Could these fins add a few precious miles to the range?

[TRONZ]

I have a hard time believing that to actually be true. The physics simply don't support it.

Just going to lightweight 16's is giving some people a 5% boost.

You just need to be PMing with the people that have already done it. A 24lb loss of rotational inertia is significant. All four stock wheels and tires are 93lbs. Two people (I know) are running 69lb setups for an unsprung loss of 26%. Rotational inertia drops significantly. Their Carwings data indicates an improvement so I am inclined to give them the benefit of the doubt to those actually doing something. If however, you would like to enlighten us with your physics formula disproving their claim, I am sure we would all be interested.

Staying OT, I encourage Aero experimentation and hope people with long freeway commutes try some of the common simple tricks. Who knows, the people "walking the walk" might even start posting their results on the public portion of MNL again. Something for the "talking the talk" folks to ponder.

 

[TomT]

Sorry, but it still doesn't add up... At a constant speed it is going to have virtually no affect since rotational mass plays no part in energy used in such a situation. If you did a lot of accelerating and accelerating in traffic, maybe, assuming you weren't very good at energy management and did not use much regeneration or used a lot of friction brakes... Whether the weight is sprung or unsprung makes no difference in terms of energy usage as only rotational mass enters the equation. Sprung or unsprung is important in terms of handling...

I have a hard time believing that to actually be true. The physics simply don't support it.

Just going to lightweight 16's is giving some people a 5% boost.

You just need to be PMing with the people that have already done it. A 24lb loss of rotational inertia is significant. All four stock wheels and tires are 93lbs. Two people (I know) are running 69lb setups for an unsprung loss of 26%. Rotational inertia drops significantly. Their Carwings data indicates an improvement so I am inclined to give them the benefit of the doubt to those actually doing something. If however, you would like to enlighten us with your physics formula disproving their claim, I am sure we would all be interested.

Staying OT, I encourage Aero experimentation and hope people with long freeway commutes try some of the common simple tricks. Who knows, the people "walking the walk" might even start posting their results on the public portion of MNL again. Something for the "talking the talk" folks to ponder.

 

[DaveEV]

I have them on my ICE (Mitsubishi Evolution IX MR) - they're stock on Evo MRs. Mitsu calls them "vortex generators". They're claimed to help reduce turbulence in the airflow coming off of the passenger compartment. Do they do anything useful? I doubt it. Certainly doesn't seem to help my mileage at all.

To be fair, Mitsubishi's goal was to decrease lift on the rear of the car by directing more air to the rear spoiler.

The VG's upset the boundary layer causing airflow to stick a bit closer to the rear window so more wind hits the rear spoiler thus reducing lift.

A side benefit is that drag was also reduced slightly.

Mitsubishi was nice enough to publish a paper showing their testing methods and results to come up with the optimal design. Going to be tough for someone without at least some good CFD software to duplicate.

http://www.mitsubishi-motors.com/corporate/about_us/technology/review/e/pdf/2004/16E_03.pdf" onclick="window.open(this.href);return false;

Mitsubishi's study found a maximum of a 0.006 reduction in Cd with well placed VGs. That's about a 2% reduction in drag. Note that you can't necessarily apply these results to the LEAF since the LEAF is a hatchback and the Evo is a sedan.

As mentioned previously, airplanes use VGs on wings to decrease stall speed - a plane stalls when airflow separates from the top of the wing. But on planes under normal conditions, it increases drag so manufacturers work on wing designs that eliminate the need for VGs while maintaining minimum stall speeds.

I'm not aware of any real wind tunnel studies on VGs on vehicles with square backs so I am skeptical of any drag reduction claims.

On the LEAF, you can see the little bumps on the trim below the windshield, but they are positioned in the direction of airflow - these are not VGs. Larger fins can be seen on the undertray under the bumper. The fins are used to help clean up turbulent air - in the rear this can help reduce drag - before the windshield I'm sure they are used to help reduce wind noise primarily.

My educated guess at the most effective location for VGs on the LEAF to reduce drag? The spoiler and sides of the car, particularly around the rear "haunches". Nissan sacrificed drag for style here as around the mid point I'm sure that airflow separates over the curve increasing drag. If they had tapered the lower part a bit more and created cleaner line from the rear bumper to the top half of the tail-lights I'd bet they could have dropped a tenth off the cD figure.

Compare the rear of a LEAF to a Prius. Pretty easy to see how much bigger of a "hole" the LEAF leaves in comparison.

 

[TonyWilliams]

Here's a really simple design you can bend out of a piece of aluminum:

These Vortex Generators were designed and tested in a wind tunnel as well as on various experimental aircraft. They are formed in pairs so that the shape and angles are built right in . This makes them easier to install as they only need to be spaced out along a straight line. Also, they can be temporarily attached to the wing with tape for testing without harming the wing surface and then moved or attached permanently. This temporary attachment capability allows the pilot to prove out their effectiveness before permanent attachment. The design also gives a generous surface area for bonding. The Vortex Generators are made from .025" 6061-T6 aluminum for maximum durability.

 

[TonyWilliams]

.My educated guess at the most effective location for VGs on the LEAF to reduce drag? The spoiler and sides of the car, particularly around the rear "haunches". Nissan sacrificed drag for style here as around the mid point I'm sure that airflow separates over the curve....

Which is why the first place I would try VG's is just slightly ahead of the highest point of the roof.