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Nissan GT-R LM concept, copyright Michael J Fuller12.28.14

This article, and the previous, en espa˝ol.

>>P
art one of my article generated some interesting thinking, as well as some more whispers.  Don't worry Nissan, no one is giving up everything.  You'll still have your precious PR Return On Investment...

One thing I've found out is that as of last week, roughly around December 17, Nissan has been testing in full 2015 specification, meaning that the hybrid system has finally been mated to the chassis.  I also understand the hybrid system has been tested to destruction back at home base and I'm hearing that all relevant parties are satisfied with the recent progress.  

Getting in to the meat of the speculation, there's been some discussion if Nissan could opt for a transverse engine layout.  I'm less keen on that idea (more below), but it brought up a conundrum.  Naturally a transverse engine layout brings up the possibility that the combustion engine is powering the front wheels.  The reason all this matter is that  the ACO regulates the layout the car to an extent, Article 1.19 says:



Car Sub-Assembly


The following sub-assemblies are defined :
• Front drive train: It is formed by the complete front suspension, wheels, brakes and drive shafts.
Rear drive train: It is formed by the complete rear suspension, wheel, brakes, gearbox and drive shafts.

I'm reading “gearbox” to mean that big lump that we're all used to seeing that transmits the power to tires.  So naturally the gearbox is in the rear, has to be, right?  However a source has confirmed that the Nissan has gearboxes, “...at both ends.”  And this leads me to believe, based on the wording of the reply given the question posed, that the ACO will consider the hybrid system's power transmission mechanism in the same vein in which they wrote the regulation and that the issue is settled regarding Art 1.19.    And based on that, I'm concluding that Nissan's combustion engine (V6, Cosworth as mentioned below, 12.17.14 update) will power the front wheels, with the flywheel based kinetic energy recovery system powering the rear wheels.  So four wheel drive as everyone else is using, but opposite as far as the end the combustion engine is powering.  But let's not cry foul, Nissan isn't pulling a fast one.  The reality is that at the end of the day 1.19 was written with a lack of imagination.  It's not like Audi has been pinning away to build a front engined LMP1 but for Art 1.19.

If the engine is powering the front wheels, what's the layout of the engine relative to the car center line?  Are there any options there?  We're back to where the conversation started for me.  I briefly considered a transverse position, but an engine of the compact nature of a contemporary F1 V6 is effectively as long as it is wide from what I can gather, and so there's a strong argument that from an aerodynamics standpoint the longitudinal layout is simply slimmer considering the need to exit the front diffuser and the high up width dimension when the engine is considered head on.

This still opens up all sorts of possibilities in my mind.  Given to flights of fancy perhaps, but with the gearbox ahead of the engin it's very easy imagine the gearcase as the natural landing for the front suspension.  Works in the rear after all.  But maybe the cross section of the gearcase isn't enough to hang the suspension, while also doubling up as part of the front structure (remember we have a much larger crash structure in the front, plus a splitter/diffuser to hang as well)?  So do you encase your gearbox in a forward composite structure (to handle necessary crash and suspension loadings)?   Does that seem to make much sense?  Maybe.  But maybe your forward composite structure actually becomes the gearcase as well?  The regulations now allow for a carbon fiber gearcase (Art 11.4.1) following Audi's shenanigans back in 2011 and 2012.  So why not?  But perhaps that last part is a bridge too far.

In the midst of all this speculation there was a private suggestion that the GT-R LM might not have a rear wing at all.  With the entire concept flipped front to rear, weight distribution and all, aero balance will follow as well.  Previously I would have guessed a front engined LMP would be running maybe 48-51% front weight distribution, just a few ticks above a mid-engined LMP (~45-48%).  But suppose there's the possibility that a proper front-engined LMP will be running much closer to 55-58%?  Front aero follows accordingly and you'd be looking at ~52-55% front downforce, the entire concept has been flipped!  Thus having said that, there seems little justification for a rear wing from what I can guess, given the power of the diffuser for rear downforce totals.  And the onus on the front engine concept is purely to achieve the front downforce numbers to “match” the weight distribution.  That's always been the case of course, but perhaps it doesn't have to achieve the front downforce number too particularly efficiently?  If by narrowing of the rear and fiddling with the rear tires large drag reductions can be found, then maybe the front end doesn't have to be all that efficient, maybe the rear end pays for whatever you do at the front?  But maybe there are ways to create the necessary front downforce.  The regulations allow for two wings at the front (mainplane and flap essentially), but I'm not sure it says you can't have two front wings in addition to a front diffuser...And by eliminating the rear wing you would chuck out a huge amount of drag, maybe 150-250 lbs drag.  You'd kill to magically find that in a conventional LMP. I've been looking for the advantage and  have now come to the conclusion that this is the linchpin of the entire concept, this is the advantage.

