When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I’m curious why you went with a custom swan neck versus something like the Voltex models?
Three reasons, Drag, Mounting, Balance
Start with mounting. I'm not a fan of trunk mounting wings. Extra especially on to carbon trunks. I have seen wings uprights fail in shear after they develop oscillation at speed becasue of a flimsy trunk. add enough speed and thats a really bad situation...
The ISF, at the times I am aiming for, mean high speed at the tracks around here. High enough that wing failure is a concern. This means that i would need to build custom uprights regardless of which element I went with.
Second, for balancing the downforce potential that I wanted the car to have a standard trunk mount set up was just not ideal. I would need a wing that could *easily* balance the large front splitter and aero tunnels I had planned. Option 2 in creating aero balance at the rear was to generate downforce under the car. I thought about all this while planning out the ISF and decided that one thing I wanted to avoid on this car is building a flat floor and diffuser. For a diffuser to actually work to the level that out weights the PITA.. you need a flat floor on its run up... and a flat floor on a car like the ISF with twin exhausts and rear differential is extra pain. I have ideas for down the road that are pretty radical- but we'll see if i ever wanna go down that path.
I have experience with flat floor and diffuser tuning. You can see how far back I mounted the wing and diffuser on my other car to get the aero-balance to align with the center balance of the weight.
I did not want to deal with this on the Lexus. This meant I would need to balance the car solely with a rear wing.
And finally drag. Generally with a 3d profiled wing like a Voltex id need to run around a 13* forward rake to get the numbers to balance the front of the car. At those angles something like the Voltex type 2 1600/1700 creates a lot of drag, I know this from experience running those same profiles. Could I make enough balance with a Voltex or other off-the-shelf wing? MAAYBE, but adjustments on an airfoil become less effective the closer you are to stall.
So, basically I was starting from scratch as far mounting. I'd also need a wing with larger profile and a more efficient NACA shape that would generate more down force at less wing angle. I couldnt find anything that was worth fabricating around so I decided to have a custom element built that tic'ed all the boxes.
The swan neck mounting was just a natural 'I may as well'
I also LOVE the RCF GT3 and really like the shape it gives the rear of the car.
I can’t find anything definitive, but the CCSR ISF has a trunk mount wing. I wonder if they modified the trunk any.
You clearly know more about aero than the average bear. Thanks for sharing.
They most likely did. If you look at cars that have a 'sports' winged model vs a standard wingless model they normally have some variation on bracing pucks. My s2000 CR has this, so did my fk8 TypeR. The Honda wings don't generate much downforce so it a pretty apples to oranges comparison to a gull GT wing but the factory still felt the need to add stabilizers.
This is what they look like on the s2000 Club Racer
I know the Viper ACR has them and so do the ZR1 and 1LE, those are actual GT wings. To be clear, trunk mounting can be done safely- the OEM's wouldn't sell them unless they were positive it wasn't going to be a hazard. For a dedicated track car there are better ways.
Also, I didn't mention it above but as much of a reason as any, I wanted to put the DF directly into the strut towers so there was no wasted force compressing weather stripping and flexing the body structure before acting on the shocks. You can see in the initial drawings I sent with the car to fab how I wanted to mount the wing directly into the cage.
And final result.
This means that the bars holding the wing mounts are acting similarly to a lever arm to translate the forces directly to the shock mounts. Doing it like this moves the pitch moment that is generated by the load at speed inward and applies forces centrally to the chassis. Imaging the force like a big sack of concrete you were carrying on track, You'd ideally want to place that load in the middle of the car and not hanging off the rear. Placing it central makes the whole platform easier to balance.
I can’t find anything definitive, but the CCSR ISF has a trunk mount wing. I wonder if they modified the trunk any.
You clearly know more about aero than the average bear. Thanks for sharing.
The CCS-P wing has a modified trunk, so I would say most definitely the CCS-R does.
-R
CCS-P trunk left, factory trunk right. Aluminum support brackets riveted to the underside of the CCS-P trunk circled in red. The the wing bolts through these brackets.
So the additional bracing allows the trunk to take the down force, and the pucks reduce the vibrations / oscillations in the trunk by reducing the gaps between the trunk and the body and creating constant tension?
