Underbody / undertray design

[hispanicpanic]

I'm building a time attack car (evo X) and i'm looking for some good reading material to help me with the design of my underbody. Can anyone point me in the right direction?

Rules in this series are relatively unlimited so i can go as extreeme with aero as i wish. I'll only have access to pretty rudimentary materials and manufacturing processes as everything will be made in my garage by myself, so no molding, glass, or carbon. I just want to be able to maximize downforce at all costs with the underbody, but also consider how well they will work when the vehicle is in yaw. Since evo's are very front heavy, they must be setup to produce downforce under yaw as many times that's the fastest way through a corner with these machines.

[NOT A TA]

If you are just beginning to educate yourself about auto aerodynamics Simon McBeath's book Competition Car Aerodynamics is a good place to start. Another starting place is Race Car Aerodynamics by Joseph Katz which covers the same basics as the McBeath book but with a bit more of the math involved.

I'm in a similar situation building a full tray for my car with no restrictions and I've searched for years for information on full under trays. There's very little technical design information in printed media. You'll find the same basic info you'll get in the books mentioned above repeated over and over as you look on the web for more information beyond the basics.

Since you're into the Time Attack stuff go watch the 2015 WTAC championships on you tube if it's still up (it's long). Also an overview here http://www.worldtimeattack.com/index.ph ... odynamics/ Andrew Brilliant did a lot of work on a WTAC EVO called NEMO you could search for more info about http://www.speedhunters.com/2013/12/project-nemo/ and also search the PMQ evo.

[krisfx]

Could you not create aluminium "bucks" of your components and then fibreglass over? My old FS team also used to create a lot of composite bodywork without an autoclave, you can probably make some form of compression bag using your vacuum.

I've read a few books on chassis/race car design but from what I found there wasn't much on underfloors. Have you looked at the competition in your potential class?

[andylaurence]

You can easily do carbon/fibreglass in the garage. We're doing the same with a new floor for the EgoBoost. It'll be a carbon/diolen cloth for stiffness/abrasion resistance respectively.

[strad]

You can make your own carbon fiber parts fairly easily, but for your purposes the first thing I would do would be to create aluminum panels to smooth the underside

[machin]

I'm building a time attack car (evo X) and i'm looking for some good reading material to help me with the design of my underbody. Can anyone point me in the right direction?

Simon McBeath's "Competition Car Aerodynamics" (or the older version called "Competition Car Downforce") is a pretty good mix of theory and practical advice.

[hispanicpanic]

thanks for the tips guys. Yes i know molding can be done in my garage, but that's just a skillset i don't have at the moment. I'm not about to experiment now..... I've never been an artist and i don't have patience to learn such skillsets at the moment.

I know all about andrew brilliant and his works with the eclipse, evo's, and more. The thing about WTAC and other successfull projects like AMB aero, is they don't disclose their underbody. They'll talk about their aero design on other parts of the car, but they always refuse to give details on the underbody. They also allow media to take pictures of the car with the disclosure that they do not take any of the underbody. Therefore, i don't have any good examples to go off of.

My plan was to not make the whole thing flat. I need more DF than what a flat underbody could provide!!

[gixxer_drew]

To be totally honest trying to make that stuff up on your own is a big difference compared to what a professional would design, no matter what books you read. I would set out to decide from the beginning if your goal is to be in a learning process, or to win. If it is to win you should think about a budget or reach out to some consultants to give you an idea what you can expect for what sort of budgets.

[andylaurence]

Finding a consultant who will work for less than the value of your car and who you think might actually know what he's talking about is akin to stumbling upon rocking horse poo in my experience.

[NOT A TA]

To be totally honest trying to make that stuff up on your own is a big difference compared to what a professional would design, no matter what books you read. I would set out to decide from the beginning if your goal is to be in a learning process, or to win. If it is to win you should think about a budget or reach out to some consultants to give you an idea what you can expect for what sort of budgets.

OK, I'll bite. I wish to learn. I'm not trying to "win" anything in particular and have no restraints due to any particular sanctioning body regulations. I can't model, mesh, run CFD programs or do any of the other computer stuff the cool kids use now. During my schooling we used drafting tables etc. and my attempts in Sketchup look more like Etch A Sketch however I'd like to learn more about what goes on under the car, so where to learn more?

[gixxer_drew]

hope I don't sound like I am talking down to you I just want to help people who are hungry to learn and this experience I'm
happy to share as you seem new to aero.

