With the fan’s tension mounting until the official unveiling of Nissan’s 2015 World Endurance Championship LMP1 challenger, the GTR-LM, Nick Holland (@NH247) muses on some of the design options that may have influenced Nissan’s engineers.
Much has been voiced about the wisdom or otherwise of Nissan/Nismo (potentially) straying from the path of ‘conventional wisdom’ and going for a mid-forward ICE unit in their proposed LMP1 2015 contender. Now it would be an act of pure folly to take such a decision having not proved the concept first; big business does not make decisions based on hunches and gut-feel even if they do want ‘Maverick’/’Bad-Boy’ branding!
Before we dig any deeper, lets set out a few points to bare in mind –
- Manufacturer LMP1’s are mandated to utilise hybrid power and this has led to four-driven wheels which clearly aids flexibility of design.
- Packaging the vehicle is all about Centre of Gravity/Pressure, they govern that the load of the car must be as low and central as possible whilst generating a suitably
- massive amount of power and torque.
- The tub dimensions are fixed by regulation, hence change what you like, but you always have a central bulkhead in front of which is the cockpit, and behind which must sit the fuel tank.
- We have also recently seen the emergence of a trend at the top-level of sports car racing to manage air-through the structure of the car. This offers these cars a distinct advantage over Formula 1 because lightweight physical structures can manage the air (or flex) rather than bouncing air off of air.
- Nissan have displayed with the Nissan-Powered Deltawing & latterly ZEOD an intent to minimise frontal area, thus reducing the air resistance on the vehicle as it passes through the air. Its been noted that the wheels on the GTR-LM look to be of a smaller diameter, and perhaps this is a based upon lessons learnt, and a further nod to reducing air resistance.
So what are the relative merits of a mid-front ICE layout ?
To-date the area ahead of the cockpit has been challenging to use. A clear view must be retained, room is needed for a pedal box and all must stay behind the front axle for safety, balance & aero-efficiency. However a short V-engine or canted over inline could be mounted on the centre axis. It then needs to be fed pressurised fuel from behind the cockpit, and receive an adequate charge of air both not impossible, but arguable air taken lower down (lower than traditionally from above the cockpit) is more likely to be contaminated with debris. The challenge is then how to deploy the power & remove the emissions…
Convention says most LMP1 ICE units will generate >550-700+ bhp the easiest thing is to use Traction Control electronics to control deployment to the front axle only. Any excess power could be captured, stored and utilised electrically, though transfer of energy from one form to another is inherently inefficient.
Power typically would be transmitted to the rear using a prop shaft and transmission, but such gear would be heavy, and destroy the advantages at the the rear of the vehicle that are being sought. Transverse mounting of the ICE would also reduce ancilliaries needed in deployment to the front axle and hence the likely preferred option.
Perhaps the biggest challenge in this area is with the exhaust gases. These are likely to be harvested for energy but the biggest issue is noxious gases ahead of the driver and equally dissipating the heat generated. Black carbon tubs are notorious for soaking up generated heat. Both gases and heat have been issues in the past, GT cars in particular recall Justin Bell & the Corvette many years back. When the ICE is behind the cockpit there is a wash effect that drives a proportion of the heat backwards. The heat can (and is mandated to) be dealt with through air-conditioning in the cockpit, but this is a further efficiency cost to be considered.
In all likelihood short side-exiting exhausts are likely to be used. This may give the required auditory enjoyment, but dependent upon specific regulations being met the accelerated hot gas (air) could allow the exploitation of some form of blown-diffuser concept. The rear diffuser is likely to be the advantage area we are seeking on the car as compared to a mid-rear engine configuration.
Having freed up (bar the relatively small bag tank) the space behind the bulkhead, we can look to store energy alongside the driver (likely matching his weight for balance) and focus on the hybrid system(s) that are going to capture further energy (and this needs as a minimum to match the ICE unit). If we take the ZEOD as an example (the (compliant) tub of which shows visual similarities to the images of the GTR-LM seen to-date) perhaps we have a clue.. Take the ICE, switching & problematic transmission away and replace it with twin motors, one to each rear wheel (centrally mounted and controlled almost as one unit) an increase in storage capacity, and given the high-torque of these motors hence no or little need for gearing we have a very neat electrical power delivery unit. Braking energy could be recovered at the rear, a fly-wheel system doing the same at the front.
A traditional HORA – ‘Heavy Old Rear Assembly’
Toyota & Porsche are utilising 6mjs and electrical storage. Audi derive 2mjs from a flywheel system its likely Nissan are simply combining these systems thus targetting the highest category (8+mjs) of hybrid power available.
The ‘tidy’, tight rear packaging leaves us with a massive area to exploit in terms of the rear diffuser, and allegedly the GTR-LM will run a narrower track at the rear, hinting that to achieve balance between front & rear downforce not all of the space between the rear wheels is required.
How Much of this is Zeod with a ‘Heavily Reworked’ Front-End?
In summary, Nissan will have arrived at their design with the support of many specialist partners, as well as hours spent with/on CAD, CFD, models and wind tunnels. They appear to be cherry-picking from their learnings to-date, as well as their competitors experiences. If they have drawn from all the positives then they are likely to have a competitive package.
What they are unlikely to have gleaned are the experiences of working all of this into a competitive team capable of dealing with the conditions thrown at them, as well as honing their chosen weapon to each track and duration encountered. But with time, patience and correctly thinking through the challenges they incur, the potential is there to take on the best and win !
What we do know for sure at the moment is we’ll see and hear the GTR-LM in all its glory when it takes to the Paul Ricard circuit at the end of March for the WEC official test weekend, The Prologue.
See you trackside!
Credits & links
Mike Fuller’s Mulsanne Corner on the Nissan GTR-LM
COTA Photos used here are from Jalopnik
European Motor News. The Full Story.. Really ?!