Starting to think 2010 Prius has flow separation issues. Comments? - Page 4 - Fuel Economy, Hypermiling, EcoModding News and Forum

zonker · 05-03-2011, 09:56 PM

Quote:

Originally Posted by donee

Hi Rokeby and Clev,

I have two long slow hills on one of my routes. On the really long hill, I am at 40 mph at the top, and 36 at the bottom 1 1/2 miles later. Both cars do this exactly. On the other hill I crest at 33 mph, and at the base I am doing 35 about 1/2 mile later. Again both cars do this the same.

Slow-Speed down hill coasting wise this car is very very similar to the 2006. In the flats, I think it coasts a little better than the 2006, but I guess that is kinda subjective....

what is the weight diffgerential between a 2g and 3g prius?

Added curb weight should improve coast down speeds of the 3g prius assuming all other variables are the same.

There is a downhill grade of the interstate near my house and if i drive my mustang to 62 mph and allow myself to coast down until the next offramp, I will see 58mph.

This same distance, with a full tank of gas and about 200lbs in the trunk, will coast down and see 61mph the at the end point.

MetroMPG · 05-03-2011, 10:14 PM

I still think your claim of a separation bubble (what you call a delamination bubble) anywhere on the roof of the car is extraordinary.

Invoking Sagan: extraordinary claims require extraordinary evidence.

If your claim (of flow separation anywhere on the roof) were true, it would be a massive mistake on the part of Toyota's aerodynamicists & designers, something I doubt would have gone un-noticed in the wind tunnel.

Frank Lee · 05-03-2011, 10:36 PM

Speaking of which, just yesterday I was noticing the AWFUL windshield/roof transition on those fugly new Kia Souls- there's an actual sharp crease designed in right there which HAS to make for separation up there.

vs. this very nice and certainly clean transition:

Frank Lee · 05-03-2011, 10:58 PM

Quote:

Originally Posted by donee

Hi Metro,

Take a look at the side-profile of a 3 rd Gen Prius, versus the streamlining template, and a 2nd Gen. The 3rd Gen looks like a 2nd Gen backwards. The 3rd Gen looks like the streamlining template backwards in side profile.

The Prius is not like other cars. Above the radiator level the surfaces are not blunt, but sloped. In other cars, these surfaces are horizontal up to the windshield. The 3rd Gen takes this even further, where the front slope is longer than the rear slope, not reaching a peak till behind the front seat. Remember, I have one of these out on my driveway.

And I used to have a 2nd Gen out on my driveway. Which was rather blunt up front, except for the windshield. And it had a long slope from above the drivers head down to the rear spoiler.

I started asking myself these questions when I was trying to figure out how they got all the under-hood space in the 3rd Gen. The 2nd Gen is really packed in there, the 3rd Gen, even with the bigger engine has lots and lots of space under the hood. Where did all that room come from? From the long front taper the 3rd Gen has.

Having a long slope , the air does not shear away over the top like the streamlining template would cause.

I guess you gotta ask yourself if you take a boatail car and run it backwards, if it would have less drag. Because that is what the 3rd Gen Prius is.

As far as further testing goes, well, the weather and other considerations are not permitting me at this time. Water patterns are commonly used to check aerodynamic device effects, and I have commented on those for the initial device.

I am running a .035" thick tubulator behind the peak height right now. It seems to give a 1 mph advantage repeatedly on the downhill test. I have had 2 runs at it so far. One warm with negligable wind, one cool with broadside 15 mph wind. This is a far cry from the 2nd Gen Prius on the same downhill.

Now device I ran originally, probably was acting like a deturbulator, as there were not many spikes, and it was wide. Apparently sail-plane pilots are experimenting with straight tapes applied close to the front of the wing, with reported benefit, as well.

Without tuft tests or a video clip of a wind tunnel test, you don't know for sure what the air is doing up there.

Although I will say- through conjecture- that since the Cd of the Gen 3 is actually better than that of the Gen 2 (AND better than most every other car on the road) that neither version is suffering from some glaring aerodynamic fault.

aerohead · 05-04-2011, 05:32 PM

Quote:

Originally Posted by donee

Hi Aerohead,

Have you done that for the 3rd Generation Prius too? That is what I concerned about. My 2nd Generation Prius did very well down hill above 45 mph. Its the 3rd Gen Prius I have that is not.

