Non-Professional Photos of 2010 Prius Thread.

Are we still fixated on whether a windshield produces upforce or downforce? I'm going to have to side with Patsparks and qbee42. The windshield does not generate lift. The Prius body as a whole does generate some lift, albeit an insignificant amount. It just can't go fast enough for that lift to have any effect. And again, no need to worry ... the weight of the Prius will keep it on terra firma.

Now, auto racing engineers and drivers do need to consider lift and downforce, especially for traction while cornering and to minimize brake wear. Here's a good read:
The Physics of Racing

 

What do you consider "minimal lift"?

The Prius probably generates around 100 lbs of lift at highway speeds. Those lift numbers will likely double or more in cross winds. I'd also guess that the Prius generates significantly more lift than your typical car because the roofline is so smoothly rounded. This seems to be verified by how easily the Prius seems to drift in cross winds.

Unfortunately, until someone who has put the Prius in a wind-tunnel reveals their data, we'll all just be guessing.

 

OK...

Yes - I am guessing based on the other wind tunnel numbers I've seen for other production vehicles. They all show lift at the front AND rear of the vehicle. The only ones that don't are sports cars which large spoilers/wings on them.

Dude, the windshield is no piece of plywood. There is a curving hood at the front, a curving roof behind it and underneath is a big jumble of a mess of parts along the underbody. On a "conventionally" shaped car - yes - there is often a high pressure area at the base of the windshield. But the Prius is not a conventionally shaped car. The whole thing from hood to trunklid is one carefully rounded shape.

And either way, you can't simply take the windshield and say "it produces 100lbs of downforce". It's the combination of parts on the whole vehicle which result in up/down force.

 

going on the premise that the windscreen produces down-force while the roof produces lift, convertible cars must feel like they are glued to the road with the roof down at speed.

We do seem to have hijacked this thread, feels like something familiar to me.
I vote that this should be the last post about aerodynamics of the Prius on this thread giving me the last word.

 

I agree that you should have the last word!

 

A non-professional photo which demostrates the extra space in tha back.
Note legs almost flat across floor and only head would prevent the hatch closing.

Lots of room.

 

Those are tempting words!

 

Wait, I think we had this conversation before...

:focus:

 

And the hatch got closed.
Maybe next time it will prevent the hatch closing.

Oh I found a little snippet after being directed there by another thread for another reason, sorry to take this there again folks.

http://www.nytimes.com/2008/12/21/automobiles/21AERO.html?_r=1&scp=1&sq=aerocorner&st=cse
An interesting read all the same.

 

Wait! As long as all the aerodynamists are focused on this thread, I'd like to hear their opinions on whether and how the slightly altered shape and new ridges on the Gen 3 might affect cross wind stability. I mean, .25 CD is great and all, but how slippery is it to cross winds? Some people used to speculate the somewhat tall slab sides of the Gen 2 (on such a light car) contributed to the highway stability problems.

 

I would guess (since I don't have enough data) that it should be somewhat improved over G2 in crosswinds, by virtue of the side cross-section having its center of area somewhat further to the rear. this means that the Center of Pressure is further behind the CG, which is where you want it to be; since any lateral disturbance will then self-correct towards the direction of travel.

I know some people here have commented on the Prius lack of lateral stability, though personally I don't think it is that bad. Certainly not as bad as the old VW bug, where the CG was further back than normal, thanks to the rear engined arrangement. Also the lighter the car, the more it is going to be affected by side gusts. And the Prius is a relatively light car, as was the rear-engined bug.

It would be interesting to know if Toyota did any W/T tests on lateral stability; they obviously did drag measurements, to derive the Cd values of 0.25 they quote.

 

Correct. Moving the center of effort aft does not reduce the sideways forces, but it does make them self correcting. A just from the side causes the rear end to shift away from the just, much like a weather cock.

The reduction of Cd on the Gen III Prius comes from a large number of small improvements. The major ones are a more streamlined underside, ridges on the front corners that move the airflow away from the front wheel wells, and improved wheel well and air dam shape. Many other areas of the car were tweaked slightly, all with an eye toward improved Cd.

Tom