Morphic Studies

[AriLea]

I like this 2000 Chevy the best.

I like the Kia Sidewinder. Most of the models have a severe looking taper to the rear as viewed from the top. It's a little off putting in some models but totally wrong in others. The Kia you did seems to hide the awkward rear wheel with tasteful scoops. I wonder if the Elio with a similar scoop set up to make it appear wider without totally killing the aerodynamics would look good.

Not that I really care about my own taste in the context of getting an autocycle produced, but, I think I like the JetSet as much as anything, even more than the Atlantric. But It can't beat the Atlantric for cd and cross-section. Anyway, those other two are definitely compelling.

The Kia, yes it takes advantage of some tricks. The dark panel at the back, similar to the Elio, removes the area from visual importance to the human perception. If the area is ugly, offset it in a different and darker color. It works.

Another trick, lighter things seem bigger than darker. Another, if something seems too tall, split it with a horizontal line, now you have two shorter things stacked up, darken one of them and now you have just one floating above(or under) another thing which is easily ignored.
Your choice of two-tone paint can do a lot of that, (Bell Areo!).

It's the classical art of impressionism at it's best.

 

[Folks]

Roughly speaking, A car going 100 Miles per hour has a drag 16 times greater than a car going 25. In other words drag quadruples with doubling of speed. That is to say the drag is 4 times more important for a car going 60 than for a car going 30.

 

[Ty]

I'll read everyone else's input before I totally decide on a guestimate. Only a true test can confirm anything, be it wind tunnel or roll-down test.
There are some challenges in the 2000 created because of style preferences. i.e, good areo doesn't always look the best, so they made concessions. Yes, true the outriggers are inherently nasty, yet they have reduced cross-section, but can be improved above the Elio current form. In their case they don't want the extra expense since they can make 84mpg with their current mix. I'd propose flexible covers and a strap-on sleave for the a-arms. Maybe a tail extension. Some of that would be ugly, some charming. All would be added expense and a little more weight.

So on the 2000 Chev (not the actual name), the trailing forms round too much, creating a 'bluff' airflow. Sailers call that 'lufting' on the sails, so I'm guessing that's the source of the term 'bluff form'. (or is it about the profile of a bluff at the far side of a hill?) It should be extended to more of a raindrop tail, both after the body and after the front fenders.
Too, I'd enclose the open wells, and drop the spoiler off. Again all of that would displace the styling, but could be accomidated. And I'll bet they didn't envision an underbelly. Just controlling the volume of ground air is likely all they considered (the cheaper/lighter choice).

So which is better as it sits? ummm, don't know. Probably Elio since they actually did some aerodynamic flow simulations, but not by much.

I read that that chopped rear end is actually more aerodynamic than a flowing rear end which is why ELIO went with a less rounded rear end.

 

[Bert]

I read that that chopped rear end is actually more aerodynamic than a flowing rear end which is why ELIO went with a less rounded rear end.

True enough. boat tailing, kammbacking, and distrupters under the vehicle, do more than simple flowing lines.

 

[AriLea]

I read that that chopped rear end is actually more aerodynamic than a flowing rear end which is why ELIO went with a less rounded rear end.

Of course that's a simplification. If the rear doesn't maintain laminar flow, then yes, just square chop it. Of if the vehicle would just be too dang long and heavy, then chopping is about all you can do. On my Atlantric, I start to narrow the body way early, so I have less of a chop.

But the chop should be balanced. That is, if it's short in one area, it creates unbalanced pressure zones, and that gets you a vortex, like a wing does, and that sucks up energy.

That's why the Elio's chop is very even vertically and horizontally. The squareness (looking from the back) of it was just to match the body lines.

Did I admit before, I handed the designer a list of 19points (more or less) about aerodynamic improvements while he was finalizing the design for P4? Don't know how much of that he accommodated. He is an expert in his own right, as is Paul. In fact sometime after that I heard they had/have a full team of experts to rely on.

