Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - View Single Post - Underfloor and Body design of Greenpower Car (similar to Electrathon)

stealth · 03-01-2016, 04:56 PM

I had a look at removing the inverted horn, and it had odd effects on the drag figures. The front section has not been changed at all. On the model that has 100mm of ground clearance, flat base, removing the inverted horn increased the drag from 5.4N to 5.9N, increase of almost 10%. The pictures shows that without the airflow that going through the horn and pushing up the wake, it allows the airflow from the top go down and push aside all of the other airflow.

However what's interesting is that for the 30mm ground clearance, the drag values are near identical. I think this is because of the size of the horn and the low ground clearance makes for a rapid expansion of the airflow which has similar drag level to having a solid back end.

It all depends on the size of the horn and the ground clearance but I think it can be used to reduce the drag if done correctly. In terms of the Cd accuracy, in terms of real world predictions, the software wouldn't be any good unless I can get some real world validation, but it's accurate and consistent for when comparing designs and their drag values.

The two rules on rollbar aerodynamics:

Aluminium or steel square or circular section roll bars are to be used and must be strong enough and of sufficient dimensions to perform satisfactorily - Means that I can't use aero profile tubing.

The top 150 mm of the roll bar must not have any fairing or other aerodynamic aid - Not really specific as I could have a fairing behind it that's mounted on the body but not attached or touching the rollbar. Kind of against the spirit of the rules but is a possible loophole so it's possible to have a plate behind it. Plus I'm only having the minimum 150mm exposed to the airflow.

Thanks for the info on the different methods. Although it would be easier to make, any sharp edges will make the air trip over and I need to make sure that the airflow stays laminar as possible for long as possible for the best performance. If I was to make another body out of corroflute, I would make it like my first body and use thin long strips and have multiple chamfers for the corners. Also incorporate the foam/fibreglass nose of the second one.
But I think I will make a fibreglass/carbonfibre bodywork that is smooth and curvy. Just need to make sure the body shape is right .

03-01-2016, 04:56 PM	#25 (permalink)
stealth EcoModding Lurker Join Date: Feb 2016 Location: Cornwall, UK Posts: 18 Stealth II - '16 Stealth Racing Stealth II 90 day: 2117.65 mpg (US) Thanks: 5 Thanked 11 Times in 7 Posts	I had a look at removing the inverted horn, and it had odd effects on the drag figures. The front section has not been changed at all. On the model that has 100mm of ground clearance, flat base, removing the inverted horn increased the drag from 5.4N to 5.9N, increase of almost 10%. The pictures shows that without the airflow that going through the horn and pushing up the wake, it allows the airflow from the top go down and push aside all of the other airflow. However what's interesting is that for the 30mm ground clearance, the drag values are near identical. I think this is because of the size of the horn and the low ground clearance makes for a rapid expansion of the airflow which has similar drag level to having a solid back end. It all depends on the size of the horn and the ground clearance but I think it can be used to reduce the drag if done correctly. In terms of the Cd accuracy, in terms of real world predictions, the software wouldn't be any good unless I can get some real world validation, but it's accurate and consistent for when comparing designs and their drag values. The two rules on rollbar aerodynamics: Aluminium or steel square or circular section roll bars are to be used and must be strong enough and of sufficient dimensions to perform satisfactorily - Means that I can't use aero profile tubing. The top 150 mm of the roll bar must not have any fairing or other aerodynamic aid - Not really specific as I could have a fairing behind it that's mounted on the body but not attached or touching the rollbar. Kind of against the spirit of the rules but is a possible loophole so it's possible to have a plate behind it. Plus I'm only having the minimum 150mm exposed to the airflow. Thanks for the info on the different methods. Although it would be easier to make, any sharp edges will make the air trip over and I need to make sure that the airflow stays laminar as possible for long as possible for the best performance. If I was to make another body out of corroflute, I would make it like my first body and use thin long strips and have multiple chamfers for the corners. Also incorporate the foam/fibreglass nose of the second one. But I think I will make a fibreglass/carbonfibre bodywork that is smooth and curvy. Just need to make sure the body shape is right .