Aerodynamic Trailblazers: How RHR Performance Wings It

This article presented by RHR Performance

We talked to Olaaf Rossi, co-owner of RHR Performance, a company that has a simple goal: Make a 21st-century approach to downforce accessible to the average racer.

On the Runway

Most entrepreneurs don't start aerodynamics companies. Sure, the Wright brothers were a notable exception, but these days a young business is much more likely to make a smartphone app than a sweet set of canards.

RHR Performance isn't your average startup, though. We talked to Olaaf Rossi, one half of the team behind the game-changing aerodynamics company. He, alongside A.J. Hartman, is determined to change how people like you and us add downforce to our race cars.

How did they get started? Simple: They met at the track. Back in 2014, Olaaf was running an S197 Mustang in NASA's Spec Mustang class, and he kept running into A.J. Hartman, who was running American Iron. After a few years, Olaaf went to A.J. with a proposal: Co-drive with him in an American Endurance Racing series race.

As Olaaf explains it, "Endurance racing is a pressure cooker, but A.J. and I got along really well." It was then that A.J. shared the details of his newest business, a small company making Mustang wings, called A.J. Hartman Racing. Olaaf had just sold his own company, one that developed custom software, so the opportunity seemed like a match made in heaven. A.J. and Olaaf partnered up and renamed A.J. Hartman Racing as RHR Performance.

Takeoff

A.J. and Olaaf had a company. Now they needed a product. At first, they went with what they knew: Mustangs. They built almost every conceivable carbon-fiber SN95 Mustang part, then started branching out: This year's focuses are the S550 Mustang and C6 Chevrolet Corvette. As Olaaf says, "We try to build parts for cars that people are racing or are going to be racing, especially cars with clear needs that nobody else has addressed." RHR also decides how far to push each platform, from a simple splitter to a complicated Time-Trials aero package that can double the car's weight at speed.

Take the C6 Corvette, for example. RHR identified two primary needs that nobody else had addressed: Canards and a rear wing. Sure, they already made a decent wing–the Fulcrum single element–but they knew a high-horsepower car needed something more. RHR now offers two different sets of canards and a big dual-element wing for the C6, in addition to a spectacularly pretty three-dimensional splitter.

In contrast, RHR knew that the S550-chassis Mustang would be pretty common in the paddock. They designed two full aerodynamics packages for this car—one built to meet American Iron rules, and one built for less restrictive classes that can add more than 1200 lbs. of downforce at 100 mph.

In addition to the aerodynamic elements, RHR offers doors, hoods, decklids, bumpers, and other goodies. Hey—if you had a beautiful carbon-fiber molding facility, wouldn't you make as much as you could, too?

Learning How to Fly

We start most of our own aerodynamic projects with a sheet of plywood, a jigsaw, and a dream. At RHR? Not so much. Take their C6 Corvette canards as an example. RHR started by buying a detailed digital 3D model of the car, then fed it into their CFD (Computational Fluid Dynamics) program and let their aerodynamicist go crazy. After a bunch of digital modeling, they tested five different iterations in the computer, finally settling on what's for sale today. They make two versions, a high-downforce and a low-drag set, with the high-downforce version adding 300 lbs. of downforce at 150 mph. All new parts the company makes come with detailed data—downforce, drag, etc.—so customers can tune their cars and their others aerodynamic aids to work perfectly at each track. The days of cardboard and plywood mock-ups are over.

What about the wind tunnel? As Olaaf tells it, that technology has mostly gone the way of the Wright brothers. No, Google Sketchup can't model air flow, but the professional-level software and hardware that RHR uses (the same stuff F1 teams have access to) is better at simulating and controlling variables than the real wind tunnels that cost $10,000 per hour. Skeptical? So were we, until he shared this data point: Formula 1 teams have a limit on the number of hours of CFD computations they're allowed each season; otherwise, they'd just constantly model every single permutation until they'd melted their computers and drained their bottomless bank accounts.

Is there a downside to the shift from tell-tales to processors? One, Olaaf admits: Figuring out how to make the physical part. The aerodynamicist can come back with a design that takes a 5-axis CNC machine 200 hours to cut a mold for, but carbon-fiber parts with that much upfront cost would be too expensive for everyone except those F1 teams. RHR spends hours translating optimal designs into realistic manufacturing processes, rather than trying to translate realistic manufacturing processes into optimal designs like we do with our plywood splitters and home-molded diffusers.

What About Your Plane?