One last word of caution, there is also the possibility the balance moves too far forward by removing the rear wing.  If it gets ahead of the car's center of gravity then the idea is a non-starter.  But obviously they would be on top of this at the concept stage, and once theoretically proven viable would then pull the trigger on iterations and development.

Lots of things to consider.
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>>S
o the Nissan camp isn't saying anything about their soon to be revealed LMP1 (December? February? Superbowl?  I'm pretty sure no one knows).  However, in spite of a complete lock down on official information, and confidentiality clauses even to the smallest supplier, there's a surprising amount of technical details floating about.  How much is accurate?  Let's chew the fat.  

The most interesting persistent rumor is the one that describes the new Nissan GT-R LM as being front engined.  It's easy to completely dismiss this one out of hand; a front engined LMP?  The last  (and only) front engined LMPs were the Panoz prototypes, the LMP1 and LMP07.  These efforts, while scoring the occasional win, ultimately struggled to keep pace with the Audi R8.  And by the end of 2003 the towel had been thrown on both cars and the Panoz LMP program was finally shuttered.  At the end of the day a front engined LMP had lots of technical problems, but few obvious benefits.

And for good reason, as the placement of the engine at the front of a modern LMP can have a fundamentally negative impact on the ability to generate competitive total downforce numbers.  The front end of a contemporary LMP1 is already aerodynamically stressed in its ability to generate front downforce.  Yes, the ACO has finally allowed true wings, however the regulation-mandated bodywork that resides above these devices ultimately impacts trailing edge airflow and pressure recovery.  And to that end modern LMPs are still rear downforce biased as it is more difficult to generate front grip than rear grip.  So to a degree, front wings haven't necessarily been the magic panacea for historic sportscar front downforce issues.  In order to get them to work effectively it is important to maximize the distance between the bodywork above and the wings themselves, in order to provide as clean an entrance, and exit, for the airflow interacting with the front wing assembly.  And therefore it doesn't take much imagination to conclude that if you then you go and place an engine, with all its ancillaries, intercoolers, oil and water radiators, all in, or close to, that precious volume you've set aside for your front wing, you might very well be hurting your ability to generate front downforce above and beyond the difficulties already being encountered.  And even if the engine isn't anywhere near the front wheel CL, you still need to be very cognizant of providing clean avenues of exit for the front wing airflow; you can't block the exit!

Brian Willis front engined LMP1 conceptHowever, what if there was a work around?  The thought always is that with a front engined car the engine itself is on, or just behind, the front wheel centerline.  But could you place the engine much further rearward behind the front wheel centerline, in order to free up front diffuser area?  Think of it as a front mid-engine.  As you don't want to give anything up to a conventional mid-engined LMP, ultimately the desire would be to not have to alter the driver's position.  But can it be done in a front engined car?  Possibly.  The problem is that if you kept the driver where you wanted and moved the engine rearward, the engine would end up hitting the driver's feet.  But what if you pushed the driver's seat position outboard from car centerline and moved the back end of the engine into the space between the driver and the theoretical passenger's volume?  Or even, what if you moved the driver inboard even, if slightly, but angled his legs outboard to clear the engine as it moved rearwards?  Either seating position might be somewhat awkward, but surely it would be doable?  The tub would have two separate footboxes with the engine in the middle in an H-pattern.  It would certainly make for a more complicated monocoque.  And access to the engine would have to be worked out to some degree.  But also remember the driver's feet are elevated on a modern LMP, so with the feet pointing outboard, but elevated, you're allowing for front diffuser exit volume.  Or at least making up for some of the deficit.

One further detail to consider, given some of the difficulties in getting a front wing to work efficiently (with or without an engine smack dab in the middle of things), the route of the standard closed splitter (the front aero concept of choice for Toyota) is one to consider.  It maximizes internal volume right where you want it and is the more efficient choice for Le Mans.  One potential benefit of the front engine in relationship to the front diffuser?  Exhaust activation of said...However I don't think they would activate the front diffuser directly as that would get too complicated pretty quickly, running the exhaust forward, not to mention everyone and their brother would throw the protest flag (Art 3.4: Blown diffuser is forbidden).  Instead I think they would work on enhancing the exit flow from the diffuser by routing the exhaust the very short distance into the area just aft of the front tires and helping energize that flow a bit more.  
However 2015 LMP1 regulations released to the public on 12.20.14 place new restrictions on the exhaust and it's ability to be utilized for improving aerodynamics regarding the underfloor (note the rules are pretty specific to the underfloor and don't say you can't use the exhaust for aerodynamic advantage).  The regulation has been rewritten with further clarifications of the base definition, "...principle which can take advantage of exhaust flow to dynamically effect the tunnel of diffuser or intent to seal its edges," but still nothing appears to outright ban the concept if used at the front of the car.  However, Article 3.4  now has provisions, amongst others, that states:

If outlet from the side :
The terminal shape of exhaust must be such that a minimum angle of 60░ is provided to the exhaust gas flow in reference to the external surface of the bodywork.  It must be located in front of the wheel arch.

