Autospeed article: adding a chin undertray to a 1st gen Prius
 

(Note: see also Adding front & rear undertray to 2nd gen. Prius )

From the Australian web magazine Autospeed -

Some of you may have seen these already...

Modifying Under-Car Airflow, Part 1

Modifying Under-Car Airflow, Part 2

Originally these articles used to be pay-access only, but they've opened them up for public access now.

The project documents the creation of a prototype front partial undertray for a 1st gen Prius, testing, and then fabrication of a permanent version.

Before:

http://us1.webpublications.com.au/st.../2456_22lo.jpg

Mockup:

http://us1.webpublications.com.au/st.../2456_25lo.jpg

Final version:

http://us1.webpublications.com.au/st.../2456_15lo.jpg

The writer reports a 10+% improvement in fuel economy at freeway speeds (100km/h) with the mod in place. I frankly find that a bit difficult to believe, though I don't doubt there was some improvement.

If you read the article you can find a few holes in his testing approach - even though he's fairly aware of things like experimenter bias, and aiming to perform tests on the same day (for consistent weather conditions).

The articles also give a good background on the subject of under car aerodynamics. Definitely worth a read if you haven't seen them yet:

Modifying Under-Car Airflow, Part 1

Modifying Under-Car Airflow, Part 2

These are great articles
 

Sure their testing left something to be desired.
And I would question their results.
C'mon ten percent improvement?:rolleyes:

However, I can see how I could apply what I learned in this
article to the '94 Honda Accord I currently drive.:)

Thank you, MetroMPG for finding this article.

Good stuff, Metro...thanks for sharing! :thumbup:

Ditto. Thanks for dredging that up, Metro.

I noticed they use "high quality" duct tape for their mods. Something we home DIY'ers can shoot for. ;) I tend to use black duct tape, so it matches the trim on my car. A real consideration, since my temporary grill block stayed on the car for six months.

IMHO, they are not hard-core hypermilers, though. I see they chose stability over low drag. Wimps.

Thanks again,
Stew

I know! :D

When I read the bit about the front tire deflectors they also tested along with the undertray, I couldn't believe it they concluded: they also reduced drag, but made the front feel end lighter, so we ditched them.

Yikes!! My Aveo has absolutely NO chin undertray!!:eek: I can see clear up to the hood from under there. With grill blocks, maybe I can top their 10% :rolleyes: WOO HOO!! Weekend project!!

It may not need one as much as this Prius did.

It's not so much an issue of being able to look up & see the hood, as it is directing airflow more cleanly past the bits of the car that stick down below the bottom edge of the front bumper.

I'll have a look when my Mother in law is done borrowing it. As I recall though, it isn't especially aerodynamically clean under there.

BTW. I noticed the undertray on my wife's Taurus while I was working on it, and got undertray envy. :D So I grabbed one off a Taurus last time I was at the junkyard. It's not solid; it has a couple of slots in the middle to allow air for cooling, I guess. It feels like really thick polyethylene. Should be easy to cut down and fit on my Cavalier.

Duct tape is AMAZING

The webmag "Autospeed" is aimed more at general auto information including better performance as well as better milage.
It is not a "hypermiling" focused magazine.

Pete.

Anyone have more ideas on the front wheel deflectors? Optimum shape, placement, etc?

I have a bit of styrofoam that I'll be using in mine. Once my testing is done, I'll cover the styrofoam in bondo and permanently attach it. See my post on the permanent grill block to see where I'm at now.

I'm thinking of a ramp-like shape that slopes out on the sides as well. This should move the air out to either side and down.

Would it be a waste of time to put a chin tray on a car higher than the bottom edge? I have installed an air dam (home depot garden edging, looks very NASCAR) on my Del Sol and I don't think i could attach a chin tray to the bottom of the garden edging. Would attaching the chin tray to the bottom of the bumper (6 inches above the chin tray) be completely useless?

MazdaMatt: probably useless, yes. You're going to have detached, turbulent flow coming off the air dam.

Raysp30: shaped deflectors like the kind the Autospeed author tried will be better than the flat "spat" type OEM's typically use. (But more likely to be damaged on stuff inside approach angles, and harder to build).

Aero concept cars usually go with shaped deflectors, eg:

http://ecomodder.com/forum/member-ae...per-cd0-15.jpg

That's basically what I did to my xB. Combined with the grille block, I basically gained 4-5% at highway speeds. It's no 10%, but it's not too shabby.

thats ironic, because my spectra5 has a chin undertray running from the bumper to the steering rack OEM!

A seminal paper was recently written by Volvo’s Dr Simone Sebben (SAE paper 2004-01-1307). It covers the computer modelling of undercar airflow,

The car is unnamed but it is likely a soon-to-be-released Volvo, ie a current, aerodynamically designed car.

Chances are, it was the 2006 Volvo C30 and the later C30 / S40 / V50 DRIVe models - which are more FE variants based on the PSA 1.6 diesel version.

Designing the rather short C30 on the same platform as the S40/V50 was an aerodynamic challenge to give it a good Cd.

The C30 DRIVe has a partial bellypan - the only Volvo that I know to have one (not counting the cosmetic "offroad"-plates) - while wheelspoilers have shown up on DRIVe models (and scores of other cars).

Link

I love the final line in the second part. {I was thinking of Dogfish Head's beer} What a laugh i got from that!

I don't have any undertary under mine VW Golf/Rabbit from '83. This is going to be my next mod.

Tnx for the nice article... :thumbup:

I know, I know.....
its an old thread


but I'm having trouble finding anything on the 1st gen prius (mine is a 2001)

I'm probably gonna do this
and I am leaning towards doing the grille blocking
but I'm afraid to limmit the air flow to the cooling system

deflectors
 

You might also want to look at Dr.Alberto Morelli's CNR 'banana' car of 1978.
The wheel treatments lowered the car from Cd 0.35,to Cd 0.201.
Here is a link
http://www.motorstown.com/images/pininfarina-cnr-01.jpg