GM HX3 Hybrid Van

[MetroMPG]

Originally Posted by Piwoslaw

I just noticed that the HX3 resembles Citroen's ECO 2000, from 1981-84. But didn't all prototypes look like that in the '80's?

Another great page full of aero eye candy. Thanks for the link, Piwoslaw.

[woodstock74]

Some of you may be familiar with my website Mulsanne's Corner. During my research for my IMSA GTP book I got to know fellow Industrial Designer Clark Lincoln. Mr. Lincoln was responsible for the famous GM Goodwrench livery on the Corvette GTPs. Clark Lincoln was also a designer for General Motors and worked in their Advanced Studio. Well turns out he was heavily involved with the HX3 Hybrid. He's graciously shared some of his wind tunnel test run notes and I've decided to share them with you all as well as they make for interesting, and very relevant reading:







The main conclusions they came to was the interrelationship/sensitivity between the slope angle of the trailing edge of the roof and that of the rear underfloor trailing edge ramp angle. The HX3 had essentially a flat underfloor. They found that if the roof trailing edge slope was effectively zero, sloping the underfloor/diffuser ramp actually INCREASED drag. But if an angled rear diffuser (15 degrees) was combined with a sloped roof trailing edge just the opposite occurred: drag REDUCTION.

More than likely the downwards "aimed" roof vorticies helped draw air through the rear diffuser, whereas without the top trailing edge slope the diffuser was creating a localized flow separation. Interesting stuff and quite a treat to take a peak into the development notes of a road car. Typically this type of information is considered verboten!

[orange4boy]

That's a very interesting set of notes especially for a van driver like myself. I would love to chop and slant the roof on my Previa like the HX3! Just a weekend job, really.

I went over to Mulsanne's Corner and found the following which was at the bottom of an article on the Toyota GT One.

Mulsanne's Corner: GT-One, 101?

Though ultimately vortices could be used for the benefit of top side race car aerodynamics, specifically in drag reduction. Juha Kivekas sums it up best, "It certainly is possible to use longitudinal vortices to fill the wake of the cockpit bulge. This could be done using delta wings on the sides of the cockpit. And actually there have been studies on lorries where angled delta wing were used near the trailing edge of the cab and have been found to increase base pressure; that is, to reduce drag. The vortices steal energy from the main flow and mix it into the wake flow and thus reduce the effective length of the wake. This is Mother Nature's explanation, we simply call it reduced drag."

This is a hot topic here at ecomodder. There have been countless arguments, experiments and claims regarding VG's and base filling drag reduction but no one has been able to find any research on the topic. The is one small reference in Hucho but that's it. Do you know where these studies were published?

[woodstock74]

Originally Posted by orange4boy

That's a very interesting set of notes especially for a van driver like myself. I would love to chop and slant the roof on my Previa like the HX3! Just a weekend job, really.

I went over to Mulsanne's Corner and found the following which was at the bottom of an article on the Toyota GT One.

Mulsanne's Corner: GT-One, 101?



This is a hot topic here at ecomodder. There have been countless arguments, experiments and claims regarding VG's and base filling drag reduction but no one has been able to find any research on the topic. The is one small reference in Hucho but that's it. Do you know where these studies were published?

I messaged Juha and he had a number of references to look into:

Hucho, "Aerodynamics of Road Vehicles", 1st English edition, page 334, chapter 8.5.4.5 Add-on devices on the rear end...
Hucho refers to: Young, R.A. "Bluff bodies ion shear flow". PhD Thesis, Cambridge University...
.... found another one also referring to the Young work:

SAE paper 2003-01-3377 "Simple and Low-Cost Aerodynamic Drag Reduction Devices for Tractor-Trailer Trucks"

SAE Paper 2005-01-3526 "An Assessment of Drag Reduction Devices for Heavy Trucks Using Design Experiments and Computational Fluid Dynamics"

[MetroMPG]

woodstock74 - thanks for posting those "napkin" development images. (I have lots of napkins... lacking in wind tunnels, unfortunately!)

I've been to your site a bunch of times. Thanks for sharing.

[cRiPpLe_rOoStEr]

Originally Posted by Piwoslaw

GM and Ford have large European divisions that have been putting out quite efficient cars that the US doesn't get to see. GM and Opel/Vauxhall are supposedly the same company, but with totally different politics. I guess the European part had to go with efficiency to stay in the market, while in the US it was the Big 3 that kept the brakes on for years. Now they're so far behind that it's hard to catch up, let alone be ahead.

Blame it on the EPA anti-Diesel policies and the NHTSA.