Over and Under or around the sides

[greenpower dude reloaded]

Stage one will be evaluation of the current body and evolving this shape for better results.

Not to criticise your inspired and inspiring work, but considering your race reports, wouldn't it be more logical to sort out your mechanicals (chain/batteries/engine operating point/...) first, or does the shape of the car have notable repercussions on said mechanicals?
The old: In order to finish first, first you have to finish. (or in endurance terms, keep your car on the track).
In any case, good luck.

The problem is i've not been updating you all enough. Obviously as we completed full race distance, the chain stayed on, the problem was the tension kept altering at Dunsfold and prior to that it was a different chassis which had some flex under load, so we sorted both of those out.

I have somebody looking into the batteries for me, and the shift map used for this last race is only a touch off being optimum maybe it should be dropped to 1740rpm, but that does depend purely on the condition of the batteries, which is nigh on impossible to judge accurately, we are working on that two though.

The other difficulty as mentioned before is that the car is garaged 150miles away, so really, the easiest thing to evaluate is the aero.

[BreezyRacer]

The problem is i've not been updating you all enough. Obviously as we completed full race distance, the chain stayed on, the problem was the tension kept altering at Dunsfold and prior to that it was a different chassis which had some flex under load, so we sorted both of those out.

I have somebody looking into the batteries for me, and the shift map used for this last race is only a touch off being optimum maybe it should be dropped to 1740rpm, but that does depend purely on the condition of the batteries, which is nigh on impossible to judge accurately, we are working on that two though.

The other difficulty as mentioned before is that the car is garaged 150miles away, so really, the easiest thing to evaluate is the aero.

Congrats on the progress you've made for the season. It's essential that you be able to look back and reflect on the program's growth. Time to set some new goals. It won't be long before you'll setting the pace instead of matching it. Just keep pushing!

When you get some time to figure your next focus let us know. We'll be here to provide our opinions about what we think works.

[tok-tokkie]

Thanks for the update. It has been a very interesting saga. Sorry that the result was not what you had aimed for.

[marcush.]

to my mind green power dude is on the right track .

congrats anyways from me !

Marcus

[Carlos]

Congratulations on a good effort of steady improvement in a difficult season of development.The design is maturing. The car is very quick. This is one of our best threads. Very gratifying to see how design elements from the conversation are incorporated into the design, especially the influence of Ciro and Slimjims suggestions on the body design. Most of the problems are teething problems and I'm sure they will be ironed out for the 2010 season. Looking forward to it already.

[marcush.]

question to the aero guys following this thread:

you mentioned VGs to be mounted in front of the front of the car body as well as in front of the drivers helmet

just out of curiosity , what is your feeling of the dimensions and actual position of these devices?

For luke this may be a do or die decision as he´s facing a maximum length of the vehicle restriction so anything forward of the car will reduce total length of the
main body...

second ,with the cockpit opening not allowed to be sealed or closed by doors or panels ,would it be best to curl the edges of the body inwards or outwards forming a
half pipe rail ?

Obviously one could customize Lauras Driving suit (or helmet ?) to close the opening with something collar like ,just like a tube of a bike tyre.....would look funny out of the car but if it lowers drag.. she could surely learn to live with that ...its also characterbuilding...
and as Rossi and co are driving bikes with a humpback ....it´s not so bad after all...

[BreezyRacer]

question to the aero guys following this thread:

you mentioned VGs to be mounted in front of the front of the car body as well as in front of the drivers helmet

just out of curiosity , what is your feeling of the dimensions and actual position of these devices?

For luke this may be a do or die decision as he´s facing a maximum length of the vehicle restriction so anything forward of the car will reduce total length of the
main body...

second ,with the cockpit opening not allowed to be sealed or closed by doors or panels ,would it be best to curl the edges of the body inwards or outwards forming a
half pipe rail ?

Obviously one could customize Lauras Driving suit (or helmet ?) to close the opening with something collar like ,just like a tube of a bike tyre.....would look funny out of the car but if it lowers drag.. she could surely learn to live with that ...its also characterbuilding...
and as Rossi and co are driving bikes with a humpback ....it´s not so bad after all...