 

[NSTG8R]

Of course that's a simplification. If the rear doesn't maintain laminar flow, then yes, just square chop it. Of if the vehicle would just be too dang long and heavy, then chopping is about all you can do. On my Atlantric, I start to narrow the body way early, so I have less of a chop.

But the chop should be balanced. That is, if it's short in one area, it creates unbalanced pressure zones, and that gets you a vortex, like a wing does, and that sucks up energy.

That's why the Elio's chop is very even vertically and horizontally. The squareness (looking from the back) of it was just to match the body lines.

Did I admit before, I handed the designer a list of 19points (more or less) about aerodynamic improvements while he was finalizing the design for P4? Don't know how much of that he accommodated. He is an expert in his own right, as is Paul. In fact sometime after that I heard they had/have a full team of experts to rely on.

Ari, I'm curious on your take on rear spoilers. I'm thinking that at highway speeds the rear could get kind of squirrelly depending on the direction the wind is coming from (I have nothing to back this hypothesis up), and a spoiler 'might' cause enough drag on the back to keep her straightened out...kind of like dart flights/arrow fletches. You're the 3-wheel guru, what do you think?

 

[AriLea]

Spoilers have a few purposes, which you use if you need it. ( let's not forget looks is often the top reason, but ignore that for now ) So basically you first find out if you need it or not. And what it does depends on the shape and the airflow in that area via the body aero effects.
Down force is one either by 1)creating high pressure zone or 2) as a inverted airfoil. Balancing out a pressure area 3) is another. and then we have; Cleaning up non-laminar flow 4), and moving the center of pressure backward 5). (A tail works better for #5 than a spoiler.)

So straightening out existing squirrellyness is a function of 4 and 5. But once you have the spoiler, you could pick up squirrelly effects if the side wind (or turbulent winds ) undermines implemented effects for any of 1 thru 5. Remember how I said a brick is predictable and a bird is not. Or also to say you can't feel a loss unless you have something to lose. But, I would think if you have problem 3, you would want the fix no mater what. However, fixing the balance at the body is the better solution for #3. So generally that is an after market product.

Well, admittedly all 5 can be fixed at the body. Well that's also a simplification, if you look at aircraft, the body has fixed 1 thru 4, at the expense of #5, so they add a bit of area to the tail.

Anyway it's all a trade off. Generally, use the least spoiler that is still suitable for the effect you need. Then you have the least to lose. So I say, you need to do testing with the existing body to find the problems. A combination of smoke in a tunnel and roll-down testing is likely the best way. It's iterative, slow, expensive, but gives the best final results. Sure-Sure, could/should use simulations first, but that just gives a best first guess.

The poor-man's way is a really big fan and the smoke stick (or load the smoke equipment in the actual car), then make cardboard models of the spoiler(s) and do roll downs on the real car.

We all know what the roll down test is yes?

 

[NSTG8R]

That's what I'm talking about! Knew I asked the right person.

Agreed on the simulation give a "best guess", and we could probably add strings taped to the vehicle [particularly the rear in this case] and a chase vehicle with a Go-Pro. Can't wait until I have something 'tangible' to toy with.

So..Computer controlled JDAM fins mounted to the back that deploy above 50mph it is!
[if nothing else, it might make people back off if they're riding your ass!]

 

[Ty]

True enough. boat tailing, kammbacking, and distrupters under the vehicle, do more than simple flowing lines.

Kammbacking I believe is the phrase I was reading about. Aerodynamics isn't always cut and dry... Pickup trucks seem like they'd be more aerodynamic with the tailgate down but because the bed fills with air and creates a cushion for the air rushing over the cab, it changes the dynamics more than people realize.

 

[NSTG8R]

Kammbacking I believe is the phrase I was reading about. Aerodynamics isn't always cut and dry... Pickup trucks seem like they'd be more aerodynamic with the tailgate down but because the bed fills with air and creates a cushion for the air rushing over the cab, it changes the dynamics more than people realize.

True...and simulated, and proven in 'real life' that keeping your tailgate up saves gas, as counterintuitive as it seems, on Mythbusters.