How to design aero for a brick (aka BMW E30)... an E30 UTCC racing odyssey

We're going to participate in this year's UTCC event at NCM in the Fall and are starting the design process to add aero to our 1991 BMW 325i that we currently race in NASA's SE30 class. We want to take a homebrew grassroots approach and try to do all the design, prototyping, and fab at home. We'll see if this too is ambitious but rubbish....worth a shot! All ideas and watch-fors welcome!

Short list is a small(ish) front splitter and reasonable rear wing as we only have 158hp and Sabine's a bit of a brick so need to not go overboard with too much aero (drag). Plus, we will still be running our SE30 suspension so need to keep that in mind when doing the DF calcs. 

Splitter:

• Thinking a simple plywood splitter construction sticking out 3"-4" from the lower valence panel
• Connected to the bumper and somewhere on the frame with some adjustable support rods. Keep it simple.

Rear wing:

• This is where we might go a bit more complicated and diverge from a foam core type design
• We've designed, printed, and installed a bunch of 3D printed parts on the car so thinking we could design a wing from a known NACA profile in CAD and use our 3D printer to print sections in PETG and assemble/epoxy on rods or something
• Still needs some thinking but should be pretty skookum if we are only making a couple hundred pounds of downforce

Other misc. thinking to help reduce lap times:

• Strip as much weight out as possible
• Tape all seams and bumper/lower valence holes
• Remove wiper arms
• Maybe do something for the grill (one piece type flat panel?)
• Remove rear bumper
• Wider, stickier tires
• A few bolt-on HP adders
• Track time, track time, track time

Sabine:

This should be doable, but with printed core instead of foam.

https://youtu.be/jsT561opKrU

Minimising cooling intakes is a known drag reducer. Try covering up as much of the underbody as possible, maybe som neater mirrors? 

In reply to Cedricn :

Great vid! Yep, thinking of stripping away as many draggy parts as possible and possibly adding an undertray. 

Need to start looking at common NACA profiles to see DF #s. Need to stay mild and easier to balance with our low HP car. 

have you corner balanced or weighed the car?

do you have an estimate of the size (area) of the splitter you're going to make?

N.A.C.A. profiles will be so/so for you.  All of the 4-digit foils originate in the '20's (iirc); the 5 and 6 digits from 30's-50's (iirc).  They're primarily intended for full size aircraft wings having Reynolds Numbers (RN) greater than 1million... which means they're looking for tradeoffs in Cl.max, Cd.min, and Cm (pitching moment).  Where as any rear element you end up building will be operating in the 200,000 to 700,000 range, which is generally known as the "Low Reynolds Number" territory... will have a more limited AoA operating range (subject to y'all use rear element angle to balance from grip), and Cm is irrelevant other than making sure your rear element structure and mounting structure are up to the task.  So, you'll want to look for foils designed with those things (Low Reynolds Number primarily) in mind.

Maybe a filler piece to cover the entire headlight and grill area? Made flush with the leading edge of the hood.  Could clean up the air flowing around the front of the car and can be easily removed after the event.

In reply to sleepyhead the buffalo :

Yes, we've weighed our car (2,371 dry) and corner balanced. There is still some weight we can pull out and not screw up our corner weighting too much. We're looking at the Low Re wings like this one: 

 Chuch Hollinger CH 10-48-13 high lift low Reynolds number airfoil

Looking for something around 200-250 lbs of Df at 110-120 (max speed at NCM through sweepers)

For the splitter, we're thinking 3"-4" max and extend it back to at least the oil pan. We have a beefy skid plate that we need to work around and don't want to disturb too much ariflow over the oil pan so will need to figure that out too. 

In reply to Ian F (Forum Supporter) :

Great idea and on the short list of projects for the TT

In reply to Cedricn :

We are going to add a splitter on the front and extend it back to help with some of the front-end airflow. We're running to SCCA TT rules so need to check if we can remove mirrors. 

....and so it begins....

We are going to be designing and building the splitter and rear wing at the same time as we're aiming to run a test session in early June so schedule is tight. 

Splitter:

Ideally, 3"-4" lip, made from some all natural, high strength composite material (aka 1/2" plywood :) ). We made a V1 a while back based on Terry Fair's (Vorshlag) 2010 E30 $2010 GRM entry so we have a nice head start but it needs work. Terry's build thread

Mounting will likely be via standard adjustable rods (4?) up front made from DIY turnbuckles and some homemade brackets attached to bumper. Rear mounting is still TBD but thinking we can mess with a frame mount we prototyped early. 