Here's a link to a pic of what I would do. The bright green is a floor extending beyond the front of the car, like a splitter. That will keep airflow from going under the car, but mainly it's to mount a large VG winglet onto, standing straight up with a squared end. It should have a pretty large chord, meaning it's kind of fat looking, as wings go. The intent here is to create a large vortex ahead of the car to reduce drag on the nose.

Then in red is a similar but smaller VG in front of the driver's helmet and roll hoop. It should be high enough that it's out of the boundary airflow and high enough that the vortex it creates hits at about the face shield level or higher.

In blue are locations for small VGs on the surface to keep the boundary layer glued to the surface change where the body starts to taper down. I wouldn't worry about tapering the sides of the body. You can leave them flat.

The dotted line at the back is for a diffuser at a very gradual angle, about maybe 4-5 degrees. That will reduce drag further. Going with more angle will increase drag though so keep the angle low. And of course you MUST have a full floor on the car with as little openings for tires, etc as possible.

In yellow is a cockpit air dam. Extend it all the way around and tie it smoothly into the roll hoop with a nice curve that blends into the curve of the roll hoop. This will control the boundary air around the cockpit area and keep you from creating turbulence in the boundary air where the roll hoop meets the body.

There is no need or desire to radius the corners of the body the way the CFD model was done. That design presumes a larger frontal area because your tires would have to be inside of the radiused portion, making the body frontal area larger than it needs to be. You want to minimize that frontal area. In addition the radiused corners of the model encourage airflow from the top to roll onto the sides of the vehicle, creating lift, of course in a minor way but it does happen. Don't let the airflow from the top spill onto the sides. A square edge does this nicely. If you wanted downforce you could even make the sides higher than the top, creating dams along the sides. It would increase drag somewhat though. BTW, if you need to make the sides around the front tires out of flexible material and then build a frame around the front tires so you can build the body right up against the front tires. That might help you to minimize frontal area even more. Oh, and shorten the track of the rear axle. That will help the car to turn.

Since most of these things are "tack ons" you could easily test the nose VG, the cockpit VG, and the small body VGs in coast down testing.

Keep in mind that with the nose and cockpit VGs you are creating a vortex at the top edge of them so the tops should be in line with your maximum drag areas. You might try tuning them by adjusting the height of the VGs, though the pic will give an idea of what I would start with.

The tail of your body tapers quite quickly right now. If you have the length available I would taper it at a slower angle to help ensure that the boundary layer stays attached. A max 10 degree angle of change is a good thumbnail angle to keep boundary flow intact.

Of course if you do these things I would truly love to hear the results of your testing. Not so much if you win races, though that is of course the goal. Do the coast down testing and see if it makes a difference. If it doesn't then don't use these ideas. I'm very sure they will though.

One last thing .. in the pic the car is maybe 10 feet from the pylons. Keep that car tight to the pylons in the corners to shorten the path as much as possible. If the car starts to scrub speed at those turning radiuses work on the ackerman to reduce that scrub as much as possible. You are going to get some scrub from your solid rear axle setup but it might not be too evident with your low drag tires. If you corner fast enough you might consider some tricks to eliminate that scrub problem too. I have some ideas on that for later on.

http://picasaweb.google.com/lh/photo/c- ... directlink

[marcush.]

open question still is if it makes sense to reduce the total body length (effectively this would have to be a wheelbase reduction or a tail length reduction)
to optimise for the leading edge VG ....
I estimate you are talking of a VG with a chord length of around 150 mm + some distance to the bodyitself so we are talking about 200-250mm reduction of total body length available...or roughly 10%
I guess this reduction would also need to be quantified in aero behaviour first before starting with the VG implementation.

would 2 differnt track width front and rear not increase frontal area ? Ignoring the regulation minimum of 500mm track would the airflow convergence below the body call for narrower track or is this simply to achieve a more teardrop shape in planview?

[BreezyRacer]

The teardrop pattern in plan view would reduce reduce drag somewhat but also keep in mind that as the body tapers back the top airflow will bleed down onto the sides so you would have a problem keeping the boundary layer attached around and behind the roll hoop area. When you also throw in the more difficult fabrication I think it becomes a wash.

