Active Aero

The one thing I didn't talk about in my last post was active aero.  Active aero opens a whole new can of worms, but I think it's doable (see Oklahoma's car - it's pretty awesome).  I'm taking a different approach, which will be a simpler system consisting of only a moving rear wing.  Anything more seems a bit unrealistic for a one year project.

The benefit of active aero is that you can reduce drag when you don't need downforce, i.e. when you're traveling in a straight line.  Honestly, I don't see any downsides either except for the additional development time and slight weight increase.  Of the aero elements on the car, the rear wing produces almost twice as much drag as the front wing and undertray combined, which is why the rear wing is the active element.

Aero Design

I've outlined why we're doing aero in a previous post; now I'm going to talk about how we're going to do it.  As a recap, we want to maximize downforce while minimize drag and weight.  We have other constraints too, such as the rules, manufacturing capability, and of course time and money.  Even so, we are afforded a great deal of design freedom in aerodynamics.

This year's aero package will consist of a front wing, a rear wing, and an undertray.

Aerodynamics and Vehicle Dynamics

The following write-up is  quick introduction to aerodynamics and how it relates to vehicle dynamics, for those interested.  After the break are snippets of an email I sent to the aero team almost a year ago, and I think it's a good place for those on the team interested in aerodynamics to start.

Aero and CFD

Having spent a good bit of time in the GM Aero Lab this summer, I understand how important a wind tunnel is to developing a good aerodynamic package. But, as a FSAE team on a budget, that's not something that we have available to us at this stage of the vehicle's development. So, our aero package is designed with the tools we do have available, namely computational fluid dynamics (CFD).

If you can't take the heat, don't design an exhaust...

For the new 2012 Duke FSAE car, I've decided to redesign the exhaust system for a number of reasons. The primary reason for redesigning the exhaust system stems from the team's decision to eliminate the rear box from the frame, which shifted the suspension placement on the frame. In other words, the A-arm and halfshaft placement gave me a rather uncomfortable amount of clearance to run the exhaust through. Also, due to the shortened wheelbase, the muffler would be sticking out too far from the back of the car.

Another important consideration was passing the sound test during the tech inspections at competition. We noticed that the decibel readings varied greatly depending on which side of the car the measurement was taken, which we attributed to the valvetrain and intake noise which was recorded when the inspector stood on the left side of the muffler. Therefore, one design aspect that I wanted to incorporate into this year's car was to run the exhaust out of the side of the car in order to eliminate this extra noise to allow us to run a smaller, more free-flowing muffler.

The Big Picture

Another year, another car. So what's new for 2012?

Well, this year's car will be a major redesign from previous years. There will be a large focus on

aerodynamics, and in fact the entire car will be designed with aero in mind. If everything goes to

plan, we will have a new frame redesign to reduce wheelbase and increase stiffness, suspension designed for our aero package, a complete repackaging of the rear half of the car to accommodate the new frame, and hopefully incremental improvements everywhere else. But the overarching theme is downforce.

Why aero?

Summer Update: Frame design

So one design goal that's been floating around for a while is a redesign of the frame, to get rid of the rear box. The main reasons: increase stiffness, shorten the wheelbase, and reduced weight. The disadvantages? Well, all the packaging in the rear has to change: intake, exhaust, radiator, drivetrain, suspension... you get the idea. But we decided at the end of the year last year that it would be feasible if we got the design and repackaging done during the summer. So earlier this summer I decided to redo the back half of the frame to remove the rear box, and sent the frame off to the rules committee for approval on "proper triangulation". It's been six weeks, and I've finally got a response from the rules committee, so the new frame design is a go if we decide to implement it.

The new frame only sheds a couple of pounds, so the weight savings are going to be negligible

with the additional weight of the bearing carriers. We will reduce the wheelbase to 60" this year

with this frame, and this frame should be stiffer, but I haven't run the FEA analysis quite yet. Packaging is on its way - exhaust, radiator, and aero have been redesigned/refitted; intake, suspension, and drivetrain are still in progress.