"This is all great," you're probably thinking, "but what about my particular Civic/Miata/M3/Mustang, and what about my particular wing/splitter/diffuser/canards?" First, we asked Olaaf when a car is "ready" for aerodynamic development. He gave two answers: As soon as a car goes over 50 mph, but it depends what your rules say, especially if you're in a series where each modification is worth a certain number of points, and it's up to competitors to stay under a limit. He's blunt about a simple fact, though: "Even a Spec Miata could benefit greatly from some aerodynamic elements."

After that, he wanted to hammer home another point: "The details definitely matter." He sees so many people put a big, beautiful wing on the rear of their car, then build a small plywood splitter because they're scared of damaging anything fancier. Then, he says, they end up running the rear wing at a real shallow angle of attack or removing rear mechanical grip to balance the car's handling. Olaaf stresses that aerodynamics is not a wing or a splitter or a spoiler. It's a holistic approach to making a car faster, and the entire car's airflow and handling needs to be a part of every decision. One example of this is the car's center of pressure, where the center of an aerodynamic package's downforce is located. This needs to match the car's center of gravity; otherwise, the car's weight distribution will change with speed, making it unpredictable and harder to drive. RHR keeps all of this in mind, giving these numbers (as well as metrics for ride height, speed, pitch, roll, and yaw) with every aerodynamic element.

Reading the Instruments

How do you figure all this out? Like for every other question, RHR had the answer.

"Another mistake is people not using their data-acquisition systems to look at what their car is doing and why," Olaaf groaned. He sees this pattern at every event: Finish the race, clean the car, download the data, check the brake pads, drink a beer, and load up the trailer. Sure, you may have made a change to your car, but you’re never really analyzing the data to see what it did. At most, Olaaf figures, most racers are just looking at segment times to figure out how fast they went.

"Well, then, what should we do?" we asked. Olaaf casually rolled into his next suggestion as easily as a waiter asking "Would you like dessert with that?"

"The best thing is to build an inverse corner radius math channel that tells you where in the turn you’re turning the most. You can see that and then plot your yaw against that. That answers the question 'Am I understeering or am I oversteering' at each specific point in the turn. Then, see if it’s a high-speed or low-speed turn, and you can tell if you're masking your aerodynamic shortcomings with mechanical changes or vice-versa.”

Basically, aerodynamic aids should increase your minimum speed in a corner (the tightest part of the turn), and increase your maximum lateral deceleration, meaning the car brakes harder. Want more math? Olaaf also shared the formula you can theoretically use to figure out how quickly a car can take each corner: "The velocity that the car can go around the corner is the square root of the coefficient of friction of the tires multiplied by the weight on the tires plus the 'weight' of downforce, multiplied by the radius of the turn, divided by the mass of the car." Otherwise known as Velocity = Sq. rt of the CF(W+D)*R/M

Different Flying Styles

So, you've done the math, figured out your car's weak spots, and ordered a sweet wing and splitter from RHR Performance. What next?

Everything changes. Olaaf is blunt: "Everything affects everything in a race car." Downforce will mean you'll need stiffer springs and higher tire pressures, as well as a higher static ride height. You'll need better brakes, too, because stopping harder will increase pad temps. You'll use more fuel and tires. You'll need more rear brake bias, because the car will have a higher percentage of weight over the rear wheels. Most importantly, though, you'll go much faster.

These are all well-known effects of adding downforce, but RHR mentioned a big one we hadn't considered: Something they call "raceability" will change, meaning your car will drive very differently. A car that was once only good for passing on the straights could suddenly be a late-braking, dive-bombing champion, and pass on the outside of turns with ease.

Landing

So, what did we learn? We learned a few things.

First, RHR performance is on the cutting-edge of consumer aerodynamics, using tools and processes normally reserved for F1 teams or Boeing to lower our lap times. They do this within real-world constraints and emphasize transparency, meaning anything you buy will be reasonably priced, and they'll help you understand how and why it works.

Second, aerodynamics is worth taking seriously as a part of race prep at any level, and almost any data acquisition platform can be used to optimize your own set-up.

Third, a car with a wing and a splitter will drive differently than one without, and it's important to adjust the rest of your set-up accordingly.

To learn more about RHR Performance, check out their website here.

This story isn't the last you'll hear about RHR Performance. We've already got plans to work with them on a few project cars, and we'll take an even deeper dive into aerodynamics then. Stay tuned.

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Comments
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sleepyhead
sleepyhead HalfDork
2/23/18 9:37 a.m.

