What is Downforce?
The term "downforce
in racing is used to described the downward force of the air on the body
surface as air passes over it at speed. Downforce can be applied
anywhere on the body front and rear. The more angle of the forward
facing surface, that air is passing over, the more the downforce is
being applied. At the same time, more angle of an opposing surface o the
air will create drag. Downforce will create more traction but drag will
slow the car.
The goal is to
apply as much downforce to a particular area of the car body to achieve
the handling feel as you want and create as little drag as possible.
That can actually be a fairly complicated process and can only be judged
properly with very sophisticated devices in a true wind tunnel.
Of course NASCAR
teams with unlimited budgets spend bajillions of dollars to figure that
out. Not very practical for RC racers. NASCAR also does extensive wind
tunnel testing to make the bodies as equal aerodynamically as possible.
Here at Mc
Allister Racing we follow the shape trends of NASCAR, not only to have
realistic look for our scale racecars but to take advantage of NASCAR
and their teams research in aerodynamics. That's why we have the most
scale appearing bodies for oval racing.
How to use downforce?
Since applying downforce to a body will create
better taction, we need to figure out how and where to apply it.
Basically a race car handling is described as oversteer, understeer or
neutral. Oversteer in aerodynamic terms means more front downforce (less
rear downforce), understeer would be more more rear downforce (less
front downforce) and neutral would be a good combination of both.
Each body will exhibit a certain characteristic
among the three possibilities mounted on a car with a given set up.
(Always keep in mind that aerodynamics is only a part of the combination
needed to set a race car up properly. Don't expect aerodynamics to work
in a vacuum and solve all your problems) The aerodynamics can be greatly
affected by adjustments to the aerodynamics components of the body to
achieve oversteer, understeer or neutral handling. We're lucky compared
to the full size NASCAR teams that do not have these adjustments
Basic Body Aero Components
Body Mounting and Rake
Mounting the body correctly is very important. Fitting the body so the tires have good clearance (no rubbing) and centered over the tires is the first step to proper handling. If anything is rubbing or dragging there's no need to even make chassis adjustments, the car won't work right at all. Smooth, straight, clean edges every where around the body will be less disruptive to air flow creating more speed. Expose as little as possible of the body posts. It's popular to use buttonhead screws instead of body clips. Great aerodynamically...not as substantial in crashes….driver's choice.
Rake is the angle the body is mounted on front to rear. Very simple...Front lower, rear higher equals more over all downforce (if using a rear spoiler). Good for shout tracks. Front higher, rear lower equals less downforce over all and much less drag. Good for very long high speed tracks. Plus the infinite variations in between. Another subtle adjustment with "Rake" is the height of the rear spoiler.
Front and Side Skirting
Using the lower skirting to seal air off will make a cleaner air flow and may help with some extra downforce with little drag penalty, but….
DO NOT have any lower edges dragging the ground! This is like dragging an anchor around the track and most important, any time your chassis or body contacts the racing surface , you have just negated all that expensive, high tech suspension under the body. Not a good idea. Always maintain ground clearance, especially in the corners where the body rolls the most and the
suspension is needed the most.
Cutting out the rear of the body and leaving the rear quarter panels extend down as sail panels is popular in some areas. We're not convinced of thevalidity of those ideas and prefer the scale appearance where the cut lines are indicated on our Stock Car bodies.
Another huge adjustment we RC racers have that the Cup Boys don't. We
can adjust the angle and height to our liking ... even remove it if we
want. A lot of Stock class racers remove them for lessdrag in a
limited horsepower situation. You still have to get the car to handle
with other adjustments ... but the theory is correct.
Just remember, higher spoiler and/or more angle equals more rear
downforce and more drag. Lower spoiler nd or less angle equals less
rear downforce and ess drag. Don't forget we are talking about front
to rear balance on handling. Likewise, ore rear downforce has the same
meaning as less front downforce. It's really a matter of orientation
to the components you are adjusting.
Wire Mounted Wing
This is the biggest departure from
the actual NASCAR bodies we have on RC Cars. Not necessarily a good
one we might add, since they are ot scale appearing. However if the
rules allow them, and most do, use them! It's a very adjustable tool
to create rear downforce and stability. There are a variety of clear
plastic models available with a wide variety of rear kickups, side
board shapes and sizes. Experimentation is the key here. Since there
are so many variations possible you can try a lot of possibilities. As
always, more angle and/or higher rear kickup equals more downforce and
more drag. Less angle and/or less rear kickup equals less rear
downforce and less drag.
The big difference from the spoiler
is being mounted higher in cleaner air for more efficiency and the
ability to move the wing around. Just moving the wing backward
relative to the body will create more rear downforce with no extra
drag penalty because of the leverage. Moving the wing forward will
create less downforce. It's best to keep the wing no higher than the
roof of the body. This allow god air pickup but doesn't create a huge
problem with keeping weight low on the car.
The side boards and flat surface of
the wing act as rudders or stabilizers like an airplane. They smooth
the airflow which has a stabilizing affect on the overall handling...
very important for high speed ovals. The Cup Guys would be jealous.
They will soon have a slimmed dow version on the NASCAR COT (car of
tomorrow) car in 2007. Always keep them straight with the flow of the
air... if not you can call them barns doors or air brakes.
Finished body in race ready form...Note ground clearance of skirting,
consistent tire clearance in wheel cut outs, position of rear wing and slight body rake.
Any current stock car bodies can work fine n a well adjusted
contemporary chassis using the adjutment tools available. Don't expect
to just change to another style of body and get instant results. The
correct setup is there, you just have to find it. That should ba art
of the fun after all.
We recommend finding a body style you like the looks of, then work
with the adjustment tools described here to create the handling balnce
that suits your driving style. Remember, aerodynamics is only part of
the overall handling equation. Changing conditions occur so be ready
to adapt with your knowledge of aerodynamic tools.