Lotus 7/Locost Aero Rebody

[Bicycle Bob]

That looks like a simply curved windshield to me. Flat stock can be bent like that over a simple frame. Slow creep or quick annealing will make it hold the shape without a frame. The lack of hardware at the base does give a very tidy appearance.

[botsapper]

Here's another reference model. AGM sports cars has the WLR, a front engine tube space frame platform with a Le Mans LMP2-like aerodynamics. Body kit only- £3000. The design is
very contemporary instead of the usual retro coke bottle body. AGM also has the Revolution-X, a cleaner rear wheel solution for the '7' design.
AGM Sports Cars - WLR

[Peter7307]

Originally Posted by JackMcCornack

That's fair, it was competing with its peers of 1954, but I think the principles of automobile aerodynamic drag reduction were well understood by then. I was being a smart alec with my "I have my Hucho and Bristol didn't" remark, and though Bristol had only been in the car biz a few years, and though it was an era when the practical lessons of 50 years of aerodynamic experience could be boiled down to two semesters, the Bristol 450 Coupe had some interesting innovations. The fins, which were assumed to be stabilizers, were more likely (IMHO) there to reduce vortexes spilling over the sides and into the wake of the roof section--that's what they look like to me here in 2009

Bristol were indeed "in the car biz only a few years" by 1954. The company began in 1910 building aircraft , but they were in business for many years prior, and cars were a post WW II exercise to use factory capacity previously needed for war production.

The "fins" on the 450 served to move the centre of aerodynamic pressure rearward and also to act as stabilisers and reduce vortexes generated.

L J K Setright wrote a detailed article on this vehicle which is well worth a read for anyone interested. It was written with the help of the makers.

Pete.

[MechEngVT]

Originally Posted by JackMcCornack

If we crank up the time machine ahead ten years, we get the 1964 Cobra Coupe, also a successful endurance racer and another source of inspiration...but to me it looks too modern, too fast, and I think an econocar version would seem like a parody rather than an homage (and I wouldn't do it anyway because like the Bristol, that body would be too expensive). Still, it would fit the Lotus 7 layout and if you got rid of the spoiler it would be pretty slippery.

I think the Cobra Daytona is ideal for what you want to do, but it doesn't work out without changes as you note. It's coupe, kamm-back, aerodynamic, and fits the cab-rearward layout.

I think the Locost puts the driver lower than the cobra appears to and you can deal with a flatter/lower roof. Adding a beltline dip toward the rear of the door will maintain some Lotus style. Making the front end more blunt could continue to ape the Lotus but substantially differentiate it from the Cobra. Changing the boattail/Kammback to more closely mimic the Superformance Daytona might help as its tail appears to be cut more vertically.

Key things to carry over from the Daytona: full front enclosure to prevent fender scooping of air and to block airflow over the suspension. Forward-tilting radiator out front vented to the low-pressure bubble in the middle of the hood and to the fender-side vents behind the front tires. Taper the boat tail both in plan- and profile-views. From your sketches on your site it looks to me like your rear fenders need more (some) plan taper.

Personally I don't care for the appearance of 20s/30s era floating fenders, but if you do it's your car. I do think they make aero design harder. The late-40s drop fenders that were attached but lower than the hood look fine (there's a version of them on my modern truck), but with a vehicle as low and compact as the Locost your fenders and hood are even anyway. If you don't like the rounded/contoured look of the Cobra front you could maintain the airflow advantages of its design but style it more sharply such as the early 2nd generation Corvettes (which were also raced contemporary with the Cobra).

edit: Might you also want to run narrower tires? The tall tire with sane aspect ratio should be good for aero but they look wide unless it's a visual trick due to the diminutive nature of the car. With the low-power engine it'll be hard to overcook even a narrow tire.

[jamesqf]

Originally Posted by MechEngVT

Personally I don't care for the appearance of 20s/30s era floating fenders, but if you do it's your car. I do think they make aero design harder.

That's something I wonder about. There are two rather contradictory factors at work (at least to design a car to my taste): you want a rather wide front stance for stability, but a narrower passenger compartment. So is it aerodynamically better to have the wheels within a wide front bodywork (like modern cars) then taper rearwards, or have them in outboard wheel pants, like Aptera?

