base drag visualization
 

here is an image which suggests what a boat tail would be all about
in the second image we see how the Schlor cars aft-body is improving things
in the 3rd image,VW's 1-liter car has attached flow all the way to its tail end
4th image is SolarWorld GT slipping along at Cd 0.14
5th image is base-drag free 2013 CUER
6th image is Dave Cloud's base-drag free 2004 'Dolphin'
7th image is Paul Jaray's 1922 'pumpkin seed',Cd 0.09
8th image is from Porsche
9th image M.A.N. intercity bus
10th image
11th image 'wake-be-gone!'
12th
13th (wear a respirator)
14th ouch!
15th image:a CFD look at things
16th semi-trailer wake CFD
17th image:simplified wake management
18th: SST's boat tail
19th:more current research with Ahmed et al model
20th:K-form BMW,1938-(aesthetic compromised truncation)
21st:a proper K-form truncation(Cd 0.186 vs 0.23 for Kamm's best)
22nd:partial wake visualization of semi
23rd: van wake CFD
24th: '1980 NASA Van' with wheel skirts and more proper boat tail
25th:she's very unhappy about her base pressure
26th: incinerating the wake ( look for the kit at all Pep Boys)
Another CFD
From long ago

That V-dub looks slick! - and I'm not just talking about the airflow! :p

The dust after the RV seems to mimic what snow does to a car while driving after sitting overnight.

V-dub
 

And oddly enough,the Schlorwagen shares an identical Cd 0.186 as with VW's current XL1.

Aerohead, on the XL1, do you think the bottom of the rear end is angled up too steeply? It seems the angle goes up too much, too fast and it will make the air collide with itself.

bottom
 

Here is an hot-link wrapped in URL tags

http://www.shining-wit.net/rick/buggy/overview/dust.jpg

Here is the same hot-link wrapped in IMG tags

http://www.shining-wit.net/rick/buggy/overview/dust.jpg

I can't figure out links to videos.

hot link
 

Thanks freebeard for the hot link! It's way better than having to click on things.
:)

'Hot-link', at least as I use it refers to offering the URL of an image on an external website, rather than an album under your control. It's quick but it's trusting the external site to not remove or change that linked object. I thought I had a bookmark to a good defense of the practice, but it doesn't 'fall to hand'. Until I find it here's a page where you can see people argue whether it's better to steal and repost the picture or just steal the bandwidth.

You can see the result if you experiment in the Preview window. You don't have to post it. Here's the same URL wrapped in Quote, Hyperlink and the Image tags.

http://ecomodder.com/forum/attachmen...p;d=1261602367

http://ecomodder.com/forum/attachmen...p;d=1261602367

On-topic: Notice the way there's a solid stream of dust carried over the top of the front tire from the rear, then blown back along a nice template curve?

stream of dust
 

Yes,the dust becomes a template for a pontoon fender which would help clean that area up.
Mercedes-Benz tested cars both ways and discovered that enveloping the wheels inside the saloon body,while increasing the frontal area,nevertheless,lowered the overall drag.
GM did this with their OLDS AEROTECH LSR March Indycar chassis in 1987.
The streamliners (enclosed wheels) always get higher speeds than the lakesters (exposed wheels) for a given horsepower.Better mpg too!

That's why they have classes. :)

Accepting the limitation is what makes it art. What I'm thinking of is a belly tank with the VW boxer cylinders and heads sticking out of the nose like a light-plane with no propellor, front wheel drive like the XR-3, long axles with tall, narrow, rock-hard front tires for traction, a reclining cockpit like an F1 car, and the two rear wheels in tandem, (like the Speed Demon has in front). If you could get any traction, it would go real good.

If the rear wheels need to be open, it could be done similar to the Junker G.38 landing gear.
http://upload.wikimedia.org/wikipedi...itz-0128_5.jpg
_____

Edit [20131012]: Like this
http://ecomodder.com/forum/member-fr...belly-tank.png
This is not well developed, yet; the proportions of the tires to the body are eyeballed, etc. But the idea basically is to have the same cross-sectional area as a P-38 tank (36" dia), but since I don't like the idea of a circular cross-section so close to the ground, it's more triangular, like a shark or ME-262.

The flat-4 boxer is in the front with exposed cylinder heads and a corrugated dry-sump tank for an external radiator. There is zero internal ducting.

The front tires are on 33" wheels with open spokes, but with a V-shaped rim like bicycles use. This is to improve cross-wind performance. The VW transaxle would be inverted to put the axle centerline above the crankshaft centerline (this saves needing to flip the ring gear). The rears are on an independent truck that is torsionally sprung.

I roughed in a Golden Submarine-style turret but I suspect that forward vision would be video on a head-mounted display. Driver is to the rear so they can tell when they're driving sideways.

heads sticking out
 

Hoerner has some data on fuselage drag as a function of various perturbing structures petruding out,or openings cut in.I'll look at that.
The lakester would be a fun ride! Fast too.:D

on.

Darn it. I edited the previous post because I didn't notice aerohead had replied on the 2nd page (and I don't like to reply to myself). So, see above.

Plus which, it's a Lakester not a belly-tank.

I don't understand why tandem rear wheels. Is it for pour weather traction while making turns.

