Making a more efficient, aerodynamic soapbox gravity race car

[orengomotors]

what do you think about the belly tank shape? it seems so simple and elegant!
and i think it will fit perfectly on my soapbox.
I have bought some shock absorbers to improve the handling, the actual ones don't have a damper, they are only a spring and a very stiff spring (1200 lb/inch). Tomorrow i will post some pictures of the udaptes!

[freebeard]

Here is my design for a belly tank. It has a dropped equator so that instead of a circular cross-section, it's flatter on the bottom.



Shocks before that KERS,

[aerohead]

Originally Posted by orengomotors

what do you think about the belly tank shape? it seems so simple and elegant!
and i think it will fit perfectly on my soapbox.
I have bought some shock absorbers to improve the handling, the actual ones don't have a damper, they are only a spring and a very stiff spring (1200 lb/inch). Tomorrow i will post some pictures of the udaptes!

Just the upper half of a 'tank',with enclosed wheels is preferred for low drag,but if you must have exposed wheels,then a belly tank-type body would be a good second choice.
Bob Rufi was the first to race a belly-tank car,on California's dry lakes
http://www.ahrf.com/images/ahrf/gall...gio045rufi.jpg

[freebeard]

The example I posted actually has a flat bottom for maybe 75% of it's area. When I was manipulating the geometry I could put the 'equator' anywhere, I chose to give it a rocker panel return, instead of the hard chine or edge The Template has. Would that be helpful for crosswinds? Or make it more likely to catch air, lift and flip over?

[orengomotors]

Originally Posted by freebeard

Here is my design for a belly tank. It has a dropped equator so that instead of a circular cross-section, it's flatter on the bottom.



Shocks before that KERS,

why is flatter? for ground clearance or because ground affects aero?

[orengomotors]

Originally Posted by aerohead

Just the upper half of a 'tank',with enclosed wheels is preferred for low drag,but if you must have exposed wheels,then a belly tank-type body would be a good second choice.
Bob Rufi was the first to race a belly-tank car,on California's dry lakes
http://www.ahrf.com/images/ahrf/gall...gio045rufi.jpg

well, let's do it! a gravity powered belly tank.
whats the optimum longitudinal shape of the belly tank? i found a lot of different belly tanks on internet.

[freebeard]

Longer than you can afford.

The traditional P-38 drop tank is 3ft in diameter and 12ft long, for a fineness ratio of 4:1. A half-body like The Template would be only 18 inches high.

12ft long at a fineness ratio of 2.5:1 would be 4ft wide and 2ft high.

Here's how I developed the shape I used:

A 6v octahedron-based geodesic sphere is stretched in the rear hemisphere 233%. The result is maximum camber at the 30-70 split.



Height is still equal to width, rather than half, but the equator is dropped. (technically the top hemisphere is prolated and the bottom hemisphere is oblated an equal amount. I forget how much) So it's symmetrical side to side but asymmetrical front to back and top to bottom. The bottom is further flattened for ground clearance.

It can be easily varied in length to set the fineness ratio, and individual dimensions can be picked off the model. Here's the process applied to an octahedron with a frequency of 4v.

[orengomotors]

so, i have to build or buy a belly tank, and the cut the bottom of it and make it flatter.

where can i find a belly tank? there's a smaller bellytank than the p-38?

[euromodder]

Originally Posted by orengomotors

whats the optimum longitudinal shape of the belly tank? i found a lot of different belly tanks on internet.

The traditional drop tank is the 150 (165) US gallon World War 2 style tank
Or the 316 US Gallon tank (which is essentially a scaled up version of the 150 US Gal tank).


You can even buy fibreglass replica's
http://www.p38-droptank.com/P38-Drop_Tank.html


PS: The later Aero 1 drop tanks are likely too fine (long/narrow) to be useful

[freebeard]

I was doing a forum search to find this thread (missed it looking under Aerodynamics) and found a thread from 2008 —Gravity racer gallery - extreme aerodynamics

http://ecomodder.com/forum/showthrea...html#post69119

A poster named amidesign from Switzerland (11 posts total) put up some pages from a PDF people were having trouble downloading. (Not working for me today)



This one and three others. The item labeled carénes JAREY is very similar to what I proposed at Permalink #91.

Edit: I followed the site link and had success at http://inter.action.free.fr/publications/index.html, next-to-last item on the page. The site is mostly about airplanes.