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1.1 Qualifications |
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I have a Bachelor of Science in Aerospace Engineering from Tri-State University in Angola, IN and have worked in the aerospace field for almost thirteen years now. I've been karting for over fourteen years and still love it. I started off in sprint road courses and did that for about five years. Then I discovered sprint sit-up and started doing that in addition to sprint. It didn't take long to transition to only sprint sit-up and the bodywork development began. Naturally the progression led to buying an enduro and more different bodywork. Both karts have gone through many changes along the way and both are going to receive new bodywork of my own design for next season. That will be another paper, fiberglass molding and fabrication. |
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1.2 Contacting the Author |
| The easiest way to reach me is through email. I check that daily and think it's the greatest thing since sliced bread. You can also visit my website and find other information relating to karting. And for the historical view, my snail mail address is also provided.
email: bunnell@en.com
web: http://www.en.com/users/bunnell
snail mail: Chuck Bunnell
11304 Thwing Road
Chardon, OH 44024
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1.3 Document Layout |
| This document will begin with a discussion of the different components available as bodywork. Each component will be described in detail and design considerations presented. A basic presentation of aerodynamics as it relates to karting is presented in the next section. The following group of major sections provide recommendations and suggestions for specific types of racing. |
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2.1.1 Nose Cone Description |
| This one is everyone's favorite and is subject to as many aerodynamic theories as there are people to ask. A nose cone generally covers the front of the kart typically running from outer wheel edge to outer wheel edge. Some varieties only cover from inner wheel edge to inner wheel leaving both front wheels in the airstream. Many shapes are available and most are dependent on what people think looks the best. Some are blunt while others are pointed and wedge shaped. The height of the nose cone is only limited by the required view of the driver. Obviously, a sprint kart can use a taller nose than an enduro. Typically the nose will mount to the underside of the frame and/or bumper and typically is about 10 inches tall. Some enduro noses have raised walls around the driver compartment to reduce the amount of air spilling' into the kart's interior. Some drivers will also add a skirt to the edge of the nose allowing it to seal itself to the pavement. |
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2.1.2 Nose Cone Purpose |
| The nose cone should redirect airflow around the kart and driver without generating additional drag or unwanted downforce or lift. Most of the airflow should be directed down the sides of the kart instead of over the top of the kart. Lift will be generated by airflow over the top of the kart unless the airflow is controlled well. More will be discussed about this later. |
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2.1.3 Nose Cone Design Considerations |
| A nose cone will see the highest dynamic pressures, (aerodynamic load), and should be stiff enough to support the aerodynamic loads without excessive deflections. Excessive deflections would be those that prevent the nose cone from smoothly redirecting the airflow as stated in the previous section. A nose cone should also be strong enough to handle the occasional bump without destruction. The definition of 'bump' will be left at the operator's discretion. The front of the kart is usually lifted by the bottom of the nose cone so it should be strong enough to support half the kart's weight as well. Common consturction materials are plastic, fiberglass and other composites. |
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2.1.4 Nose Cone Mounting Concerns |
| The nose cone is generally the largest component and is usually the hardest to mount. It must be centered and straight relative to the kart's center line. If not, a persistent pull to one side or the other could result. The angle of the nose cone relative to the ground, (angle of attack), is very important and can be used as a tuning aid. The nose cone can either be neutral, (zero lift and zero downforce), or develop lift or downforce depending on its angle of attack. Minimum drag will be achieved with a neutral setting though handling problems may be best solved by adjusting the nose cone's angle of attack. Providing adjustable mounting is not always simple and will vary from kart to kart. A common way is installing a heim joint in the bumper mount. Adjusting the heim in or out will change the length of the upper bumper arm causing the bumper to rotate about its lower mount. Many mounting points are better than fewer mounting points. This will distribute the load and put less stress on the nose cone near the mounting points. Large diameter washers should be used to distribute the bearing load from the mounts. It is also desirable to provide a rubber biscuit or other similar cushioning between the mounts and the body work to provide a cushioned interface which should help the bodywork last longer. Do not overtighten the mounting fasteners as that wil crush fiberglass and lead to premature breakage. Plastic is much more tolerant of tight fasteners. And always use self-locking fasteners. |
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2.2.1 Belly Pan Description |
| A belly pan is usually a flat piece of material that covers the entire bottom of the kart. On an enduro it would run from the nose cone all the way back to the bumper or tail cone, and from one side of the kart to the other. Sprint karts are usually limited to between the frame rails though that could be different now. Some karters add ground effects to the belly pan usually looking to add downforce to the rear of the kart. |