"You'll need more rear brake bias, because the car will have a higher percentage of weight over the rear wheels"

I think the more correct statement is: "you'll need more rear brake bias, because the downforce will mitigate the braking-based forward inertial weight shift, making the rear brakes more effective.

There isn't a higher percentage of weight over the rear wheels, otherwise you've done what they suggest you not do:
"One example of this is the car's center of pressure, where the center of an aerodynamic package's downforce is located. This needs to match the car's center of gravity; otherwise, the car's weight distribution will change with speed, making it unpredictable and harder to drive"

There is a higher percentage of force over the rear wheels, thanks to the aerodynamic downforce;  but "weight" is usually reserved to describe the downforce contribution of the vehicle's mass.

sorry to be pedantic, ymmv

thanks for the article, I look forward to picking apart... I mean... reading future installments cheeky

Tom Suddard
Tom Suddard Digital Experience Director
2/23/18 9:58 a.m.

I'll admit–that was a bit of a linguistic shortcut to keep this article accessible to a broad audience. 

But, if we're truly being pedantic, I am technically correct. Why? Because a wing, uprights, bracing, and diffuser weigh more than a splitter. Therefore, a car with a downforce-adding aerodynamic package will have more weight over the rear wheels than it did before adding the aero goodies. Sure, only a few pounds, but that's what being pedantic is all about. cheeky

sleepyhead
sleepyhead HalfDork
2/23/18 10:04 a.m.

I'll post the GIF I go to whenever I realize I don't want to get into a pedantic spiral....

Tom Suddard
Tom Suddard Digital Experience Director
2/23/18 10:08 a.m.

Did somebody say spiral?

maschinenbau
maschinenbau Dork
2/23/18 10:12 a.m.

I'll admit, I clicked for GMT360's with aero kits. I never know what to expect on this site.

Tom Suddard
Tom Suddard Digital Experience Director
2/23/18 10:14 a.m.

Now THAT is an article I'd write. 

nderwater
nderwater UltimaDork
2/23/18 10:53 a.m.
maschinenbau said:

I'll admit, I clicked for GMT360's with aero kits. I never know what to expect on this site.

759NRNG
759NRNG SuperDork
2/23/18 1:20 p.m.

I own the orphan of them all 2004 Bravada.....yeah where's the dang article ......I seem to recall that the youngest unser brother actually piloted an early trailblazer(gmt360) up Pikes Peak a while ago with some success.... 

sleepyhead
sleepyhead HalfDork
2/23/18 1:32 p.m.
Tom Suddard said:

Did somebody say spiral?

dude, everyone knows it's pronounced "zhaif"

 

Stealthtercel
Stealthtercel Dork
2/23/18 2:06 p.m.

Another guy here who thought "Cool! an aerodynamic Trailblazer!" and immediately clicked the link.  They're clever, these Suddards.

sleepyhead
sleepyhead HalfDork
2/23/18 2:17 p.m.
Stealthtercel said:

Another guy here who thought "Cool! an aerodynamic Trailblazer!" and immediately clicked the link.  They're clever, these Suddards.

honestly, this photo:

has all the elements for how to make such a beast... at least theoretically... I don't think anyone's tried it practically, yet

te72
te72 New Reader
2/23/18 11:25 p.m.

I've stared at my Supra for many an hour, scheming on how to plant it into the ground even more, how to make it as slippery as possible while doing so too... and yet... I'm still not sure that's a rabbit hole I wanna go down.

 

I'll probably focus on just the underside of the vehicle first. One thing at a time...

G_Jay
G_Jay New Reader
2/24/18 7:54 a.m.

In reply to Tom Suddard :

Regarding your reply to the rear brake bias from aero comment, a couple pounds aren't significant and if the aero downforce is balanced it shouldn't matter either.  What you didn't mention but will also shift the balance is the center of drag being raised due to a wing mounted up high.  Even with no downforce the resulting pitch moment will shift the tire normal forces rearward.

Knurled.
Knurled. MegaDork
2/24/18 8:38 a.m.

In reply to G_Jay :

Either way, the effect is that of having proportionally higher vertical load on the rear tires.  Assuming that you don't translate this greater load into harder braking...

 

Brake hard enough and you don't need rear brakes at all.  You typically only see this on short wheelbase/high CG devices like bicycles though, where max braking involves the back tire hovering over the ground.

 

 

GTXVette
GTXVette Dork
2/24/18 9:07 a.m.

