chance to make some progressive aerodynamic changes
2000 CART is on the verge of
announcing a new engine formula for 2005 that will last for 10 or
more years. But what about the aerodynamic package? CART
must come up with an aerodynamic package that will improve the
racing while keeping speeds in check. We talked to
aerodynamicist Dr. Mark Handford
CART has a dilemma. Champ Cars are too fast for some oval tracks, and
attempts to slow them down using a modified version of the Handford Device
for small and medium sized ovals has resulted in too much turbulence and
too little passing.
Any race car that derives a large percentage of
its downforce from aerodynamic grip will be adversely affected by dirty air. A
race car that either has no wings (i.e. NASCAR Winston Cup) or one that
has an excessive amount of wing downforce (an IRL car) is less likely to
be disturbed when the air gets turbulent. In the Winston Cup car's
case because they have no wings/aerofoils per se to be disrupted, and in the IRL's case,
they make so much downforce, even when they lose some in dirty air, there
is still enough to generate adequate grip.
While the IRL's goal is to make for a better racing show
by allowing the drivers to race full throttle at many tracks, CART's goal
is to keep the driver as big a part of the equation as possible, because
in the end, as with any sporting event, it is the best race driver people
come to see win. Racing
full throttle an entire race distance is not deemed as challenging by most
hard-core race fans, although it is mentally draining and rather
entertaining because it leads to a lot of close, side-by-side racing.
In an attempt to keep turn speeds reasonable and prevent
full throttle racing, CART has, over the years, reduced the amount of
downforce generated by a cars wings and the cars underbody/underwing
ground-effects. Tunnel blockers and/or reductions in underwing exit
area were used to decrease underwing downforce and lower downforce wings were mandated. Eventually the
Handford device was mandated to create straightaway drag and to further reduce the
downforce efficiency of the rear wing.
CART's problem is that the Handford Device creates enough
turbulence that a car following loses a lot of its downforce, especially
from the front wings. This results in the trailing car
'washing' out or 'understeering' and, therefore,
can never get close enough to the car ahead at the exit of a turn to
slipstream past on the following straightaway. There is some passing, but the
Handford Mk II Device has not created the type of exciting racing on small ovals that we
saw at Michigan last weekend where the turns make it possible for the
drivers to run three different lines to avoid the 'dirty' air.
CART must not apply band-aide solutions
CART has stated that it wants to reduce the power of the engines by
about 150 HP (see related article)
and go back to the higher downforce wings used prior to the Handford
Device. In other words, reduce the HP so you don't need the
parachute-effect of the Handford Device to keep speeds in check.
While this solution may work in the short term, we have our doubts this
proposal will give the long term desired results, and worse yet, CART is
reducing the HP to weight ratio of the cars to the point they will no
longer be able to make the claim 'Champ Cars are the fastest race cars in the
world'. We know the Handford Device concept can produce some
spectacular racing as evidenced by the last three Michigan 500's, so
CART's attempt to mimic that success on all it's oval tracks was a good
idea. However, the devil's in the details, and CART neglected them.
CART's problem is further complicated by the fact it races
on a wide variety of circuits, making it harder to come up with a set of
rules that makes the racing good at all venues. Therefore, any new
aerodynamic rules are going to have to be modular, or adjustable enough to
accommodate the variety of tracks.
Dr. Mark Handford
Long-term aerodynamic proposal
We decided to contact Dr. Mark Handford, creator of the Handford Device(s),
to first find out what went wrong with the latest Handford Device's, and
to discuss an idea for a better solution to CART's problem. Dr.
Handford explained that the Handford Mk II devices (small and medium oval
) were designed to the performance standards CART gave him. However,
the mistake CART made was not track testing them in traffic first.
They found out once the season started that they don't work well for the
reasons described above. If all oval tracks had three racing grooves
like Michigan, they might have worked well. Unfortunately, most have
only one real racing groove, and the follow-the-leader train through the
turns remains follow-the-leader down the straights because the gap coming
out of the corner caused by the 'dirty' air is too large to overcome down
the following straight, which is usually never long enough to make the
We asked Dr. Handford to evaluate an alternative
proposal. What if Champ cars generated most of their downforce from
the car's underbody/underwing rather than the wings/aerofoils? Isn't the underwing
affected by the leading car's turbulence? The answer was a definite
yes! The theory behind this proposal is simple, maintain the current
level of downforce, but make most of it with the car's underwing, rather
than the aerofoils, so a car can race closer with another car and not be
affected as much by its dirty air.