For now I’m going to wrap up suspension and get a couple years of track time before I decide whether I want to take the car further. I still want to learn as much as possible about aero though. I think once you start aero mods, you really start to compromise the daily uses of the car, and I use mine a lot during the summer.
Sorry to constantly derail your thread Will... Every time I open it I learn something, but it leads to questions!
So the additional bracing allows the trunk to take the down force, and the pucks reduce the vibrations / oscillations in the trunk by reducing the gaps between the trunk and the body and creating constant tension?
For now I’m going to wrap up suspension and get a couple years of track time before I decide whether I want to take the car further. I still want to learn as much as possible about aero though. I think once you start aero mods, you really start to compromise the daily uses of the car, and I use mine a lot during the summer.
Sorry to constantly derail your thread Will... Every time I open it I learn something, but it leads to questions!
No, no derail at all. I dont mind one bit. That's why this thread is here.
Your plan sounds like a great one. Aero can be done at a level where it wont compromise drive ability- but its main bonuses cant be achieved unless you're already pretty comfortable on track at the limit. I find (at least here on the west coast) that people tend to rush into aero mods for whatever reason. They can actually make you develop some really bad driving habits aswell as be really difficult to exploit if you don't have a solid understanding of the fundamentals of set up and feel.
No, no derail at all. I dont mind one bit. That's why this thread is here.
Your plan sounds like a great one. Aero can be done at a level where it wont compromise drive ability- but its main bonuses cant be achieved unless you're already pretty comfortable on track at the limit. I find (at least here on the west coast) that people tend to rush into aero mods for whatever reason. They can actually make you develop some really bad driving habits aswell as be really difficult to exploit if you don't have a solid understanding of the fundamentals of set up and feel.
I've seen too much power too soon do the same thing.
So i finally got the last parts in for the exterior. Waiting on a few tech things for the remaining data- but the car is now ready to drive.
4x4 90* dry carbon ro the splitter fences. These are temporary until I get the 3d ones with the vortex generators out of the mold. I bonded little gurney flaps on the edges of this one since I am not running spats at the moment. going to do some testing and dial things in.
The are the width of the front tire edge this will hopefully do something to help the air squash under the tire.
And FINALLY the wing showed up- Its a big boy.
Just loaded the car up onto the trailer for a last min track day tomorrow. It'll be a 100% shake it down so im not really going for times (its a smaller more technical track) but ill be able to tell what sort of mechanical balance im working with as well as to just ensure that nothing falls off of it.
I must say its looking pretty tuff all together..
Now to get some sleep for the early day tomorrow. Expect a video soon.
So yesterday was good and bad. For one it was the WORST trackday as far as traffic i've been to. The organizer is sort of know for this but I had assumed that the mix of fathers day and the heat would have thinned out the car count a bit. I basically spent the whole day starting flier laps only to have to bail out of them because of much much slower cars being allowed in the session or someone spinning causing a yellow. The worst was when id set up a clean lap by managing traffic only to have the flagger release some Miatas onto the racing line as i'm coming down the front straight at 125 mph. Needless to say I wasn't able to find myself in a situation where i could get the full potential out of the car. Still though, the times i managed in the heat on this track layout are pretty impressive. This track generally doesn't suit cars of this weight but it was feeling good. I had a couple of limp mode triggers after bouncing off the rev limiter that i want to figure out- as well as some higher temperatures than i like to see (105f ambient)
I think its a couple of things as far as the cooling. #1 is was just a really hot day. Second, i think that the front ducting works so well its cramming so much air into the bay that its creating high pressure and backing up the flow though the radiator. I got a PM from someone that was there telling me that my hood was actually lifting down the front straight. I ordered a large hood vent to try and relive even more of the pressure than the vented hood already does. Also i ordered recessed louvers for the bottom of the splitter, the oem under covers have some sculpted venting just below the radiator to extract heat. I'm thinking i have to build something like that into the carbon splitter now to. Its not ideal for DF but according to data the car is running at 220-235f after two laps, so something needs to be done.
