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Dollars spent: $50 on the metal, had the wood
Hours spent: 5+
How effective: 2: Huge difference in front down force, seems to have significantly smoothed airflow around front wheels. Needs coast down testing this weekend. Planned to test at Track Night event this week but was rained out
0=slower, 1, no improvement, 2 =slightly better,3= big improvement
Materials used:
Home Depot Speed Shop (TM) metal, 5/8 Birch 5 layer ply
For a while I've been wondering what can be done to improve the aero on the Exocet. Despite being light and quick in the corners, over 80mph it's a dog. At Atlanta Motorsports Part a mildly worked 1.8 Miata was a match or even a little faster above 80, even with my
turned up to 12 psi (180+ whp). It's all about aero...
Hours and hours on the internet produced little info about open wheel car aero. I concluded that basically the best thing you can do is close in the wheels. They are reported to represent up to 40% of the drag on an open wheel car. They also apparently generate a bit of lift due to the rotation and forcing air under them.
My first step was a front splitter / wing "Prototype frame" built out of steel with mounting for a 5/8" birch ply plate. I've been looking for a way to test various Aero tweaks to the front of the Exocet. I've had mixed opinions about using a wing, air dam or combination. Also been told that this will make the car "aero dynamically unstable in yaw" which is a scary way of saying I could end up ****ed in a high speed corner.
Given the significant expertise in this forum I'm looking for input. So far I've got some video of the airflow and have tested the setup to 65 mph. It's safe, stable and definitely overkill in the full splitter configuration. For the first time I start to get rear wheel lock up under hard braking at 45 mph. Never had that before.
kart community has done the basic research as best I can tell so I'm publishing my finding to see what folks think. Open wheel is a different world than
Pull up some old formula car designs.
They have gone through myriad of changes over the decades, specially through the 70's.
Maybe even the FE design with individual wheel 'covers'?
Sixshooter, I'm digging that idea. Nice teardrop shaped wheel covers. Well beyond my fabrication ability but I'd bet they are about the lowest drag solution available based on my reading.
There have been enough issues with the stock fenders and mounts that I'm not willing to mount to the hub itself. Whatever I end up with has to be mounted to the frame and allow for suspension travel. Perhaps a similar "bullet" design in front of the wheel and still leave the back open? If I go that route then I also need to deal with air exiting the engine bay and develop good barge boards rather than the flat fire wall. Hoped to plow all of the air out of the way at the front and not worry about the area inside the wheel, but I understand it doesn't really work that way.
Looking at the 70s / 80s F1 cars, can anyone clarify if the wing designs with the end plates in the middle of the wheel are the optimal design or simply the best that was allowed by the rules.
Old F1 cars seem like a good start, but they're basically unlimited budget and they still had to comply with a rulebook. The Lovefab NSX / Enviate Hypercar is the first thing that comes to my mind when I think modern, no rules open wheel car. I think I read that Andrew Brilliant designed their aero package? Don't quote me on that.
The problem with the airplane design is that it was only a low drag effort. A wing in front of the tire could actually create useful downforce instead. I see your boards in front of the wheel on your current design and they are screaming to be laid back and create movement of air over the top of the wheel rather than just blocking and creating a huge frontal area.
Look at the front of the red car and then also the very different design of the other one. Both are trying to do what you are looking to do.
Look at the front of the red car and then also the very different design of the other one. Both are trying to do what you are looking to do.
I think not. The red car has deliberately tried to neutralise the impact of the front wheels on aero. The other has just tried to get as much df at the front as it can. I don't know enough about aero to comment on the aero comparison between the two highly different philosophies there, but in Rick's shoes I would be looking at the nose of the red car very closely. At minimum, close fitting guards front and rear (a la clubbie style) would be a good first step, and if they can feature streamlining like the aircraft spats above so much the better. Remember, the theory says the streamlining after the body in question is about 4 times as effective as that in front.
I also note that there may be some ambiguity about outcomes here - is this simply(!?) an exercise in drag reduction, or in using aero to generate lap times? It seems to be the former, but if you are tracking the car I suggest you look at the latter. Straightline speed will help the latter, but the way to fastest lap time is not to maximise top speed. It will be a trade-off between top speed (low drag) and max downforce (max drag), and the best trade-off will vary between different tracks depending on their nature.
