Chassis design, theories vs. facts

I've been pondering this for quite some time now. What is the first basis in chassis design? meaning what is the ultimate goal in trying to build the better race chassis. Easily answered by going around the corner as fast as possible but how is that achieved? Stiffness and rigidity? Or is the chassis simply there as a giant suspension component to co-exist with the shocks, and springs etc.?

What makes one chassis better then another? You definately have differences in which is better depending application, e.g. rally, open wheel, sports cars. Do you want a softer chassis for rallying? A stiffer one for open wheel/ sports car racing?

What is going on with the chassis under load (going around a corner?). I know it flexes, but i want to know how's and why's. I know we have engineers on here who probably know about this type of stuff, and probably some other experts as well.

Does anyone care to shed some light. Btw this all came from reading an article on www.dpcars.net about his DP1 project. It's pretty cool i suggest anyone whos interested to check it out!

 

Here are two other sites that may apply/relpy to your questions...


http://www.champcarfanatics.com/forums/?styleid=1

http://forums.autosport.com/forumdisplay.php?forumid=8

 

Primarily the chassis is there simply to hold everything together and allow each component (engine, suspension) to act as they were designed.

Cornering is all about roll centres, traction and downforce.
Straight line speed is all about hp and aerodynamics/frontal area.

Chassis flex affects the cars ability to perform all of the above, and thus becomes an uncontrolled variable. Thus you want it as rigid as possible, remembering that a heavy car is a slow car, plus you have to fit a driver in, and all the other components within the rules, etc.

The ultimate goal is to keep the tyres contact patch as large as possible, thus maximising grip. Good control of the wheel does this, thus soft springs and perfect shock settings. The more rigid your chassis the softer you can run your springs, but also modern aerodynamics require that the chassis maintains a level as possible platform so the gap under the car remains consistent.

It's all a compromise, but you should design everything else before the chassis.
Pete

 

Thanks, it's also nice that you spoke english (or in a not too technical vocabulary). that helps me understanding. A very simple theory with simple analysis, i like it! Anymore?? This thread could be so interesting don't let it die guys.

 

www.mulsannescorner.com Have fun. Also you should pick up a copy of Race Car Engineering ( www.racecar-engineering.com ).

 

At the F1 level the ultimate goal is no longer solely increasing rigidity. In the past half decade or so they've gotten to the point where they are working on controlled flex. ie, certain portions of the chassis the goal is to be 100% stiff, but others are built to flex be for various reasons. I haven't heard of any other series getting into this though (except go-karts of course).

Check Amazon for chassis setup books, motor racing, etc. as well.

 

Already have it, not much time to read it though..

 

I design chassis and vehicles for a living.

I will tell you the secret:

"Every part of the car is there only to make the tires work"

Think about this for a moment. The job of the vehicle is to extract every bit of ability from the tires. (this includes the job of the driver).

The chassis is tuned in stiffness, weight distibution, CG location, packaging, and suspension dynamic to make whatever the tires that it drives work as well as possible. (within the rules - road or race)

The chassis material is only important for weight, stiffness, and cost.
The basic suspension geometry is based on how much travel is needed, and camber control of the wheels.
The final tuning of dampers/springs and alignment is to fine tune the wear and grip of the tires to suit environment and driver.

In theory a chassis should have absolute stiffness. This is of course not possible. packaging and cost limitations prevent this. When the chassis is rigid, the suspension can work as designed. If the chassis flexes, the suspension changes. tenths of a milimeter can change a cars behavior drastically.

I could go on forever about suspension tuning for low/high speed grip vs downforce vs whatever etc...

But you know know the secret. Everything else follows.

Cheers
Eric

 

Are you considering aerodynamics as part of the overall chassis design? Surely in today's world they have a lot to do with overall performance.....

 

Interesting. What is your schooling back ground for college? I plan on going into Meng. or industrial design, just as soon as i fill my math and science requirements. Got any pointers for a noob?