The tail of the 3rd is close to that of the 2nd Gen Prius. Its the lead into the peak height that is different between the two cars, I believe.

donee,I've been unable to get a factory side shot of the( 3rd-gen US,4th-gen Japan),so I don't have an image of the car in true-length.Without it I can't analyze the car.
Since the new Prius has a rear spoiler,that's kind of a tip off that the backlight is a little dirty.
It also violates W.A.Mair's boat-tail architecture for attached flow.
Its 'close',and I think Prius' designers comment about being 'close to ideal' suggests that it's not 'there yet.' A standing pack of Lucky Strikes on top of the spoiler might make up the difference.
My friend already complains that at standard slope,the new Prius backlight is virtually useless as for rear visibility.

donee · 05-04-2011, 07:31 PM

Quote:

Originally Posted by zonker

what is the weight diffgerential between a 2g and 3g prius?

Added curb weight should improve coast down speeds of the 3g prius assuming all other variables are the same.

There is a downhill grade of the interstate near my house and if i drive my mustang to 62 mph and allow myself to coast down until the next offramp, I will see 58mph.

This same distance, with a full tank of gas and about 200lbs in the trunk, will coast down and see 61mph the at the end point.

Hi Zonker,

Good Point. I had not been thinking about that.

But, the 2nd Gen was pretty consistent down the highway hill. The things that slowed it down was a good head wind, heavy rain or weather below 32 F.

The 2nd Gen weighed 2890 lbs (if I remember correctly), and the 3rd Gen is 3042 pounds according to the Toyota website.

I have the same stuff in the trunk of this car, as was in the trunk of the last one , minus the box the cheap socket wrenches were in. The box was mashed up good in the impact.

So, based on weight, if the drag was the same, the 3rd Gen should be coming down the hill the same or faster. Its not. With the 2nd Gen is was common for me to have to hit brakes to avoid hitting the car in front of me. With the 3rd Gen, I have to goose it to keep from getting hit from behind.

It could all be tires. But, in the meantime I want to investigate Aero.

donee · 05-04-2011, 07:34 PM

Quote:

Originally Posted by Frank Lee

Without tuft tests or a video clip of a wind tunnel test, you don't know for sure what the air is doing up there.

Although I will say- through conjecture- that since the Cd of the Gen 3 is actually better than that of the Gen 2 (AND better than most every other car on the road) that neither version is suffering from some glaring aerodynamic fault.

Well,

My boss's Lexus is a .25 Cd too. And it does not look anything like a Prius.

The CdA is going to be allot bigger in the 3rd Gen by the tire widths and wider body of the 3rd Gen. Because that difference is going to be bigger than .26 / .25 .

donee · 05-04-2011, 07:43 PM

Quote:

Originally Posted by aerohead

donee,I've been unable to get a factory side shot of the( 3rd-gen US,4th-gen Japan),so I don't have an image of the car in true-length.Without it I can't analyze the car.
Since the new Prius has a rear spoiler,that's kind of a tip off that the backlight is a little dirty.
It also violates W.A.Mair's boat-tail architecture for attached flow.
Its 'close',and I think Prius' designers comment about being 'close to ideal' suggests that it's not 'there yet.' A standing pack of Lucky Strikes on top of the spoiler might make up the difference.
My friend already complains that at standard slope,the new Prius backlight is virtually useless as for rear visibility.

That is a difference between the two cars aero-mod wise (both have flush hub caps, and I trialled the A-pillar turbulators with negative results on the Gen 3, and positive results on the Gen 2). My 3rd Gen has the stock rear spoiler. My 2nd Gen had a 3/8" high by 3/4 inch long "Volt bump" or so I call it, that was 24 inches long. I was going to do that, then noticed the 3rd Gen spoiler has a slightly longer upward protruding rear 1 1/2 inch. Based on that, I left it alone , thinking the Toyota engineers improved that issue already.

I do not have a camera with a long lens, to minimize paralax. So, I cannot get you a worthwhile side picture. On Prius Chat, there was a guy who took pictures of his 3rd Gen next to a 2nd Gen parked next to each. The 2nd Gen had a much squarer on-axis cross section. Which makes it more like other aero structures, than cars. The 3rd Gen is more like other cars, obviously wider than it is tall.