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2.2.2 Belly Pan Purpose |
| A belly pan should reduce turbulence between the kart and road surface below. This is accomplished by providing a smooth airflow path compared to a kart without a belly pan. A kart without a belly pan presents a varying height to the road surface which repeatedly will draw the airflow in and out as the kart moves forward. This forced compression and expansion of the airstream consumes energy and results in drag and turbulence. Maintaining smooth airflow over / under / around the kart is very important in order to keep drag minimized. |
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2.2.3 Belly Pan Design Considerations |
| Belly pans can be difficult to assemble while meeting all design goals. The belly pan needs to be smooth and flat yet rigid enough to resist deflecting due to aerodynamic loads. The mounting fasteners should not protrude down into the airstream. Mounting also needs to allow the belly pan to float relative to the chassis. It should not be mounted such that it stiffens the chassis. Sometimes that can be used as a tuning tool, but generally the belly pan should not interfere with the chassis. Common construction materials are plastic, aluminum, fiberglass and other composites. |
| Plastic is often used for belly pans since it is inexpensive and light weight. Care must be taken when selecting which plastic to use. Common choices are high density polyethylene, (HDPE), polyvinylchloride, (PVC), polycarbonate, (Lexan), and polypropylene. Each has it's own advantages and disadvantages. Plastic is not usually thin enough to countersink in order to make the fasteners flush. It also discolors and sometimes swells due to contact with oils, grease and fuels. Warmer temperatures can also cause the plastic to sufficiently expand and start buckling or become wavy. Neither is very desirable since the end result is a wavy surface. Cold temperatures also make some plastics brittle and subject to shattering. Plastics do offer good abrasion resistance and are easy to work with. Properly installed and maintained, a plastic belly pan will work well and offer a reasonable life. |
| Aluminum sheet is also used for belly pans owing to its excellent material properties. Aluminum wil be the lightest and stiffest material available though it is usually the most expensive. One distinct advantage of aluminum is that it may be dimpled to provide a countersink of sorts in very thin metal in order to use flat head screws which will provide a totally smooth bottom kart. It doesn't suffer from any of the problems plastics do. |
| Fiberglass and other composites tend to fall between aluminum and plastics in price. They can be the stiffest and most rigid but sometimes at the expense of brittleness. Mounting can be a problem since countersinking will not be available due to the very thin sections. |
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2.3.1 Column Fairing Description |
| The column fairing is a panel, or collection of panels, usually mounted to The steering column supports providing a smoother airflow around and over the steering wheel and driver. Sometimes column fairings are mounted to the steering column itself allowing movement of the fairing though this is probably not very desirable. The size of the column fairing is the most governed due to safety considerations. It is highly recommended to adhere those safety regulations. An effective column fairing can be made that meets all safety regulations. |
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2.3.2 Column Fairing Purpose |
| The column fairing should receive the airflow redirected by the nosecone and continue it's redirection around the steering wheel and driver. The continuing goal is to smoothly direct the airstream around the kart and driver and then smoothly bring it back together. Column fairings on a sprinter tend to be much larger and more important then those found on an enduro. The obvious reason is the driver sitting up in the airstream. Kind of like holding your hand out the window. The coulmn fairing on a sprinter has to be larger enough to smoothly redirect the airflow around the driver and avoid the direct impact. Generally the column fairing will be as large as the rules allow in order to provide as much smooth surface as possible and to dedirect the airflow as smoothly as possible. |
| Column fairings on an enduro tend to merely protect the instruments on the steering wheel. Typically the fairing will be almost horizontal though a small windshield is added to some. It's debatable what the effects are. |
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2.3.3 Column Fairing Design Considerations |
| The same basic rules apply to column fairings from belly pans and nose cones. A light, stiff piece is desired that can withstand the aerodynamic load placed on it. Ideally, the airflow from the nose cone should impact the column fairing at a small angle. This is hard to determine and varies with speed. Generally the airflow will leave the nose cone tangentially. But that direction is short lived as the airflow is always trying to return to its original path or position. As we push our way through the air, it pushes back trying to return to its starting state. The faster we move through the air, the harder it pushes back. But that's because we've pushed it further aside faster. Common construction materials are plastic, fiberglass and other composites. |
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2.3.4 Column Fairing Mounting Considerations |
| Vibration loads are very important since everything on the kart is excited by the rotating components. The column fairing tends to suffer the most since its mounting brackets tend to be longer than any other component's mounting brackets. The key to making good mounting brackets is to avoid fatigue related failures. The bracket should be such that it doesn't bend back and forth during motion. The bracket must be stiff. This applies to all brackets used for bodywork, but particuarly those used for column fairings. |