Mulsanne's Corner:  We're curious about the origins of the vertical fin concept.  We also undertand that Porsche approached the FIA with this solution about 18 months ago?  Is this correct?  Could you lay out a time line of Delta Motorsports involvement?

Nick Carpenter, Delta Motorsport:  Timing broadly as follows:

July 2008 : First meeting of the Sportscar Technical Working Group to discuss the high-yaw issue. At this meeting it was decided that the constructors should (a) consider possible solutions, and (b) get together to see if they could agree on a common approach to analysing the problem, and also that we would put in a proposal to the FIA for an independent study.

September 2008: Second meeting of the TWG. The constructors had begun to investigate the problem (and it may even have been this early that Porsche first proposed the fin, but I don’t think it was till a bit later), but it became clear that they weren’t going to share enough (VERY sensitive) data between them to allow comparisons of the various different cars and particularly to compare their different methodologies (from CFD to full-scale testing in a tunnel with a moving floor).

Early in October: we were asked by the FIA to carry out a CFD and multi-body analysis of the characteristics of the cars while spinning at high speed, and we delivered this in early January. Epsilon and KWMotorsport very kindly shared their CAD data with us (or specifically with Totalsim) to allow a full aero map of the two cars (one open, one closed) at a wide range of roll, yaw and pitch angles, and these results were fed into the multi-body sim to ensure that the numerical model behaved in the same way as the real cars, which it seemed to do.

Mid-Jan 2009: Further TWG group meeting to discuss the results of the study and to see whether there were any ideas that could be implemented in time for the start of the 2009 season. The curved plank was discussed as a comparatively minor change that might help at low risk of making the problem work (the law of unintended consequences was always in our minds but as a group, everyone felt we should try to implement something if at all possible). We fed the results back to the FIA at the start of February and it was decided that the plank change was “doable” in time for the Sebring race.

We then embarked on a program of analysis of a wide range of devices (including the fin) in May ’09 after further discussions about which devices tested by the constructors showed promise (and we came up with a few of our own too!). As usual, some of the devices worked on the open car and some on the closed car but the consistency of their effect was unpredictable. We shared these initial results with the group and iterated the various shapes, then carrying out further testing.

With the to-ing and fro-ing to constructors, as well as giving the constructors time to test alternatives and validate our results, we submitted our final proposals in mid-September (2009).

We then attended an ACO meeting in Paris at the start of October to allow discussion of the results that had been circulated in our report. The constructors gradually fed back their thoughts, concerns, comments etc between this meeting and the end of 2009, and we held another TWG meeting towards the end of January this year, at which it was decided that the fin should be put before the next FIA World Council meeting.

Throughout the program we were all very aware of the need to do something as fast as possible, but this was always tempered by the knowledge that we shouldn’t rush into anything with a device that might make the problem worse or introduce a different one.

 
Mulsanne's Corner: What were the parameters the FIA/ACO set in place for the solution?  Presumably they outlined parameters and said, "how ever you get there"?

Nick Carpenter, Delta Motorsport:  The parameters were pretty broad really. Having made the mods to the underfloor shape in 2002/3, we were left with working on the upper body (because a wholesale re-think of what a Sportscar should be was deemed unfeasible). The constructors came up with ideas (including the fin from Porsche), we came up with some, and we tested – and iterated – them all until we found a device that made a significant reduction to the problem.

Mulsanne's Corner:  What you can tell us about the methodology Delta Motorsport used to come to the conclusion that vertical fins will eliminate the possibility of LMPs taking off in sudden high speed yaw situations?  Were any other solutions considered? 

Nick Carpenter, Delta Motorsport:  There are two main areas of concern.  Lift (a vertical force that physically lifts the whole car up) and overturning moment (“OM”). OM is a moment that will tend to roll a car backwards, against the direction of travel, and is made up of contributions from lift and drag, both resolved around the rearmost contact patch (the leeward wheels when sliding sideways). The early simulations (as well as videos of the accidents in 2008) showed that OM was the main culprit.

We looked at many devices such as louvres, cut-outs in the inner when arches, longitudinal strakes, changes to sidepod geometry, RWEP geometry changes and many different sizes and shapes of fin. Quite a few showed promising results on one car but not the other, and we were obviously looking for something that could be applied to both open and closed cars in a consistent and fair fashion.

I don’t think anyone would assert that we’ve “eliminated the possibility of LMPs taking off” – there are just too many variables to give that unequivocal an answer. As you no doubt saw from Mark Webber’s recent accident, motorsport is a dangerous pastime, but what we’ve tried to do with the fin is (a) minimise the chances of getting into a potentially dangerous attitude, and (b) reduce the risk of take off if a driver does find himself there.

 
Mulsanne's Corner:  How does the fin effect airflow to the rear wing in normal yaw (cornering) situations?  We understand the fin generates an overturning moment of its own though presumably its ability to eliminate the lift generated by the leading side rear fender makes this easily overlooked?  Is there any situation where the fin's overturning moment would be cause for concern?

Nick Carpenter, Delta Motorsport:  One of the constructors shared the results of their low-yaw work with the Technical Working Group (in broad terms at least), and this showed no adverse effects.  All the fins tested showed some degree of improvement, with the bigger fins producing the largest benefit. The tests we ran didn’t show any vehicle attitudes where the fin had an adverse effect.

 
Mulsanne's Corner:  What was Delta's role with Totalsim and Intec Dynamics handling the CFD and simulations?

Nick Carpenter, Delta Motorsport:  Delta ran the program, sub-contracting the CFD and multi-body elements of the work. The FIA needed a “one stop shop” for the whole program, which is what we offered. We defined the programs of work, carried out the CAD design work, coordinated all the CFD and multi-body work, interpreted the results and wrote/presented the reports.