As for body length, a longer body is more aerodynamic so whatever you do you want the body to be at max length. The part that needs to be lengthened though is where the body starts to taper back to the tail. As for your dims on the nose VG, I would say that's a good place to start. I would add that the chord should be thick to create a nice big vortex, maybe 75 mm if you can get a profile to work like that. You can get all scientific about sizing, etc but if it were me I would make the splitter and then thru coast down testing on one day in one place, try a few different sizes and heights of VGs and see if it works as planned. Just so you know, the splitter will add some drag unless you open it up with some holes/vents where the splitter meets the body. The splitter can extend out quite a lot without affecting the drag, BTW. That will give you more freedom in testing the VG location.

The main reason for the narrower rear track is to keep the rear tires out of the aero path at the rear of the car along with the fact that with a solid axle you will have less scrub with a narrower track. But you don't want the track to be any wider than required in the front either, so if you must make them both 500 mm. Just know that in addition to all this aero you should make every effort to chase out chassis scrub in cornering. Whether you can "flat foot" every corner is not the point. It's weather you lose 3 mph while cornering due to chassis/tire scrub.

Marcush, you seem to have a pretty good understanding of the rules in this class of racing where I have essentially none. Are you a competitor of our friend GreenPower, or a partner?

[flynfrog]

do the rules allow for 3 wheeled cars?

[marcush.]

nono ,it´s just curiosity driving me.. this threat is just too good not to be fueled with new input constantly ...
googled the web about greenpower F24+ racing and got the rules ... .In my view it should be the first to read , reread and read again to make sure you understand the
dos and don´ts first and out of this you get a picture in which direction to develop.
As for the solid rear ..this is of course a major point to consider ,especially with the efficiency in mind ...of course this is very much worth looking after.(we all race more powerful cars ,so we don´t think along those lines normally ,don´t we?),
I ´d say a diff equivalent is something Luke should try to implement...if it is allowed..

[BreezyRacer]

nono ,it´s just curiosity driving me.. this thread is just too good not to be fueled with new input constantly ...
googled the web about greenpower F24+ racing and got the rules ... .In my view it should be the first to read , reread and read again to make sure you understand the
dos and don´ts first and out of this you get a picture in which direction to develop.
As for the solid rear ..this is of course a major point to consider ,especially with the efficiency in mind ...of course this is very much worth looking after.(we all race more powerful cars ,so we don´t think along those lines normally ,don´t we?),
I ´d say a diff equivalent is something Luke should try to implement...if it is allowed..

Well of course, yes, start with the rules. I guess when I started replying to this thread I didn't take the time to do that. Kudos to you for doing so.

As for the rear axle I would just drive one side and leave the other side on it's own bearing unit. These cars aren't powerful enough for a diff, I don't think. I have a race car with single rear axle setup (mandated) and in that case I use front caster to hike up the inside rear in corners to fix the scrub/push problem.

[greenpower dude reloaded]

WOW Guys!! you're all great I can't believe your all soo keen on this project. It's excellent! and I really welcome all your ideas with arms wide open.

I'll see If I can remember to answer all your points.

Rear axle is fresh in my mind so i'll tell you our set up! we have a solid rear axle but thats only for mounting purposes, both wheels run on their own respective bearings and one has a sprocket mounted directly on to the 6 bolt mounting. I looked at the idea of using a tricycle diff but it lost efficiency, and i'm not yet convinced on the gains. would love to try it out but money and now restrictions on the chassis batteries very close either side of the axle mean we don't. Currently have space.

Flyn. I would love nothing more than to run a fully enclosed three wheeler, we made a pair of SEM cars which achieved 2904mpg (UK) at school almost 10yrs ago. alas neither fully enclosed OR three wheelers are permitted.