IMHO few people with that knowledge are going to write a book about it or fill everyone in, so info is scarce. The Katz book is the closest, but that's not going to take you to pro level. Just set out to try all your ideas and learn from everywhere and anywhere.

That is still how it's done at the highest levels.

Without a test method you won't get far. Read a thousand SAE papers while you are at it, that's really all the aeros I know and I ever do is we do is read then get ideas and try them using out knowledge and experience. Anyone can do that if they spend the time. I lay in bed unable to sleep at night imagining air flow. Some of my best ideas came like that. People made big downforce long before CFD existed. It's far from the only way.

When I was starting out I used everything from pressure gauges to rainy days behind big rigs. House fans, dry lake dust patterns, even the kitchen sink (literally). Knowledge is out there, but it's not on Google. It is in your experience and ingenuity to find it. Experience can be found in expensively if you devote your time to the craft. My $.02.

Side note, the Willem Toet posts on linked in are solid info.

[NOT A TA]

I've been interested in aero stuff for over 40 years however no formal training or extensive auto aero experience. BTDT with drafting semi's, fans, tuft tests etc. Since the internet was invented I read articles, tech papers and watch any videos, fluids classes, or whatever else I can find and that's how I knew to refer the OP of this thread to NEMO. Willem Toet does an excellent job with his posts and video's and the car I'm currently building ( '70 Trans Am) is the arguably better version of his first race car, which was also a 2nd gen F body.

I originally built the car about 25 years ago and used it for street, drags, road tracks, and LSR's. I'm doing a complete rebuild of the car and have a thread on the aero related modifications over on Track HQ in the Aero section. http://www.trackhq.com/forums/f360/very ... aero-8905/ Most of the aero things are done and I'm currently working on the design of a full undertray. It will be 4 sections that are height and pitch adjustable independent of the body so I can play with interacting changes in body rake, splitter, tray height/pitch, tunnels, diffuser, and rear wing position.

[cheechthechi]

I've been interested in aero stuff for over 40 years however no formal training or extensive auto aero experience. BTDT with drafting semi's, fans, tuft tests etc. Since the internet was invented I read articles, tech papers and watch any videos, fluids classes, or whatever else I can find and that's how I knew to refer the OP of this thread to NEMO. Willem Toet does an excellent job with his posts and video's and the car I'm currently building ( '70 Trans Am) is the arguably better version of his first race car, which was also a 2nd gen F body.

The irony here is that the poster above you is the person who did all the Aero work on NEMO. For me being a very amateur aerodynamicist working for a smaller TA team, everything gixxer_drew gave in his advice is 100% spot on based on my own experiences. Also seconded on Willem Toet's articles and SAE papers, both are great resources. But to the OP good luck on your learning journey, aero is fun although quite confusing at times.

[NOT A TA]

I've been interested in aero stuff for over 40 years however no formal training or extensive auto aero experience. BTDT with drafting semi's, fans, tuft tests etc. Since the internet was invented I read articles, tech papers and watch any videos, fluids classes, or whatever else I can find and that's how I knew to refer the OP of this thread to NEMO. Willem Toet does an excellent job with his posts and video's and the car I'm currently building ( '70 Trans Am) is the arguably better version of his first race car, which was also a 2nd gen F body.

The irony here is that the poster above you is the person who did all the Aero work on NEMO. For me being a very amateur aerodynamicist working for a smaller TA team, everything gixxer_drew gave in his advice is 100% spot on based on my own experiences. Also seconded on Willem Toet's articles and SAE papers, both are great resources. But to the OP good luck on your learning journey, aero is fun although quite confusing at times.

As I mentioned above I read anything I can find about aero stuff since the internet was invented and am well aware of his work on Nemo. The link I posted is to another forum he's also a member on and visits occasionally. I lurked here for many years and joined last year thinking I might get involved with the Khmansin challenge but doubt I'll be able to because I just don't have the computer skills.

[cheechthechi]

Fair enough, not sure what your background is but many local universities with engineering programs offer courses on CFD and CAD. Usually it is more theoretically based, but it helps to understand what is going on with the software. Most schools give the option of taking classes as a non matriculated student, and the student status also gives you access to highly discounted cad and cfd software (usually limited term subscription). I am by no means an expert, but that is how I got started with CFD.

Beyond that , as you say, it's just using experimental methods...although I have found that the difficulty in road testing is getting repeatable results .