EDIT: mind telling me what your job consist of? basically the technical part. Do you use a lot of different math's or are there just a handful of theorems you use? I'm sure it is depending on the task at hand but any insight with this would be appreciated as well.

 

Mechanical Engineering is a VERY broad major/career, it can cover evreything from racecar suspension, to designing sheet metal packaging/enclosures for military electronics.

Depending on what area of ME you want, you can either deal with ALL numbers, some numbers, or almost no numbers at all.

ALL numbers is more in the core design and analysis of designs.

Some numbers are where you wear multiple hats in the design process.

When you barely deal with numbers, you are more into the design and management of projects, where your numbers are more management related than actual formulas.

But regardless which genre of ME you go into, a strong mechanical engineering background can go a long way.

Biggest thing I would recommend is getting as much Real World experience as possible. The worst thing is a 4.0 graduate from a top school who gets into the real world and has zero real world experience and can't get a job, or gets a job and fails miserably.

Go on Co-ops, work summers, work on weekends/nights part time, however if your school has a Formula SAE program, that is BY FAR the best thing you can do as a college student for real world experience if you are looking to get into an industry related in any way or form with motorsports.

As reference, I'm a young Mechanical Engineer, concentrated in manufacturing, 4 years as core fsae member. Graduated and designed BMW racecars/suspension (utilizing Ohlins) for 5 months, than went to a defense contractor, then more contract work for a machine designer...tried to get a taste of everything and as much as experience as possible without committing long term before I found what I really wanted to do.

And now I'm involved in private equity/mutual fund investing

However, on the side I still do motorsport engineer work, build/design racecars, and will continue to race at club evel as a driver (maybe at some point if its worth it get a pro team together for publicity of a business?).

And as for the topic at hand, its been covered pretty well.

It depends on what kinds of chassis you are talking about. Composite Monocqoue, hybrid monocoques, steel space frames, or OEM style unibodies. There is a big difference between all of them, both in thier purpose and design process.

Ultimately, if you are after a performance or pure racing vehicle, putting aerodynamics aside (usually formula/prototype mostly) the chassis' purpose and goal is to be as stiff as possible, keeping the suspension mounts static in 3d space so they can work as they were designed to. Once the chassis flexes, the points move in relation to each other, and all your hard work on roll center/wheelrates/etc is now fubarred.

And in the last couple decades energy absorption and the overall safety factor has exponentially grown, to the point where safety is taking precedence over rigidity in some cases.

 

Aeronautical engineering is where most race car engineers come from.

Pete

 

VERY true! One of my PhDs is in Mechanical Engineering, but I can't get a job in the field at 59 years old (other than teaching), as I have almost zero practical experience. It seems to me what should work in theory often does not in the real world, and that's where things matter..

 

Interesting, I like math, and enjoy it, my problem is applying what i've learned to what i need to figure out. That is the most difficult part for me at the moment. My brain just goes on overload and i confuse myself. Did you have this problem? If so how did you work around it? Through that i figure a little bit of math will be good for me than just straight mathmatics all day. What would you suggest for that?

Also i've heard of co-ops, and i definately want to get out t here and get experience, even to find out i won't really enjoy it. What's the best way of going about that? Second, both schools i plan on applying to, University of Washington and Western Washington University; bot have the FSAE formula program. the only problem is i figure it is fairly ahrd to get into as the list would be very long.... But like everything else in college im sure it is just a waiting game.

Thanks for your help by the way(everyone). Hopefully you can answer some of my questions.

 

If you are interested in chassis fabrication/design I would NOT recommend industrial design. An industrial design major that has a transportation influence focuses mainly on styling and human factors in interiors.

 

Well, first of all, seeing as you have not even started college yet, I'd suggest trying to figure out the general idea of what you'd like to do, and if you are just generally interested in engineering, go to a good engineering school.