I think its a couple of things as far as the cooling. #1 is was just a really hot day. Second, i think that the front ducting works so well its cramming so much air into the bay that its creating high pressure and backing up the flow though the radiator. I got a PM from someone that was there telling me that my hood was actually lifting down the front straight. I ordered a large hood vent to try and relive even more of the pressure than the vented hood already does. Also i ordered recessed louvers for the bottom of the splitter, the oem under covers have some sculpted venting just below the radiator to extract heat. I'm thinking i have to build something like that into the carbon splitter now to. Its not ideal for DF but according to data the car is running at 220-235f after two laps, so something needs to be done.
Wow... that is pretty crazy. I would never have thought it was possible for your setup to be hitting temps that high that quickly. Definitely interested to see what ultimately fixes it.
Do you think the overly crowded track could have played a significant role as well?
Streets of Willow is kinda known for being punishing on cooling systems. Its a lot of high revving and shifting but not a lot of high speeds or straights. Its probably one of the hardest track on a car in SoCal. Likely being stuck behind cars didn't help at all either.
So last night I came up with a quick prototype piece. I built a reverse scoop and used the provisions to affix it to where the old under tray used to be.
I had to bend at around the sway bar and clearance it for the main waterline and oil filter housing..
I then added a wicker flap to the back of the splitter to help with air extraction.
This should draw quite a bit of air out from under the hood.
The big down side is it may very well kill the splitter efficiency by slowing the air under the blade down as it interacts with the slow spill off out of the radiator. Its always better to vent the air out of the hood if possible. I also made a flat piece that replaces the curved duct and meets with the splitter (much better for aero). I'm going to test them back to back and see if there's a difference in temps and shock pot travel. If there is a difference in temps i'll know that high pressures in the bay was the problem. If there was also a difference in shock pot travel ill know that the temp fix was at a trade for front aero grip and can add more hood ducting which i already bought and is being made by the carbon guy now. There's also the chance the the lower vent fix by some stroke of luck wont affect the aero loads and also help the cooling. That would be sweet but I doubt that will be the case. Cars are hard.
I've long thought making the front fender slits functional would be a big help in this space. I learned a very long time ago air never goes in where it can't get out, and if you're heating the air on the way through the cross section of the exit needs to be 2-3x the area of the inlet. Look at some of the WWII aircraft with the radial air cooled engines for thoughts on this. We argued about this a long time ago, Lexus make no claims at all for the "vents" actually venting anything before the RC F marketing material. I've also learned to be very skeptical of marketing brochure and car magazine claims. They're all too frequently based in fantasy, not engineering.
All that said, given your setup, would it be possible to open up the area at the back of the engine bay to let the air flow externally through the fender gap, or have you already done that?
I've long thought making the front fender slits functional would be a big help in this space. I learned a very long time ago air never goes in where it can't get out, and if you're heating the air on the way through the cross section of the exit needs to be 2-3x the area of the inlet. Look at some of the WWII aircraft with the radial air cooled engines for thoughts on this. We argued about this a long time ago, Lexus make no claims at all for the "vents" actually venting anything before the RC F marketing material. I've also learned to be very skeptical of marketing brochure and car magazine claims. They're all too frequently based in fantasy, not engineering.
All that said, given your setup, would it be possible to open up the area at the back of the engine bay to let the air flow externally through the fender gap, or have you already done that?
So yes I have thought about this. Assuming i understand where your talking about when you say at the back of the bay, I think were talking about venting into the rear of the front wheel well and not the back of the hood at bottom of the windshield (that area is almost always a high pressure zone and will do the opposite of venting air.)
I'm not really sure how that would work to be honest; Because I have diffusers on my splitter their efficiency also depends on the speed that air can expand and get vented out of the well.
Removing the OEM plastic used to seal the wheel well and bay may actually have a similar detriment as lifting the rear of the hood. On a car without diffusers it may be a solution if you'd already enlarged the fender vents to be as functional as I have but in my case im not so sure.
My gut is telling me on my car there is so much going on in that zone with the spinning wheels (that has its own challenges), tire squirt off the 295 width tires and the diffusers to really be sure. The trade off on DF from the diffusers may be worse than the air vent and wicker i made and actually may make the high pressure in the bay worse. Only way to know for sure is to continue test or get into a wind tunnel. Easiest solution would be to just cut more holes in areas with the least complex interactions, like the hood. Lucky for me i'm an expert at hacking up perfectly good body panels.
06-11-20, 05:31 PM