It's to make it a 4-wheel vehicle. Else it would be a reverse trike and run in an motorcycle class. Most Lakesters have half of the increase in drag coming from the rear wheels.

The front wheels have spokes so they don't act like rudders on the wrong end.

Got it :)

cylinder heads
 

I finally have Hoerner's data and I'll present it as he presented it:
*bare fuselage.......................................... ............ Cd 0.08
*with opening and pilot........................................... Cd 0.15
*with windshield........................................ ............ Cd 0.20
*with cockpit and engine (radial).............................. Cd 0.37
The VW heads won't disturb like a radial ( more like a J-3 Cub ) but will degrade the Cd.Not much to go on.:confused:

It's hard to know why the windshield make drag worse without a picture.

That's quite a jump in Cd. Assume 5-7 cylinders, that's 2 1/2 to 3 1/2 times the frontal area of 2 tandem cylinders, twice. So 0.22 becomes 0.07 increase?

That's not so bad and where the Cub has a narrow cabin. the eco-lakester would have the cylinders at the stagnation point of a bluff body with 10:1 blister recesses to capture, channel and reattach the turbulence.

I'm going out to the country to work on the VLVW but I'm starting to think that everything it needs—powertrain, wheels/tires and roll cage would get better results in a purpose-built body.

becomes
 

I wouldn't know how to proceed without doing the same logic.Just taking a percentage of the disruption.
If a streamlined forced-air duct covered the heads,fed from a ram-air inlet the 'blisters' could have as low as Cd 0.10 according to one of Hoerner's armament turret data.
Adding the ideal canopy to the fuselage adds 0.007 to the overall drag of a L/D= 8.5 Cd 0.082 fuselage.It looks like the heads could have a very minor impact.
You'd have two very small 'canopies'.

worse
 

Imagine scooping out a hole to create the cockpit,then attaching a flat screen angled up very steeply,with no curvature or radii at all.And no turtledeck head fairing behind the pilots head to assist in cleaning up the disturbance.
Like a 1950s British convertible sports car with Cd 0.70-75.
I'll try an get an image scanned Saturday when I come in.

The heads are less than 36" across so maybe a convergent nozzle in front, but the exit would be flush, below and to the rear of the axle, mostly ahead of the maximum width.

First thing out of the box modeler and into a new thread will be an electric rear-wheel drive version. The tires, motors and front suspension won't be on the market until next year, but i want to get that out there and then maybe look for a sponsor for the
VW powered version.

added image# 28
 

There's a 28th image added up at the thread beginning.It looks like it's one of Hucho's wind tunnel scale models.Early Cadillac.

What are the chances that color picture is of a die-cast model in a modern tunnel?

I haven't started that thread yet, but I shouldn't blame the software. Here's where it's at right now:

http://ecomodder.com/forum/member-fr...11-5-38-12.png

Bridgestone Tall/Narrow tires, Edison2 in-wheel suspension in front and Protean Energy in-wheel motors in back. They all should be on the market within a year.

Aerohead, I'm wondering about the aerodynamics just ahead of the windshield on that Cadillac. If one were to put a sort of reverse kammback ahead of the windshield, would that eliminate the dip in the airflow helping improve the Cd? The arrow is the point that I'm talking about:

http://i1289.photobucket.com/albums/...pse5b73102.png

Obviously a real kammback/boattail would greatly improve Cd as well, but we all know about that! ;)

aerohead may have something to say next time he checks in, but meanwhile...

At the location you indicate, in that era, they would have used a deep V-shape. Later Tatra and others found a 3-piece windshield with narrow 'wind-wings' incorporated in the sides beneficial. Probably because a flat, vertical windshield is best optically, and safety trumps aerodynamics. Eventually you get the late-50s GM Wraparound windshield that had a lot of distortion.

Actually, an aerodynamic fore-roof truncated to a flat plate sounds a lot like my VW Beetle. :)

chances
 

I believe that they're all 1:18-scale die-cast models.And I didn't track down the source,but I'd bet the photo is from Wolf Hucho's personal scale wind tunnel.
If you GOGGLE him,a site will come up with other images.There's a thread I did on him a ways back.

dip
 

*The majordomos would say,round off the leading edge of the radiator shell first to get the air attached onto the hood.
*Kamm would site a cooling system extractor at the cowl to help energize the flow over the screen.(you'd lose your ventilation air though)
*The upright windshield is causing a Prandtl Line of Discontinuity,the air avoiding the extreme acceleration around the hard edge by deforming the streamlines into a virtual radius.If 'hard-styling' mandated the upright design you'd be stuck with it.Otherwise you'd soften the header and A-Pillars leading edges to get attached flow.(In one thread there's a photo taken inside the A2 Wind tunnel where you see this effect on a 1930s High Boy Bonneville car.The radius is just enough to guarantee attached flow)
In Hucho's books he illustrates just how little radius is required.(the caveat is that larger radii help in crosswind/yawed flow,with the 'Bug' aerodynamic nose( see Schl'o'r wagen of 1939)being ideal for sub-transonic speeds).

Hucho's site is Aerodynamik mit Wolf-Heinrich Hucho

And his wind tunnel :
http://aerowolf.com/wind_on_rauchkanal.htm