Motor Trend explains Prius' "blockish" front corners / wheel arch interaction

[bwilson4web]

Hi,

Sorry, but I don't know how to edit down a YouTube video, a 'Motor Trend' Prius vs Insight viideo, but there is about 5-10 seconds in this 4:48 video where the presenter claims:

• blunt front end near lights - directs the air from the front out so it does not interact with the wheel well air and this reduces reduce drag (I'm skeptical!) If he'd suggested upwards to avoid the side, maybe, but directing the air out further from the sides strikes me as a great way to induce early flow separation and drag.
• rear side edges - supports lower drag too, perhaps if it interacts with the Kamel (sp?) back?

http://www.youtube.com/watch?v=O87UmsDvHBU

Tuft testing when the new vehicles show up will answer a lot of questions. In this case, I'm skeptical of the first claim and was wondering if you' all might have any thoughts. Warning, this is a 'Motor Trend' piece that came out because both Honda and Toyota 'loaned' them the cars.

Bob Wilson

ps. I just put the link in the video reference and converted the 'Motor Trend' reference.

[MetroMPG]

Hi Bob - can you provide a link to the video? I had a look around but couldn't find it.

thanks.

[NeilBlanchard]

Hi,

I think this is it?

http://www.youtube.com/watch?v=a2ZYeCJRhVY

Wait, that's not Car & Driver...

[bwilson4web]

Sorry about the YouTube link. I think it works now. (Must remember, drink coffee then post, drink coffee then post ...)

Bob Wilson

[NeilBlanchard]

Hi Bob,

It's Motor Trend (not Car and Driver!) -- that would explain it!

Been there myself -- it takes about two mugs of strong coffee for me...

[aerohead]

The way my brain is going to interpret the guy's comment,is that the flow is already destroyed across the front wheelhouse cavity,so let's use the nose of the car to encourage useful air to follow the flank of the car just above the wheel arch,to fortify the flow down the sides of the car,allowing any body camber to work a little better,reaching the tail with good flow.Otherwise,the air gets torn up into circulation which cannot translate angular momentum into static pressure recovery.If that's what he means,then I'm okay with what he's saying.

[NeilBlanchard]

Hi,

Now that this has been brought up, I've noticed that several recent Toyotas (and other brands) have the recessed pockets on the lower outside corners of the front bumper -- even the new Insight has something. Is it really an aerodynamic feature, or just a "memory" of a brake cooling intake? Or, a styling choice?

The comment in the video seems to be referring either to the bulging headlight cover, or the vertical fog light recess just below -- I did not think that he was referring to the front end as a whole.

I like the belly pan on the Prius, and it is interesting how the rear window slope is actually steeper on the Prius. What is the Cd of the new Insight? We know that the new Prius is 0.25; same as the old Insight -- which says something about different approaches. The old Insight with it's tapered tail and rear wheel skirts looks like it has better aero...

[Bicycle Bob]

I think he was talking about the fog light recess working as a boundary layer turbulator, but I'd rather hear it from the wind tunnel guys.

[Frank Lee]

From the video it appears to me describing the cut-off edges on the rear of the Prius as "fins" is quite a stretch. But the aero benefits of the sharp trailing edges make sense to me.

The Honda stats are kind of amusing to me: 98 hp, 41 mpg combined. My old-school, low-tech, dirt cheap, 2-valve OHV "tractor" engined Tempo has 98 hp and can get 41+ when hypermiled. Ooooo, progress!

[Cd]

I'd like to know how that air pressure affects aerodynamics of blunt front ends.
With all of that air smacking into a "wall" at the front of the car, I'm pretty sure that the air pressure would be greater than that of a car with a bullet shaped nose.
Apparently, this sort of thing does not affect the Cd of the car, but surely it must have some kind of negative effect ....right ?