'Ideal' shape for low drag

[California98Civic]

Approximations of Hucho's CD 0.16 “ideal" shape in the wind tunnel (from our thread for wind tunnel images) are below. Also attached are 4 pages from Hucho, 4th edition (pp.45-46, 212-213), which include wind tunnel images (p.212 might be best). They describe such ideal shapes in the R&D process. I would love to hear from aerohead about the benefits he sees to the template shape in comparison to the one Hucho often seems to emphasize, calling it a "basic body." Respectfully, james.





HUCHO, 45-6, 212-3:

[JulianEdgar]

I don't have that edition (5th edition is on its way - I've been waiting over 2 months) but the 1987 edition I do have covers similar ground.

This diagram, for example, (P201):



Obviously, there isn't just one 'template' shape that is best.

(In this diagram note also how the plan views of the shapes differ considerably.)

[JulianEdgar]

Originally Posted by Piotrsko

Because it would be optimized for the conditions experienced not just a calculated set of non infinite parameters. Or as aerohead calls it rolling floor effects. If you take your calculated profile and then modify it for local conditions, either the ordinates would be copies or very similar depending on how the aspect ratio is dealt with. Otoh, I have seen 1/1 aspect ratio low drag profiles and they are........ odd.

I don't understand your point. Taking an aerofoil designed for aircraft flying in ground effect as the starting point for a low drag shape for a car doesn't seem to me to make much sense.

Originally Posted by Piotrsko

By the way, look out the window of a commercial airline in flight and notice how lumpy the upper surface is. Definitely not surgical smooth. Ditto for one piece composite or military although those are smoother.

That's right, and I'd be very surprised if the design of the practical wing shape doesn't take that surface roughness into account. (As opposed to a simulation of a perfectly smooth aerofoil.)

[JulianEdgar]

Originally Posted by JulianEdgar

I don't have that edition (5th edition is on its way - I've been waiting over 2 months) but the 1987 edition I do have covers similar ground.

This diagram, for example, (P201):



Obviously, there isn't just one 'template' shape that is best.

(In this diagram note also how the plan views of the shapes differ considerably.)

Note also how solid line shape (VW blunt body) likely has a large wake and AWA shape likely has very small wake - and yet the two shapes have the same drag.

If you look at the direction and strengths (ie vectors) of the likely lift forces occurring on the two shapes, you can start getting a feel for why this is so.

Lift is very important!

[aerohead]

Originally Posted by California98Civic

Approximations of Hucho's CD 0.16 “ideal" shape in the wind tunnel (from our thread for wind tunnel images) are below. Also attached are 4 pages from Hucho, 4th edition (pp.45-46, 212-213), which include wind tunnel images (p.212 might be best). They describe such ideal shapes in the R&D process. I would love to hear from aerohead about the benefits he sees to the template shape in comparison to the one Hucho often seems to emphasize, calling it a "basic body." Respectfully, james.





HUCHO, 45-6, 212-3:

Sure could use an overhead, plan-view of this model. It began with Klemperer in 1922. When Buchheim et al. re-investigated it in 1981,as the Volkswagen 'Drop' shape, in plan-view,the car was 100% boat-tailed.Which is lost on the viewer when limited to the side elevation . The car's performance is completely predicated upon the full-boat tail.