There are courses you will take first year/semester that are designed to "weed out" all the kids who won't make it in the long run. Its a strange method, but it works very well.

Unless you have an extremely high IQ and are a genius, you'll most likely get frustrated within the first week or two of your core engineering courses. It'll be boring, not seem relevant to anything...but trust the professor, its how it works.

Getting past this hurdle is the hardest part. Once you realize how much work it takes and how competitive a good engineering school is, this is what will make you a good engineer.

You need to be able to think by yourself, and really push yourself.

I'd suggest looking into those schools and the extra-curricular programs they have.



As for the aeronautical engineering background behind most motorsport engineers, I don't agree.

First of all, you have to separate "race engineers" from actual design engineers in professional motorsports, HUGE difference. Also depends on what part of the world you are talking about.

There are many forms of engineers in motorsport, and I don't think it can be generalize by any specific background. You have engineers on the team side, and on the manufacturer side. For example Grand Am DP, you have design/mechanical/materials/etc engineers at the manufacturer, however the "engineers" on the teams running the cars usually are not even engineers, just very experienced mechanics in many cases. Data Acq in these higher levels of pro motorsports is where you can find some electrical and computer engineers as well.

Then you get to F1, and thats an entirely different world.

 

Have you asked race car designers what degree they did. The article I read a while ago stated very clearly that that is where MOST engineers come from.

Think about the materials race cars use, it's the same stuff that gets taught in aeronautical engineering. Think also about the aerodynamics stuff ...

I did a Mechanical Engineering certificate when much, much younger ... people who design buildings and (relatively speaking) crude (steel, etc.) components do that. Yeah, obviously the degree (which was a further couple of years) takes it up a notch, but race cars are NOT designed out of metal anymore. Mechanical engineering when I was involved is to fuel plant designers, etc.

Pete

 

Well, I hate to break it to you, but go check out a mechanical engineering curriculum at a top engineering college (MIT, Cornell, RPI, etc) it involves a LOT more than you are alluding to.

Plus, if you include the largest engineering "area" in the world (europe) you are talking elite universities with motorsports programs, and motorsport engineering degrees.

For example, F1: Aerodynamic Engineer (usually dual meche's, with a lot of misc experience, very common to have aircraft experience) do aero, Materials engineers work with mechanical designers (including ME, FEA/CFD specialist, electric engineers, etc), etc etc etc all the way down to industrial engineers on working out the logistics of organizing the teams equipment and how everything is implemented.

As I stated before, it depends on what type of motorsports and what type of engineer we are referring to.

In todays engineering programs many are joint "mechanical and aerospace engineering," and its under that umbrella which everything usually falls. However, the specific degrees are not in "aeronautical engineering."

Do you have the article reference? If its from 20years ago, I guarantee its not valid anymore.

(technically you could call me a racecar designer...I'm a ME)

Other than formula chassis, everything still uses metal, even F1 uses Metal components in many places. There is a larger mix of hybrid monocoques and whatnot though.

Composites is the new field to get into, but its outside of my interests. Its a big mix of materials/chemical/mechanical/etc. Tough industry.

 

Yes, probably right.

If you want to be a modern race car engineer/designer then this is where it's at.

Best
Pete

 

Enough said

Pete

 

And he (AMN) bought some parts from me that I designed for his Lotus Elise...

 

Impressive!

Pete

 

I don't think a few courses in structual engineering would hurt. Top level teams have seperate engineers for each area of speciality; aerodynamics, structure, motor, etc. Those who are capable of totally designing, engineering and building a car on their own, IMO, no longer exist.

 

I don't get it? Whats that prove?

 

Oh, they definitely DO exist, but they are smart enough to know its not worth it to try to do it by themselves.

The smart ones team up with others who can do a specific area of the car better. They then form companies and build cars usually as a partial/side business to a full engineering firm (refer to basically every large racecar manufacturer thats based from an engineering firm ).