Dr. Handford explained that the underwing
should be less sensitive to
turbulence for a number of reasons:
The ground plane will attenuate vertical velocity fluctuations.
The length of the underwing will integrate turbulence (which has both
positive and negative downforce benefits over short intervals of time) over a
longer time period than a short (say, 12inch) chord wing.
The underwing/ground-plane generates downforce from a venturi-effect AND
circulation-mechanism rather than just the latter (which is the case with a
wing) so ideally the underwing is more-nearly just sensitive to mass-flow rather
than mass-flow AND local angle-of-attack.
The underwing generally develops much lower peak suctions so
it's less likely to suffer catastrophic flow change (stall, etc.) due
Lola (top) and Reynard (bottom) underwing exit. The exit would be significantly increased under the solution
(Click to enlarge)
"So, for all of the above reasons, it makes sense to use
more of the underwing and less of the aerofoil for downforce. However, we
must remember, due to higher speeds, a considerably smaller underwing
needed for Super Speedways compared to road and street circuits.
Therefore, to contain costs a
modular approach is needed. I think this would follow a David Bruns statement (1997) where he said why don't we just mandate
geometry and leave the rest free. This is simple to police and (like an engine air restrictor) tackles the most basic control variable determining
the downforce. This would take us back to Kirk Russell's underwing blockers (first
introduced in 1997). We may need to mandate that specific blockers are fitted
so the constructor (Lola, Reynard, etc.) is unlikely to realize a benefit by making a whole new underwing (with lower exhaust pipes, etc) just
for the small (i.e. lower) tunnel exit geometry. In other words CART would
mandate that specific pieces be fitted to the car to try to eliminate "special"
This should allow CART teams to purchase just one underwing for all races and fit CART-standard exit-blockers from an
inventory of such pieces, as needed. However, in all of the above, it is important to remember that the driver of a
following car will inevitably suffer some loss of downforce from running in air that is;
1) Turbulent, and 2) effectively a tail wind, commonly know as a 'hole in
the air'. It is this effective tail-wind that will (even without turbulence) reduce
the downforce available to a following car because the mass flow of air
under the car is reduced." The less air flowing under the
car, the less downforce generated.
He went on to say, "we think (but do not know without some research) that an underwing will suffer less from both
effects (relative to an aerofoil), but it may be that while it does indeed
suffer less from turbulence, the underwing still suffers from the
effective tail-wind. In which case it still follows that you want to rely
on underwing downforce, but we should be under no illusions that we can ever make a
following Champ Car able to drive right up under the rear wing of the
car-in-front because the car in front reduces the amount of air available
to flow under the trailing car's underwing. In this latter
case the only way to have Michigan-type racing on smaller ovals is to make the draft opportunity a
big potential benefit and that means longer and wider straights to allow the
following car to build up speed to pass using the draft generated by a
Recommendation, but research needed
If CART wants to develop an aerodynamic package that will produce better
racing over the long haul, we recommend they invest in some research and
do it right this time. CART should help fund the research into this idea of higher
underwing downforce because there are two objectives,
both of which do not contribute to helping Lola, Reynard, or Swift stay in business.
However, it directly affects CART and its ability to justly portray itself as the pinnacle of exciting open-wheeled racing.
CART needs a good show to stay in business so it is CART who should pay.
Given CART races on such a wide variety of circuits, the two objectives of the research would be:
Detailed study of the circuits (computer simulation) to
catalog the effect of running different levels of downforce/drag/horsepower on each
track. This data should be summarized and then an identification be
made of the desired number (four ?) of different packages to adequately cover the
requirements of CART's four type of tracks . Rather than go into
scientific details, what we are looking for is basically the need to ensure that the
cars are generally grip-limited in the turns without an excessive horsepower-surplus available on corner exit (otherwise either any fool can
drive them, or would be quite likely to spin on exit). This would take an expert
group about 3-months.
For at least two of these
"downforce-packages"; determine what level of total downforce
that it will take for better racing if the vast majority of the downforce is created by the
underwing. This requires wind
tunnel testing to match the options, followed by at least two full-size cars
(manufactured or modified from existing/old chassis) and several track
tests. This would take an expert group about 6-months.
