say, again, that lift still occurs at any tangent on the shape, but is opposed by the same gross lift on the opposing tangent, creating a net zero lift situation.

[winkosmosis]

Originally Posted by Nerys

No sir you are wrong. by definition that is not lift that is simple a pressure gradient. I spent my early life designing and building model airplanes and took 3 years of AE. this is one area where I do have a small amount (and it is pretty small) of knowledge.

a tear drop has ZERO base drag designed properly. Drag is ZERO.

Parasitic drag however is non zero. IE surface drag and induced drag via the pressure gradient. drag does not equal drag. There are many forms sources and variations of drag.

a symmetrical object by definition can not generate lift. ITS SYMMETRICAL. you have to make it NON SYMMETRICAL to gain lift. with a symmetrical wing airplane we do this with INCIDENCE of the wing and angle of attack.

this is why a flat plate wing can fly why a paper plane can fly.

a base ball produces ZERO lift a golf ball produces ZERO lift. unless you SPIN them which uses parasitic drag to effect the pressure profile and generate lift but thats another subject all together. (think curve ball and "slicing")

this is where you guys are getting confused his is why you guys are unclear and this is why you are mistaken.

your not fully grasping what drag is and the fact that there are many UNRELATED forms of drag at play on our cars.

Parasitic Drag has nothing to do with Base drag etc.. etc...

you also do not understand how drag is effective and added up in the equation of overall drag.

you think an aero cover reduces drag. It does not. While the effect is reduced drag the cover did not reduce it. The cover stopped it from every being created to begin with by removing the blunt tail.

while it sounds semantic in discussion mathmatically its a night and day difference.

the produce of lift by the curved aero cover has ABSOLUTELY NOTHING to do with the reduction of drag by not letting it be formed by a blunt rear shape base drag.

they are UNRELATED.

Let me say this again.

Every surface on a vehicle exerts a force on the vehicle. Every point has a certain force vector.

The parts of a vehicle with positive pitch are exerting lift on the vehicle, and the opposite is true of the parts with negative pitch. Yet you must have angled and curved surfaces to optimize drag. The total lift/downforce of the vehicle is irrelevant here, because NET neutrality indicates NOTHING regarding drag. A brick is totally neutral, but it has very high drag.

[Christ]

Does a brick maintain attached flow? (Joking, of course.)

If I correctly understand what you're saying, the brick is neutral because it's shape is evenly proportioned on all surfaces along the stream, correct?

Completely OT question - Since wind forces can erode a surface, would a sufficient high speed wind eventually turn a clay brick into a teardrop profile?