Pete
Lyons' fantastic Can-Am Cars in Detail:
 |
November/December 2014
Reload
to see the latest news
All news content copyright Michael J. Fuller, unless
otherwise noted |
Mulsanne's Corner Paddock
Motorsports and other interesting merchandise. Or, cleaning out my house. | |  12.28.14
This article, and the previous, en español.
>>Part
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. | Mulsanne's Corner Book Store
A selection of sports car related DVDs and books, with a technical slant.
|  *12.17.14 *with continuing updates
>>So
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!
 However,
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 ½ 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.
| 
|
|
Paul T. Glessner, M.S.,
aerodynamicist and automotive enthusiast, presents both
his company
Vehicle Aerodynamics Consultants (VAC) and the well regarded -
"The Secrets & Basics of
Vehicle Aerodynamics" Seminar. | 
VAC
can expertly analyze your vehicle design project via CFD to explicit
levels or simply discuss a more prudent approach. Either way, our goal
is both a satisfied client and a more efficient design.
Paul
has spoken at Bondurant's SoHPD, SAE's headquarters and SEMA's and
PRI's conventions. Paul's seminar both educates and entertains. The day
long seminar can be held at your location with the organizer paying
only $100. Click on the above banner to read about Paul's background
and testimonials
from enthusiasts like Jay Leno and clients like GM, SEMA, TRAXXAS,
Bondurant SHPD, Flying Lizards Racing, Borla, SHAPE CORP and many
Formula SAE universities and more. Let VAC handle your project
and/or allow your education of vehicle aerodynamics to be both captivating and entertaining as well.
www.aeroseminars.com | | 562.714.6686 aeroseminars.com |
|
|
