CART's chance to make some progressive aerodynamic changes  

 by Mark Cipolloni
June 31, 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

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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 that generated 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 pass.

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 less 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:

  1. The ground plane will attenuate vertical velocity fluctuations. 

  2. 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. 

  3. 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. 

  4. The underwing generally develops much lower peak suctions so it's less likely to suffer catastrophic flow change (stall, etc.) due to turbulence. 

Lola (top) and Reynard (bottom) underwing exit.  The exit would be significantly increased under the solution proposed here.
(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 will be 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 underwing exit 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" underwing designs.

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 Handford Device."

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: 

  1. 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. 

  2. 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 lines of:

  1. High downforce, high drag, big (adjustable) conventional wing, big underwing (road and street circuits) 

  2. Medium downforce, medium drag, small conventional wing, big underwing (1.0-mile oval, Elkhart & Rio) 

  3. Reduced downforce, medium drag, very small but "dirty" wing device, big underwing (1.5-mile flat oval such as Rockingham England, maybe Germany) 

  4. 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. 

  Downforce Levels (lbs)
Description Wings Underwing Total
Before Tunnel Blockers (1992 - mile oval)
(5-element cascade rear wing, rock-hard tires)
3,000 2,200 5,200
Before Tunnel Blockers, but smaller tunnels 
than in 1992 (1995 - mile oval, tires better but still not as good as today)
1,800 2,200 4,000
Now with Handford II (1.0-mile oval package). Drag level about the same as above wings 1,700 2,000 3,700
Now with Handford II (1.5-mile oval).  Drag level artificially higher than need be due to excessive HP 800 1,900 2,700
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*. -200 3,900 3,700
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*. -200 2,900 2,700
*Note: 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 teams. 

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 around).

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.

The author can be contacted at markc@autoracing1.com

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