kb525

colors are changes in air pressure. Theres a graph top left that shows the color range. Typically blue is low and red is high. What you clearly see here is HUGE turbulence behind the car which is even more extreme when runing without a floor. In reality because of the power to weight of rc cars pure downforce is probably more important than drag (except for a 'chute)

im interested in knowing the air speed and if you used the car in a floating state or on the ground

MatsNorway

The wind tunnel got a kind of a ground but it gives drag (see closely at the beginning with the 2D slice view on. To prevent this from having a big effect you need to have a fine mesh.

Model is standing on the ground.
When it is not the air goes below the wheels.

Speed is 100km`t

As you say drag should be secondary to downforce.
At least when you got no power limits.

The CFD is probably not accurate enough to give good design clues. But some pointers can be given.



For instance. Where the rear "wing" stops there is a big (turbulent)
low pressure zone below/behind it. More visible on the "real" model as the lower section has moving air.

Im guessing you would need that bit of lexan to prevent the body from buckling.

But by making small holes/sections in it you would be able to either reduce the drag or improve downforce due to the air on the inside getting sucked out better.

The flat bottom model got worse coeficient of drag. (grafh) And it is probably related to that. It is dodgy to comprare the models in the video as is. Due to different sizes on the wind tunnel and mesh.


Another hot tip for those who design these cars and have issues with blow
overs on the straights. Make the front of the chassie as narrow as possible
so that the air can go easier into the body rather than provide lift on the chassie. Foam bumpers etc will add lift.

But as long as Pro10 cars must be solid axle, diffusers and such will be a challenge.. If you can have a solid axle with belt drive in the senter. you get more space for tunnels. I would like to see that.

But considering the body itself gives some downforce due to the air going trough it. 1* One would need to make sure both effects works together.

1*(Must not be mistaken for a diffuser effect, its more like a ejector)

2wdrive

Thanks for the explanation. Drivers always cut the whole back out. You can always stiffen the body up with other stuff. The air can't get out fast otherwise. During the Benelux race 1 month ago i saw a pro10 with a body that had stripes of carbon on it for reinforcement

An underbody doesn't provide something we want in rc racing. It creates understeer at speed. On every pancar there is a big hole between the front suspension and it is there for that reason. We never get blow overs from speed alone. Only when we drive full speed over curbs, big bumps or twigs and stones the car can go airborn. It does not happen often, maybe once or twice a year for me. It is just part of pancar racing.

ps:
Can you adjust the simulation that the car goes through a turn instead of the air going straight over the body ? Would be interesting to see the lines then.

also would be cool to see what happens when you cut open a body behind the wheel wells? The Nissan GTP has optional panels that can be cut open. These panels are behind the front and back wheels.

Kensei

@MatsNorway

You say:"For instance. Where the rear "wing" stops there is a big (turbulent)
low pressure zone below/behind it. More visible on the "real" model as the lower section has moving air.

Im guessing you would need that bit of lexan to prevent the body from buckling.

But by making small holes/sections in it you would be able to either reduce the drag or improve downforce due to the air on the inside getting sucked out better."


How to go at it putting all of this into practice? (as in cutting a new body)

- most people cut away almost all of the material right below the rear wing? Creating turbulent low pressure zone? Therefore leave more material there? That means cut it lower? (less material cut away). Leaving approximately how much material there, for instance 1 or 2 cm? (or more?)
Thus prevent the rear wing from buckling from air pressure? And therefore more downforce is created?

- furthermore in doing so less turbulent low pressure in that area?

- on top of that by making holes or sections in the lower cut part below the rear wing drag is reduced and/or downforce is improved because the air on the inside is getting sucked out better? Is it both reducing drag and improving downforce or just one of them?

- how many holes/sections and what diameter would you suggest would work?
(to be on the safe side: these holes/sections are to be made in the lower cut part below the rear wing?)

tudor_47

Colin,
the front end widening kit will be back in shop next week.

IRS axle can be bought from IRS directly and also from rc-bodies.de in europe.
From IRS you can get a kit with all the parts needed to complete the axle : http://teamirsrc.com/index.php?main_...products_id=64


oh, our rear end widening kit is in the shop now.
/Johnny

MatsNorway

Kensei: Kensei:
I will perhaps take a closer look on it later. to see the potensial gains better. Its a done deal really, its good. do it.


Depends on the shape. Modern Prototypes has a front diffuser. They do however then ventilate the air out to the top and sides. I believe that is a bit hard to do? at least to the top.
John Stranahan on this forum (owner of the model) has been aware of this and has done improvements to the " under" body to gain downforce. He has pictures of it in here somewhere.


http://lemansprototypes.over-blog.it...-69413568.html
http://lemansprototypes.over-blog.it...2-6139447.html

A couple of degrees perhaps but not much more. It would only simulate a slide.


If they are on the top of the body behind the wheels:
The centrifugal effect and so on from the wheels are not possible to simulate. with this program.
And they contribute hugely to such designs in full size cars. ofc if the air goes out there without it it will give bigger gains in a real life situation. Will check it out.

If you mean behind the wheels on the side it would give gains vs a closed wheel pit. But since the bodies are open underneath i think that a huge cut out/arc like shown below would reduce the area the suction gets to work at. Unless you give it a floor below.
http://www.oldracingcars.com/Images/...03-800x430.jpg
http://www3.clikpic.com/Turbobanana/...6_edited-1.jpg
http://www.car-stock-photos.com/phot...an-am_car.jpeg
http://www.theepochtimes.com/n2/spor...ced-61714.html
the last one got a "floor/lip" close to the cutout to prevent air from going under.

They did not do it back then. Even tho it seems so obvious.
http://www.flickr.com/photos/22166506@N06/4990865138/

rokosam

Preparing my Blitz P908 for the real thing!!!



By rokosam at 2012-07-30


By rokosam at 2012-07-30

tudor_47

I've got one of thoose too waiting to get mounted..
how would it compare to the serpent porsche 962?

rokosam

Sorry, I have only tested the "oficial" Protoform P905B by the moment, but one friend has tried this and it gives a lot more steering compared with the Protoform and better times with his 235 CRC Calandra GenX10

Kensei

@MatNoway

Kensei:
I will perhaps take a closer look on it later. to see the potensial gains better. Its a done deal really, its good. do it.


What you mean is cut lower under the rear wing and than make holes in it?
Any experience as to how much lower, in cm's and how many holes of which diameter?

closs

i' ve tried this body but it's way too nervous for me might be good on front end lazy car
make sure you don't mount it too much forward
also it's slow on straight line too much drag
when you first try i don't sauce the front tires and run 40's
if i can see right it's seems your car is a hatzenbach they have loads of rear traction
so it might be better than on my speedline

closs

had some time today tried the nissan with the holes open no change at all
understeer fest all the way
if someone finds a way to make this body turn let us know
i quit loosing my time with it

2wdrive

I am still scratching my head how you can put the Nissan GTP on the speedline. The frontwheels of the speedline is 228mm wide but the body is 225mm at the front? I think I am missing something?

Can you measure the width of the front wheels of your speedline and the Nissan GTP? Maybe I was told wrong. I want to try the Nissan GTP on my other car with 227mm wide frontwheels but don't have the body yet.

MatsNorway

Have you tried the body rokosam posted?

rokosam

This Blitz worked very well with my friendīs Calandra GenX10 235 (he ended 2nd at the last race, well I didnīt race that day..) , I will post my impressions with it and yes thereīs a beloved RCDevil PC10H3X pro10 chassis (Ascari/Hatzenbach) under that body.