Rear wing:

We are going to 3D print these on our Creality CR-6 Max printer using PETG bonded using CA and then coated with clear 105 epoxy from West Marine. For the wing profile, we've landed on this profile Chuck Hollinger CH 10-48-13 high lift low Reynolds number airfoil It's similar to the Nine Lives profile but their's looks to have a bit more camber. The smart person would just buy the Nine Lives Rear Wang as it's a proven design, high-quality, American-made by some great guys, and one heck of a value. We may go that route eventually, but wanted to give this 3D-printed concept a try. 

As part of our research, we ran across an incredible website that is a wealth of knowledge for all-things go-fast, aero, with real-world calcs and data. Shout-out to Mario @ Occam's Racer for some great content. Check him out and buy him a coffee for some of the password-protected content. 

We'll be posting videos and pics here and our our social sites in the coming days. More to come!

Quick update on the rear wing design. The design concept is to use multiple hollow aluminum rods as the main spars connected through a series of aluminum airfoil shapes that will bear most of the load. The 3D printed pieces, although bonded and fairly stout, will have the main job of the aero work and not necessarily load-bearing (although there will be some there too). We plan to build the aluminum spars/airfoils and then run static bench load tests to failure to understand our load capabilities and safety factor assuming no more than 250 lbs. of Df at our speeds (less than 120mph). If it's feasible then we will proceed to low-speed track testing with camera(s) to film any deflection. If that's good then we'll start to up the speeds. If the bench tests are not within a decent safety factor then we'll scrap it all and get a wing.  

Starting to test different designs for the rear wing. For wing spars, we're prototyping three 1" diameter x 0.125" wall 6061-T6 tubes that should take most of the load. Calculating stresses, we used 250 pound distributed load and are at ~1.7X safety factor per tube. So using three 1" tubes should provide plenty of safety factor but will bench test to see if calcs and empirical data are closely aligned. 

Big shout-out to the guys at Chattanooga Tourenwagen and GTD Racing for the inspiration to try 3D printing a rear wing. They blazed the trail so trying to learn from their experiences! 

CH10 airfoil V1: 

CH10 airfoil V2:

Added leading edge and trailing edge support rod holes.

Working in the garage this week on a V1 splitter based on a design we built last year for TREC but decided not to use. Video drop on Thursday so check it out on our YouTube channel for more details!

Lots of great info out on the interwebs for inspiration. We took a simple approach using CAD (cardboard aided design), some finished plywood, bar stock for the brackets, and basic shop tools. 

Place cardboard under front valence and hold in place with a jack and jack stands:

Trace valence for initial profile:

Offset that profile the width you want to make your splitter. We went with 4" in the front and slightly smaller on the sides:

Quick fitment check:

Transfer pattern outline to plywood and another fit check:

Machined some brackets using square bar stock tubing. Turnbuckles from HD:

Will need to stay off of the curbs!:

Mounting using L-brackets rivnutted to the frame:

A bit of paint and final mounting:

#AeroBrickTechnologies 

#PatinaRacing

#Sabine

#NASAMidSouth

#SE30

#ST6

#TREC4

#NeedMoreSponsors 

Quick update video on our 3D printed rear wing design. Still some work to do....

3D printed wing design video

In reply to cpatersontn :

I may be coming in a bit late in your timeline, but you probably don't need that many spars. Locating the large one at the Cp (~1/4 chord), and one ~2/3- 3/4 chord should be sufficient especially with aluminum tube. Also curious on the choice of such a cambered airfoil when trying to reduce total drag effects. What chord length? The thinner (fore/aft in car orientation), and wider (in car left/ right) - ie higher aspect ratio - you can get it, the less draggy it will be as well. 
Think of the wing as a tuning tool, you only want to make enough downforce to balance the front aero. 9LR wings are constantly run 0-1 A0A because they make WAY too much downforce (and therefore drag) for a grassroots front-limited racecar. 

In reply to Xratti :

Although digging in, the CH-10 is one of the most efficient (L/D) airfoils in low Reynolds numbers, so I very well may be mistaken with my original comment.

In reply to Xratti :

Finally getting back to this thread... We chose the CH-10 as it's a known rather than design a new airfoil as it's a decently efficient design. We are going to do a lot more work over the winter playing with much thinned walls, less spars, likely with some carbon fiber reinforcement. The chord is ~10", ~65"-70" length. Also going to be working on splitter refinements, especially if this revised wing provides a lot more downforce so will need to balance the front/back. Also looking at the full monty of elements like splitter, flat floor, etc.. Next challenge will be spring rates and damping as the current set-up is fairly "soft" and not set-up for this level of aero.