# Automotive Aerodynamics for a 30mph avg open wheeled racecar

1. Jul 27, 2012

### WannaBeME

I am on the Formula SAE team at school where you design and build an open wheeled race car powered by a 600 cc motorcycle engine. We compete against other schools in different events including skid pad, autocross, endurance, etc. Last year we were a first year team and had a pretty basic simple design that worked and this year we want to actually be competitive. I am really passionate about the aerospace industry hoping to work with airplanes when I graduate so I have a great desire to do something aero related for the formula car. An aero package consisting of front and rear spoilers isn't really desired by the team because the advantages are negligible when you figure in the disadvantages. They believe at the speeds that are experienced in our racing (30 mph avg maybe up to 60 on straights) just isn't fast enough to justify doing any aero work.

I personally wouldn't care if it's advantages were negligible because I just want to do something aero related for the car but convincing the team to spend resources on it is pretty hard. I have been thinking about maybe something other than a wing package like a diffuser and vortex generators or something of the like. The problem is I need to do some calculations in order to prove to the team that it will theoretically benefit the car.

My questions are, does anyone think that any kind of aero package, aside from basic drag reduction, would be of benefit with the speeds we experience? If so are there any recommended books that I could look into that would help me in calculating figures that would assist me in convincing the team to pursue an aero package? Thanks for the help!

2. Jul 27, 2012

### Ranger Mike

read post on last page of Jul24-12, 10:34 AM

Re: Race car suspension Class in this forum

it takes 1.16 hp to go 30 mph
7.14 hp to go 55 mph
11.8 hp to go 65 mph
unless you got mucho HP...anything you can do to reduce aero DRAG is only going to help

3. Jul 27, 2012

### jack action

Open wheel aerodynamics are the worst to work with and very difficult to predict theoretically (At least, without CFD).

The best (simple) tools I can offer you to learn your way around that and get a feel of what will affect car aerodynamics and performance is this acceleration simulator and this drag and lift coefficients calculator. Read the theory at the bottom of the pages.

Personally, I don't think either that trying to create downforce on a Formula SAE is worth it. Assuming downforce will help you when cornering, you have to understand that usually downforce comes with a price: increased drag. Drag that will slow you down on the straight line. So you might end up working for nothing when you average everything.

Again, this is assuming that whatever you built will create downforce (which again can be tricky to guess or calculate with open wheel car). But, whether it works or not, the drag increase will probably be there anyway!

I'll go along with Ranger Mike and, aerodynamic wise, I think your best bet is to work on drag reduction. And, after you understand the basics to reduce drag, you should built different small prototype and actually test them to see which one is better. There is no better proof than that to convince your team ... and impress the judges at the competition!

4. Aug 13, 2012

### xxChrisxx

The first practical advice of setting up a winning package is: Find out what everyone else is doing/what's recently been done.

The regs havent changed in ages, and with simulation people converge on roughly the correct solution fairly quickly. If you actually look at most Formula Student cars, maybe 5-10% have aero, this is for a reason.

Aero on FSAE is largely irrelevent, even drag as you have so much power in comparison the speeds you are going you can make it look like the side of a barn and still do fine.

The three things you need to make a successful FSAE car:
1. The right tyres.
2. The best suspension setup and geometry.
3. Low weight.

I've known people fart around with aero packages for months, trying to reduce drag pursuing those extra two 10ths. When the spring rates were wholly unsuitable for the tyres... getting that right gains you seconds.

5. Aug 13, 2012

### jack action

Although I respect your opinion xxChrisxx, I think your advice for Formula SAE send students with the wrong idea in mind; A mind setting that I have seen too often. Formula SAE is not a race: It's an engineering competition. You can earn up to 32,5% of your points without even presenting a car (Cost and Manufacturing, Presentation, Design). There is also 10% of the points dedicated to fuel economy. It's twice as much as what you can expect for the skid pad event. So even if you had one of the slowest car, you can still earn more than 40% of the maximum score. So, if you simply copy «what everyone else is doing» you might win a race - and rarely I've seen people who don't understand what they're doing, building a winning car - but it might cost you the engineering competition.

So, if there is one student in the team that works on aerodynamics, even if it is to show that it is not worth it, the research can give you good points on design and presentation. If you reduce drag and win points in fuel economy, I don't see anything wrong with that, especially if you previously predicted it in your presentation.

I share with you an article from Racecar Engineering, August 2002, talking about the Concordia car of that year. I know it pretty well, as the concept of «stay small, simple and cheap» was developed by me and two of my friends back in autumn 1999. We decided on that concept mainly because of who we were as a team: We had no money, very little support from the university and most of the students had no idea on how a car worked - let alone knowing how to tune it for racing. All of this was based on the experience of 1999, when a team went to the competition and finished 99th out of a 100. A team that I refused to participate in, as it was a predictable disaster from the get-go.

It was planned to be a 2-year project (to compete in 2001). We didn't do much in the first year because of (more) team problems. The team was split in two: people who wanted to work on the project and people who wanted to compete in 2000 by using the principle of «copy what other people do». They had no clue what they were doing, failed miserably and, just like the previous year, they were a laughing stock at the competition (Once again, the car couldn't do any of the events, barely passing the tech inspection). I graduated in 2000, so I did not work closely on the car presented in the article. They work hard to present it in 2001 (I remember helping them a few days before the competition, machining those suspension components), but there were real problems with team effort in Concordia back then. They finally chose to wait another year instead of being laughed at once again.

To have such coverage in the Racecar Engineering article was probably the proudest moment for the team: Recognition of the engineering work that went into the car, trying to look at things in a different way. I still believe that this car could have been the first of a series, improved year after year. I remember that the idea was to become the expert on the mono-cylinder for the competition.

6. Aug 19, 2012

### xxChrisxx

It appears that i'm talking rubbish. This months racecar engineering has an article on fsae aero. It appears the trend is towards low speed downforce, due to last years rule changes.

The aero work has come on so agressively from when i last looked at it. It may be an idea to at least begin an aero programme even if its not implemented this year. So benchmarking the cars performance, running pressure probes for validation etc.