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Zeyad Gamal
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Group: Forum Members
Posts: 17,
Visits: 118
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Hi guys, We are participating in the shell Eco marathon competition where we manufacture fuel efficient cars. Due to rule changes for the 2019 season, we are now required to have a door on each side of the car. So we are now required to make a door on the other side of our current vehicle. I was wondering if anyone has any suggestion on how we can cut the shape of the door and then put the part we cut back in its place and add a hinge to it ? The main issue is that if we cut the door we will have a tiny gap when we put it back again, anyone got any idea how we can fix that ?
The body is made from carbon fiber and epoxy resin, manufactured by resin infusion technique.
 
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Steve Broad
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Group: Forum Members
Posts: 408,
Visits: 4.1K
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Looking at the fit of the windscreen and light covers, the gap caused by a thin saw cut will be small in comparison :-)
However, if you plan to improve the fit of these items to improve the aerodynamics, then you may need to do something to help the air past the door gaps. One option would be to glue a small strip along the rear edge of the door, overlapping the gap.
With regard the the front edge of the door, perhaps a rubber strip would work?
This may or may not help, depending on whether any aerodynamic gain is offset by the increased weight. The air that will be affected is the boundary layer, which isn't moving relative to the car so I am not sure whether small door gaps will have any affect on aero efficiency.
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Furrari
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Group: Awaiting Activation
Posts: 63,
Visits: 99
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Hi. Looking at the overall car I think the small gap around any doors you add will be very small in comparison to other problem areas. If you are realy bothered about this, do the regs allow tape over the joints.
In my opinion the biggest Aero problem is the drag imposed by the large amount of clearance around the wheels, particularly the back. These areas need to be drastically tightened up with the wheels filling the wheel apperture. Further improvements in this area would be to add covers to both the inside and outside of the wheels.
The aero of the edges of the windscreen area could also be improved by adding a big a radius to the outside corners to promote a better boundary layer. This could further improved by adding a curved blade or vane, about 2” clear of the corner and slightly forwards to guide the air coming off the screen down the side of the car.
A small splitter on the front would also help by raising the pressure centre at the front, channelling the air over the top of the car rather than underneath. This splitter would ideally need to be 3/4” clear of the ground but I don’t know if conditions will allow this.
I can’t tell from the pics, but is the floor a continuous, flat surface as it needs to be as each change of surface will cause drag. A diffuser would also help as it would reduce/fill the vacuum left by the car behind it.
All this lot is easy to say but not so easy to do. Keep up the good work.
M
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Warren (Staff)
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Group: Administrators
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As a simple fix to get a recessed lip around the door, cut the door out, using flash tape or polypropylene parcel tape tape over the inside of the door around the edges (so the resin doesn't stick.), Tape the door back in to place from the outside. Wet lay up a flange on the inside on the body and overlapping onto the tape on the door. Allow to cure, remove door and tidy up the rough flange, cut it to uniform size and sand any flash off and shape it so the door sits nicely on the flange.
You could go further by bonding some strip a few mm thick onto the inside of the door before covering in tape and laminating the flange. That way the flange would be recessed further than the door and you could then use some foam strip on the flange to give a nice seal around the door.
Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant
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Furrari
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Group: Awaiting Activation
Posts: 63,
Visits: 99
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Hi, me again.
Looking at the pictures again, just a couple of questions.
Do you have any window glass. If you haven’t the drag will be incredible.
Are you allowed to fit a valance to the rear wheel area so there is no cut out. Don’t know the regs, but it may have to be removable.
It looks as though there is a flange sticking out past the body line round the wheel arches and the windows. Is this needed as it will cause a lot of drag and turbulence. It will break up the boundary layer. If stiffening is needed can this flange go on the inside.
M
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Zeyad Gamal
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Group: Forum Members
Posts: 17,
Visits: 118
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+xHi, me again.Looking at the pictures again, just a couple of questions.Do you have any window glass. If you haven’t the drag will be incredible.Are you allowed to fit a valance to the rear wheel area so there is no cut out. Don’t know the regs, but it may have to be removable.It looks as though there is a flange sticking out past the body line round the wheel arches and the windows. Is this needed as it will cause a lot of drag and turbulence. It will break up the boundary layer. If stiffening is needed can this flange go on the inside.M We use polycarbonate instead of glass as it is much safer and glass might shatter. The side windows are open only because the car is not running and it gets too hot inside, but during the competition the side windows will be covered. I was not very clear with my question but the main reason I'm worried about the door gap is mainly because it might cause problems in opening or closing the door, or even make the installation difficult. The main concern is not aerodynamic performance as we have much bigger gaps already, and because the car usually runs at very low speeds (20 kmh avg).
