Over and Under or around the sides

[greenpower dude reloaded]

Hi Goony,
the rules can be found here http://www.greenpower.co.uk/racing/rules.php we race in F24+

[marcush.]

1 Wheels out. Tiny frontal area but more draggy shape. Wheels out has never attracted me. Doesn't seem as realiable as wheels in in an endurance race. Option of banging wheels an bending critical parts, less protection for the driver. etc etc. Hasn't won a major competition for almost as long as I can remember, interestingly most of the field are wheels out.

2 Wheels In and low to the ground, Massive FA, no escaping that. Great for development, lots of space to try new things etc. Can get an excellent shape which balances the FA out.

3 High up, wheels in. anything up to 200mm gound clearance. At the end of the day you are putting kids in these cars, and there is no two ways about it rolling over is one of the most dangerous things that could happen. So we will not be persuing this route. there are many other actual advatanges to this design I'm just not prepared to persue it. If I were driving it'd be a different matter.

Why not front wheels in rear wheels out ...this way the basic shape of the vehicle could reduce in crosssection and give a proper taper more continously in x direction.
Yes I know ,the drawback is a considerable rise of licked surface you´d face and of course again ,a new chassis .

looking at the dimensions of the main components driver,Batteries and motor ,I ´d say a chassis width of around 310/320mm should be a possibility with a track of 500
mm minus tyre width something like 65/70 wide channels should be a possible aim for the floor of the car

[greenpower dude reloaded]

A four wheeler in the body of a three wheeler is something I considered before, but concerns over the mounting of the rear axle saw the end of that idea. We've got a lovely three wheeler body that we could use to do that.

The driver is about 350mm wide at their widest point and the regs require 25mm of foam either side then there is 25mm of honeycomb either side too and we are all of a sudden up to 450mm so channels in this chassis at least (and after rebuilding the chassis virtually from scratch just two months ago I really want to keep it) is unlikely still something I want to investigate though.

OK Hat eating time.... I've dropped that first shape down and the Cd has fallen! its currently reading 0.102 oohh yeahh!!! that's before any real refinement. I've already got a new profile to try!

[BreezyRacer]

Congrats on the big change. Frankly it seems mighty big change for just a ride height change but I imagine the lower nose helped break down the high drag area on the nose. Now you're fully immersed in it .. the "change this, change that" process of learning and tweaking.

BTW, what are you doing for rear view mirrors? I wonder if perhaps you lowered the bodywork between the front axle and at the back of the tire bulges place your mirrors? Of course the downside would be that the body would have to continue to raise as it goes back to cover the rear tires so it might be a bit tricky .. unless the rear tires were smaller OD.

[greenpower dude reloaded]

I'm not sure either reading was ever all that correct but it shows an improvement.. We had an a really lovely placing for our mirrors once before. They were hidden in the wheel arches of Whoosh. The plan is to hide them behind a bit of a windscreen.

I'm just reading Paraview tutorials at the moment. so we should be able to get some more useful results out of this sim.

I am currently getting a touch of negative lift so it's clear the tail now needs to be flat on the underside, much as I'd have anticipated but this was more to prove a point anyway.

so let's get developing!

pics to follow

[greenpower dude reloaded]

HAHA!! that hat shaln't be eaten just yet!! it didn't mesh properly it came out as s sort of thin triangle.

I'm going to run another sim tonight will keep you posted

[greenpower dude reloaded]

I've had no luck running the low shape again but a few modifications to the other shape saw us down to 0.33 last night. (I think that in reality it's a fair bit lower than that, this is relatively unrefined CFD quite open mesh etc.)

It had a lot of low pressure on the sides. I suspect the rounding off of the edges will ease this considerably, but I could be wrong. It may mean we can get away with flat sides and can knock the FA down a bit then.

I'm going to need to start meshing a bit tighter as well really, but I shaln't try that until I've got to a more finalised shape. It seems like we are a long way off sub 0.15 but I bet it's not as bad as it seems. I'm going to try a fairing directly behind the drivers head which designed poorly can slow you down dramatically, but correctly could lower our Cd by a lot. When Jaguar Land Rover competed last year they worked out the drivers head contributes to about 25% of all drag on one of these vehicles.

[marcush.]

I feel the low body wheels sticking out on top aproach could work very well ,as you could vover this small section of the wheels quite tightly even for the front wheels ,as you will not have a lot of sideways movement of the wheel when turning corners in this area close to the steering axis.
I could also imagine to tie the front and rear top fairings then efectively creating a fin along the main body ,this may help reducing the spilling of air down the sides.

As for the radius of the body sides to the floor ,I seem to remember that this contributes a lot to lift generation ,so the radius should not be to large?

[greenpower dude reloaded]

At the moment, the sides keep appearing to be areas of low pressure this sort of colour little bit more green anyway, i'd almost quite like to get some air down there. We'll see how it all turns out if nothing else it's worth a try.

The underneath would be rounded off though so it should balance out a little bit.



Now for a quick plee
I'm desperately after somebody who can model a crash helmet (or point me in the direction of where I can find on) for me as you can see this thing is far from accurate and I would like to start development of a cowling behind the driver soon

[marcush.]

luke ,

what sort of helmet does laura use? I remember my amazement when comparing Simpson
dragrace helmets to Arai/Bell etc some years ago .These seemed to be really huge compared to the dragrace ones for the same headsize and both carried full approval...

[greenpower dude reloaded]

Laura has an XS Caberg DNA full face helmet. I'm not sure the fact its XS actually makes a difference size wise or whether they just put more padding in?

[marcush.]

exactly.
most suppliers have only one or two helmet shellsizes and make up the sizes by different inner linings.So maybe theres an area to find a bit of FA ???

[BreezyRacer]

I would try an email , etc to the helmet company if you can find a contact.

Here's what I found at a generic CAD site ..
http://www.turbosquid.com/3d-models/mot ... del/333561

[marcush.]

Caberg website does give the following info for their current fullface helmets:

2 shell sizes for the carbon fibre helmets
only
1shellsize for all non carbonfibre helmets ,so indeed you get the same outer size helmet no matter how small the drivers head is....

[greenpower dude reloaded]

OK!! sorry (again) been busy running what seems like hundreds of models this is the best one i've managed so far.



I haven't had (until now) figures as low as the models I had somebody run for me before. Even though I ran the same models. SO although this figures sound high I don't think that the Cd is all that believable and that it's better to look at the relative improvements between designs.

The first car we tried and had someone else ran output a Cd of 0.28 on their program and 0.42 on mine.

After a lot of minor changes I have got that down to 0.26 on my software so that's a drop of 39%. The same drop on the other software (which is much closer to reality) would give us 0.17 which i suspect is about right. We also have a much smaller FA now as well.

So @ 40mph now we would require 0.3hp to over come the aero drag.

Before we started this we would have required... 0.4hp so thats roughly 70 watts saved! thats very nearly 3amps!! and when we only draw 20 that's a big difference!!