Full-size testing is needed because wind tunnels cannot compete with
race-drivers in determining this rather subjective question. A pair of
big-underwinged-cars should be made and a similar pair of (current cars) with
small-underwings (and biggish aerofoils) should be made and run on the same
day on a small variety of tracks.
According to Dr. Handford, about 15 days of wind tunnel testing and about 100 days of supporting model
making/design would be needed to experiment with the options (about $300,000
in total plus the full-size car and on tracking testing costs). This would lead into a series of "packages" probably along the
High downforce, high drag, big (adjustable)
conventional wing, big
underwing (road and street circuits)
Medium downforce, medium drag, small conventional wing, big
underwing (1.0-mile oval, Elkhart & Rio)
Reduced downforce, medium drag, very small but "dirty" wing device,
big underwing (1.5-mile flat oval such as Rockingham England, maybe
Existing Super Speedway package - low downforce, low drag, Handford
device, small underwing (very high speed tracks - Michigan, Fontana,
Texas, maybe Germany).
The following table provided by Dr. Handford contains some
approximate downforce numbers for comparison purposes. It only
contains downforce numbers for two of the four configurations (#2 and #3) mentioned
above. #4 is essentially what we have now at Michigan and that seems
to work well. #1 is essentially what we have now for road and street
circuits, except we would be adding more underwing downforce to make
overtaking a bit easier.
Before Tunnel Blockers, but smaller tunnels
than in 1992 (1995 - mile oval, tires better but still not as good as today)
Now with Handford II (1.0-mile oval package).
Drag level about the same as above wings
Now with Handford II (1.5-mile oval).
Drag level artificially higher than need be due to excessive HP
Future with high downforce
underwing (1.0-mile oval). Same total downforce as now. The proposed rear wing
lift would diminish in a draft behind a car*.
Future with high downforce underwing (1.5-mile oval). Same total
downforce as now. The proposed rear wing lift would diminish in a draft behind a car*.
Although the wings/aerofoils alone would
produce uplift rather than downforce, their main contribution would be to
provide aerodynamic adjustment to help the driver and engineer balance the
car for each circuit.
The objective in all this is a broad range of adjustability within each package,
almost to the extent that it overlapped the next package. This would allow
the teams and CART to agree what package to apply to a particular race
but would leave the constructors and teams to operate knowing that they will
be prepared for everything if they simply have one of each package. That
way CART can even change its mind just days before an event to switch it to
have more or less downforce with little impact on the expenditure required by the
Circuit simulations are needed to investigate the target levels of
downforce and drag for each package to make sure they are appropriate to the intended
circuits (e.g. need to be able to do a 1.0-mile oval without having to shift
gears but without being "easily" full throttle all the way
After all the above is complete a new rule-book could be written to clean-up the current
legacy of 20-years of piecemeal change to the aerodynamic/chassis rules.
This would also give a major opportunity to introduce safer cars (bigger
cockpits, more crushable structure etc).
If CART implements the recommended 1.8 liter highly
turbocharged boost engine, horsepower can be keep almost constant for a 10 or
more year period by lowering boost in gradual increments each year to
offset manufacturer gains. Similarly, if the aerodynamics gains
can, for the most part, be limited to gains made from better overbody
and underbody designs during those same 10 years (i.e. CART mandated wings
that take the wing/aerofoil variable out of the designers hands), the
cars should not only remain stable and racy in 'dirty' air, they should,
in theory, get even more stable and racier during that time
period. And if the designers start to make the cars too 'planted'
to the ground, CART can tweak the exit tunnel size. A well thought
out plan would give them that flexibility.
This together with an announcement for a new 1.8 liter highly
turbocharged engine beginning in 2003, gives Bobby Rahal a marvelous opportunity to make a big splash with such a
raft of progressive changes! However, it doesn't take a financial wizard to see that this
research would cost a lot of money if done thoroughly, but then we don't see any other way of
guaranteed progress. Maybe there just is NO way to make open wheel racing
as close as NASCAR Winston Cup racing given the dependence of the cars on
a much higher percent of aerodynamic downforce for grip (and the more lenient
rule book). However, we need to do the best we can to make the cars as good as they
can be because we don't see the oval track owners knocking down walls and building
longer straights anytime soon.
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