 When Talking Braking, they say the Front Controls 70%, and yes that is weight shift and front end dive and a couple other Forces Too.  Would making the forces from Wing Be Better Used Pushing down In FRONT of the Rear Tires .   Now saying that I see the problem is Height and we already have Outlaw Sprint cars, so Duh

olaaf
olaaf
2/25/18 5:12 p.m.

In reply to sleepyhead :

One thing to note is that the center of pressure should never be in front of the cg- it makes handling very twitchy- you want it close, but behind the cg. Also, during braking the aero balance will shift, which direction and how much depends on the package. However, by pitching fore, the rear wing AOA increases, and thus produces more downforce. In a few weeks we'll publish an aero map for the S550 project on the RHR website. No matter what, the balance will shift, but how much it shifts is part of the game. In our S550 project, we'll illustrate an example where we had designed a more effective front splitter iteration that was NOT chosen, because while it was better performing all around, it was highly sensitive to pitch.

grover
grover Reader
2/25/18 8:48 p.m.

Bummer, I was hoping to see a cool aero suv

sleepyhead
sleepyhead HalfDork
2/26/18 6:44 a.m.

In reply to olaaf :

first, welcome to the forum olaaf!  thanks for popping in here.

Thinking about it, I understand the imperative of keeping the aerodynamic downforce balanced to be slightly behind the c.g.; otherwise you'll end up with a high-speed oversteer, effectively making it difficult to trust the downforce.

The AoA increase through brake application pitching is interesting... and makes sense; although I wonder how much of that is a component the increased rake of the body providing better flow attachment over the rear window, vs. the AoA of the wing.  Although, this change in AoA is clearly an important one when setting the angle of the wing statically, so you don't exceed the maximum lift coefficient of your foil section.

more generally, I understand there's a great amount of nuance required when it comes to communicating about Aerodynamics, and the complication of doing that succinctly because of the technical nature of that nuance.  Since you might see me some in the comments on this series, I'll give you the heads up of: I've got a BS in Aero, more through force of shear will, compared to most of the other people around me that tended to soak this stuff up like a sponge.  I'll also note, that my degree is a decade and a half behind me, and I spent most of that time performing a discipline closer to controls than aero... so I'm a bit rusty on this stuff... and cars are different enough from airplanes to further calcify my apparent technical understanding?  appreciation?  whatever.

thanks for providing the community an insight to your process, and I look forward to adding to my toolkit of knowledge on the subject.

olaaf
olaaf New Reader
2/26/18 8:59 a.m.

In reply to sleepyhead :

Hi Sleepyhead- thanks for the welcome-

And, you are right on about flow attachment, I’ll post some velocity slices on our blog when I get to the Aero maps, you will see marked differences is velocity and pressure during pitch over the roof and rear window. One thing I’ve noticed in the real world is that since so few invest in a quality splitter- (our own testing shows a large flat blade splitter on our S550 model produces of Cl of .29 and a Clf of .32 at static ride height, vs. a Cl of .62 and Clf of .79 for a AI legal splitter that has tunnels and a 3D airfoil shape on the leading edge, and a Cl of 1.05 and Clf of 1.38 for our psychotic unlimited splitter), the result generally means that most racers are nowhere near rear wing stall (in my experience at the track) at no pitch.

One other thing you can check on our blog (new post about our new diffusor) is that during pitching, it’s contribution to DF increases significantly.

And, you have me there with a BS in aero- I’m software engineer- our Aero consultant has a PhD, and he does all the hard work.

Thanks for chiming in,

olaaf

DjGreggieP
DjGreggieP Reader
2/26/18 11:28 a.m.

In for this. I want to develop a better understanding of aerodynamics. Thank you both Sleepyhead and Olaaf

sleepyhead
sleepyhead HalfDork
2/26/18 12:04 p.m.
olaaf said:

In reply to sleepyhead :

And, you have me there with a BS in aero- I’m software engineer- our Aero consultant has a PhD, and he does all the hard work.

Thanks for chiming in,

olaaf

No, I wouldn't say that... in general I try to avoid the "one-up-manship" that tends to frustrate most aerodynamics debates.  I was trying to use that as a shorthand for "I understand some of this stuff, so feel free to speak to me on that level".  It's probably closer to say that we both have a "practical understanding" of aerodynamics... only I went through a "classical training regime, followed by atrophy and self study" to achieve it.  You just went straight to "practical understanding" cheeky... after all, you get to play with this stuff on a much more frequent basis than I do, and with cooler simulation codes.

And, I'm all for more people being able to obtain that proficiency.

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