We have a very well set up, If i do say so myself. Steering set up, and a very minimal wheelbase at 1100mm and a track of 530mm minimum being 500, 530 being practical. With an incredibly minimal amount of space to turn the wheels that gives us a total width of 680 at it's widest point. I can get the height of the car down a touch though which should knock about 0.03m2 off the current FA of 0.349m2. Putting a radius on the edge will also knock a bit more off too. I'm also toying with the idea of raising the ground clearance a touch more, maybe a further 25mm to take it up to 75mm in order to knock the FA down a bit more. this could give us more scope with a sculpted underneath.

I'd like to integrate the roll hoop into the body a bit more, and have been looking at a doing just that. I want to trial a few things to try and help with the pressure behind the crash helmet. It may be VG's or maybe some sort of fairing.

I was wondering about sealing the cockpit with thin rubber that has a slit down the middle. Laura would then birth out hopefully within the alloted 6secs. It's neither a door or a removable panel as prohibited by the regulations.

Unfortunately there is a maximum length of 2800mm and unfortunately we are right on the edge now. so we would be unable to fit either a splitter or elongate the tail. A splitter may however be a good option if/when we attempt a speed run at an airfield one day. I'm also right on the cusp of cracking OpenFOAM cracking from the point of view of being able to use it, it's open source why would i try and steal it!?

VG's are something I deffinately would like to try though. As you have noticed the vehicle does taper a touch too much and could really do with being nearer 10degs as you said rather that the current 18, i'm told about 16 is where the trouble starts a few CFD runs in the past have proved that to be the case.

I tested and had hope to have for the final a "halfpipe" around the cockpit. this shakes off about 10% of our current Cd.

I'm sorry if i've missed off any points but this should be help get this thread going again!

[BreezyRacer]

Good to hear from you again! Given your short body length requirements VGs are even more important but in addition to that we have a post around here on dimpling. It's viewtopic.php?f=6&t=7546 and worth a read or two. I would do some surface texturing along the back of the vehicle as far forward as the beginning of the cockpit opening, again to deal with the angle change. Then use the VGs in addition to the texturing. The texturing will help with keeping the boundary air attached and the VGs will act higher up in the airstream, maybe 20 mm above the surface. Maybe even try some on the roll hoop too.

[marcush.]

[quote="greenpower dude reloaded"]



We have a very well set up, If i do say so myself. Steering set up, and a very minimal wheelbase at 1100mm and a track of 530mm minimum being 500, 530 being practical. With an incredibly minimal amount of space to turn the wheels that gives us a total width of 680 at it's widest point. I can get the height of the car down a touch though which should knock about 0.03m2 off the current FA of 0.349m2. Putting a radius on the edge will also knock a bit more off too. I'm also toying with the idea of raising the ground clearance a touch more, maybe a further 25mm to take it up to 75mm in order to knock the FA down a bit more. this could give us more scope with a sculpted underneath.



The raising of the floor should definitively net some gain in FA ,maybe the best way would be to open two channels in the bottom along the car ,sneaking around the seat which I estimate does not need to be more than 35cm wide ,there should be space for a good savings in crossectional area,without raising the car at all,and you could do it to serve as structural element as well .....double purpose ..always good .I guess theres scope for more than 25 mm channels in height,so you maybe can claim almost the same reduction in FA as if you were rising the whole car.plus you could do the body development in two distinctive steps,first top surface and a simple chassis ,second step new chassis with sculpted floor but identical planview-parting line.

unfortunately there is a maximum length of 2800mm and unfortunately we are right on the edge now. so we would be unable to fit either a splitter or elongate the tail. A splitter may however be a good option if/when we attempt a speed run at an airfield one day. I'm also right on the cusp of cracking OpenFOAM cracking from the point of view of being able to use it, it's open source why would i try and steal it!?

So the adoption of a VG would make a shorter tail and a shorter nose section a must,as the 1100mm wheelbase is not where you could find the required 250mm...


VG's are something I deffinately would like to try though. As you have noticed the vehicle does taper a touch too much and could really do with being nearer 10degs as you said rather that the current 18, i'm told about 16 is where the trouble starts a few CFD runs in the past have proved that to be the case.

I tested and had hope to have for the final a "halfpipe" around the cockpit. this shakes off about 10% of our current Cd.