Aerodynamic lift- A real problem

[Christ]

Originally Posted by winkosmosis

3. I set it to show 40 posts per page.

I couldn't find that setting... I'll have to check it out.

EDIT: Here's to page 12 of uselessness.

[thatguitarguy]

Though I think this thread has degraded to the point that it should be hermetically sealed and buried, here is an on topic post:



I've always wondered about the handling of the Sunraycer. I know it was built as an experimental vehicle for a specific purpose, and was successful in that purpose, it is so much like a wing, that I wonder why it didn't flip over with every gust?

[Christ]

My take on it is that while it would generate shape-induced positive lift, it wouldn't have been enough to counteract the weight of the vehicle. Also, you see those diffusers on the rear tail? They're there, IIRC, to ensure stability of the vehicle by piping the lower airstream directly out the back, rather than letting vortices form at the tips of the transition, which would cause mass instability and oscillation.

Reference the wing tips of F1 cars for an explanation of the vortex that occurs on edges which separate high pressure areas from low pressure areas, I think you'll find it interesting. There's a link in this thread (probably 2 pages back or so) that has F1 stuff on it, I believe it discusses the occurrence in enough detail so that the average layman (not saying anything about you specifically) could grasp a good understanding.

[Nerys]

your kidding right? I never said lift was upward. you and only you did. I said lift was a specific for of force that is directional. (whatever it was go read it again) either way LIFT has direction. "UP" is relative. to the propeller FORWARD is UP for all intents and purposes it is the "direction" the lift is directed at.

your tear drop has no direction. forces are equal on all sides. NO LIFT.

No lift in its general use is NOT upward motion. its FORCE in one general direction as a result of a pressure difference around an aero shape.

whether that be a WING lifting an airplane up a FIN on a rocket lifting around the ROLL axis causing a rocket to spin in a propeller pushing/pulling an airplane forward or a CAR exerting a force via a shape based pressure gradient other than neutral. (ie you can lift UP or DOWN or even sideways any which way the pressure gradient and shape dictate.

The wall is you won't separate LIFT from Pressure. I used simpler terms because you did not seem to "grasp" the other terminology at play.

LIFT is by definition a DIRECTIONAL FORCE. if its not directional its NOT LIFT since thats a required component for you to be able to call it LIFT.

please just go look up lift under the CONTEXT of this discussion ie an Aero shape on an airplane or a CAR.

[Nerys]

from the SIDE the sunracer is very wing like but if you look at its 3 dimensional profile it actually would not generate all that much lift. It also never went very fast. its also not a true flat bottom airfoil (you can see it bulges on the bottom) this too will reduce lift though it would increase compression of the airstream between the vehicle and the road.

The vortex control tabs on the back are interesting. I wonder why they have them other than on the tips. Their wind tunnel testing must have shown the presence of vorticies alolng the trailing edge to require their presence. My guess it from the wheels.

its also possible that because of the knife edge in the rear that even "disturbed" airflow would create an artificial wake so they needed to stabilize the air before separation to minimize wake. This might also be enhanced by the bulge below the car which would increase turbulent flow after the stream is compressed and then released behind the bulge.

[winkosmosis]

Look at the Sunraycer. The shape is an an aerofoil and about as ideal as you can get. It's not the same top and bottom so it almost definitely creates some lift. But it's more aerodynamic than if it were shaped like a flat brick.

You could make it neutral by shaping the top and bottom the same, so that the forces on the top and bottom equal out... But that wouldn't happen while it drives along on the ground, because you'd be compressing air underneath. You could curve the bottom just enough that it evens out the top's bernoulli effect after you factor in ground effect.... But you'd also be increasing drag beyond a flat bottom because it takes energy to compress air.

[Christ]

Nerys -

Is your shift key broken?

I'm well aware that lift is directional. I'm also aware that if you look at the forces in constant airstream that are applied to a teardrop shape, there is a low pressure zone along it's widest point at every tangent. That's what I said, nothing different.

That low pressure zone, if altered in any way, would cause movement of the object in question. How hard is that to understand?

Airspace is not a constant. It changes without regard to objects flying through it, and it changes in direct proportion to those objects as well.

You're applying data that only applies in a static world, when you say that a tear drop is not capable of producing lift on any tangent of it's widest point. This world is not static. Welcome to fluid dynamics.

If you apply exactly identical pressures to opposing points of an object, the pressures cancel each other out. When one of those pressures changes, even slightly, the equilibrium moves out from the center of the object they're applied to, and the object will continue to move in that direction until the equilibrium is satisfied.

Am I speaking quantum mechanics here?

This isn't theoretical physics, it's real life.

[Nerys]

but thats not the same thing.

your now changing incidence or Angle of attack. the point was your trying to say if you create pressure you create lift. THIS IS WRONG. Period.

now you sound like your trying to reword what your saying to be slightly more inline with what I AM SAYING but with the demeanor that you came up with it so I am still wrong ?

is this some sort of a joke? just because that altered pressure zone causes movement DOES NOT MAKE IT LIFT. it just makes it FORCE.

if I put my hand on your chest and SHOVE. is that lift? NO. its a PUSH.

if lift is the result then whatever ALTERED the pressure zone is creating the lift NOT THE SHAPE.

a flat plate wing DOES NOT GENERATE LIFT unless you increase its incidence or increase the angle or attack THEN you get lift.

but the WING is not generating that lift. the Combination of the wing airstream and INCIDENCE OR AOA is generating the lift.

Your tear drop DOES NOT GENERATE LIFT.

if your going down the road and your nose tips UP a bit you will generate lift but this is lift as a result of your shape AND THE INCIDENCE YOU ADDED BY TIPPING UP.

NOT simply from your tear drop.

all data must be applied in a static world to be understood then APPLIED to the dynamic world to experiment with. if you don't understand the static math you can possible understand the dynamic implications.

[winkosmosis]

You guys are making this way more complicated than necessary. You aren't seeing the forest for the trees.


The optimal shape for a practical vehicle travelling on the ground is NOT a teardrop. It's a half a teardrop. That shape produces downforce on the front, lift at the rear, and a net upward force.

In order to make the half teardrop neutral on the front end, you must curve the bottom, which counteracts the downforce from the top with lift from the bottom, but also increases drag because air must be compressed to go under the vehicle.

In order to make the half teadrop neutral at the rear, you need a upward angled bottom surface aka "a diffuser". This is limited by the amount of air you have flowing under the vehicle.

Or you can be neutral by shaping the vehicle like a brick

[Christ]

I don't think trees are very aerodynamic...

It's OK, I'm going to disconnect myself from that discussion. We're obviously talking about two different things, and neither of us will ever see the perspective of the other.