[hypermiler01]

Originally Posted by jamesqf

That's something I wonder about. There are two rather contradictory factors at work (at least to design a car to my taste): you want a rather wide front stance for stability, but a narrower passenger compartment. So is it aerodynamically better to have the wheels within a wide front bodywork (like modern cars) then taper rearwards, or have them in outboard wheel pants, like Aptera?

The frontal area width measurement that matters is the widest point on the car. There is no advantage to making the nose narrower than the rear fenders. By making the front wide and the sides straight, you eliminate turbulent airflow over complicated shapes.

[Bicycle Bob]

Originally Posted by jamesqf

That's something I wonder about. There are two rather contradictory factors at work (at least to design a car to my taste): you want a rather wide front stance for stability, but a narrower passenger compartment. So is it aerodynamically better to have the wheels within a wide front bodywork (like modern cars) then taper rearwards, or have them in outboard wheel pants, like Aptera?

Biplanes loose about 10% to interference between the wings, which are far better separated than most front wheel pods. One has to forget about designing 3 nice streamlined shapes, and treat the space between the wheels and the body as a duct, with obstructions. An unstreamlined brake line or ball joint may look insignificant, but the relatively high cd means that it has a thick, slow wake of air that the main flow has to go around. When you are done with all that detailing, there may be a slight gain from the reduction in visible frontal area. Directional stability is likely to go down, though, as if some feathers were added to the front of an arrow.

[basjoos]

Originally Posted by JackMcCornack

And you guys have convinced me--I'll try 20 square inches for the radiator inlet.

Make the radiator inlet driver adjustable to the current heat load as you are driving. On my car I can adjust it from 0 square inches to 50 square inches depending on the outside air temps, airspeed, and engine load. From a cold start its always set at 0 square inches for the first 10 to 15 miles. From now until April it stays mostly at 0 square inches.

[JackMcCornack]

jamesqf mused re...
> ...outboard wheel pants, like Aptera?

I've assumed the Aptera needs a wide front track to give it reasonable roll-over resistance and a small cabin to keep frontal area down. There is some ratio of track to cabin width where wheel pants make aerodynamic sense, where even though wheel pants give the car a higher Cd than a single body unit, if they reduce frontal area enough, then the CdA will be lower than a single body. Either the Aptera aerodynamicists determined that the dimensions of the Aptera make wheel pants the lowest drag option, or the stylists at Aptera determined that wheel pants look cool. My experienced guess is that Bicycle Bob is right and the Aptera is inducing more drag with its three bodies (and don't forget the control arms holding those bodies together) than it's saving with lower frontal area.

> Make the radiator inlet driver adjustable to the current heat load as you are driving. On my car I can adjust it from 0 square inches to 50 square inches depending <snip>

Good idea. I'm wondering how big the maximum opening needs to be to cool my 32 hp diesel. Basjoos, do you ever drive with the full 50 inch opening, and if so, how high a horsepower load do you think you're feeding it then? I doubt you're at full throttle much, and brief bursts can be carried by thermal inertia, but do you ever ask for more than 32 hp for extended time?

[jamesqf]

Originally Posted by JackMcCornack

I've assumed the Aptera needs a wide front track to give it reasonable roll-over resistance and a small cabin to keep frontal area down. There is some ratio of track to cabin width where wheel pants make aerodynamic sense, where even though wheel pants give the car a higher Cd than a single body unit, if they reduce frontal area enough, then the CdA will be lower than a single body.

Yeah, that's pretty much what I was asking, but you said it better than I did. Basically, I wouldn't want the cabin as wide as it is on a typical donor car, but I think changing the front wheel track width much gets you into serious work. Then there's also space needed above the wheel for vertical travel. and the open wheel well, both of which go away with a full pant.

I doubt you're at full throttle much, and brief bursts can be carried by thermal inertia, but do you ever ask for more than 32 hp for extended time?

If you live in the mountains. The Insight will do just fine with a half radiator block much of the year, as long as it's on the level. Climb to a 9000 ft pass on a warm day (or even in the winter), and it'll be running 10-15 degrees above the 195 F thermostat setting in short order.