This article was first published in 2006.
In this series (see
Blowing the Vortex
Part 1 and
Blowing the Vortex
Part 2) we’ve already covered how
vortex generators work and what they do on the Mitsubishi Evo Lancer. But what
about fitting them on your own car? The first step is to source – or make – some
Making Your Own
Vortex generators are often pretty simple shapes.
The ones trialled by Mitsubishi on the Evo were categorized as either bumps...
....or deltas. The dimensions are given as multiples
of the height (h) with 25mm high ones typically proving to be the most effective
on the Lancer. For testing purposes, these vortex generators can be made of
anything that can easily shaped – wood, clay, even papier mache.
This Décor brand plastic spoon closely resembles
the bump-shaped vortex generators trialled on the Evo. With the handles cut
...it’s not hard to quickly make a bunch of vortex
generators very similar in shape to the Mitsubishi ones and see how well they
Aircraft vortex generators used on wings are often
just flat pieces of aluminium slightly angled to the flow....
...which are quite easy to make using aluminium
However, while it might be worth making your own
simple ones for initial test purposes, producing effective and durable vortex
generators is a much more difficult ask and may well be more trouble than it’s
worth. That’s especially the case when there are at least two different design
commercial vortex generators available quite cheaply, both designed for road
Australian company offers that vortex generators folded from sheet aluminium. A
car kit that comprises nine vortex generators, cleaning wipes, a template and
instructions costs AUD$110 including (Australian) delivery.
Airtabs are made in the US and are widely
available. They can be bought directly from www.buyairtab.com
at a cost of
US$2.50 each and are available in black or white. In Australia, the Kenworth
ALLRig dealer network stocks clear Airtabs at a cost of AUD$5.50 each – see
the nearest dealer.
Airtabs are made from ABS plastic and are quite
differently shaped from the vortex generators we’ve so far examined, although
the shape is used in some wing applications. They come with a pressure-sensitive
adhesive tape on their base. The main Airtab website is at
Both the manufacturers of Fuelsavers and Airtab
vortex generators make major claims for the effectiveness of their products.
Fuelsavers claim fuel economy improvements of “up
to 11 per cent” and have testimonials claiming 11 per cent fuel economy
improvements on 5 and 8-tonne pantechnicon trucks, 12.5 per cent on a 1990
Holden Commodore, and 9.5 per cent on a Subaru Outback.
However, is this technically likely? The Bosch
Automotive Handbook (6th edition, P 890) shows changes in fuel
consumption with changes in aerodynamic drag. For a medium sized car with a drag
coefficient of 0.30, a reduction in drag by 0.04 (ie a 13 per cent decrease)
reduces fuel consumption at a constant 120 km/h by 7 per cent. In the European
highway cycle it reduces fuel consumption by 2 per cent and in the city cycle,
by 0 per cent.
Based on this data it is difficult to believe that
the fitting of vortex generators would reduce drag to the extent that fuel
consumption improvements of over 10 per cent are realised in normal use.
Both vortex generator manufacturers suggest using
lots of vortex generators and purchasers are advised to position them at the end
of the vehicle as well as at body transitions (eg from roof to rear window).
However, even given their more numerous use, it needs to be kept in mind that
when Mitsubishi placed vortex generators at the end of the Evo Lancer’s roof,
the drag reduction was less than 2 per cent (assuming a 0.35 drag coefficient).
Blowing the Vortex
Airtab’s fuel economy claims are more modest, with
a 4-6 per cent improvement cited. The devices have been fitted to many trucks
and semi-trailers and it is for these vehicles that the claims are made.
Airtab’s testimonials page at
is very interesting,
with higher stability, better rear visibility in wet conditions, and improved
fuel economy all claimed by users.
Incidentally, near the bottom of the Airtab
testimonials page is this incredible pic of a truck racing at Pikes Peak. The
truck is fitted with Airtabs across the rear of the roof. The website says:
The amazing photo shows how the 16 Airtabs on
the roof smoothly bend the airflow down into the area behind the cab. The photo
shows the Airtabs create an array of vortices that smoothes airflow behind the
cab so it can closely follow the wing's contour to create more downforce and
traction. The bending of the air coming off the cab allows the wing to operate
in clean, undisturbed air, improving the wing's effectiveness. The effect of the
wing can be clearly seen as it lofts the air upwards. Rare weather conditions
make the vortices look like a layer of white fog in this remarkable photograph.
However, without another photo showing the foggy
airflow without the Airtabs in position, not a lot of conclusions can be drawn.
But it is a fascinating shot!
For our money, Airtabs are the vortex generators to
buy. The company producing them makes claims which are more in keeping with
technically feasible outcomes, the devices themselves are arguably better
looking than folded aluminium designs (and certainly are much less dangerous
protrusions to have mounted on vehicles) and are cheaper.
But do they do anything for cars? Next week we’ll