Formula frame design

[open_wheels]

Hello,

I have been following this forum for a while now, as it has been a good way for me to get great information on open wheel design. I have been racing a formula vee for a few years and for several reasons I would like to build one, frame to bodywork. Because so much parts are spec VW parts, this seems much less complicated than what most people do on this forum. Historically FV have been built without FEA, showing how simple most of these chassis are.


I do not have a mechanical engineering background, but I do have an electrical engineering degree. All that to say that I have a limited understanding of how a race chassis works, but I can and want to learn.


Wheel base, track, transaxle, engine, suspension geometry (at least at the front), steering box... are all spec in FV, which I believe simplifies greatly the chassis design.

I have already lay down the suspension anchor points, and built a basic frame. I would like to run a stress analysis on this frame.

- Could anybody recommend a free/trial version for a FEA software?
- Knowing the vehicle weight, track, wheelbase, cornering Gs... How do I deduce relevant torsional loads?
- When running an FEA, do you need to model and locate every single component that goes in the car (driver, battery, fire bottle etc), or can you just go with the estimates of corner weights?
- Do I need to model each suspension arm (FV use a front axle beam, and zero roll rear suspensions), or can I just apply the torsional loads directly onto the frame, provided I adapt the loads? How do you adapt these loads?



Thanks!

[open_wheels]

Hello,

I have been following this forum for a while now, as it has been a good way for me to get great information on open wheel design. I have been racing a formula vee for a few years and for several reasons I would like to build one, frame to bodywork. Because so much parts are spec VW parts, this seems much less complicated than what most people do on this forum. Historically FV have been built without FEA, showing how simple most of these chassis are.


I do not have a mechanical engineering background, but I do have an electrical engineering degree. All that to say that I have a limited understanding of how a race chassis works, but I can and want to learn.


Wheel base, track, transaxle, engine, suspension geometry (at least at the front), steering box... are all spec in FV, which I believe simplifies greatly the chassis design.

I have already lay down the suspension anchor points, and built a basic frame. I would like to run a stress analysis on this frame.

- Could anybody recommend a free/trial version for a FEA software?
- Knowing the vehicle weight, track, wheelbase, cornering Gs... How do I deduce relevant torsional loads?
- When running an FEA, do you need to model and locate every single component that goes in the car (driver, battery, fire bottle etc), or can you just go with the estimates of corner weights?
- Do I need to model each suspension arm (FV use a front axle beam, and zero roll rear suspensions), or can I just apply the torsional loads directly onto the frame, provided I adapt the loads? How do you adapt these loads?



Thanks!

[exFSAE]

With regard to load... your restraints are ultimately the footprints of the tires. The load is inertial from lateral acceleration.

I suppose worst case you could apply a point load at the CG. In reality it's a distributed inertial load... and good luck with that.

[Neil_Roberts]

Since you are using a zero-roll rear suspension (right?), the torsional stiffness of the chassis is irrelevant for handling. That's why a simple ladder frame works just fine.

Frankly, mechanical performance is not where it's at in FV, with the exception of minimizing power loss due to chassis loads on the engine.

Aerodynamic drag reduction is really where it's at in FV, and a surprisingly large fraction of that drag comes from engine cooling. If you are going to be competitive, you will have to get the cooling flow paths exactly right.

If you still want an FEA of the frame, the easy way to do it is to hire one of the students here who has the software and the expertise to use it correctly. There is a lot to learn about using FEA, so your time would be better spent on doing other things.

[open_wheels]

Yes I have been using a zero roll suspension, and I intend to use it for this new chassis too. You are right, ladder frames have been used extensively since the mid 70s in FV, partly because there is no real need for torsional rigidity with the zero roll (let me come back to this later though).

The issue with ladder frames is that you need to use bigger and heavier members for it. Because of the weight limit in that class there is then less weight budget to provide more structure for driver protection, for side impacts for example.

Interestingly, mechanical performance does play a roll in that class, it has been shown over the past few years with the dominance of one (well designed) car over the rest of the field. As you point out, the car I am thinking of certainly has a real aero advantage, but that's not it. Part of its dominance comes from the performance of the chassis.

Now back to torsional rigidity, I understand zero roll is the suspension to go with in FV, because it does not load the rear end, which somehow should not be loaded because of the open differential FV use.
Whether it uses a ladder frame, or a spaceframe, still, there has to be a minimum torsional rigidity requirement for a zero roll chassis.

There has to be someone here who knows how to determine that.

[Neil_Roberts]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by open_wheels:
I understand zero roll is the suspension to go with in FV, because it does not load the rear end, which somehow should not be loaded because of the open differential FV use. </div></BLOCKQUOTE>

The first step on the road to building a race car is building a solid understanding of how they work. I strongly recommend investing in your own copies of Prepare to Win, Tune to Win, and Engineer to Win. Of course you will need to know a lot more than that to build a successful car, but they will go a long way toward helping you build a safe one.