This wording might make the execution a bit more difficult in the end (the 60
░ minimum angle bit), though perhaps still worth pursuing.

The second issue is the placement of the trailing edge of the cockpit.  Again, everything is driven by the front engine.  And with the engine up front the driver will inevitably be pushed rearward, and therefore the cockpit trailing edge gets really close to the rear wing, certainly much closer than on a mid-engined car.  So airflow quality would certainly be suspect for parts of the rear end of the car as well as the rear wing.  Such was the struggle on the Panoz GTR that Andy Thorby cut the roof off and created the Panoz LMP1 “Batmobile.”  With closed tops mandatory that's no longer a viable route.  But if you've been able to keep the driver's butt positioned to a similar spot as in a conventional mid engined car you're out of the woods regarding the cockpit to wing relationship. 

The other factor to keep in mind as well, the further rearwards in the wheelbase the driver gets pushed back, the closer they get to the inevitable diffuser ramp.  Which leads to the need to raise the driver to clear the tunnels.  This increases the cockpit height overall, which isn't good for aero as again it's something the mid-engined guys don't have to deal with.  It would also be a CG hit too. So it further stresses the motivation to work hard on packaging the driver so that they don't have to be significantly moved from conventional.  Other issues to consider, a propshaft running through the tub.  But not if the combustion engine powers the front wheels with hybrid driving the rear--this has been mentioned but I haven't given it much credence or checked regulatory implocations (regs seem to say no as they define the "rear drive train" as containing the gearbox).  But what about a transverse engine up front?  It would make the engine shorter within the wheelbase and a little easier to package the driver.  Naturally all of this complicates things, they aren't non-starters by any stretch.  Could these details compromise reliability?  Perhaps.

The French motorsports magazine Autohebdo claims the Nissan LMP's rear tires will be narrower than the fronts, and that the car's rear track will be narrower than the front as well. So does that even make sense?  Yes actually, considering Le Mans as your primary goal.  Narrow rear tires, as well as a narrow rear width (presumably to the 1800 mm minimum), will impart a hardwired drag reduction that the mid-engined LMP1s would struggle to duplicate.  I also understand that air management for coolers, radiators, etc., will be handled exclusively at the front of the car and that there will be no, or very little, airflow through or out the rear of car; this suggests a zero height above the underfloor rear engine cover trailing edge which would allow better extraction of the underfloor via engine cover trailing edge gurneys.  However 2015 LMP1 regulations now mandate that the trialling edge of the rear bodywork be at least 50 mm above the diffuser.

One of the limiting factors for the Panoz LMP1 was with the rethought front weight distribution you really needed an accompanying bespoke tire.  This never materialized during the Panoz' campaign and at the end of the day the effort was leaving something on the table.  However, over the course of the past 5 years, there's been a massive swing in thinking about weight distribution and Michelin has subsequently designed front tires to take this, and higher subsequent front aero loads, into account.  Therefore a hindrance encountered the last time someone went the front engined route is no longer.

The Nissan LMP will use a flybrid kinetic energy recovery system developed by Torotrak.  At the beginning of 2014 Torotrak purchased Flybrid Automotive.  Flybrid Automotive might be familiar as they developed the KERs system raced by Dyson Racing, installed in their Lola B12/60, for the last two races of the 2012 ALMS season.  And while the Nissan has turned it's first laps at the Arizona Testing Center, it did so without the KERS system in place.  As of mid December sources indicate there had been some delays and the system had not been mated to the chassis yet. 

So what about the engine?  At 3-cylinders and 1.5 liters it was reasonable to think that the Nissan DIG-T R  engine out of the ZEOD as Ż of a future LMP1 engine.  However, the ZEOD engine was developed by RML and I'm being told that the engine in the Nissan is probably sourced from Cosworth.  In fact, it's been mentioned that Nissan is the benefactor of Cosworth's un-raced 2014 F1 engine (V6).  A little bit more digging and other sources confirm a V6 engine layout and Cosworth involvement.  How far that involvement extends is unknown at the moment.  Power is reportedly “around” 600 for the engine, with total system horsepower supposedly north of 1000.  How far north?  I've heard a number, but it belies belief and so far I've been unable to qualify it.

Connecting the dots, how did Bowlby get there from here?  To an extent Delta Wing and ZEOD showed the way and shook up concepts about weight distribution and packaging.  Was that some of the takeaway from those two projects?  Maybe.  Would anyone else have considered a front engined LMP?  Given recent experience I highly doubt it. 

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