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Steve Broad
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Group: Forum Members
Posts: 408,
Visits: 4.1K
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+x+xHi, me again.Looking at the pictures again, just a couple of questions.Do you have any window glass. If you haven’t the drag will be incredible.Are you allowed to fit a valance to the rear wheel area so there is no cut out. Don’t know the regs, but it may have to be removable.It looks as though there is a flange sticking out past the body line round the wheel arches and the windows. Is this needed as it will cause a lot of drag and turbulence. It will break up the boundary layer. If stiffening is needed can this flange go on the inside.M We use polycarbonate instead of glass as it is much safer and glass might shatter. The side windows are open only because the car is not running and it gets too hot inside, but during the competition the side windows will be covered. I was not very clear with my question but the main reason I'm worried about the door gap is mainly because it might cause problems in opening or closing the door, or even make the installation difficult. The main concern is not aerodynamic performance as we have much bigger gaps already, and because the car usually runs at very low speeds (20 kmh avg). At that sort of speed, why not simply velrco the doors on?
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Zeyad Gamal
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Group: Forum Members
Posts: 17,
Visits: 118
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+x+x+xHi, me again.Looking at the pictures again, just a couple of questions.Do you have any window glass. If you haven’t the drag will be incredible.Are you allowed to fit a valance to the rear wheel area so there is no cut out. Don’t know the regs, but it may have to be removable.It looks as though there is a flange sticking out past the body line round the wheel arches and the windows. Is this needed as it will cause a lot of drag and turbulence. It will break up the boundary layer. If stiffening is needed can this flange go on the inside.M We use polycarbonate instead of glass as it is much safer and glass might shatter. The side windows are open only because the car is not running and it gets too hot inside, but during the competition the side windows will be covered. I was not very clear with my question but the main reason I'm worried about the door gap is mainly because it might cause problems in opening or closing the door, or even make the installation difficult. The main concern is not aerodynamic performance as we have much bigger gaps already, and because the car usually runs at very low speeds (20 kmh avg). At that sort of speed, why not simply velrco the doors on? Because of the safety regulations, the doors must be easily opened from the inside and the outside, and must lock properly. Any kind of tape is prohibited as it might trap the driver in case of an emergency.
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Steve Broad
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Group: Forum Members
Posts: 408,
Visits: 4.1K
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+x+x+x+xHi, me again.Looking at the pictures again, just a couple of questions.Do you have any window glass. If you haven’t the drag will be incredible.Are you allowed to fit a valance to the rear wheel area so there is no cut out. Don’t know the regs, but it may have to be removable.It looks as though there is a flange sticking out past the body line round the wheel arches and the windows. Is this needed as it will cause a lot of drag and turbulence. It will break up the boundary layer. If stiffening is needed can this flange go on the inside.M We use polycarbonate instead of glass as it is much safer and glass might shatter. The side windows are open only because the car is not running and it gets too hot inside, but during the competition the side windows will be covered. I was not very clear with my question but the main reason I'm worried about the door gap is mainly because it might cause problems in opening or closing the door, or even make the installation difficult. The main concern is not aerodynamic performance as we have much bigger gaps already, and because the car usually runs at very low speeds (20 kmh avg). At that sort of speed, why not simply velrco the doors on? Because of the safety regulations, the doors must be easily opened from the inside and the outside, and must lock properly. Any kind of tape is prohibited as it might trap the driver in case of an emergency. I doubt that velcro would stop someone getting in or out of the car, a tug or a kick and job done! As a bonus there is no risk of a lock failing to open :-) However, regs are regs.
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Zeyad Gamal
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Group: Forum Members
Posts: 17,
Visits: 118
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+x+x+x+x+xHi, me again.Looking at the pictures again, just a couple of questions.Do you have any window glass. If you haven’t the drag will be incredible.Are you allowed to fit a valance to the rear wheel area so there is no cut out. Don’t know the regs, but it may have to be removable.It looks as though there is a flange sticking out past the body line round the wheel arches and the windows. Is this needed as it will cause a lot of drag and turbulence. It will break up the boundary layer. If stiffening is needed can this flange go on the inside.M We use polycarbonate instead of glass as it is much safer and glass might shatter. The side windows are open only because the car is not running and it gets too hot inside, but during the competition the side windows will be covered. I was not very clear with my question but the main reason I'm worried about the door gap is mainly because it might cause problems in opening or closing the door, or even make the installation difficult. The main concern is not aerodynamic performance as we have much bigger gaps already, and because the car usually runs at very low speeds (20 kmh avg). At that sort of speed, why not simply velrco the doors on? Because of the safety regulations, the doors must be easily opened from the inside and the outside, and must lock properly. Any kind of tape is prohibited as it might trap the driver in case of an emergency. I doubt that velcro would stop someone getting in or out of the car, a tug or a kick and job done! As a bonus there is no risk of a lock failing to open :-) However, regs are regs. Agreed. However the regulations are there to simply stop people from abusing such ideas, its a student competition, and a single injury will not fair well in the media.
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