Limitations of rake on my closed wheel flat floor race car

[turbotoaster]

hi guys,

Been reading this forum for a while, more so on information outside of the f1 circle as there are alot of open and clever chaps on here.

Anyway I was wondering if anyone wanted to pitch in (pun intended) on the limitations of chassis rake.

Now we know all about the Red Bull way of doing things but that having a front wing makes it a little bit different than my car.


Here attached is a couple of pics so you can see what the car is, fully flat floor, splitter also has front diffusers.





Currently ran with a chassis rake of 1.5 degrees, but as with most production based cars your always front limited when it comes to aero, after meeting simon mcbeath he thinks even with my relevatively small wing 250/110 chord I wont be able to max it out and still maintain a 40/60 aero balance.

Since im running plenty of rake currently to try and push the centre of pressure forward, im happy to increase rake more if i can gain more front downforce and increase the AofA on the rear wing to increase overall downforce.

Been reading Kats this morning to try and get an understanding and looking at the graphs, they only show up to 1 degree but the angle of increase makes me think that it will still increase past that rake angle up an to a point.

For reference the leading edge of the splitter is 60mm from ground and will not decrease below that from the rake change, so the underbody and diffuser will always be supplied with a good source of air.

Also for reference the current rubber skirts havent been setup for the final ride height, but whatever chassis rake is decided upon they will be adjusted to be horizontal to the ground(40mm for regs) as they are to low.

Any questions please ask and I will do my best to answer

Thank you in advance

Lee

[DiogoBrand]

Since you don't run at F1 speeds and don't have nearly as much downforce, or downforce as complicated, my guess is that your rake angle should be determined by mechanical grip rather than aerodynamic grip. Meaning you should adjust it to balance under/oversteer rather than prioritizing aero.

[godlameroso]

How are you dealing with pressure build up in the front wheel wells? *NM I didn't see the vents on the first picture.

[rjsa]

How are you dealing with pressure build up in the front wheel wells? *NM I didn't see the vents on the first picture.

Look again.

[turbotoaster]

How are you dealing with pressure build up in the front wheel wells? *NM I didn't see the vents on the first picture.

large vents plus please see picture below and you can see how much i have sculped the bodywork in behind the front tyre to help with extraction

[turbotoaster]

Since you don't run at F1 speeds and don't have nearly as much downforce, or downforce as complicated, my guess is that your rake angle should be determined by mechanical grip rather than aerodynamic grip. Meaning you should adjust it to balance under/oversteer rather than prioritizing aero.

the car doesnt have a massive amount of downforce, its circa 400kg at 100mph when balanced 40/60 to match static weight and from testing at 300bhp it reaches aero vmax at 135mph, with the plan to turn that up to 400bhp im expecting its vmax to be 145mph.

Thanks for your advice

[godlameroso]

You seem to have thought this out pretty well. The only thing I can advise is to start making detail changes to work the airflow a little more efficiently. For example I see you've gone to great lengths to vent pressure in the wheel well but the air coming off the opening is still pretty turbulent maybe some flow conditioners directly behind the front wheels could help in that regard. The sharp walls on the rear diffuser lowers it's effectiveness, perhaps it's not easy for you to do so, but smoothing out the transition of the horizontal fence and the vertical section would have a big impact. Perhaps mounting the rear wing lower and further back would allow the diffuser to help the rear wing allowing you to run a bit less wing and less drag with roughly the same amount of downforce. When designing aero shapes, there's no shame in copying nature, the people I used to work with would always look to nature first when faced with an aero problem. Front splitters for example are just barbaric iteration of a stingray type shape. Nature has had billions of years to optimize shapes for specific purposes, even something as mundane as the skin of a shark can help with reducing aero drag. I'm sorry all I can do is bounce ideas back and forth, and hope it inspires you to investigate further.

[turbotoaster]

You seem to have thought this out pretty well. The only thing I can advise is to start making detail changes to work the airflow a little more efficiently. For example I see you've gone to great lengths to vent pressure in the wheel well but the air coming off the opening is still pretty turbulent maybe some flow conditioners directly behind the front wheels could help in that regard. The sharp walls on the rear diffuser lowers it's effectiveness, perhaps it's not easy for you to do so, but smoothing out the transition of the horizontal fence and the vertical section would have a big impact. Perhaps mounting the rear wing lower and further back would allow the diffuser to help the rear wing allowing you to run a bit less wing and less drag with roughly the same amount of downforce. When designing aero shapes, there's no shame in copying nature, the people I used to work with would always look to nature first when faced with an aero problem. Front splitters for example are just barbaric iteration of a stingray type shape. Nature has had billions of years to optimize shapes for specific purposes, even something as mundane as the skin of a shark can help with reducing aero drag. I'm sorry all I can do is bounce ideas back and forth, and hope it inspires you to investigate further.

I agree on the diffuser, its on my list to do as i need to pull it off to run some wiring on the loom.

I cant move the wing any further back because of MSA regs

I would like to vent the front wheels more but im only allowed 50mm above the front axle, as you say the air is pretty turbulant and simon mcbeath said its hard to use it for anything at that point, would the conditioners clean them up a bit so i can make use of the air?

Alot of the big CFD developed time attack cars have just simply gone for max venting and done nothing behind the wheel, if you good 'under suzuki' developed by andrew brilliant and 'rp968' which was developed by head of caterham f1 aero(forgot his name so i copied them

[godlameroso]

They would certainly help, Super GT teams spend a lot of money controlling wheel wake.

Notice how the front wheel wake is directed towards the side exhaust, also look at the rear there are "boxes" with flow conditioners directly behind the rear wheels.

[turbotoaster]

They would certainly help, Super GT teams spend a lot of money controlling wheel wake.

Notice how the front wheel wake is directed towards the side exhaust, also look at the rear there are "boxes" with flow conditioners directly behind the rear wheels.

Where are you thinking I should aim the air from the tyres, up towards the intercooler duct?

the rear im afraid i cant do alot with as the rear clam that you see I designed to be fully tilting to allow me access to the enginebay, the clam is bolted to the wing uprights which are in turn bolted to the chassis.

I did try and come up with a solution but it would stop the clam from moving

[godlameroso]

Could be, it certainly works for the new NSX and Ford GT, LMP1 cars use similar strategies.

Are you allowed to run winglets off the rear diffuser?

[Paul]

Are you worried about drag? Maybe dropping downforce at the rear by having a shallower rear wing will improve both the balance and lap times?

[turbotoaster]

Could be, it certainly works for the new NSX and Ford GT, LMP1 cars use similar strategies. https://porschenewsroom.s3.amazonaws.co ... al_720.jpg

Are you allowed to run winglets off the rear diffuser?

i will have a look and see what spare material i have around and see if i can make some vertical strakes to direct the air away from the car.

I can do what i like with the diffuser, im at the limit interms of how far back from the chassis it can be, but width is no issue, I did make some rear tyre winglets at one point but decided for the moment they werent worth it for the moment and they will be a pain to support will all the clam movement

[Fifty]

They would certainly help, Super GT teams spend a lot of money controlling wheel wake. http://www.inopowers.net/images/2016/05 ... SPORTS.jpg

Notice how the front wheel wake is directed towards the side exhaust, also look at the rear there are "boxes" with flow conditioners directly behind the rear wheels.

Am I the only one who can't see this picture? If not, could you find another link? In trying to follow along so I can steal ideas!!!!

[godlameroso]

Look at DTM cars they have a similar philosophy.