Underfloor and Body design of Greenpower Car (similar to Electrathon)

[stealth]

Sorry, I meant the F24 car with the outrigger, thanks for the info. Planning to have single speed at the moment for this car since it's easier to do and more reliable. In the future, I might swap out the rear subframe to one that would allow multiple gearing to see what the difference would be which would be interesting.

Having cambered wheels (10 degrees) does improve the aerodynamics of the car, reduce drag and especially the frontal area. The front wheels with their space requirement for full steering lock means that they are widest part of the car and minimising this will also help the airflow stay attached to the surface for longer. I have tested this using different models in my flow simulation software.

One of the most efficient Shell Eco-Marathon cars ever, called PAC Car II has -8 degrees of camber, they investigated the effect that cambered wheels has on the roll resistance and found out that it doesn't add too much and 8 - 10 degrees is the sweet spot for amount of camber vs rolling resistance. If the rolling resistance was too high, they wouldn't have done it.
ETH - PAC-Car II - Aerodynamics
5.jpg Photo by neilcooper | Photobucket

[stealth]

Hello everyone, been a long time since the last post and a lot has happened since then. Over the summer, I have been built my new car and only just managed to make to the last three races including the International Final. The build took about 3 1/2 months from start to finish and took hundreds of hours to complete but I'm fairly happy about how it all came out.




The chassis is a carbon fibre semi-monocoque that has been made on a massive jig, using a laminate type construction with 10mm foam core and a heavy carbon skin on each side. The top is the same, except with fibreglass to reduce costs. Underneath the car, there is a tunnel between the wheels to reduce FA and improve rear end aerodynamics as mentioned earlier in the thread. It uses the mandatory 240W electric motor and 2 x 12v car batteries, has 24 ah capacity when discharged 23-25A. Weighs about 65 - 70 kg without driver, but including batteries and motor.

I went to start line of the first race, with no practice or testing all, and managed to finish 6th place in F24+ which has a ultra-competetive field. I went to the final being a little bit more prepared, and was battling hard against other teams for the entire hour race, Finished 5th but only 14 seconds within 3rd place. out of a field of almost 40 cars. There was about 5 - 6 cars within a minute of each other at the end of the hour so was a well earned result. I will be improving the car for the next year with some aero tweaks and weight saving.

Also since you lot like your MPGs etc, I have also worked out my car's MPG equivalent, probably not too accurate but within the ballpark. Don't know whether it's a record or not for this forum

36,650Wh in a gallon of petrol.
36 miles in a hour race.
576Wh used in the race
16Wh/mile
36,650/16 = 2290 MPG!

You can also follow me on Twitter for any more race or build updates.
https://twitter.com/Stealth_Racing

[Bicycle Bob]

I did the math for a foam-core monocoque velomobile, and for the required strength, the skins were about as thick as good paint. What they really need is toughness - maybe aramid fiber over airex foam, to minimize the extra weight needed to resist tearing and punctures in the real world. You have to think more about how it will flex, and try to take advantage of both the rigid and flexing aspects of the overall shape.
In a crash, carbon does not absorb much energy before breaking into bits, whereas a Spectra or Aramid structure will take a beating slowing you down and turn into a protective bag. They may need a few runs of carbon or 'glass in the compression zones.

[Fingie]

I've been thinking of building a EV velo, too.

the regulations were loosened a bit.

[freebeard]

That looks really good. I see it has the horn-shaped diverter and the drains on either side of the cockpit.

Another alternative to carbon fiber is basalt. Similar strength and it bends instead of shattering.

[Joe of Loath]

Looks great! Similar design and specs to our F24+ car, although we used a steel chassis with plywood semi-monocoque.

I can't remember reading in the thread - do you have any previous experience racing Greenpower (or any other track racing)? If you don't, expect heaps of improvement as your driving skills improve. A fast car is all well and good, but working out how to navigate Goodwood without lifting off or braking is worth about 10-15 seconds!

[kach22i]

Originally Posted by stealth

.........Underneath the car, there is a tunnel between the wheels to reduce FA and improve rear end aerodynamics

Could you please post a photo of the underside?

Something under construction would be fine.

I would hate to think about scratching up such a beautiful finish by flipping it over.

[freebeard]

Permalink #45



Much like the aerocivic, with [sponsons?] filling between the tires.