Old F1 cars seem like a good start, but they're basically unlimited budget and they still had to comply with a rulebook. The Lovefab NSX / Enviate Hypercar is the first thing that comes to my mind when I think modern, no rules open wheel car. I think I read that Andrew Brilliant designed their aero package? Don't quote me on that.
It wasn't Andrew Brilliant. I don't recall the name however it's an F1 aerodynamicist who's also a professor at a university. Developing the aero on this car is a project that he had been working on with his class.
Its also interesting to see the evolution of designs from one decade to the next.
The exocet representing something of a 60's design. The aisdam setup from the op is somewhat similar to the designs from the 70's where the front wheels were shrouded by the front airdam/wing.
For some truly unlimited designs, check out the Adrian Newey designed Aston Martin hypercar as well as the car he designed for Gran Turismo (I believe).
Originally Posted by Leafy
Right but old 60s and 70s F1 cars are within most of our fabrication skills.
The exocet isn't an easy shape to work with. The nose is too high and wide, without enough gap between the wheels and body to create a decent channel of airflow. Are you trying to create less drag or more downforce?
If you are aiming for drag reduction, you want to create a tear drop in front of each front wheel the directs the air both up and outside the wheel. You can do the same on the rear wheel and then basically fill in all the body gabs and create as smoother flow as possible. If you are aiming for downforce instead create a scope in front of the wheel to lift the air up over. This both shields the airflow from the spinning wheel as well as create a little bit of downforce. In both cases you really want to let the air flow in and past the suspension arms as much as possible so you aren't having to divert it into the main airflow path. Creating an air dam like you have is just going to slow you down as you are effectively turning the front of the car into a sedan with a large cross section.
A flat front splitter will be partially effective as it will work over areas where there is a pressure difference due to deflection of air such as the nose area and in front of the wheels (maybe). If you are chasing more downforce you could replace it with a wing element shape more like an F1 wing but this gets hard to make. A splitter is easy and cheap and sort of works ok.
In both cases you really want to let the air flow in and past the suspension arms as much as possible so you aren't having to divert it into the main airflow path.
But the suspension arms are a drag disaster. I couldnt tell you if round tube or stock stamped are worse, teardrop shape is ok but expensive and hard. Best to try and keep them out of the air flow.
But the suspension arms are a drag disaster. I couldnt tell you if round tube or stock stamped are worse, teardrop shape is ok but expensive and hard. Best to try and keep them out of the air flow.
They are bad but to fully shield them I think is worse. There will be decent airflow under and some between. You could make a teardrop shield attached to the front to deflect the air either side.
Thanks for the input guys. I did a whole lot of additional reading and ended up doing something along the lines of what Madjak suggested. Coast down testing shows pretty decent improvement of maybe 15-20% less speed loss at 50 MPH with the design below. Also identified that under the hood is a high pressure area at speed. Installing a block off plate over the radiator significantly improved coast down with the hood on. This reduction in high pressure under the hood may also take care of my lift issues at speed. Will know more after some testing on May 1.
In stock form the car with no hood is actually more aerodynamic than with the hood. Suspect this is because despite the lack of sides, air is not extracted well from the engine bay (bunched up and tumbling against the firewall?)
As the design continues to evolve, I'm very curious about how other people have tested aero mods.
Current process is to coast down from 60 mph to a TBD speed between 2 fixed points. Controlling for other variables a minimum of 3 runs are used and averaged. The same loop is used to make sure the car is up to temperature (including a longer drive before the first run). Any run with oncoming traffic or a car visible in front of me is discarded. Testing must be done back to back to compensate for changes in air temperature, humidity, etc. There's a small impact of the loss of fuel, but if 5-10 lbs of fuel is enough to make a difference here, I'm chasing the wrong things.
Here's what I came up with. Considering changing to a "V" shape in front of each wheel and seeing how that impacts things. Also considering designs for smoothing air behind the wheels. However I can put my hand behind the wheel at 60 MPH and the air is nearly still between the front wheel and the rear wheel (not sure if this is good, bad or indifferent).
Feel like the car kind of looks like this now:
These are the upper "fender" mounts. Quite strong actually.
04-06-2017, 11:38 PM
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